[ { "text": "A new analysis of the GJ581 extrasolar planetary system: We have done a new analysis of the available observations for the GJ581\nexoplanetary system. Today this system is controversial due to choices that can\nbe done in the orbital determination. The main ones are the ocurrence of\naliases and the additional bodies - the planets f and g - announced in Vogt et\nal. 2010. Any dynamical study of exoplanets requires the good knowledge of the\norbital elements and the investigations involving the planet g are particularly\ninteresting, since this body would lie in the Habitable Zone (HZ) of the star\nGJ581. This region,for this system, is very attractive of the dynamical point\nof view due to several resonances of two and three bodies present there. In\nthis work, we investigate the conditions under which the planet g may exist. We\nstress the fact that the planet g is intimately related with the orbital\nelements of the planet d; more precisely, we conclude that it is not possible\nto disconnect its existence from the determination of the eccentricity of the\nplanet d. Concerning the planet f, we have found one solution with period\n$\\approx 450$ days, but we are judicious about any affirmation concernig this\nbody because its signal is in the threshold of detection and the high period is\nin a spectral region where the ocorruence of aliases is very common. Besides,\nwe outline some dynamical features of the habitable zone with the dynamical map\nand point out the role played by some resonances laying there.", "category": "astro-ph_EP" }, { "text": "Null transit detections of 68 radial velocity exoplanets observed by\n TESS: In recent years the number of exoplanets has grown considerably. The most\nsuccessful techniques in these detections are the radial velocity (RV) and\nplanetary transits techniques, the latter significantly advanced by the Kepler,\nK2 and, more recently, the TESS missions. The detection of exoplanets both by\nmeans of transit and by RVs is of importance, because this would allows\ncharacterizing their bulk densities, and internal compositions. The Transiting\nExoplanet Survey Satellite (TESS) survey offers a unique possibility to search\nfor transits of extrasolar planets detected by RV. In this work, we present the\nresults of the search for transits of planets detected with the radial velocity\ntechnique, using the photometry of the TESS space mission. We focus on systems\nwith super-Earths and Neptunes planets on orbits with periods shorter than 30\ndays. This cut is intended to keep objects with a relatively high transit\nprobability, and is also consistent with duration of TESS observations on a\nsingle sector. Given the summed geometric transit probabilities, the expected\nnumber of transiting planets is $3.4 \\pm 1.8$. The sample contains two known\ntransiting planets. We report null results for the remaining 66 out of 68\nplanets studied, and we exclude in all cases planets larger than 2.4\nR$_{\\oplus}$, under the assumption of central transits. The remaining two\nplanets orbit HD~136352 and have been recently been announced.", "category": "astro-ph_EP" }, { "text": "Reflected spectroscopy of small exoplanets III: probing the UV band to\n measure biosignature gasses: Direct-imaging observations of terrestrial exoplanets will enable their\natmospheric characterization and habitability assessment. Considering the\nEarth, the key atmospheric signatures for the biosphere is O$_2$ and the\nphotochemical product O$_3$. However, this O$_2$-O$_3$ biosignature is not\ndetectable in the visible wavelengths for most of the time after the emergence\nof oxygenic photosynthesis life (i.e., the Proterozoic Earth). Here we\ndemonstrate spectroscopic observations in the ultraviolet wavelengths for\ndetecting and characterizing O$_2$ and O$_3$ in Proterozoic Earth-like planets,\nusing ExoReL$^\\Re$. For an O$_2$ mixing ratio 2 to 3 orders of magnitude less\nthan the present-day Earth, and an O$_3$ mixing ratio of $10^{-7}-10^{-6}$, we\nfind that O$_3$ can be detected and its mixing ratio can be measured precisely\n(within $~1$ order of magnitude) in the ultraviolet ($0.25-0.4\\ \\mu$m) in\naddition to visible-wavelength spectroscopy. With modest spectral resolution\n($R=7$) and S/N ($\\sim10$) in the ultraviolet, the O$_3$ detection is robust\nagainst other potential gases absorbing in the ultraviolet (e.g., H$_2$S and\nSO$_2$), as well as the short-wavelength cutoff between 0.2 and 0.25 $\\mu$m.\nWhile the O$_3$ detection does not rely on the near-infrared spectra, extending\nthe wavelength coverage to the near-infrared ($1-1.8\\ \\mu$m) would provide\nessential information to interpret the O$_3$ biosignature, including the mixing\nratio of H$_2$O, the cloud pressure, as well as the determination of the\ndominant gas of the atmosphere. The ultraviolet and near-infrared capabilities\nshould thus be evaluated as critical components for future missions aiming at\nimaging and characterizing terrestrial exoplanets, such as the Habitable Worlds\nObservatory.", "category": "astro-ph_EP" }, { "text": "Isotope velocimetry: Experimental and theoretical demonstration of the\n potential importance of gas flow for isotope fractionation during evaporation\n of protoplanetary material: We use new experiments and a theoretical analysis of the results to show that\nthe isotopic fractionation associated with laser-heating aerodynamic levitation\nexperiments is consistent with the velocity of flowing gas as the primary\ncontrol on the fractionation. The new Fe and Mg isotope data are well explained\nwhere the gas is treated as a low-viscosity fluid that flows around the molten\nspheres with high Reynolds numbers and minimal drag. A relationship between the\nratio of headwind velocity to thermal velocity and saturation is obtained on\nthe basis of this analysis. The recognition that it is the ratio of flow\nvelocity to thermal velocity that controls fractionation allows for\nextrapolation to other environments in which molten rock encounters gas with\nappreciable headwinds. In this way, in some circumstances, the degree of\nisotope fractionation attending evaporation is as much a velocimeter as it is a\nbarometer.", "category": "astro-ph_EP" }, { "text": "CRISM south polar mapping: First Mars year of observations: We report on mapping of the south polar region of Mars using data from the\nCompact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument. Our\nobservations have led to the following discoveries: 1. Water ice is present in\nthe form of pole-circling clouds originating from the circum-Hellas region,\nbeginning prior to Ls=162 and diminishing markedly at Ls=200-204. 2. It has\npreviously been inferred by temperature measurements(Titus et al., 2003) and\nCO2-H2O mixture spectral models (Langevin et al., 2007) that surface water ice\nwas present in the Cryptic Region in the final stages of sublimation. The high\nresolution of CRISM has revealed regions where only water ice is present (not a\nCO2-H2O ice mixture). This water ice disappears completely by Ls=252 and may be\nthe source of water vapor observed by CRISM in southern latitudes between\nLs=240-260 (Smith, et al., this issue). 3. We have estimated surface CO2 ice\ngrain size distributions for the South Pole Residual Cap (SPRC) and the\nseasonal CO2 ice cap that covers it throughout summer spring and summer. Our\nanalysis suggests that grain sizes peak at Ls=191-199 with an apparent grain\nsize of ~7 +/-1 cm. By the end of the summer period our analysis demonstrates\nminimum apparent grain sizes of ~5 +/-1 mm predominate in the SPRC. 4. Fine\ngrained CO2 ice condenses from Ls=0-40, and extends symmetrically away from the\ngeographic pole, extending beyond 80 deg S by Ls=4-10. No evidence for unusual\nCO2 depositional processes in the Cryptic Region is observed up to Ls=16.", "category": "astro-ph_EP" }, { "text": "Nano dust impacts on spacecraft and boom antenna charging: High rate sampling detectors measuring the potential difference between the\nmain body and boom antennas of interplanetary spacecraft have been shown to be\nefficient means to measure the voltage pulses induced by nano dust impacts on\nthe spacecraft body itself (see Meyer-Vernet et al, Solar Phys. 256, 463\n(2009)). However, rough estimates of the free charge liberated in post impact\nexpanding plasma cloud indicate that the cloud's own internal electrostatic\nfield is too weak to account for measured pulses as the ones from the TDS\ninstrument on the STEREO spacecraft frequently exceeding 0.1 V/m. In this paper\nwe argue that the detected pulses are not a direct measure of the potential\nstructure of the plasma cloud, but are rather the consequence of a transitional\ninterruption of the photoelectron return current towards the portion of the\nantenna located within the expanding cloud.", "category": "astro-ph_EP" }, { "text": "Long term evolution of planetary systems with a terrestrial planet and a\n giant planet: We study the long term orbital evolution of a terrestrial planet under the\ngravitational perturbations of a giant planet. In particular, we are interested\nin situations where the two planets are in the same plane and are relatively\nclose. We examine both possible configurations: the giant planet orbit being\neither outside or inside the orbit of the smaller planet. The perturbing\npotential is expanded to high orders and an analytical solution of the\nterrestrial planetary orbit is derived. The analytical estimates are then\ncompared against results from the numerical integration of the full equations\nof motion and we find that the analytical solution works reasonably well. An\ninteresting finding is that the new analytical estimates improve greatly the\npredictions for the timescales of the orbital evolution of the terrestrial\nplanet compared to an octupole order expansion. Finally, we briefly discuss\npossible applications of the analytical estimates in astrophysical problems.", "category": "astro-ph_EP" }, { "text": "Fuzzy Characterization of Near-Earth-Asteroids: Due to close encounters with the inner planets, Near-Earth-Asteroids (NEAs)\ncan have very chaotic orbits. Because of this chaoticity, a statistical\ntreatment of the dynamical properties of NEAs becomes difficult or even\nimpossible. We propose a new way to classify NEAs by using methods from Fuzzy\nLogic. We demonstrate how a fuzzy characterization of NEAs can be obtained and\nhow a subsequent analysis can deliver valid and quantitative results concerning\nthe long-term dynamics of NEAs.", "category": "astro-ph_EP" }, { "text": "Observability of Debris Discs around M-stars: Debris discs are second generation dusty discs formed by collisions of\nplanetesimals. Many debris discs have been found and resolved around hot and\nsolar-type stars. However, only a handful have been discovered around M-stars,\nand the reasons for their paucity remain unclear. Here we check whether the\nsensitivity and wavelength coverage of present-day telescopes are simply\nunfavourable for detection of these discs or if they are truly rare. We\napproach this question by looking at the Herschel/DEBRIS survey that has\nsearched for debris discs including M-type stars. Assuming that these cool-star\ndiscs are \"similar\" to those of the hotter stars in some sense (i.e., in terms\nof dust location, temperature, fractional luminosity, or mass), we check\nwhether this survey should have found them. With our procedure we can reproduce\nthe $2.1^{+4.5}_{-1.7}$% detection rate of M-star debris discs of the DEBRIS\nsurvey, which implies that these discs can indeed be similar to discs around\nhotter stars and just avoid detection. We then apply this procedure to IRAM\nNIKA-2 and ALMA bands 3, 6 and 7 to predict possible detection rates and give\nrecommendations for future observations. We do not favour observing with IRAM,\nsince it leads to detection rates lower than for the DEBRIS survey, with\n0.6%-4.5% for a 15 min observation. ALMA observations, with detection rates\n0.9%-7.2%, do not offer a significant improvement either, and so we conclude\nthat more sensitive far-infrared and single dish sub-millimetre telescopes are\nnecessary to discover the missing population of M-star debris discs.", "category": "astro-ph_EP" }, { "text": "Super stellar abundances of alkali metals suggest significant migration\n for Hot Jupiters: We investigate the origin of the measured over-abundance of alkali metals in\nthe atmospheres of hot gas giants, relative to both their host stars and their\natmospheric water abundances. We show that formation exterior to the water snow\nline followed by inward disc-driven migration results in excess accretion of\noxygen-poor, refractory-rich material from within the snow-line. This naturally\nleads to enrichment of alkali metals in the planetary atmosphere relative to\nthe bulk composition of its host star but relative abundances of water that are\nsimilar to the stellar host. These relative abundances cannot be explained by\nin situ formation which places the refractory elements in the planetary deep\ninterior rather than the atmosphere. We therefore suggest that the measured\ncompositions of the atmospheres of hot Jupiters are consistent with significant\nmigration for at least a subset of hot gas giants. Our model makes robust\npredictions about atmospheric composition that can be confirmed with future\ndata from JWST and Ariel.", "category": "astro-ph_EP" }, { "text": "Polarimetric Study of Near-Earth Asteroid (1566) Icarus: We conducted a polarimetric observation of the fast-rotating near-Earth\nasteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles\n$\\alpha$= 57 deg--141deg around the 2015 summer solstice. We found that the\nmaximum values of the linear polarization degree are\n$P_\\mathrm{max}$=7.32$\\pm$0.25 % at phase angles of\n$\\alpha_\\mathrm{max}$=124$\\pm$8 deg in the $V$-band and\n$P_\\mathrm{max}$=7.04$\\pm$0.21 % at $\\alpha_\\mathrm{max}$=124$\\pm$6 deg in the\n$R_\\mathrm{C}$-band. Applying the polarimetric slope-albedo empirical law, we\nderived a geometric albedo of $p_\\mathrm{V}$=0.25$\\pm$0.02, which is in\nagreement with that of Q-type taxonomic asteroids. $\\alpha_\\mathrm{max}$ is\nunambiguously larger than that of Mercury, the Moon, and another near-Earth\nS-type asteroid (4179) Toutatis but consistent with laboratory samples with\nhundreds of microns in size. The combination of the maximum polarization degree\nand the geometric albedo is in accordance with terrestrial rocks with a\ndiameter of several hundreds of micrometers. The photometric function indicates\na large macroscopic roughness. We hypothesize that the unique environment\n(i.e., the small perihelion distance $q$=0.187 au and a short rotational period\nof $T_\\mathrm{rot}$=2.27 hours) may be attributed to the paucity of small\ngrains on the surface, as indicated on (3200) Phaethon.", "category": "astro-ph_EP" }, { "text": "A Fireball and Potentially Hazardous Binary Near-Earth Asteroid (164121)\n 2003 YT$_1$: We present a fireball detected in the night sky over Kyoto, Japan on UT 2017\nApril 28 at ${\\rm 15^{h}\\,58^{m}\\,19^{s}}$ by the SonotaCo Network. The\nabsolute visual magnitude is $M_{\\rm v}$=$-$4.10$\\pm$0.42mag. Luminous light\ncurves obtain a meteoroid mass $m$=29$\\pm$1g, corresponding to the size $a_{\\rm\ns}$=2.7$\\pm$0.1cm. Orbital similarity assessed by D-criterions (cf. $D_{\\rm\nSH}$=0.0079) has identified a likely parent, the binary near-Earth asteroid\n(164121) 2003 YT$_1$. The suggested binary formation process is a YORP-driven\nrotational disintegration (Pravec & Harris 2007). The asynchronous state\nindicates the age of $<$10$^4$yr, near or shorter than the upper limit to\nmeteoroid stream lifetime. We examine potential dust production mechanisms for\nthe asteroid, including rotational instability, resurfacing, impact,\nphotoionization, radiation pressure sweeping, thermal fracture and sublimation\nof ice. We find some of them capable of producing the meteoroid-scale\nparticles. Rotational instability is presumed to cause mass shedding, in\nconsideration of the recent precedents (e.g. asteroid (6478) Gault), possibly\nreleasing mm-cm scale dust particles. Impacts by micrometeorites with size\n$\\simeq$1mm could be a trigger for ejecting the cm-sized particles. Radiation\npressure can sweep out the mm-sized dust particles, while not sufficient for\nthe cm-sized. For the other mechanisms, unprovable or unidentified. The\nfeasibility in the parental aspect of 2003 YT$_1$ is somewhat reconciled with\nthe fireball observation, yielding an insight into how we approach potentially\nhazardous objects.", "category": "astro-ph_EP" }, { "text": "A 4565 Myr old andesite from an extinct chondritic protoplanet: The age of iron meteorites implies that accretion of protoplanets began\nduring the first millions of years of the solar system. Due to the heat\ngenerated by 26Al decay, many early protoplanets were fully differentiated with\nan igneous crust produced during the cooling of a magma ocean and the\nsegregation at depth of a metallic core. The formation and nature of the\nprimordial crust generated during the early stages of melting is poorly\nunderstood, due in part to the scarcity of available samples. The newly\ndiscovered meteorite Erg Chech 002 (EC 002) originates from one such primitive\nigneous crust and has an andesite bulk composition. It derives from the partial\nmelting of a noncarbonaceous chondritic reservoir, with no depletion in alkalis\nrelative to the Sun photosphere and at a high degree of melting of around 25\npercents. Moreover, EC 002 is, to date, the oldest known piece of an igneous\ncrust with a 26Al-26Mg crystallization age of 4,565.0 million years (My).\nPartial melting took place at 1,220 C up to several hundred kyr before,\nimplying an accretion of the EC 002 parent body ca. 4,566 My ago. Protoplanets\ncovered by andesitic crusts were probably frequent. However, no asteroid shares\nthe spectral features of EC 002, indicating that almost all of these bodies\nhave disappeared, either because they went on to form the building blocks of\nlarger bodies or planets or were simply destroyed.", "category": "astro-ph_EP" }, { "text": "Synchronous Satellites of Venus: Synchronous satellites of Venus have long been thought unstable, but we use\nPoincare's surface of section technique to show that synchronous\nquasi-satellites orbiting just outside Venus' Hill sphere are quite stable, at\nleast for centuries. Such synchrosats always remain within a few degrees of\nVenus' equator, and drift very slowly in longitude. These synchrosats could be\nuseful for continuous monitoring of points on Venus' surface, such as active\nlandforms or long-lived landers.", "category": "astro-ph_EP" }, { "text": "Atomic iron and nickel in the coma of C/1996 B2 (Hyakutake): production\n rates, emission mechanisms, and possible parents: Two papers recently reported the detection of gaseous nickel and iron in the\ncomae of over 20 comets from observations collected over two decades, including\ninterstellar comet 2I/Borisov. To evaluate the state of the laboratory data in\nsupport of these identifications, we re-analyzed archived spectra of comet\nC/1996 B2 (Hyakutake), one of the nearest and brightest comets of the last\ncentury, using a combined experimental and computational approach. We developed\na new, many-level fluorescence model that indicates that the fluorescence\nemission of Fe I and Ni I vary greatly with heliocentric velocity. Combining\nthis model with laboratory spectra of an Fe-Ni plasma, we identified 22 lines\nof Fe I and 14 lines of Ni I in the spectrum of Hyakutake. Using Haser models,\nwe estimate the nickel and iron production rates as Q(Ni) = 2.6 - 4.1 x 10^22\ns^-1 and Q(Fe) = 0.4 - 2.8 x 10^23 s^-1. From derived column densities, the\nNi/Fe abundance ratio log10[Ni/Fe] = -0.15 +/- 0.07 deviates significantly from\nsolar abundance ratios, and it is consistent with the ratios observed in solar\nsystem comets. Possible production and emission mechanisms are analyzed in\ncontext of existing laboratory measurements. Based on the observed spatial\ndistributions, excellent fluorescence model agreement, and Ni/Fe ratio, our\nfindings support an origin consisting of a short-lived unknown parent followed\nby fluorescence emission. Our models suggest that the strong heliocentric\nvelocity dependence of the fluorescence efficiencies can provide a meaningful\ntest of the physical process responsible for the Fe I and Ni I emission.", "category": "astro-ph_EP" }, { "text": "Solar wind dynamics around a comet - A 2D semi-analytical kinetic model: We aim at analytically modelling the solar wind proton trajectories during\ntheir interaction with a partially ionised cometary atmosphere, not in terms of\nbulk properties of the flow but in terms of single particle dynamics. We first\nderive a generalised gyromotion, in which the electric field is reduced to its\nmotional component. Steady-state is assumed, and simplified models of the\ncometary density and of the electron fluid are used to express the force\nexperienced by individual solar wind protons during the interaction. A\nthree-dimensional (3D) analytical expression of the gyration of two interacting\nplasma beams is obtained. Applying it to a comet case, the force on protons is\nalways perpendicular to their velocity and has an amplitude proportional to\n1/r^2. The solar wind deflection is obtained at any point in space. The\nresulting picture presents a caustic of intersecting trajectories, and a\ncircular region is found that is completely free of particles. The particles do\nnot lose any kinetic energy and this absence of deceleration, together with the\nsolar wind deflection pattern and the presence of a solar wind ion cavity, is\nin good agreement with the general results of the Rosetta mission. The\nqualitative match between the model and the in situ data highlights how\ndominant the motional electric field is throughout most of the interaction\nregion for the solar wind proton dynamics. The model provides a simple general\nkinetic description of how momentum is transferred between these two\ncollisionless plasmas. It also shows the potential of this semi-analytical\nmodel for a systematic quantitative comparison to the data.", "category": "astro-ph_EP" }, { "text": "Deep Pa$\u03b2$ Imaging of the Candidate Accreting Protoplanet AB Aur b: Giant planets grow by accreting gas through circumplanetary disks, but little\nis known about the timescale and mechanisms involved in the planet assembly\nprocess because few accreting protoplanets have been discovered. Recent visible\nand infrared (IR) imaging revealed a potential accreting protoplanet within the\ntransition disk around the young intermediate-mass Herbig Ae star, AB Aurigae\n(AB Aur). Additional imaging in H$\\alpha$ probed for accretion and found\nagreement between the line-to-continuum flux ratio of the star and companion,\nraising the possibility that the emission source could be a compact disk\nfeature seen in scattered starlight. We present new deep Keck/NIRC2\nhigh-contrast imaging of AB Aur to characterize emission in Pa$\\beta$, another\naccretion tracer less subject to extinction. Our narrow band observations reach\na 5$\\sigma$ contrast of 9.6 mag at 0.6$''$, but we do not detect significant\nemission at the expected location of the companion, nor from other any other\nsource in the system. Our upper limit on Pa$\\beta$ emission suggests that if AB\nAur b is a protoplanet, it is not heavily accreting or accretion is stochastic\nand was weak during the observations.", "category": "astro-ph_EP" }, { "text": "Expected Fragment Distribution from the First Interstellar Meteor CNEOS\n 2014-01-08: In 2014, the fireball of the first interstellar meteor CNEOS 2014-01-08 (IM1)\n(Siraj & Loeb 2019), was detected off the northern coast of Papua New Guinea. A\nrecently announced ocean expedition will retrieve any extant fragments by\ntowing a magnetic sled across a 10 km x 10 km area of ocean floor approximately\n300 km north of Manus Island (Siraj, Loeb, & Gallaudet 2022). We formulate a\nmodel that includes both the probabilistic mass distribution of meteor\nfragments immediately after the fragmentation event, the ablation of the\nfragments, and the geographic distribution of post-ablation fragments along the\nground track trajectory of the bulk fragment cloud. We apply this model to IM1\nto provide a heuristic estimate of the impactor's post-ablation fragment mass\ndistribution, constructed through a Monte Carlo simulation. We find between ~8%\nand ~21% of fragments are expected to survive ablation with a mass $\\geq$ .001\ng, depending on the impactor's empirical yield strength. We also provide an\nestimation for the geographic distribution of post-ablation fragments.", "category": "astro-ph_EP" }, { "text": "On the Earth's tidal perturbations for the LARES satellite: Frame dragging, one of the outstanding phenomena predicted by General\nRelativity, is efficiently studied by means of the laser-ranged satellites\nLARES, LAGEOS and LAGEOS 2. The accurate analysis of the orbital perturbations\nof Earth's solid and ocean tides has been relevant for increasing the accuracy\nin the test of frame-dragging using these three satellites. The Earth's tidal\nperturbations acting on the LARES satellite are obtained for the 110\nsignificant modes of corresponding Doodson number and are exhibited to enable\nthe comparison to those of the LAGEOS and LAGEOS-2 satellites. For LARES we\nrepresent 29 perturbation modes for l=2,3,4 for ocean tides.", "category": "astro-ph_EP" }, { "text": "Three faint-source microlensing planets detected via resonant-caustic\n channel: We conducted a project of reinvestigating the 2017--2019 microlensing data\ncollected by the high-cadence surveys with the aim of finding planets that were\nmissed due to the deviations of planetary signals from the typical form of\nshort-term anomalies. The project led us to find three planets including\nKMT-2017-BLG-2509Lb, OGLE-2017-BLG-1099Lb, and OGLE-2019-BLG-0299Lb. The\nlensing light curves of the events have a common characteristic that the\nplanetary signals were produced by the crossings of faint source stars over the\nresonant caustics formed by giant planets located near the Einstein rings of\nhost stars. For all planetary events, the lensing solutions are uniquely\ndetermined without any degeneracy. It is estimated that the host masses are in\nthe range of $0.45\\lesssim M/M_\\odot \\lesssim 0.59$, which corresponds to early\nM to late K dwarfs, and thus the host stars are less massive than the sun. On\nthe other hand, the planets, with masses in the range of $2.1\\lesssim M/M_{\\rm\nJ}\\lesssim 6.2$, are heavier than the heaviest planet of the solar system, that\nis, Jupiter. The planets in all systems lie beyond the snow lines of the hosts,\nand thus the discovered planetary systems, together with many other\nmicrolensing planetary systems, support that massive gas-giant planets are\ncommonplace around low-mass stars. We discuss the role of late-time\nhigh-resolution imaging in clarifying resonant-image lenses with very faint\nsources.", "category": "astro-ph_EP" }, { "text": "An enhanced slope in the transmission spectrum of the hot Jupiter\n WASP-104b: We present the optical transmission spectrum of the hot Jupiter WASP-104b\nbased on one transit observed by the blue and red channels of the DBSP\nspectrograph at the Palomar 200-inch telescope and 14 transits observed by the\nMuSCAT2 four-channel imager at the 1.52 m Telescopio Carlos Sanchez. We also\nanalyse 45 additional K2 transits, after correcting for the flux contamination\nfrom a companion star. Together with the transit light curves acquired by DBSP\nand MuSCAT2, we are able to revise the system parameters and orbital ephemeris,\nconfirming that no transit timing variations exist. Our DBSP and MuSCAT2\ncombined transmission spectrum reveals an enhanced slope at wavelengths shorter\nthan 630 nm and suggests the presence of a cloud deck at longer wavelengths.\nWhile the Bayesian spectral retrieval analyses favour a hazy atmosphere,\nstellar spot contamination cannot be completely ruled out. Further evidence,\nfrom transmission spectroscopy and detailed characterisation of the host star's\nactivity, is required to distinguish the physical origin of the enhanced slope.", "category": "astro-ph_EP" }, { "text": "Theoretical transmission spectra of exoplanet atmospheres with\n hydrocarbon haze: Effect of creation, growth, and settling of haze particles.\n I. Model description and first results: Recently, properties of exoplanet atmospheres have been constrained via\nmulti-wavelength transit observation, which measures an apparent decrease in\nstellar brightness during planetary transit in front of its host star (called\ntransit depth). Sets of transit depths so far measured at different wavelengths\n(called transmission spectra) are somewhat diverse: Some show steep spectral\nslope features in the visible, some contain featureless spectra in the\nnear-infrared, some show distinct features from radiative absorption by gaseous\nspecies. These facts infer the existence of haze in the atmospheres especially\nof warm, relatively low-density super-Earths and mini-Neptunes. Previous\nstudies that addressed theoretical modeling of transmission spectra of\nhydrogen-dominated atmospheres with haze used some assumed distribution and\nsize of haze particles. In this study, we model the atmospheric chemistry,\nderive the spatial and size distributions of haze particles by simulating the\ncreation, growth and settling of hydrocarbon haze particles directly, and\ndevelop transmission spectrum models of UV-irradiated, solar-abundance\natmospheres of close-in warm ($\\sim$ 500 K) exoplanets. We find that the haze\nis distributed in the atmosphere much more broadly than previously assumed and\nconsists of particles of various sizes. We also demonstrate that the observed\ndiversity of transmission spectra can be explained by the difference in the\nproduction rate of haze monomers, which is related to the UV irradiation\nintensity from host stars.", "category": "astro-ph_EP" }, { "text": "Aerosols optical properties in Titan's Detached Haze Layer before the\n equinox: UV observations with Cassini ISS Narrow Angle Camera of Titan's detached haze\nis an excellent tool to probe its aerosols content without being affected by\nthe gas or the multiple scattering. Unfortunately, its low extent in altitude\nrequires a high resolution calibration and limits the number of images\navailable in the Cassini dataset. However, we show that it is possible to\nextract on each profile the local maximum of intensity of this layer and\nconfirm its stability at $500 \\pm 8$ km during the 2005-2007 period for all\nlatitudes lower than 45$^\\circ$N. Using the fractal aggregate scattering model\nof Tomasko et al. (2008) and a single scattering radiative transfer model, it\nis possible to derive the optical properties required to explain the\nobservations made at different phase angles. Our results indicates that the\naerosols have at least ten monomers of 60 nm radius, while the typical\ntangential column number density is about $2\\cdot 10^{10}$ agg.m$^{-2}$.\nMoreover, we demonstrate that these properties are constant within the error\nbars in the southern hemisphere of Titan over the observed time period. In the\nnorthern hemisphere, the size of the aerosols tend to decrease relatively to\nthe southern hemisphere and are associated with a higher tangential opacity.\nHowever, the lower number of observations available in this region due to the\norbital constraints is a limiting factor in the accuracy of these results.\nAssuming a fixed homogeneous content we notice that the tangential opacity can\nfluctuate up to a factor 3 among the observations at the equator. These\nvariations could be linked with short scale temporal and/or longitudinal events\nchanging the local density of the layer.", "category": "astro-ph_EP" }, { "text": "A Flat Inner Disk Model as an Alternative to the Kepler Dichotomy in the\n Q1 to Q16 Planet Population: We use simulated planetary systems to model the planet multiplicity of Kepler\nstars. Previous studies have underproduced single planet systems and invoked\nthe so called Kepler dichotomy, where the planet forming ability of a Kepler\nstar is dichotomous, producing either few or many transiting planets. In this\npaper we show that the Kepler dichotomy is only required when the inner part of\nplanetary disks are just assumed to be flared. When the inner part of planetary\ndisks are flat, we reproduce the observed planet multiplicity of Kepler stars\nwithout the need to invoke a dichotomy. We find that independent of the disk\nmodel assumed, the mean number of planets per star is approximately 2 for\norbital periods between 3 and 200 days, and for planetary radii between 1 and 5\nEarth radii. This contrasts with the Solar System where no planets occupy the\nsame parameter space.", "category": "astro-ph_EP" }, { "text": "Defining the Flora Family: Orbital Properties, Reflectance Properties\n and Age: The Flora family resides in the densely populated inner main belt, bounded in\nsemimajor axis by the $\\nu_6$ secular resonance and the Jupiter 3:1 mean motion\nresonance. The presence of several large families that overlap dynamically with\nthe Floras (e.g., the Vesta, Baptistina, and Nysa-Polana families), and the\nremoval of a significant fraction of Floras via the nearby $\\nu_6$ resonance\ncomplicates the Flora family's distinction in both proper orbital elements and\nreflectance properties. Here we use orbital information from the Asteroids\nDynamic Site, color information from the Sloan Digital Sky Survey, and albedo\ninformation from the Wide-field Infrared Survey Explorer to obtain the median\norbital and reflectance properties of the Floras by sampling the core of the\nfamily in multidimensional phase space. We find the median Flora SDSS colors to\nbe $a^*$ = 0.126 $\\pm$ 0.007 and $i-z = -0.037 \\pm 0.007$; the median Flora\nalbedo is $p_V$ = 0.291 $\\pm$ 0.012. These properties allow us to define ranges\nfor the Flora family in orbital and reflectance properties, as required for a\ndetailed dynamical study. We use the young Karin family, for which we have an\nage determined via direct backward integration of members' orbits, to calibrate\nthe Yarkovsky drift rates for the Flora family without having to estimate the\nFloras' material properties. The size-dependent dispersion of the Flora members\nin semimajor axis (the \"V\" plot) then yields an age for the family of\n$910^{+160}_{-120}$ My, with the uncertainty dominated by the uncertainty in\nthe material properties of the family members (e.g., density and surface\nthermal properties). We discuss the effects on our age estimate of two\nindependent processes that both introduce obliquity variations among the family\nmembers on short (My) timescales: 1) the capture of Flora members in spin-orbit\nresonance, and 2) YORP-driven obliquity variation.", "category": "astro-ph_EP" }, { "text": "HAT-P-65b and HAT-P-66b: Two Transiting Inflated Hot Jupiters and\n Observational Evidence for the Re-Inflation of Close-In Giant Planets: We present the discovery of the transiting exoplanets HAT-P-65b and\nHAT-P-66b, with orbital periods of 2.6055 d and 2.9721 d, masses of $0.527 \\pm\n0.083$ M$_{J}$ and $0.783 \\pm 0.057$ M$_{J}$ and inflated radii of $1.89 \\pm\n0.13$ R$_{J}$ and $1.59^{+0.16}_{-0.10}$ R$_{J}$, respectively. They orbit\nmoderately bright ($V=13.145 \\pm 0.029$, and $V=12.993 \\pm 0.052$) stars of\nmass $1.212 \\pm 0.050$ M$_{\\odot}$ and $1.255^{+0.107}_{-0.054}$ M$_{\\odot}$.\nThe stars are at the main sequence turnoff. While it is well known that the\nradii of close-in giant planets are correlated with their equilibrium\ntemperatures, whether or not the radii of planets increase in time as their\nhosts evolve and become more luminous is an open question. Looking at the\nbroader sample of well-characterized close-in transiting giant planets, we find\nthat there is a statistically significant correlation between planetary radii\nand the fractional ages of their host stars, with a false alarm probability of\nonly 0.0041%. We find that the correlation between the radii of planets and the\nfractional ages of their hosts is fully explained by the known correlation\nbetween planetary radii and their present day equilibrium temperatures, however\nif the zero-age main sequence equilibrium temperature is used in place of the\npresent day equilibrium temperature then a correlation with age must also be\nincluded to explain the planetary radii. This suggests that, after contracting\nduring the pre-main-sequence, close-in giant planets are re-inflated over time\ndue to the increasing level of irradiation received from their host stars.\nPrior theoretical work indicates that such a dynamic response to irradiation\nrequires a significant fraction of the incident energy to be deposited deep\nwithin the planetary interiors.", "category": "astro-ph_EP" }, { "text": "Origin of the peculiar eccentricity distribution of the inner cold\n Kuiper belt: Dawson and Murray-Clay (2012) pointed out that the inner part of the cold\npopulation in the Kuiper belt (that with semi major axis a<43.5 AU) has orbital\neccentricities significantly smaller than the limit imposed by stability\nconstraints. Here, we confirm their result by looking at the orbital\ndistribution and stability properties in proper element space. We show that the\nobserved distribution could have been produced by the slow sweeping of the 4/7\nmean motion resonance with Neptune that accompanied the end of Neptune's\nmigration process. The orbital distribution of the hot Kuiper belt is not\nsignificantly affected in this process, for the reasons discussed in the main\ntext. Therefore, the peculiar eccentricity distribution of the inner cold\npopulation can not be unequivocally interpreted as evidence that the cold\npopulation formed in-situ and was only moderately excited in eccentricity; it\ncan simply be the signature of Neptune's radial motion, starting from a\nmoderately eccentric orbit. We discuss how this agrees with a scenario of giant\nplanet evolution following a dynamical instability and, possibly, with the\nradial transport of the cold population.", "category": "astro-ph_EP" }, { "text": "Stellar Spin-Orbit Alignment for Kepler-9, a Multi-transiting Planetary\n system with Two Outer Planets Near 2:1 Resonance: We present spectroscopic measurements of the Rossiter-McLaughlin effect for\nthe planet b of Kepler-9 multi-transiting planet system. The resulting\nsky-projected spin-orbit angle is $\\lambda=-13^{\\circ} \\pm 16^{\\circ}$, which\nfavors an aligned system and strongly disfavors highly misaligned, polar, and\nretrograde orbits. Including Kepler-9, there are now a total of 4\nRossiter-McLaughlin effect measurements for multiplanet systems, all of which\nare consistent with spin-orbit alignment.", "category": "astro-ph_EP" }, { "text": "An Observational Diagnostic for Distinguishing Between Clouds and Haze\n in Hot Exoplanet Atmospheres: The nature of aerosols in hot exoplanet atmospheres is one of the primary\nvexing questions facing the exoplanet field. The complex chemistry, multiple\nformation pathways, and lack of easily identifiable spectral features\nassociated with aerosols make it especially challenging to constrain their key\nproperties. We propose a transmission spectroscopy technique to identify the\nprimary aerosol formation mechanism for the most highly irradiated hot Jupiters\n(HIHJs). The technique is based on the expectation that the two key types of\naerosols -- photochemically generated hazes and equilibrium condensate clouds\n-- are expected to form and persist in different regions of a highly irradiated\nplanet's atmosphere. Haze can only be produced on the permanent daysides of\ntidally-locked hot Jupiters, and will be carried downwind by atmospheric\ndynamics to the evening terminator (seen as the trailing limb during transit).\nClouds can only form in cooler regions on the night side and morning terminator\nof HIHJs (seen as the leading limb during transit). Because opposite limbs are\nexpected to be impacted by different types of aerosols, ingress and egress\nspectra, which primarily probe opposing sides of the planet, will reveal the\ndominant aerosol formation mechanism. We show that the benchmark HIHJ,\nWASP-121b, has a transmission spectrum consistent with partial aerosol coverage\nand that ingress-egress spectroscopy would constrain the location and formation\nmechanism of those aerosols. In general, using this diagnostic we find that\nobservations with JWST and potentially with HST should be able to distinguish\nbetween clouds and haze for currently known HIHJs.", "category": "astro-ph_EP" }, { "text": "Exoplanetary Spin-Orbit Alignment: Results from the Ensemble of\n Rossiter-McLaughlin Observations: One possible diagnostic of planet formation, orbital migration, and tidal\nevolution is the angle psi between a planet's orbital axis and the spin axis of\nits parent star. In general, psi cannot be measured, but for transiting planets\none can measure the angle lambda between the sky projections of the two axes\nvia the Rossiter-McLaughlin effect. Here, we show how to combine measurements\nof lambda in different systems to derive statistical constraints on psi. We\napply the method to 11 published measurements of lambda, using two different\nsingle-parameter distributions to describe the ensemble. First, assuming a\nRayleigh distribution (or more precisely, a Fisher distribution on a sphere),\nwe find that the peak value is less than 22 degrees with 95% confidence.\nSecond, assuming a fraction f of the orbits have random orientations relative\nto the stars, and the remaining fraction (1-f) are perfectly aligned, we find\nf<0.36 with 95% confidence. This latter model fits the data better than the\nRayleigh distribution, mainly because the XO-3 system was found to be strongly\nmisaligned while the other 10 systems are consistent with perfect alignment. If\nthe XO-3 result proves robust, then our results may be interpreted as evidence\nfor two distinct modes of planet migration.", "category": "astro-ph_EP" }, { "text": "Crowding Out of Giants by Dwarfs: An Origin for the Lack of Companion\n Planets in Hot Jupiter Systems: We investigate formation of close-in terrestrial planets from planetary\nembryos under the influence of a hot Jupiter (HJ) using gravitational N-body\nsimulations that include gravitational interactions between the gas disk and\nthe terrestrial planet (e.g., type I migration). Our simulations show that\nseveral terrestrial planets efficiently form outside the orbit of the HJ,\nmaking a chain of planets, and all of them gravitationally interact directly or\nindirectly with the HJ through resonance, which leads to inward migration of\nthe HJ. We call this mechanism of induced migration of the HJ as \"crowding\nout.\" The HJ is eventually lost by collision with the central star, and only\nseveral terrestrial planets remain. We also find that the efficiency of the\ncrowding-out effect depends on model parameters; for example, the heavier the\ndisk is, the more efficient the crowding out is. When planet formation occurs\nin a massive disk, the HJ can be lost to the central star and is never\nobserved. On the other hand, for a less massive disk, the HJ and terrestrial\nplanets can coexist; however, the companion planets can be below the detection\nlimit of current observations. In both cases, systems with the HJ and\nterrestrial planets have little chance for detection. Therefore, our model\nnaturally explains the lack of companion planets in HJ systems regardless of\nthe disk mass. In effect, our model provide a theoretical prediction for future\nobservations; additional planets can be discovered just outside the HJ, and\ntheir masses should generally be small.", "category": "astro-ph_EP" }, { "text": "Transit detections of extrasolar planets around main-sequence stars - I.\n Sky maps for hot Jupiters: The findings of more than 350 extrasolar planets, most of them nontransiting\nHot Jupiters, have revealed correlations between the metallicity of the\nmain-sequence (MS) host stars and planetary incidence. This connection can be\nused to calculate the planet formation probability around other stars, not yet\nknown to have planetary companions. We locate the promising spots for current\ntransit surveys on the celestial plane and strive for absolute values of the\nexpected number of transits in general. We used data of the Tycho catalog for\nabout 1 million objects to locate all the stars with 0m < m_V < 11.5m on the\ncelestial plane. We took several empirical relations between the parameters\nlisted in the Tycho catalog, such as distance to Earth, m_V, and (B-V), and\nthose parameters needed to account for the probability of a star to host an\nobservable, transiting exoplanet. The empirical relations between stellar\nmetallicity and planet occurrence combined with geometrical considerations were\nused to yield transit probabilities for the MS stars in the Tycho catalog.\nMagnitude variations in the FOV were simulated to test whether this\nfluctuations would be detected by BEST, XO, SuperWASP and HATNet. We present a\nsky map of the expected number of Hot Jupiter transit events on the basis of\nthe Tycho catalog. The comparison between the considered transit surveys yields\nsignificantly differing maps of the expected transit detections. The\nsky-integrated magnitude distribution predicts 20 Hot Jupiter transits with\norbital periods between 1.5 d and 50 d and m_V < 8m, of which two are currently\nknown. In total, we expect 3412 Hot Jupiter transits to occur in front of MS\nstars within the given magnitude range. The most promising observing site on\nEarth is at latitude = -1.", "category": "astro-ph_EP" }, { "text": "Neptune on tiptoes: dynamical histories that preserve the cold classical\n Kuiper belt: The current dynamical structure of the Kuiper belt was shaped by the orbital\nevolution of the giant planets, especially Neptune, during the era following\nplanet formation, when the giant planets may have undergone planet-planet\nscattering and/or planetesimal-driven migration. Numerical simulations of this\nprocess, while reproducing many properties of the belt, fail to generate the\nhigh inclinations and eccentricities observed for some objects while\nmaintaining the observed dynamically \"cold\" population. We present the first of\na three-part parameter study of how different dynamical histories of Neptune\nsculpt the planetesimal disk. Here we identify which dynamical histories allow\nan in situ planetesimal disk to remain dynamically cold, becoming today's cold\nKuiper belt population. We find that if Neptune undergoes a period of elevated\neccentricity and/or inclination, it secularly excites the eccentricities and\ninclinations of the planetesimal disk. We demonstrate that there are several\nwell-defined regimes for this secular excitation, depending on the relative\ntimescales of Neptune's migration, the damping of Neptune's orbital inclination\nand/or eccentricity, and the secular evolution of the planetesimals. We model\nthis secular excitation analytically in each regime, allowing for a thorough\nexploration of parameter space. Neptune's eccentricity and inclination can\nremain high for a limited amount of time without disrupting the cold classical\nbelt. In the regime of slow damping and slow migration, if Neptune is located\n(for example) at 20 AU, then its eccentricity must stay below 0.18 and its\ninclination below 6{\\deg}.", "category": "astro-ph_EP" }, { "text": "Gran Telescopio Canarias OSIRIS Transiting Exoplanet Atmospheric Survey:\n Detection of potassium in XO-2b from narrowband spectrophotometry: We present Gran Telescopio Canarias (GTC) optical transit narrow-band\nphotometry of the hot-Jupiter exoplanet XO-2b using the OSIRIS instrument. This\nunique instrument has the capabilities to deliver high cadence narrow-band\nphotometric lightcurves, allowing us to probe the atmospheric composition of\nhot Jupiters from the ground. The observations were taken during three transit\nevents which cover four wavelengths at spectral resolutions near 500, necessary\nfor observing atmospheric features, and have near-photon limited sub-mmag\nprecisions. Precision narrow-band photometry on a large aperture telescope\nallows for atmospheric transmission spectral features to be observed for\nexoplanets around much fainter stars than those of the well studied targets\nHD209458b and HD189733b, providing access to the majority of known transiting\nplanets. For XO-2b, we measure planet-to-star radius contrasts of\nR_pl/R_star=0.10508+/-0.00052 at 6792 Ang, 0.10640+/-0.00058 at 7582 Ang, and\n0.10686+/-0.00060 at 7664.9 Ang, and 0.10362+/-0.00051 at 8839 Ang. These\nmeasurements reveal significant spectral features at two wavelengths, with an\nabsorption level of 0.067+/-0.016% at 7664.9 Ang due to atmospheric potassium\nin the line core (a 4.1-sigma significance level), and an absorption level of\n0.058+/-0.016% at 7582 Ang, (a 3.6-sigma significance level). When comparing\nour measurements to hot-Jupiter atmospheric models, we find good agreement with\nmodels which are dominated in the optical by alkali metals. This is the first\nevidence for potassium in an extrasolar planet, an element that has long been\ntheorized along with sodium to be a dominant source of opacity at optical\nwavelengths for hot Jupiters.", "category": "astro-ph_EP" }, { "text": "Vertically resolved magma ocean-protoatmosphere evolution: H$_2$,\n H$_2$O, CO$_2$, CH$_4$, CO, O$_2$, and N$_2$ as primary absorbers: The earliest atmospheres of rocky planets originate from extensive volatile\nrelease during magma ocean epochs that occur during assembly of the planet.\nThese establish the initial distribution of the major volatile elements between\ndifferent chemical reservoirs that subsequently evolve via geological cycles.\nCurrent theoretical techniques are limited in exploring the anticipated range\nof compositional and thermal scenarios of early planetary evolution, even\nthough these are of prime importance to aid astronomical inferences on the\nenvironmental context and geological history of extrasolar planets. Here, we\npresent a coupled numerical framework that links an evolutionary,\nvertically-resolved model of the planetary silicate mantle with a\nradiative-convective model of the atmosphere. Using this method we investigate\nthe early evolution of idealized Earth-sized rocky planets with end-member,\nclear-sky atmospheres dominated by either H$_2$, H$_2$O, CO$_2$, CH$_4$, CO,\nO$_2$, or N$_2$. We find central metrics of early planetary evolution, such as\nenergy gradient, sequence of mantle solidification, surface pressure, or\nvertical stratification of the atmosphere, to be intimately controlled by the\ndominant volatile and outgassing history of the planet. Thermal sequences fall\ninto three general classes with increasing cooling timescale: CO, N$_2$, and\nO$_2$ with minimal effect, H$_2$O, CO$_2$, and CH$_4$ with intermediate\ninfluence, and H$_2$ with several orders of magnitude increase in\nsolidification time and atmosphere vertical stratification. Our numerical\nexperiments exemplify the capabilities of the presented modeling framework and\nlink the interior and atmospheric evolution of rocky exoplanets with\nmulti-wavelength astronomical observations.", "category": "astro-ph_EP" }, { "text": "A Dynamical Analysis of the Kepler-80 System of Five Transiting Planets: Kepler has discovered hundreds of systems with multiple transiting exoplanets\nwhich hold tremendous potential both individually and collectively for\nunderstanding the formation and evolution of planetary systems. Many of these\nsystems consist of multiple small planets with periods less than ~50 days known\nas Systems with Tightly-spaced Inner Planets, or STIPs. One especially\nintriguing STIP, Kepler-80 (KOI-500), contains five transiting planets: f, d,\ne, b, and c with periods of 1.0, 3.1, 4.6, 7.1, 9.5 days, respectively. We\nprovide measurements of transit times and a transit timing variation (TTV)\ndynamical analysis. We find that TTVs cannot reliably detect eccentricities for\nthis system, though mass estimates are not affected. Restricting the\neccentricity to a reasonable range, we infer masses for the outer four planets\n(d, e, b, and c) to be $6.75^{+0.69}_{-0.51}$, $4.13^{+0.81}_{-0.95}$,\n$6.93^{+1.05}_{-0.70}$, and $6.74^{+1.23}_{-0.86}$ Earth masses, respectively.\nThe similar masses but different radii are consistent with terrestrial\ncompositions for d and e and $\\sim$2% H/He envelopes for b and c. We confirm\nthat the outer four planets are in a rare dynamical configuration with four\ninterconnected three-body resonances that are librating with few degree\namplitudes. We present a formation model that can reproduce the observed\nconfiguration by starting with a multi-resonant chain and introducing\ndissipation. Overall, the information-rich Kepler-80 planets provide an\nimportant perspective into exoplanetary systems.", "category": "astro-ph_EP" }, { "text": "2001 QR322: a dynamically unstable Neptune Trojan?: Since early work on the stability of the first Neptunian Trojan, 2001 QR322,\nsuggested that it was a dynamically stable, primordial body, it has been\nassumed this applies to both that object, and its more recently discovered\nbrethren. However, it seems that things are no longer so clear cut. In this\nwork, we present the results of detailed dynamical simulations of the orbital\nbehaviour of 2001 QR322. Using an ephemeris for the object that has\nsignificantly improved since earlier works, we follow the evolution of 19683\ntest particles, placed on orbits within the observational error ellipse of 2001\nQR322's orbit, for a period of 1 Gyr. We find that majority of these \"clones\"\nof 2001 QR322 are dynamically unstable, exhibiting a near-exponential decay\nfrom both the Neptunian Trojan cloud (decay halflife ~550 Myr) and the Solar\nsystem (decay halflife ~590 Myr). The stability of the object within Neptune's\nTrojan cloud is found to be strongly dependent on the initial semi-major axis\nused, with those objects located at semimajor axis equal or greater than 30.30\nAU being significantly less stable than those interior to this value, as a\nresult of their having initial libration amplitudes very close to a critical\nthreshold dividing regular and irregular motion, located at ~70-75 deg (full\nextent of angular motion). This result suggests that, if 2001 QR322 is a\nprimordial Neptunian Trojan, it must be a representative of a population that\nwas once significantly larger than that we see today, and adds weight to the\nidea that the Neptune Trojans may represent a significant source of objects\nmoving on unstable orbits between the giant planets (the Centaurs).", "category": "astro-ph_EP" }, { "text": "Expanding Mars Climate Modeling: Interpretable Machine Learning for\n Modeling MSL Relative Humidity: For the past several decades, numerous attempts have been made to model the\nclimate of Mars with extensive studies focusing on the planet's dynamics and\nthe understanding of its climate. While physical modeling and data assimilation\napproaches have made significant progress, uncertainties persist in\ncomprehensively capturing and modeling the complexities of Martian climate. In\nthis work, we propose a novel approach to Martian climate modeling by\nleveraging machine learning techniques that have shown remarkable success in\nEarth climate modeling. Our study presents a deep neural network designed to\naccurately model relative humidity in Gale Crater, as measured by NASA's Mars\nScience Laboratory ``Curiosity'' rover. By utilizing simulated meteorological\nvariables produced by the Mars Planetary Climate Model, a robust Global\nCirculation Model, our model accurately predicts relative humidity with a mean\nerror of 3\\% and an $R^2$ score of 0.92. Furthermore, we present an approach to\npredict quantile ranges of relative humidity, catering to applications that\nrequire a range of values. To address the challenge of interpretability\nassociated with machine learning models, we utilize an interpretable model\narchitecture and conduct an in-depth analysis of its internal mechanisms and\ndecision making processes. We find that our neural network can effectively\nmodel relative humidity at Gale crater using a few meteorological variables,\nwith the monthly mean surface H$_2$O layer, planetary boundary layer height,\nconvective wind speed, and solar zenith angle being the primary contributors to\nthe model predictions. In addition to providing a fast and efficient method to\nmodeling climate variables on Mars, this modeling approach can also be used to\nexpand on current datasets by filling spatial and temporal gaps in\nobservations.", "category": "astro-ph_EP" }, { "text": "Mass-Radius Relation for Rocky Planets based on PREM: Several small dense exoplanets are now known, inviting comparisons to Earth\nand Venus. Such comparisons require translating their masses and sizes to\ncomposition models of evolved multi-layer-interior planets. Such theoretical\nmodels rely on our understanding of the Earth's interior, as well as\nindependently derived equations of state (EOS), but have so far not involved\ndirect extrapolations from Earth's seismic model -PREM. In order to facilitate\nmore detailed compositional comparisons between small exoplanets and the Earth,\nwe derive here a semi-empirical mass-radius relation for two-layer rocky\nplanets based on PREM: ${\\frac{R}{R_\\oplus}} = (1.07-0.21\\cdot \\text{CMF})\\cdot\n(\\frac{M}{M_\\oplus})^{1/3.7}$, where CMF stands for Core Mass Fraction. It is\napplicable to 1$\\sim$8 M$_{\\oplus}$ and CMF of 0.0$\\sim$0.4. Applying this\nformula to Earth and Venus and several known small exoplanets with radii and\nmasses measured to better than $\\sim$30\\% precision gives a CMF fit of\n$0.26\\pm0.07$.", "category": "astro-ph_EP" }, { "text": "Orbit injection of planet-crossing asteroids: Solar system Centaurs originate in transneptunian space from where planet\norbit crossing events inject their orbits inside the giant planets' domain.\nHere, we examine this injection process in the three-body problem by studying\nthe orbital evolution of transneptunian asteroids located at Neptune's\ncollision singularity as a function of the Tisserand invariant, T. Two\ninjection modes are found, one for T>0.1, or equivalently prograde inclinations\nfar from the planet, where unstable motion dominates injection, and another for\nT<= 0.1, or equivalently polar and retrograde inclinations far from the planet,\nwhere stable motion dominates injection. The injection modes are independent of\nthe initial semi-major axis and the dynamical time at the collision\nsingularity. The simulations uncovered a region in the polar corridor where the\ndynamical time exceeds the solar system's age suggesting the possibility of\nlong-lived primordial polar transneptunian reservoirs that supply Centaurs to\nthe giant planets' domain.", "category": "astro-ph_EP" }, { "text": "On a Possible Giant Impact Origin for the Colorado Plateau: It is proposed and substantiated that an extraterrestrial object of the\napproximate size and mass of Planet Mars, impacting the Earth in grazing\nincidence along an approximately N-NE to S-SW route with respect to the current\norientation of the North America continent, at about 750 million years ago (750\nMa), is likely to be the direct cause of a chain of events which led to the\nrifting of the Rodinia supercontinent and the severing of the foundation of the\nColorado Plateau from its surrounding craton. It is further argued that the\nimpactor was most likely a rogue exoplanet, which originated from one of the\npast crossings of our Solar System through the Galactic spiral arms, during the\nSun's orbital motion around the center of the Milky Way Galaxy. New advances in\ngalactic dynamics have shown that the sites of galactic spiral arms are\nlocations of density-wave collisionless shocks. The perturbations from such\nshocks are known to lead to the formation of massive stars, which evolve\nquickly and die as supernovae. The blastwaves from supernova explosions, in\naddition to the spiral-arm collisionless shocks themselves, could perturb the\norbits of the streaming disk matter, occasionally producing rogue exoplanets\nthat can reach the inner confines of our Solar System. The similarity of the\nperiod of spiral-arm crossings of our Solar System, with the approximate period\nof major extinction events in the Phanerozoic Eon of the Earth's history, as\nwell as with the (half) period of the supercontinent cycle, indicates that the\nglobal environment of the Milky Way Galaxy may have played a major role in\ninitiating Earth's tectonic activities.", "category": "astro-ph_EP" }, { "text": "TraMoS project III: Improved physical parameters, timing analysis, and\n star-spot modelling of the WASP-4b exoplanet system from 38 transit\n observations: We report twelve new transit observations of the exoplanet WASP-4b from the\nTransit Monitoring in the South Project (TraMoS) project. These transits are\ncombined with all previously published transit data for this planet to provide\nan improved radius measurement of Rp = 1.395 +- 0.022 Rjup and improved transit\nephemerides. In a new homogeneous analysis in search for Transit Timing\nVariations (TTVs) we find no evidence of those with RMS amplitudes larger than\n20 seconds over a 4-year time span. This lack of TTVs rules out the presence of\nadditional planets in the system with masses larger than about 2.5 M_earth, 2.0\nM_earth, and 1.0 M_earth around the 1:2, 5:3 and 2:1 orbital resonances. Our\nsearch for the variation of other parameters, such as orbital inclination and\ntransit depth also yields negative results over the total time span of the\ntransit observations. Finally we perform a simple study of stellar spots\nconfigurations of the system and conclude that the star rotational period is\nabout 34 days.", "category": "astro-ph_EP" }, { "text": "Very wide companion fraction from Gaia DR2: a weak or no enhancement for\n hot jupiter hosts, and a strong enhancement for contact binaries: There is an ongoing debate on whether hot jupiter hosts are more likely to be\nfound in wide binaries with separations of $\\gtrsim 100$ AU. In this paper, we\nsearch for comoving, very wide companions with separations of $10^3-10^4$ AU\nfor hot jupiter hosts and main-sequence contact binaries in Gaia DR2, and\ncompare the very wide companion fractions with their object-by-object-matched\nfield star samples. We find that $11.9\\pm 2.5$% of hot jupiter hosts and\n$14.1\\pm 1.0$% of contact binaries have companions at separations of\n$10^3-10^4$ AU. While the very wide companion fraction of hot jupiter hosts is\na factor of $1.9\\pm0.5$ larger than their matched field star sample, it is\nconsistent, within $\\sim1\\sigma$, with that of matched field stars if the\nmatching is only with field stars without close companions (within $\\sim50$ AU)\nas is the case for hot jupiter hosts. The very wide companion fraction of\ncontact binaries is a factor of $3.1\\pm0.5$ larger than their matched field\nstar sample, suggesting that the formation and evolution of contact binaries\nare either tied to or correlated with the presence of wide companions. In\ncontrast, the weak enhancement of very wide companion fraction for hot jupiter\nhosts implies that the formation of hot jupiters is not as sensitive to those\nenvironment properties. Our results also hint that the occurrence rates of dual\nhot jupiter hosts and dual contact binaries may be higher than the expected\nvalues from random pairing of field stars, which may be due to their underlying\nmetallicity and age dependence.", "category": "astro-ph_EP" }, { "text": "NELIOTA Lunar Impact Flash Detection and Event Validation: NELIOTA (NEO Lunar Impacts and Optical TrAnsients) is an ESA-funded lunar\nmonitoring project, which aims to determine the size-frequency distribution of\nsmall Near-Earth Objects (NEOs) via detection of impact flashes on the surface\nof the Moon. A prime focus, high-speed, twin-camera system providing\nsimultaneous observations in two photometric bands at a rate of 30\nframes-per-second on the 1.2 m Kryoneri telescope of the National Observatory\nof Athens was commissioned for this purpose. A dedicated software processes the\nimages and automatically detects candidate lunar impact flashes, which are then\nvalidated by an expert user. The four year observing campaign began in February\n2017 and has so far detected more than 40 lunar impact events. The software\nroutinely detects satellites, which typically appear as streaks or dots\ncrossing the lunar disk. To avoid confusing these events with real flashes, we\ncheck different available catalogs with spacecraft orbital information and\nexclude spacecraft identifications.", "category": "astro-ph_EP" }, { "text": "The impact of the Kasatochi eruption on the Moon's illumination during\n the August 2008 lunar eclipse: The Moon's changeable aspect during a lunar eclipse is largely attributable\nto variations in the refracted unscattered sunlight absorbed by the terrestrial\natmosphere that occur as the satellite crosses the Earth's shadow. The\ncontribution to the Moon's aspect from sunlight scattered at the Earth's\nterminator is generally deemed minor. However, our analysis of a published\nspectrum of the 16 August 2008 lunar eclipse shows that diffuse sunlight is a\nmajor component of the measured spectrum at wavelengths shorter than 600 nm.\nThe conclusion is supported by two distinct features, namely the spectrum's\ntail at short wavelengths and the unequal absorption by an oxygen collisional\ncomplex at two nearby bands. Our findings are consistent with the presence of\nthe volcanic cloud reported at high northern latitudes following the 7-8 August\n2008 eruption in Alaska of the Kasatochi volcano. The cloud both attenuates the\nunscattered sunlight and enhances moderately the scattered component, thus\nmodifying the contrast between the two contributions.", "category": "astro-ph_EP" }, { "text": "TESS Input Catalog versions 8.1 and 8.2: Phantoms in the 8.0 Catalog and\n How to Handle Them: We define various types of \"phantom\" stars that may appear in the TESS Input\nCatalog (TIC), and provide examples and lists of currently known cases. We\npresent a methodology that can be used to check for phantoms around any object\nof interest in the TIC, and we present an approach for correcting the\nTIC-reported flux contamination factors accordingly. We checked all 2077 TESS\nObjects of Interest (TOIs) known as of July 21st 2020 (Sectors 1 to 24) and\nsent corrections for 291 stars to MAST where they are integrated into the\npublicly available TIC-8, updating it to TIC 8.1. We used the experience gained\nto construct an all-sky algorithm searching for \"phantoms\" which led to 34\nmillion updates integrated into TIC 8.2.", "category": "astro-ph_EP" }, { "text": "Tidal Heating Models for the Radii of the Inflated Transiting Giant\n Planets WASP-4b, WASP-6b, WASP-12b, and TrES-4: In order to explain the inflated radii of some transiting extrasolar giant\nplanets, we investigate a tidal heating scenario for the inflated planets\nWASP-4b, WASP-6b, WASP-12b, WASP-15b, and TrES-4. To do so, we assume that they\nretain a nonzero eccentricity, possibly by dint of continuing interaction with\na third body. We calculate the amount of extra heating in the envelope that is\nthen required to fit the radius of each planet, and we explore how this\nadditional power depends on the planetary atmospheric opacity and on the mass\nof a heavy-element central core. There is a degeneracy between the core mass\n$M_{\\rm core}$ and the heating $\\dot{E}_{\\rm heating}$. Therefore, in the case\nof tidal heating, there is for each planet a range of the couple $\\{M_{\\rm\ncore},e^2/Q'_p\\}$ that can lead to the same radius, where $Q'_p$ is the tidal\ndissipation factor and $e$ is the eccentricity. With this in mind, we also\ninvestigate the case of the non-inflated planet HAT-P-12b, which can admit\nsolutions combining a heavy-element core and tidal heating. A substantial\nimprovement of the measured eccentricities of such planetary systems could\nsimplify this degeneracy by linking the two unknown parameters $\\{M_{\\rm\ncore},Q'_p\\}$. Further independent constraints on either of these parameters\nwould, through our calculations, constrain the other.", "category": "astro-ph_EP" }, { "text": "The Solar Twin Planet Search. V. Close-in, low-mass planet candidates\n and evidence of planet accretion in the solar twin HIP 68468: [Methods]. We obtained high-precision radial velocities with HARPS on the ESO\n3.6 m telescope and determined precise stellar elemental abundances (~0.01 dex)\nusing MIKE spectra on the Magellan 6.5m telescope. [Results]. Our data indicate\nthe presence of a planet with a minimum mass of 26 Earth masses around the\nsolar twin HIP 68468. The planet is a super-Neptune, but unlike the distant\nNeptune in our solar system (30 AU), HIP 68468c is close-in, with a semi-major\naxis of 0.66 AU, similar to that of Venus. The data also suggest the presence\nof a super-Earth with a minimum mass of 2.9 Earth masses at 0.03 AU; if the\nplanet is confirmed, it will be the fifth least massive radial velocity planet\ndiscovery to date and the first super-Earth around a solar twin. Both\nisochrones (5.9 Gyr) and the abundance ratio [Y/Mg] (6.4 Gyr) indicate an age\nof about 6 billion years. The star is enhanced in refractory elements when\ncompared to the Sun, and the refractory enrichment is even stronger after\ncorrections for Galactic chemical evolution. We determined a NLTE Li abundance\nof 1.52 dex, which is four times higher than what would be expected for the age\nof HIP 68468. The older age is also supported by the low log(R'HK) (-5.05) and\nlow jitter. Engulfment of a rocky planet of 6 Earth masses can explain the\nenhancement in both lithium and the refractory elements. [Conclusions]. The\nsuper-Neptune planet candidate is too massive for in situ formation, and\ntherefore its current location is most likely the result of planet migration\nthat could also have driven other planets towards its host star, enhancing thus\nthe abundance of lithium and refractory elements in HIP 68468. The intriguing\nevidence of planet accretion warrants further observations to verify the\nexistence of the planets that are indicated by our data and to better constrain\nthe nature of the planetary system around this unique star.", "category": "astro-ph_EP" }, { "text": "A Twilight Search for Atiras, Vatiras and Co-orbital Asteroids:\n Preliminary Results: Near-Earth Objects (NEOs) that orbit the Sun on or within Earth's orbit are\ntricky to detect for Earth-based observers due to their proximity to the Sun in\nthe sky. These small bodies hold clues to the dynamical history of the inner\nsolar system as well as the physical evolution of planetesimals in extreme\nenvironments. Populations in this region include the Atira and Vatira\nasteroids, as well as Venus and Earth co-orbital asteroids. Here we present a\ntwilight search for these small bodies, conducted using the 1.2-m Oschin\nSchmidt and the Zwicky Transient Facility (ZTF) camera at Palomar Observatory.\nThe ZTF twilight survey operates at solar elongations down to $35^\\circ$ with\nlimiting magnitude of $r=19.5$. During a total of 40 evening sessions and 62\nmorning sessions conducted between 2018 November 15 and 2019 June 23, we\ndetected 6 Atiras, including 2 new discoveries 2019 AQ$_3$ and 2019 LF$_6$, but\nno Vatiras or Earth/Venus co-orbital asteroids. NEO population models show that\nthese new discoveries are likely only the tip of the iceberg, with the bulk of\nthe population yet to be found. The population models also suggest that we have\nonly detected 5--$7\\%$ of the $H<20$ Atira population over the 7-month survey.\nCo-orbital asteroids are smaller in diameters and require deeper surveys. A\nsystematic and efficient survey of the near-Sun region will require deeper\nsearches and/or facilities that can operate at small solar elongations.", "category": "astro-ph_EP" }, { "text": "Gaussian Processes and Nested Sampling Applied to Kepler's Small\n Long-period Exoplanet Candidates: There are more than 5000 confirmed and validated planets beyond the solar\nsystem to date, more than half of which were discovered by NASA's Kepler\nmission. The catalog of Kepler's exoplanet candidates has only been extensively\nanalyzed under the assumption of white noise (i.i.d. Gaussian), which breaks\ndown on timescales longer than a day due to correlated noise (point-to-point\ncorrelation) from stellar variability and instrumental effects. Statistical\nvalidation of candidate transit events becomes increasingly difficult when they\nare contaminated by this form of correlated noise, especially in the\nlow-signal-to-noise (S/N) regimes occupied by Earth--Sun and Venus--Sun\nanalogs. To diagnose small long-period, low-S/N putative transit signatures\nwith few (roughly 3--9) observed transit-like events (e.g., Earth--Sun\nanalogs), we model Kepler's photometric data as noise, treated as a Gaussian\nprocess, with and without the inclusion of a transit model. Nested sampling\nalgorithms from the Python UltraNest package recover model evidences and\nmaximum a posteriori parameter sets, allowing us to disposition transit\nsignatures as either planet candidates or false alarms within a Bayesian\nframework.", "category": "astro-ph_EP" }, { "text": "Transit Timing Observations from Kepler: VI. Potentially interesting\n candidate systems from Fourier-based statistical tests: We analyze the deviations of transit times from a linear ephemeris for the\nKepler Objects of Interest (KOI) through Quarter six (Q6) of science data. We\nconduct two statistical tests for all KOIs and a related statistical test for\nall pairs of KOIs in multi-transiting systems. These tests identify several\nsystems which show potentially interesting transit timing variations (TTVs).\nStrong TTV systems have been valuable for the confirmation of planets and their\nmass measurements. Many of the systems identified in this study should prove\nfruitful for detailed TTV studies.", "category": "astro-ph_EP" }, { "text": "The first super-Earth Detection from the High Cadence and High Radial\n Velocity Precision Dharma Planet Survey: The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright\nFGKM dwarfs (within 50 pc) during 2016$-$2020 for low-mass planet detection and\ncharacterization using the TOU very high resolution optical spectrograph\n(R$\\approx$100,000, 380-900nm). TOU was initially mounted to the 2-m Automatic\nSpectroscopic Telescope at Fairborn Observatory in 2013-2015 to conduct a pilot\nsurvey, then moved to the dedicated 50-inch automatic telescope on Mt. Lemmon\nin 2016 to launch the survey. Here we report the first planet detection from\nDPS, a super-Earth candidate orbiting a bright K dwarf star, HD 26965. It is\nthe second brightest star ($V=4.4$ mag) on the sky with a super-Earth\ncandidate. The planet candidate has a mass of 8.47$\\pm0.47M_{\\rm Earth}$,\nperiod of $42.38\\pm0.01$ d, and eccentricity of $0.04^{+0.05}_{-0.03}$. This RV\nsignal was independently detected by Diaz et al. (2018), but they could not\nconfirm if the signal is from a planet or from stellar activity. The orbital\nperiod of the planet is close to the rotation period of the star (39$-$44.5 d)\nmeasured from stellar activity indicators. Our high precision photometric\ncampaign and line bisector analysis of this star do not find any significant\nvariations at the orbital period. Stellar RV jitters modeled from star spots\nand convection inhibition are also not strong enough to explain the RV signal\ndetected. After further comparing RV data from the star's active magnetic phase\nand quiet magnetic phase, we conclude that the RV signal is due to\nplanetary-reflex motion and not stellar activity.", "category": "astro-ph_EP" }, { "text": "Dust Ejection from Planetary Bodies by Temperature Gradients: Laboratory\n Experiments: Laboratory experiments show that dusty bodies in a gaseous environment eject\ndust particles if they are illuminated. We find that even more intense dust\neruptions occur when the light source is turned off. We attribute this to a\ncompression of gas by thermal creep in response to the changing temperature\ngradients in the top dust layers. The effect is studied at a light flux of 13\nkW/(m*m) and 1 mbar ambient pressure. The effect is applicable to\nprotoplanetary disks and Mars. In the inner part of protoplanetary disks,\nplanetesimals can be eroded especially at the terminator of a rotating body.\nThis leads to the production of dust which can then be transported towards the\ndisk edges or the outer disk regions. The generated dust might constitute a\nsignificant fraction of the warm dust observed in extrasolar protoplanetary\ndisks. We estimate erosion rates of about 1 kg/s for 100 m parent bodies. The\ndust might also contribute to subsequent planetary growth in different\nlocations or on existing protoplanets which are large enough not to be\nsusceptible to particle loss by light induced ejection. Due to the ejections,\nplanetesimals and smaller bodies will be accelerated or decelerated and drift\noutward or inward, respectively. The effect might also explain the entrainment\nof dust in dust devils on Mars, especially at high altitudes where gas drag\nalone might not be sufficient.", "category": "astro-ph_EP" }, { "text": "EPIC247098361b: a transiting warm Saturn on an eccentric $P=11.2$ days\n orbit around a $V=9.9$ star: We report the discovery of EPIC247098361b using photometric data of the\nKepler K2 satellite coupled with ground-based spectroscopic observations.\nEPIC247098361b has a mass of M$_{P}=0.397\\pm 0.037$ M$_J$, a radius of\nR$_{P}=1.00 \\pm 0.020$ R$_J$, and a moderately low equilibrium temperature of\n$T_{eq}=1030 \\pm 15$ K due to its relatively large star-planet separation of\n$a=0.1036$ AU. EPIC247098361b orbits its bright ($V=9.9$) late F-type host star\nin an eccentric orbit ($e=0.258 \\pm 0.025$) every 11.2 days, and is one of only\nfour well characterized warm Jupiters having hosts stars brighter than $V=10$.\nWe estimate a heavy element content of 20 $\\pm$ 7 M$_{\\oplus}$ for\nEPIC247098361b, which is consistent with standard models of giant planet\nformation. The bright host star of EPIC247098361b makes this system a well\nsuited target for detailed follow-up observations that will aid in the study of\nthe atmospheres and orbital evolution of giant planets at moderate separations\nfrom their host stars.", "category": "astro-ph_EP" }, { "text": "Identification and characterization of the host stars in planetary\n microlensing with ELTs: Microlensing offers a unique opportunity to probe exoplanets that are\ntemperate and beyond the snow line, as small as Jovian satellites, at\nextragalactic distance, and even free floating exoplanets, regimes where the\nsensitivity of other methods drops dramatically. This is because microlensing\ndoes not depend on the brightness of the planetary host star. The microlensing\nmethod thus provides great leverage in studying the exoplanets beyond the snow\nline, posing tests to the core accretion mechanism, especially on the run-away\nphase of gas accretion to form giant planets. Here we propose to robustly and\nroutinely measure the masses of exoplanets beyond 1 AU from their host stars\nwith the microlensing method; our experiment relies on directly imaging and\nresolving the host star (namely the lens) from the background source of the\nmicrolensing events, which requires the high spatial resolution delivered by\nthe ELTs. A direct result from this project will be planet occurrence rate\nbeyond the snow line, which will enable us to discern different planet\nformation mechanisms.", "category": "astro-ph_EP" }, { "text": "Meteorites and the RNA World: A Thermodynamic Model of Nucleobase\n Synthesis within Planetesimals: The possible meteorite parent body origin of Earth's pregenetic nucleobases\nis substantiated by the guanine (G), adenine (A) and uracil (U) measured in\nvarious meteorites. Cytosine (C) and thymine (T) however are absent in\nmeteorites, making the emergence of a RNA and later RNA/DNA/protein world\nproblematic. We investigate the meteorite parent body (planetesimal) origin of\nall nucleobases by computationally modeling 18 reactions that potentially\ncontribute to nucleobase formation in such environments. Out of this list, we\nidentify the two most important reactions for each nucleobase and find that\nthese involve small molecules such as HCN, CO, NH3, and water that ultimately\narise from the protoplanetary disks in which planetesimals are built. The\nprimary result of this study is that cytosine is unlikely to persist within\nmeteorite parent bodies due to aqueous deamination. Thymine has a\nthermodynamically favourable reaction pathway from uracil, formaldehyde and\nformic acid, but likely did not persist within planetesimals containing H2O2\ndue to an oxidation reaction with this molecule. Finally, while FT synthesis is\nfound to be the dominant source of nucleobases within our model planetesimal,\nNC synthesis may still be significant under certain chemical conditions (e.g.\nwithin CR2 parent bodies). We discuss several major consequences of our results\nfor the origin of the RNA world.", "category": "astro-ph_EP" }, { "text": "Multicolor Photometry of Tiny Near-Earth Asteroid 2015 RN$_{35}$ Across\n a Wide Range of Phase Angles: Possible Mission Accessible A-type Asteroid: Studying small near-Earth asteroids is important to understand their\ndynamical histories and origins as well as to mitigate the damage of the\nasteroid impact to the Earth. We report the results of multicolor photometry of\nthe tiny near-Earth asteroid 2015 RN$_{35}$ using the 3.8 m Seimei telescope in\nJapan and the TRAPPIST-South telescope in Chile over 17 nights in 2022 December\nand 2023 January. We observed 2015 RN$_{35}$ across a wide range of phase\nangles from 2$^{\\circ}$ to 30$^{\\circ}$ in the $g$, $r$, $i$, and $z$ bands in\nthe Pan-STARRS system. These lightcurves show that 2015 RN$_{35}$ is in a\nnon-principal axis spin state with two characteristic periods of $1149.7\\pm0.3$\ns and $896.01\\pm0.01$ s. We found that a slope of a visible spectrum of 2015\nRN$_{35}$ is as red as asteroid (269) Justitia, one of the very red objects in\nthe main belt, which indicates that 2015 RN$_{35}$ can be classified as an A-\nor Z-type asteroid. In conjunction with the shallow slope of the phase curve,\nwe suppose that 2015 RN$_{35}$ is a high-albedo A-type asteroid. We\ndemonstrated that surface properties of tiny asteroids could be well\nconstrained by intensive observations across a wide range of phase angles. 2015\nRN$_{35}$ is a possible mission accessible A-type near-Earth asteroid with a\nsmall $\\Delta v$ of 11.801 km s$^{-1}$ in the launch window between 2030 and\n2035.", "category": "astro-ph_EP" }, { "text": "On the Method to Infer an Atmosphere on a Tidally-Locked Super Earth\n Exoplanet and Upper limits to GJ 876d: We develop a method to infer or rule out the presence of an atmosphere on a\ntidally-locked hot super Earth. The question of atmosphere retention is a\nfundamental one, especially for planets orbiting M stars due to the star's\nlong-duration active phase and corresponding potential for stellar-induced\nplanetary atmospheric escape and erosion. Tidally-locked planets with no\natmosphere are expected to show a Lambertian-like thermal phase curve, causing\nthe combined light of the planet-star system to vary with planet orbital phase.\n We report Spitzer 8 micron IRAC observations of GJ 876 taken over 32\ncontinuous hours and reaching a relative photometric precision of 3.9e-04 per\npoint for 25.6 s time sampling. This translates to a 3 sigma limit of 5.13e-05\non a planet thermal phase curve amplitude. Despite the almost photon-noise\nlimited data, we are unable to conclusively infer the presence of an atmosphere\nor rule one out on the non-transiting short-period super Earth GJ 876d. The\nlimiting factor in our observations was the miniscule, monotonic photometric\nvariation of the slightly active host M star, because the partial sine wave due\nto the planet has a component in common with the stellar linear trend. The\nproposed method is nevertheless very promising for transiting hot super Earths\nwith the James Webb Space Telescope and is critical for establishing\nobservational constraints for atmospheric escape.", "category": "astro-ph_EP" }, { "text": "Orbit determination methods for interplanetary missions: development and\n use of the Orbit14 software: In the last years, a new generation of interplanetary space missions have\nbeen designed for the exploration of the solar system. At the same time,\nradio-science instrumentation has reached an unprecedented level of accuracy,\nleading to a significant improvement of our knowledge of celestial bodies.\nAlong with this hardware upgrade, software products for interplanetary missions\nhave been greatly refined. In this context, we introduce Orbit14, a precise\norbit determination software developed at the University of Pisa for processing\nthe radio-science data of the BepiColombo and Juno missions. Along the years,\nmany tools have been implemented into the software and Orbit14 capitalized the\nexperience coming from simulations and treatment of real data. In this paper,\nwe present a review of orbit determination methods developed at the University\nof Pisa for radio-science experiments of interplanetary missions. We describe\nthe basic theory of the process of parameters estimation and refined methods\nnecessary to have full control on experiments involving spacecraft orbiting\nmillions of kilometers far from the Earth. Our aim is to give both an extensive\ndescription of the treatment of radio-science experiments and step-to-step\ninstructions for those who are approaching the field of orbit determination in\nthe context of space missions. We show also the work conducted on the Juno and\nBepiColombo missions by means of the Orbit14 software. In particular, we\nsummarize the recent results obtained with the gravity experiment of Juno and\nthe simulations performed so far for the gravimetry-rotation and relativity\nexperiments of BepiColombo.", "category": "astro-ph_EP" }, { "text": "Hints on the origins of particle traps in protoplanetary disks given by\n the $M_{\\rm{dust}}-M_{\\star}$ relation: Demographic surveys of protoplanetary disks, carried out mainly with ALMA,\nhave provided access to a large range of disk dust masses ($M_{\\rm{dust}}$)\naround stars with different stellar types and in different star-forming\nregions. These surveys found a power-law relation between $M_{\\rm{dust}}$ and\n$M_{\\star}$ that steepens in time, but which is also flatter for transition\ndisks (TDs). We performed dust evolution models, which included perturbations\nto the gas surface density with different amplitudes to investigate the effect\nof particle trapping on the $M_{\\rm{dust}}-M_{\\star}$ relation. These\nperturbations were aimed at mimicking pressure bumps that originated from\nplanets. We focused on the effect caused by different stellar and disk masses\nbased on exoplanet statistics that demonstrate a dependence of planet mass on\nstellar mass and metallicity. Models of dust evolution can reproduce the\nobserved $M_{\\rm{dust}}-M_{\\star}$ relation in different star-forming regions\nwhen strong pressure bumps are included and when the disk mass scales with\nstellar mass (case of $M_{\\rm{disk}}=0.05\\,M_\\star$ in our models). This result\narises from dust trapping and dust growth beyond centimeter-sized grains inside\npressure bumps. However, the flatter relation of $M_{\\rm{dust}}-M_{\\star}$ for\nTDs and disks with substructures cannot be reproduced by the models unless the\nformation of boulders is inhibited inside pressure bumps. In the context of\npressure bumps originating from planets, our results agree with current\nexoplanet statistics on giant planet occurrence increasing with stellar mass,\nbut we cannot draw a conclusion about the type of planets needed in the case of\nlow-mass stars. This is attributed to the fact that for $M_\\star<1\\,M_\\odot$,\nthe observed $M_{\\rm{dust}}$ obtained from models is very low due to the\nefficient growth of dust particles beyond centimeter-sizes inside pressure\nbumps.", "category": "astro-ph_EP" }, { "text": "Disintegration of Long-Period Comet C/2021 A1 (Leonard): We present imaging observations of the disintegrating long-period comet\nC/2021 A1 (Leonard). High resolution observations with Hubble Space Telescope\nshow no evidence for surviving fragments, and place a 3 sigma upper limit to\ntheir possible radius about 60 m (albedo 0.1 assumed). In contrast, wide field\nobservations from the Swan Hill Observatory, Australia, show an extensive\ndebris cloud, the cross-section and estimated mass of which are consistent with\ncomplete disintegration of the nucleus near mid- December 2021 (at about 0.8\nau). Two methods give the pre-disruption nucleus radius, r = 0.6+/-0.2 km.\nTidal, collisional, sublimation and pressure-confined explosion models provide\nimplausible explanations of the disintegration. However, rotational instability\ndriven by outgassing torques has a very short timescale (of order 0.1 year)\ngiven the orbit and size of the C/2021 A1 nucleus, and offers the most\nplausible mechanism for the disruption. Initial rotational breakup is\naccelerated by the exposure and strong sublimation of previously buried\nvolatiles, leading to catastrophic destruction of the nucleus.", "category": "astro-ph_EP" }, { "text": "Photophoresis in the circumjovian disk and its impact on the orbital\n configuration of the Galilean satellites: Jupiter has four large regular satellites called the Galilean satellites: Io,\nEuropa, Ganymede, and Callisto. The inner three of the Galilean satellites\norbit in a 4:2:1 mean motion resonance; therefore their orbital configuration\nmay originate from the stopping of the migration of Io near the bump in the\nsurface density distribution and following resonant trapping of Europa and\nGanymede. The formation mechanism of the bump near the orbit of the innermost\nsatellite, Io, is not yet understood, however. Here, we show that photophoresis\nin the circumjovian disk could be the cause of the bump, using analytic\ncalculations of steady-state accretion disks. We propose that photophoresis in\nthe circumjovian disk could stop the inward migration of dust particles near\nthe orbit of Io. The resulting dust depleted inner region would have a higher\nionization fraction, and thus admit increased\nmagnetorotational-instability-driven accretion stress than the outer region.\nThe increase of the accretion stress at the photophoretic dust barrier would\nform a bump in the surface density distribution, halting the migration of Io.", "category": "astro-ph_EP" }, { "text": "Obliquities of \"Top-Shaped\" Asteroids May Not Imply Reshaping by YORP\n Spin-up: The timescales over which the YORP effect alters the rotation period and the\nobliquity of a small asteroid can be very different, because the corresponding\ntorques couple to different aspects of the object's shape. For nearly\naxisymmetric, \"top-shaped\" near-Earth asteroids such as 101955 Bennu, spin\ntimescales are an order of magnitude or more longer than obliquity timescales,\nwhich are of order 10^5 to 10^6 yr. The observed low obliquities (near 0 or 180\ndegrees) of top-shaped asteroids do not constitute evidence that they acquired\ntheir present shapes and spins through YORP spin-up, because low obliquities\nare expected regardless of the spin-up or reshaping mechanism.", "category": "astro-ph_EP" }, { "text": "Probable Spin-Orbit Aligned Super-Earth Planet Candidate KOI-2138.01: We use rotational gravity darkening in the disk of \\emph{Kepler} star\nKOI-2138 to show that the orbit of $2.1-R_\\oplus$ transiting planet candidate\nKOI-2138.01 has a low projected spin-orbit alignment of $\\lambda=1^\\circ\\pm13$.\nKOI-2138.01 is just the second super-Earth with a measured spin-orbit alignment\nafter 55 Cancri e, and the first to be aligned. With a 23.55-day orbital\nperiod, KOI-2138.01 may represent the tip of a future iceberg of\nsolar-system-like terrestrial planets having intermediate periods and\nlow-inclination circular orbits.", "category": "astro-ph_EP" }, { "text": "Interplanetary Laser Tri-lateration Network: simulation with INPOP\n planetary ephemerides: This study is done in the context of the project titled Interplanetary Laser\nTri-lateration Network (ILTN) proposed by \\cite{2018P&SS..153..127S} and\ninvestigated more in details by \\cite{2022P&SS..21405415B} and\n\\cite{2022P&SS..21505423B}. The original idea was to propose interplanetary\nmeasurements (in this case between Venus, Mars and the earth) as a way to\nmeasure the solar system expansion. But some recent interests on the\nmeasurement of asteroid masses and more generally the study of the mass\ndistribution in the outer solar system appear with the ILTN. In this work, we\nare investigating how different possible configurations of interplanetary\nmeasurements of distances can be introduced in planetary ephemeris construction\nand how they improve our knowledge of planet orbits and other related\nparameters.", "category": "astro-ph_EP" }, { "text": "Microlensed Radio Emission from Exoplanets: In this paper, we investigate the detectability of radio emission from\nexoplanets, especially hot Jupiters, which are magnified by gravitational\nmicrolensing. Because hot Jupiters have orbital periods much shorter than the\ncharacteristic timescale of microlensing, the magnification curve has a unique\nwavy feature depending on the orbital parameters. This feature is useful to\nidentify radio emission from exoplanets and, in addition to magnification,\nmakes it easier to detect exoplanets directly. We also estimate the expected\nevent rate red of the detectable level of microlensed planetary radio\nemissions, assuming the LOFAR and the first phase of the Square Kilometre\nArray.", "category": "astro-ph_EP" }, { "text": "Earth as an Exoplanet. III. Using Empirical Thermal Emission Spectra as\n Input for Atmospheric Retrieval of an Earth-Twin Exoplanet: In this study, we treat Earth as an exoplanet and investigate our home planet\nby means of a potential future mid-infrared (MIR) space mission called the\nLarge Interferometer For Exoplanets (LIFE). We combine thermal spectra from an\nempirical dataset of disk-integrated Earth observations with a noise model for\nLIFE to create mock observations. We apply a state-of-the-art atmospheric\nretrieval framework to characterize the planet, assess the potential for\ndetecting the known bioindicators, and investigate the impact of viewing\ngeometry, seasonality, and patchy clouds on the characterization. Key findings\ninclude: (1) we are observing a temperate habitable planet with significant\nabundances of $\\mathrm{CO_2}$, $\\mathrm{H_2O}$, $\\mathrm{O_3}$, and\n$\\mathrm{CH_4}$; (2) seasonal variations in the surface and equilibrium\ntemperature, and in the Bond albedo are detectable; (3) the viewing geometry\nand the spatially and temporally unresolved nature of our observations only\nhave a minor impact on the characterization; (4) Earth's variable H2O profile\nand patchy cloud coverage lead to biased retrieval results for the atmospheric\nstructure and trace gas abundances; (5) the limited extent of Earth's seasonal\nvariations in biosignature abundances makes the direct detection of its\nbiosphere through atmospheric seasonality unlikely. Our results suggest that\nLIFE could correctly identify Earth as a planet where life could thrive, with\ndetectable levels of bioindicators, a temperate climate, and surface conditions\nallowing liquid surface water. Even if atmospheric seasonality is not easily\nobserved, our study demonstrates that next generation, optimized space missions\ncan assess whether nearby temperate terrestrial exoplanets are habitable or\neven inhabited.", "category": "astro-ph_EP" }, { "text": "A Potential Aid in the Target Selection for the Comet Interceptor\n Mission: The upcoming Comet Interceptor mission involves a parking phase around the\nSun-Earth L2 point before transferring to intercept the orbit of a long period\ncomet, interstellar object or a back-up target in the form of a short-period\ncomet. The target is not certain to be known before the launch in 2029. During\nthe parking phase there may thus arise a scenario wherein a decision needs to\nbe taken of whether to go for a particular comet or whether to discard that\noption in the hope that a better target will appear within a reasonable time\nframe later on. We present an expectation value-based formalism that could aid\nin the associated decision making provided that outlined requirements for its\nimplementation exist.", "category": "astro-ph_EP" }, { "text": "Reduced atmospheres of post-impact worlds: The early Earth: Impacts may have had a significant effect on the atmospheric chemistry of the\nearly Earth. Reduced phases in the impactor (e.g., metallic iron) can reduce\nthe planet's H$_2$O inventory to produce massive atmospheres rich in H$_2$.\nWhilst previous studies have focused on the interactions between the impactor\nand atmosphere in such scenarios, we investigate two further effects, 1) the\ndistribution of the impactor's iron inventory during impact between the target\ninterior, target atmosphere, and escaping the target, and 2) interactions\nbetween the post-impact atmosphere and the impact-generated melt phase. We find\nthat these two effects can potentially counterbalance each other, with the\nmelt-atmosphere interactions acting to restore reducing power to the atmosphere\nthat was initially accreted by the melt phase. For a $\\sim10^{22}\\,\\mathrm{kg}$\nimpactor, when the iron accreted by the melt phase is fully available to reduce\nthis melt, we find an equilibrium atmosphere with H$_2$ column density\n$\\sim10^4\\,\\mathrm{moles\\,cm^{-2}}$\n($p\\mathrm{H2}\\sim120\\,\\mathrm{bars}\\mathrm{,}~X_\\mathrm{H2}\\sim0.77$),\nconsistent with previous estimates. However, when the iron is not available to\nreduce the melt (e.g., sinking out in large diameter blobs), we find\nsignificantly less H$_2$ ($7\\times10^2-5\\times10^3\\,\\mathrm{moles\\,cm^{-2}}$,\n$p\\mathrm{H2}\\lesssim60\\,\\mathrm{bars}\\mathrm{,}~X_\\mathrm{H2}\\lesssim0.41$).\nThese lower H$_2$ abundances are sufficiently high that species important to\nprebiotic chemistry can form (e.g., NH3, HCN), but sufficiently low that the\ngreenhouse heating effects associated with highly reducing atmospheres, which\nare problematic to such chemistry, are suppressed. The manner in which iron is\naccreted by the impact-generated melt phase is critical in determining the\nreducing power of the atmosphere and re-solidified melt pool in the aftermath\nof impact.", "category": "astro-ph_EP" }, { "text": "Composition of Terrestrial Exoplanet Atmospheres from Meteorite\n Outgassing Experiments: Terrestrial exoplanets likely form initial atmospheres through outgassing\nduring and after accretion, although there is currently no first-principles\nunderstanding of how to connect a planet's bulk composition to its early\natmospheric properties. Important insights into this connection can be gained\nby assaying meteorites, representative samples of planetary building blocks. We\nperform laboratory outgassing experiments that use a mass spectrometer to\nmeasure the abundances of volatiles released when meteorite samples are heated\nto 1200 $^{\\circ}$C. We find that outgassing from three carbonaceous chondrite\nsamples consistently produce H$_2$O-rich (averaged ~66 %) atmospheres but with\nsignificant amounts of CO (~18 %) and CO$_2$ (~15 %) as well as smaller\nquantities of H$_2$ and H$_2$S (up to 1 %). These results provide experimental\nconstraints on the initial chemical composition in theoretical models of\nterrestrial planet atmospheres, supplying abundances for principal gas species\nas a function of temperature.", "category": "astro-ph_EP" }, { "text": "Is there a background population of high-albedo objects in\n geosynchronous orbits around Earth?: Old, digitized astronomical images taken before the human spacefaring age\noffer a unique view of the sky devoid of known artificial satellites. In this\npaper, we have carried out the first optical searches ever for non-terrestrial\nartifacts near the Earth following the method proposed in Villarroel et al.\n(2022). We use images contained in the First Palomar Sky Survey to search for\nsimultaneous (during a plate exposure time) transients that in addition to\nbeing point-like, are aligned. We provide a shortlist of the most promising\ncandidates of aligned transients, that must be examined with the help of a\nmicroscope to separate celestial sources from plate defects with coincidentally\nstar-like brightness profiles. We further explore one possible, but not unique,\ninterpretation in terms of fast reflections off high-albedo objects in\ngeosynchronous orbits around Earth. If a future study rules out each multiple\ntransient candidate, the estimated surface density becomes an upper limit of\n$<10^{-9}$ objects km$^{-2}$ non-terrestrial artifacts in geosynchronous orbits\naround Earth. Finally, we conclude that observations and analysis of multiple,\nsimultaneously appearing and vanishing light sources on the sky merit serious\nfurther attention, regardless of their origin.", "category": "astro-ph_EP" }, { "text": "Short-term variability on the surface of (1) Ceres. A changing amount of\n water ice?: Context: The dwarf planet (1) Ceres - next target of the NASA Dawn mission -\nis the largest body in the asteroid main belt; although several observations of\nthis body have been performed so far, the presence of surface water ice is\nstill questioned.\n Aims: Our goal is to better understand the surface composition of Ceres, and\nto constrain the presence of exposed water ice.\n Methods: We acquired new visible and near-infrared spectra at the Telescopio\nNazionale Galileo (TNG, La Palma, Spain), and reanalyzed literature spectra in\nthe 3-$\\mu$m region.\n Results: We obtained the first rotationally-resolved spectroscopic\nobservations of Ceres at visible wavelengths. Visible spectra taken one month\napart at almost the same planetocentric coordinates show a significant slope\nvariation (up to 3 %/10$^3\\AA$). A faint absorption centered at 0.67 $\\mu$m,\npossibly due to aqueous alteration, is detected in a subset of our spectra. The\nvarious explanations in the literature for the 3.06-$\\mu$m feature can be\ninterpreted as due to a variable amount of surface water ice at different\nepochs.\n Conclusions: The remarkable short-term temporal variability of the visible\nspectral slope, and the changing shape of the 3.06-$\\mu$m band, can be hints of\ndifferent amounts of water ice exposed on the surface of Ceres. This would be\nin agreement with the recent detection by the Herschel Space Observatory of\nlocalized and transient sources of water vapour over this dwarf planet.", "category": "astro-ph_EP" }, { "text": "Spin Evolution and Cometary Interpretation of the Interstellar Minor\n Object 1I/2017 'Oumuamua: Observations of the first interstellar minor object 1I/2017 'Oumuamua did not\nreveal direct signs of outgassing that would have been natural if it had\nvolatile-rich composition. However, a recent measurement by Micheli et al\n(2018) of a substantial non-gravitational acceleration affecting the orbit of\nthis object has been interpreted as resulting from its cometary activity, which\nmust be rather vigorous. Here we critically re-assess this interpretation by\nexploring the implications of measured non-gravitational acceleration for the\n'Oumuamua's rotational state. We show that outgassing torques should drive\nrapid evolution of 'Oumuamua's spin (on a timescale of a few days), assuming\ntorque asymmetry typical for the Solar System comets. However, given the highly\nelongated shape of the object, its torque asymmetry is likely higher, implying\neven faster evolution. This would have resulted in rapid rotational fission of\n'Oumuamua during its journey through the Solar System and is clearly\nincompatible with the relative stability of its rotational state inferred from\nphotometric variability. Based on these arguments, as well as the lack of\ndirect signs of outgassing, we conclude that the classification of 'Oumuamua as\na comet (invoked to explain its claimed anomalous acceleration) is\nquestionable.", "category": "astro-ph_EP" }, { "text": "Probing the inner boundaries of Saturn's A ring with the Iapetus -1:0\n nodal bending wave: The Iapetus -1:0 nodal bending wave, the first spiral wave ever described in\nSaturn's rings, has been seen again for the first time in 29 years. We\ndemonstrate that it is in fact the nodal bending wave, not the 1:0 apsidal\ndensity wave as previously reported. We use wavelet analysis to determine the\nwavelength profile, thus deriving the surface density at every point in the\nregion covered by the bending wave. This profile is consistent with surface\ndensities measured from more localized spiral density waves in the outer\nCassini Division and the inner and mid-A Ring, varying smoothly from the low\nvalues of the former to the higher values of the latter.\n Most remarkably, our analysis indicates that there is no significant change\nin surface density across the boundary between the outer Cassini Division and\nthe inner-A ring, despite the very abrupt increase in optical depth and\nreflected brightness at this location. We consider anew the nature of the\nclassically identified \"inner edge of the A ring,\" given that it does not\nappear to be correlated with any abrupt increase in surface density. There is\nan abrupt increase in surface density at the Pandora 5:4 density wave, ~300 km\noutward of the A ring's inner edge. Further study is needed to robustly\ninterpret our findings in terms of particle properties and abundances, much\nless to explain the origins of the implied structure.", "category": "astro-ph_EP" }, { "text": "The International Deep Planet Survey II: The frequency of directly\n imaged giant exoplanets with stellar mass: Radial velocity and transit methods are effective for the study of short\norbital period exoplanets but they hardly probe objects at large separations\nfor which direct imaging can be used. We carried out the international deep\nplanet survey of 292 young nearby stars to search for giant exoplanets and\ndetermine their frequency. We developed a pipeline for a uniform processing of\nall the data that we have recorded with NIRC2/Keck II, NIRI/Gemini North,\nNICI/Gemini South, and NACO/VLT for 14 years. The pipeline first applies\ncosmetic corrections and then reduces the speckle intensity to enhance the\ncontrast in the images. The main result of the international deep planet survey\nis the discovery of the HR 8799 exoplanets. We also detected 59 visual multiple\nsystems including 16 new binary stars and 2 new triple stellar systems, as well\nas 2,279 point-like sources. We used Monte Carlo simulations and the Bayesian\ntheorem to determine that 1.05[+2.80-0.70]% of stars harbor at least one giant\nplanet between 0.5 and 14M_J and between 20 and 300 AU. This result is obtained\nassuming uniform distributions of planet masses and semi-major axes. If we\nconsider power law distributions as measured for close-in planets instead, the\nderived frequency is 2.30[+5.95-1.55]%, recalling the strong impact of\nassumptions on Monte Carlo output distributions. We also find no evidence that\nthe derived frequency depends on the mass of the hosting star, whereas it does\nfor close-in planets. The international deep planet survey provides a database\nof confirmed background sources that may be useful for other exoplanet direct\nimaging surveys. It also puts new constraints on the number of stars with at\nleast one giant planet reducing by a factor of two the frequencies derived by\nalmost all previous works.", "category": "astro-ph_EP" }, { "text": "Modeling of the zodiacal emission for the AKARI/IRC mid-infrared all-sky\n diffuse maps: The zodiacal emission, which is the thermal infrared (IR) emission from the\ninterplanetary dust (IPD) in our Solar System, has been studied for a long\ntime. Nevertheless, accurate modeling of the zodiacal emission has not been\nsuccessful to reproduce the all-sky spatial distribution of the zodiacal\nemission, especially in the mid-IR where the zodiacal emission peaks. We\ntherefore aim to improve the IPD cloud model based on Kelsall et al. 1998,\nusing the AKARI 9 and 18 micron all-sky diffuse maps. By adopting a new fitting\nmethod based on the total brightness, we have succeeded in reducing the\nresidual levels after subtraction of the zodiacal emission from the AKARI data\nand thus in improving the modeling of the zodiacal emission. Comparing the\nAKARI and the COBE data, we confirm that the changes from the previous model to\nour new model are mostly due to model improvements, but not temporal variations\nbetween the AKARI and the COBE epoch, except for the position of the\nEarth-trailing blob. Our results suggest that the size of the smooth cloud, a\ndominant component in the model, is by about 10% more compact than previously\nthought, and that the dust sizes are not large enough to emit blackbody\nradiation in the mid-IR. Furthermore we significantly detect an\nisotropically-distributed IPD component, owing to accurate baseline measurement\nwith AKARI.", "category": "astro-ph_EP" }, { "text": "The 8 Micron Phase Variation of the Hot Saturn HD 149026b: We monitor the star HD 149026 and its Saturn-mass planet at 8.0 micron over\nslightly more than half an orbit using the Infrared Array Camera (IRAC) on the\nSpitzer Space Telescope. We find an increase of 0.0227% +/- 0.0066% (3.4 sigma\nsignificance) in the combined planet-star flux during this interval. The\nminimum flux from the planet is 45% +/- 19% of the maximum planet flux,\ncorresponding to a difference in brightness temperature of 480 +/- 140 K\nbetween the two hemispheres. We derive a new secondary eclipse depth of 0.0411%\n+/- 0.0076% in this band, corresponding to a dayside brightness temperature of\n1440 +/- 150 K. Our new secondary eclipse depth is half that of a previous\nmeasurement (3.0 sigma difference) in this same bandpass by Harrington et al.\n(2007). We re-fit the Harrington et al. (2007) data and obtain a comparably\ngood fit with a smaller eclipse depth that is consistent with our new value. In\ncontrast to earlier claims, our new eclipse depth suggests that this planet's\ndayside emission spectrum is relatively cool, with an 8 micron brightness\ntemperature that is less than the maximum planet-wide equilibrium temperature.\nWe measure the interval between the transit and secondary eclipse and find that\nthat the secondary eclipse occurs 20.9 +7.2 / -6.5 minutes earlier (2.9 sigma)\nthan predicted for a circular orbit, a marginally significant result. This\ncorresponds to e*cos(omega) = -0.0079 +0.0027 / -0.0025 where e is the planet's\norbital eccentricity and omega is the argument of pericenter.", "category": "astro-ph_EP" }, { "text": "VUV-absorption cross section of carbon dioxide from 150 to 800 K and\n applications to warm exoplanetary atmospheres: Most exoplanets detected so far have atmospheric T significantly higher than\n300K. Often close to their star, they receive an intense UV photons flux that\ntriggers important photodissociation processes. The T dependency of VUV\nabsorption cross sections are poorly known, leading to an undefined uncertainty\nin atmospheric models. Similarly, data measured at low T similar to that of the\nhigh atmosphere of Mars, Venus, and Titan are often lacking. Our aim is to\nquantify the T dependency of the abs. cross section of important molecules in\nplanetary atmospheres. We want to provide both high-resolution data at T\nprevailing in these media and a simple parameterization of the absorption in\norder to simplify its use in photochemical models. This study focuses on carbon\ndioxide. We performed experimental measurements of CO$_2$ absorption cross\nsection with synchrotron radiation for the wavelength range (115--200nm). For\nlonger wavelengths (195--230nm), we used a deuterium lamp and a 1.5m Jobin-Yvon\nspectrometer. We used these data in our 1D thermo-photochemical model in order\nto study their impact on the predicted atmospheric compositions. The cross\nsection of CO$_2$ increases with T. It can be separated in two parts: a\ncontinuum and a fine structure superimposed on the continuum. The variation of\nthe continuum of absorption can be represented by the sum of three gaussian\nfunctions. Using data at high T in thermo-photochemical models modifies\nsignificantly the abundance and the photodissociation rates of many species, in\naddition to CO$_2$, such as methane and ammonia. These deviations have an\nimpact on synthetic transmission spectra, leading to variations of up to 5 ppm.\nWe present a full set of HR ($\\Delta \\lambda$=0.03nm) absorption cross sections\nof CO$_2$ from 115 to 230nm for T ranging from 150 to 800K.", "category": "astro-ph_EP" }, { "text": "Saturn Ring Seismology: Evidence for Stable Stratification in the Deep\n Interior of Saturn: Seismology allows for direct observational constraints on the interior\nstructures of stars and planets. Recent observations of Saturn's ring system\nhave revealed the presence of density waves within the rings excited by\noscillation modes within Saturn, allowing for precise measurements of a limited\nset of the planet's mode frequencies. We construct interior structure models of\nSaturn, compute the corresponding mode frequencies, and compare them with the\nobserved mode frequencies. The fundamental mode frequencies of our models match\nthe observed frequencies (of the largest amplitude waves) to an accuracy of\n$\\sim 1 \\%$, confirming that these waves are indeed excited by Saturn's\nf-modes. The presence of the lower amplitude waves (finely split in frequency\nfrom the f-modes) can only be reproduced in models containing gravity modes\nthat propagate in a stably stratified region of the planet. The stable\nstratification must exist deep within the planet near the large density\ngradients between the core and envelope. Our models cannot easily reproduce the\nobserved fine splitting of the $m=-3$ modes, suggesting that additional effects\n(e.g., significant latitudinal differential rotation) may be important.", "category": "astro-ph_EP" }, { "text": "Uranus at equinox: Cloud morphology and dynamics: As the 7 December 2007 equinox of Uranus approached, ring and atmosphere\nobservers produced a substantial collection of observations using the 10-m Keck\ntelescope and the Hubble Space Telescope. Those spanning the period from 7 June\n2007 through 9 September 2007 we used to identify and track cloud features,\ndetermine atmospheric motions, characterize cloud morphology and dynamics, and\ndefine changes in atmospheric band structure. We confirmed the existence of the\nsuspected northern hemisphere prograde jet, locating its peak near 58 N, and\nextended wind speed measurements to 73 N. For 28 cloud features we obtained\nextremely high wind-speed accuracy through extended tracking times. The new\nresults confirm a small N-S asymmetry in the zonal wind profile, and the lack\nof any change in the southern hemisphere between 1986 (near solstice) and 2007\n(near equinox) suggests that the asymmetry may be permanent rather than\nseasonally reversing. In the 2007 images we found two prominent groups of\ndiscrete cloud features with very long lifetimes. The one near 30 S has\ndeparted from its previous oscillatory motion and started a significant\nnorthward drift, accompanied by substantial morphological changes. The complex\nof features near 30 N remained at a nearly fixed latitude, while exhibiting\nsome characteristics of a dark spot accompanied by bright companion features.\nSmaller and less stable features were used to track cloud motions at other\nlatitudes, some of which lasted over many planet rotations, though many could\nnot be tracked beyond a single transit. A bright band has developed near 45 N,\nwhile the bright band near 45 S has begun to decline, both events in agreement\nwith the idea that the asymmetric band structure of Uranus is a delayed\nresponse to solar forcing, but with a surprisingly short delay of only a few\nyears.", "category": "astro-ph_EP" }, { "text": "Constraining the oblateness of transiting planets with photometry and\n spectroscopy: Rapid planetary rotation can cause the equilibrium shape of a planet to be\noblate. While planetary oblateness has mostly been probed by examining the\nsubtle ingress and egress features in photometric transit light curves, we\ninvestigate the effect of oblateness on the spectroscopic Rossiter-McLaughlin\n(RM) signals. We found that a giant planet, with planet-to-star radius ratio of\n0.15 and Saturn-like oblateness of 0.098, can cause spectroscopic signatures\nwith amplitudes up to 1.1 ms$^{-1}$ which is detectable by high-precision\nspectrographs such as ESPRESSO. We also found that the spectroscopic oblateness\nsignals are particularly amplified for transits across rapidly rotating stars\nand for planets with spin-orbit misalignment thereby making them more prominent\nthan the photometric signals at some transit orientations. We compared the\ndetectability of oblateness in photometry and spectroscopy and found that\nphotometric light curves are more sensitive to detecting oblateness than the\nspectroscopic RM signals mostly because they can be sampled with higher cadence\nto better probe the oblateness ingress and egress anomaly. However, joint\nanalyses of the light curve and RM signal of a transiting planet provides more\naccurate and precise estimate of the planet's oblateness. Therefore, ESPRESSO\nalongside ongoing and upcoming photometric instruments such as TESS, CHEOPS,\nPLATO and JWST will be extremely useful in measuring planet oblateness.", "category": "astro-ph_EP" }, { "text": "The Dynamics of Co-orbital Giant Exomoons -- Applications for the\n Kepler-1625 b and Kepler-1708 b Satellite Systems: Exomoons are a missing piece of exoplanetary science. Recently, two promising\ncandidates were proposed, Kepler-1625 b-I and Kepler-1708 b-I. While the latter\nstill lacks a dynamical analysis of its stability, Kepler-1625 b-I has already\nbeen the subject of several studies regarding its stability and origin.\nMoreover, previous works have shown that this satellite system could harbour at\nleast two stable massive moons. Motivated by these results, we explored the\nstability of co-orbital exomoons using the candidates Kepler-1625 b-I and\nKepler-1708 b-I as case studies. To do so, we performed numerical simulations\nof systems composed of the star, planet, and the co-orbital pair formed by the\nproposed candidates and another massive body. For the additional satellite, we\nvaried its mass and size from a Mars-like to the case where both satellites\nhave the same physical characteristics. We investigated the co-orbital region\naround the Lagrangian equilibrium point $L_4$ of the system, setting the\norbital separation between the satellites from $\\theta_{min} = 30^{\\circ}$ to\n$\\theta_{max} = 90^{\\circ}$. Our results show that stability islands are\npossible in the co-orbital region of Kepler-1708 b-I as a function of the\nco-orbital companion's mass and angular separation. Also, we identified that\nresonances of librational frequencies, especially the 2:1 resonance, can\nconstrain the mass of the co-orbital companion. On the other hand, we found\nthat the proximity between the host planet and the star makes the co-orbital\nregion around Kepler-1625 b-I unstable for a massive companion. Finally, we\nprovide TTV profiles for a planet orbited by co-orbital exomoons.", "category": "astro-ph_EP" }, { "text": "Desorption Kinetics and Binding Energies of Small Hydrocarbons: Small hydrocarbons are an important organic reservoir in protostellar and\nprotoplanetary environments. Constraints on desorption temperatures and binding\nenergies of such hydrocarbons are needed for accurate predictions of where\nthese molecules exist in the ice vs. gas-phase during the different stages of\nstar and planet formation. Through a series of temperature programmed\ndesorption (TPD) experiments, we constrain the binding energies of 2 and\n3-carbon hydrocarbons (C$_{2}$H$_{2}$ - acetylene, C$_{2}$H$_{4}$ - ethylene,\nC$_{2}$H$_{6}$ - ethane, C$_{3}$H$_{4}$ - propyne, C$_{3}$H$_{6}$ - propene,\nand C$_{3}$H$_{8}$ - propane) to 2200-4200 K in the case of pure amorphous\nices, to 2400-4400 K on compact amorphous H$_{2}$O, and to 2800-4700 K on\nporous amorphous H$_{2}$O. The 3-carbon hydrocarbon binding energies are always\nlarger than the 2-carbon hydrocarbon binding energies. Within the 2- and\n3-carbon hydrocarbon families, the alkynes (i.e., least-saturated) hydrocarbons\nexhibit the largest binding energies, while the alkane and alkene binding\nenergies are comparable. Binding energies are $\\sim$5-20% higher on water ice\nsubstrates compared to pure ices, which is a small increase compared to what\nhas been measured for other volatile molecules such as CO and N$_{2}$. Thus in\nthe case of hydrocarbons, H$_{2}$O has a less pronounced effect on sublimation\nfront locations (i.e., snowlines) in protoplanetary disks.", "category": "astro-ph_EP" }, { "text": "Light Curve Analysis of Ground-Based Data from Exoplanets Transit\n Database: Photometric observations of exoplanet transits can be used to derive the\norbital and physical parameters of an exoplanet. We analyzed several transit\nlight curves of exoplanets that are suitable for ground-based observations\nwhose complete information is available on the Exoplanet Transit Database\n(ETD). We analyzed transit data of planets including HAT-P-8 b, HAT-P-16 b,\nHAT-P-21 b, HAT-P-22 b, HAT-P-28 b and HAT-P-30 b using the AstroImageJ (AIJ)\nsoftware package. In this paper, we investigated 82 transit light curves from\nETD, deriving their physical parameters as well as computing their mid-transit\ntimes for future Transit Timing Variation (TTV) analyses. The Precise values of\nthe parameters show that using AIJ as a fitting tool for follow-up observations\ncan lead to results comparable to the values at the NASA Exoplanet Archive (the\nNEA). Such information will be invaluable considering the numbers of future\ndiscoveries from the ground and space-based exoplanet surveys.", "category": "astro-ph_EP" }, { "text": "Lie-series for orbital elements -- I. The planar case: Lie-integration is one of the most efficient algorithms for numerical\nintegration of ordinary differential equations if high precision is needed for\nlonger terms. The method is based on the computation of the Taylor-coefficients\nof the solution as a set of recurrence relations. In this paper we present\nthese recurrence formulae for orbital elements and other integrals of motion\nfor the planar $N$-body problem. We show that if the reference frame is fixed\nto one of the bodies -- for instance to the Sun in the case of the Solar System\n--, the higher order coefficients for all orbital elements and integrals of\nmotion depend only on the mutual terms corresponding to the orbiting bodies.", "category": "astro-ph_EP" }, { "text": "Radial Velocity Discovery of an Eccentric Jovian World Orbiting at 18 au: Based on two decades of radial velocity (RV) observations using Keck/HIRES\nand McDonald/Tull, and more recent observations using the Automated Planet\nFinder, we found that the nearby star HR 5183 (HD 120066) hosts a 3$M_J$\nminimum mass planet with an orbital period of $74^{+43}_{-22}$ years. The orbit\nis highly eccentric (e$\\simeq$0.84), shuttling the planet from within the orbit\nof Jupiter to beyond the orbit of Neptune. Our careful survey design enabled\nhigh cadence observations before, during, and after the planet's periastron\npassage, yielding precise orbital parameter constraints. We searched for\nstellar or planetary companions that could have excited the planet's\neccentricity, but found no candidates, potentially implying that the perturber\nwas ejected from the system. We did identify a bound stellar companion more\nthan 15,000 au from the primary, but reasoned that it is currently too widely\nseparated to have an appreciable effect on HR 5183 b. Because HR 5183 b's wide\norbit takes it more than 30 au (1\") from its star, we also explored the\npotential of complimentary studies with direct imaging or stellar astrometry.\nWe found that a Gaia detection is very likely, and that imaging at 10 $\\mu$m is\na promising avenue. This discovery highlights the value of long-baseline RV\nsurveys for discovering and characterizing long-period, eccentric Jovian\nplanets. This population may offer important insights into the dynamical\nevolution of planetary systems containing multiple massive planets.", "category": "astro-ph_EP" }, { "text": "Galactic tide and secular orbital evolution: Equation of motion for the galactic tide is treated for the case of a comet\nsituated in the Oort cloud of comets. We take into account that galactic\npotential and mass density depend on a distance from the galactic equator and\non a distance from the rotational axis of the Galaxy. Secular evolution of\norbital elements is presented. New terms generated by the Sun's oscillation\nabout the galactic plane are considered. The inclusion of the new terms into\nthe equation of motion of the comet leads to orbital evolution which may be\nsignificantly different from the conventional approach. The usage of the\nsecular time derivatives is limited to the cases when orbital period of the\ncomet is much less than i) the period of oscillations of the Sun around the\ngalactic equator, and, ii) the orbital period of the motion of the Sun around\nthe galactic center.", "category": "astro-ph_EP" }, { "text": "Mony a Mickle Maks a Muckle: Minor Body Observations with Optical\n Telescopes of All Sizes: I review the current capabilities of small, medium and large telescopes in\nthe study of minor bodies of the Solar System (MBOSS), with the goal of\nidentifying those areas where the next generation of Extremely Large Telescopes\n(ELTs) are required to progress. This also leads to a discussion of the\nsynergies between large and small telescopes. It is clear that the new\nfacilities that will become available in the next decades will allow us to\ndiscover smaller and more distant objects (completing size distributions) and\nto characterise and even resolve larger individual bodies and multiple systems,\nhowever we must also recognise that there is still much to be learned from wide\nsurveys that require more time on more telescopes than can ever be available on\nELTs. Smaller telescopes are still required to discover and characterise large\nsamples of MBOSS.", "category": "astro-ph_EP" }, { "text": "Using Dust Shed from Asteroids as Microsamples to Link Remote\n Measurements with Meteorite Classes: Given the compositional diversity of asteroids, and their distribution in\nspace, it is impossible to consider returning samples from each one to\nestablish their origin. However, the velocity and molecular composition of\nprimary minerals, hydrated silicates, and organic materials can be determined\nby in situ dust detector instruments. Such instruments could sample the cloud\nof micrometer-scale particles shed by asteroids to provide direct links to\nknown meteorite groups without returning the samples to terrestrial\nlaboratories. We extend models of the measured lunar dust cloud from LADEE to\nshow that the abundance of detectable impact-generated microsamples around\nasteroids is a function of the parent body radius, heliocentric distance, flyby\ndistance, and speed. We use monte carlo modeling to show that several tens to\nhundreds of particles, if randomly ejected and detected during a flyby, would\nbe a sufficient number to classify the parent body as an ordinary chondrite,\nbasaltic achondrite, or other class of meteorite. Encountering and measuring\nmicrosamples shed from near-earth and main-belt asteroids, coupled with\ncomplementary imaging and multispectral measurements, could accomplish a\nthorough characterization of small, airless bodies.", "category": "astro-ph_EP" }, { "text": "Andrade rheology in time-domain. Application to Enceladus' dissipation\n of energy due to forced libration: The main purpose of this work is to present a time-domain implementation of\nthe Andrade rheology, instead of the traditional expansion in terms of a\nFourier series of the tidal potential. This approach can be used in any fully\nthree dimensional numerical simulation of the dynamics of a system of many\ndeformable bodies. In particular, it allows large eccentricities, large mutual\ninclinations, and it is not limited to quasi-periodic perturbations. It can\ntake into account an extended class of perturbations, such as chaotic motions,\ntransient events, and resonant librations.\n The results are presented by means of a concrete application: the analysis of\nthe libration of Enceladus. This is done by means of both analytic formulas in\nthe frequency domain and direct numerical simulations. We do not a priori\nassume that Enceladus has a triaxial shape, the eventual triaxiality is a\nconsequence of the satellite motion and its rheology. As a result we obtain an\nanalytic formula for the amplitude of libration that incorporates a new\ncorrection due to the rheology.\n Our results provide an estimation of the amplitude of libration of the core\nof Enceladus as 0.6% of that of the shell. They also reproduce the observed 10\nGW of tidal heat generated by Enceladus with a value of $0.17\\times\n10^{14}$Pa$\\cdot$s for the global effective viscosity under both Maxwell and\nAndrade rheology.", "category": "astro-ph_EP" }, { "text": "Understanding the Planetary Formation and Evolution in Star\n Clusters(UPiC)-I: Evidence of Hot Giant Exoplanets Formation Timescales: Planets in young star clusters could shed light on planet formation and\nevolution since star clusters can provide accurate age estimation. However, the\nnumber of transiting planets detected in clusters was only $\\sim 30$, too small\nfor statistical analysis. Thanks to the unprecedented high-precision\nastrometric data provided by Gaia DR2 and Gaia DR3, many new Open Clusters(OCs)\nand comoving groups have been identified. The UPiC project aims to find\nobservational evidence and interpret how planet form and evolve in cluster\nenvironments. In this work, we cross-match the stellar catalogs of new OCs and\ncomoving groups with confirmed planets and candidates. We carefully remove\nfalse positives and obtain the biggest catalog of planets in star clusters up\nto now, which consists of 73 confirmed planets and 84 planet candidates. After\nage validation, we obtain the radius--age diagram of these planets/candidates.\nWe find an increment of the fraction of Hot Jupiters(HJs) around 100 Myr and\nattribute the increment to the flyby-induced high-e migration in star clusters.\nAn additional small bump of the fraction of HJs after 1 Gyr is detected, which\nindicates the formation timescale of HJ around field stars is much larger than\nthat in star clusters. Thus, stellar environments play important roles in the\nformation of HJs. The hot-Neptune desert occurs around 100 Myr in our sample. A\ncombination of photoevaporation and high-e migration may sculpt the hot-Neptune\ndesert in clusters.", "category": "astro-ph_EP" }, { "text": "A Survey of CO, CO2, and H2O in Comets and Centaurs: CO and CO$_2$ are the two dominant carbon-bearing molecules in comae and have\nmajor roles in driving activity. Their relative abundances also provide strong\nobservational constraints to models of solar system formation and evolution but\nhave never been studied together in a large sample of comets. We carefully\ncompiled and analyzed published measurements of simultaneous CO and CO$_2$\nproduction rates for 25 comets. Approximately half of the comae have\nsubstantially more CO$_2$ than CO, about a third are CO-dominated and about a\ntenth produce a comparable amount of both. There may be a heliocentric\ndependence to this ratio with CO dominating comae beyond 3.5 au. Eight out of\nnine of the Jupiter Family Comets in our study produce more CO$_2$ than CO. The\nsix dynamically new comets produce more CO$_2$ relative to CO than the eight\nOort Cloud comets that have made multiple passes through the inner solar\nsystem. This may be explained by long-term cosmic ray processing of a comet\nnucleus's outer layers. We find (Q$_{CO}$/Q$_{H_2O}$)$_{median}$ = 3 $\\pm$ 1\\%\nand (Q$_{CO_2}$/Q$_{H_2O}$)$_{median}$ = 12 $\\pm$ 2\\%. The inorganic volatile\ncarbon budget was estimated to be Q$_{CO}$+Q$_{CO_2}$)/Q$_{H_2O}$ $\\sim$ 18\\%\nfor most comets. Between 0.7 to 4.6 au, CO$_2$ outgassing appears to be more\nintimately tied to the water production in a way that the CO is not. The\nvolatile carbon/oxygen ratio for 18 comets is C/O$_{median}$ $\\sim$ 13\\%, which\nis consistent with a comet formation environment that is well within the CO\nsnow line.", "category": "astro-ph_EP" }, { "text": "The PHOENIX Exoplanet Retrieval Algorithm and Using H$^{-}$ Opacity as a\n Probe in Ultra-hot Jupiters: Atmospheric retrievals are now a standard tool to analyze observations of\nexoplanet atmospheres. This data-driven approach quantitatively compares\natmospheric models to observations in order to estimate atmospheric properties\nand their uncertainties. In this paper, we introduce a new retrieval package,\nthe PHOENIX Exoplanet Retrieval Analysis (PETRA). PETRA places the PHOENIX\natmosphere model in a retrieval framework, allowing us to combine the strengths\nof a well-tested and widely-used atmosphere model with the advantages of\nretrieval algorithms. We validate PETRA by retrieving on simulated data for\nwhich the true atmospheric state is known. We also show that PETRA can\nsuccessfully reproduce results from previously published retrievals of WASP-43b\nand HD 209458b. For the WASP-43b results, we show the effect that different\nline lists and line profile treatments have on the retrieved atmospheric\nproperties. Lastly, we describe a novel technique for retrieving the\ntemperature structure and $e^{-}$ density in ultra-hot Jupiters using H$^{-}$\nopacity, allowing us to probe atmospheres devoid of most molecular features\nwith JWST.", "category": "astro-ph_EP" }, { "text": "Effect of near-earth thunderstorms electric field on the intensity of\n ground cosmic ray positrons/electrons in Tibet: Monte Carlo simulations are performed to study the correlation between the\nground cosmic ray intensity and near-earth thunderstorms electric field at YBJ\n(4300 m a.s.l., Tibet, China). The variations of the secondary cosmic ray\nintensity are found to be highly dependent on the strength and polarity of the\nelectric field. In negative fields and in positive fields greater than 600\nV/cm, the total number of ground comic ray positrons and electrons increases\nwith increasing electric field strength. And these values increase more\nobviously when involving a shower with lower primary energy or a higher zenith\nangle. While in positive fields ranging from 0 to 600 V/cm, the total number of\nground comic ray positrons and electrons declines and the amplitude is up to\n3.1% for vertical showers. A decrease of intensity occurs for inclined showers\nin positive fields less than 500 V/cm, which is accompanied by smaller\namplitudes. In this paper, the intensity changes are discussed, especially\nconcerning the decreases in positive electric fields. Our simulation results\nare in good agreement with ground-based experimental results obtained from\nARGO-YBJ and the Carpet air shower array. These results could be helpful in\nunderstanding the acceleration mechanisms of secondary charged particles caused\nby an atmospheric electric field.", "category": "astro-ph_EP" }, { "text": "ALMA Images the Eccentric HD 53143 Debris Disk: We present ALMA 1.3 mm observations of the HD~53143 debris disk - the first\ninfrared or millimeter image produced of this ~1 Gyr-old solar-analogue.\nPrevious HST STIS coronagraphic imaging did not detect flux along the minor\naxis of the disk which could suggest a face-on geometry with two 'clumps' of\ndust. These ALMA observations reveal a disk with a strikingly different\nstructure. In order to fit models to the millimeter visibilities and constrain\nthe uncertainties on the disk parameters, we adopt an MCMC approach. This is\nthe most eccentric debris disk observed to date with a forced eccentricity of\n$0.21\\pm0.02$, nearly twice that of the Fomalhaut debris disk, and also\ndisplays apocenter glow. Although this eccentric model fits the outer debris\ndisk well, there are significant interior residuals remaining that may suggest\na possible edge-on inner disk, which remains unresolved in these observations.\nCombined with the observed structure difference between HST and ALMA, these\nresults suggest a potential previous scattering event or dynamical instability\nin this system. We also note that the stellar flux changes considerably over\nthe course of our observations, suggesting flaring at millimeter wavelengths.\nUsing simultaneous TESS observations, we determine the stellar rotation period\nto be $9.6\\pm0.1$ days.", "category": "astro-ph_EP" }, { "text": "Two Strengths of Ordinary Chondritic Meteoroids as Derived from their\n Atmospheric Fragmentation Modeling: The internal structure and strength of small asteroids and large meteoroids\nis poorly known. Observation of bright fireballs in the Earth's atmosphere can\nprospect meteoroid structure by studying meteoroid fragmentation during the\nflight. Earlier evaluations showed that meteoroid strength is significantly\nlower than that of the recovered meteorites. We present detailed study of\natmospheric fragmentation of seven meteorite falls, all ordinary chondrites,\nand 14 other fireballs, where meteorite fall was predicted but the meteorites,\nprobably also ordinary chondrites, were not recovered. All observations were\nmade by the autonomous observatories of the European Fireball Network and\ninclude detailed radiometric light curves. A model, called the semi-empirical\nfragmentation model, was developed to fit the light curves and decelerations.\nVideos showing individual fragments were available in some cases. The results\ndemonstrated that meteoroids do not fragment randomly but in two distinct\nphases. The first phase typically corresponds to low strengths of 0.04 - 0.12\nMPa. In 2/3 of cases, the first phase was catastrophic or nearly catastrophic\nwith at least 40% of mass lost. The second phase corresponds to 0.9 - 5 MPa for\nconfirmed meteorite falls and to somewhat lower strengths, from about 0.5 MPa\nfor smaller meteoroids. All these strengths are lower than tensile strengths of\nordinary chondritic meteorites cited in the literature, 20 - 40 MPa. We\ninterpret the second phase as being due by cracks in meteoroids and the first\nphase as separation of weakly cemented fragments, which reaccumulated at\nsurfaces of asteroids after asteroid collisions.", "category": "astro-ph_EP" }, { "text": "Planet Occurrence Rate Correlated to Stellar Dynamical History: Evidence\n from Kepler and Gaia: The dynamical history of stars influences the formation and evolution of\nplanets significantly. To explore the influence of dynamical history on planet\nformation and evolution from observations, we assume that stars who experienced\nsignificantly different dynamical histories tend to have different relative\nvelocities. Utilizing the accurate Gaia-Kepler Stellar Properties Catalog, we\nselect single main-sequence stars and divide these stars into three groups\naccording to their relative velocities, i.e. high-V, medium-V, and low-V stars.\nAfter considering the known biases from Kepler data and adopting prior and\nposterior correction to minimize the influence of stellar properties on planet\noccurrence rate, we find that high-V stars have a lower occurrence rate of\nsuper-Earths and sub-Neptunes (1--4 R$_{\\rm \\oplus}$, P<100 days) and higher\noccurrence rate of sub-Earth (0.5--1 R$_{ \\oplus}$, P<30 days) than low-V\nstars. Additionally, high-V stars have a lower occurrence rate of hot Jupiter\nsized planets (4--20 R$_{\\oplus}$, P<10 days) and a slightly higher occurrence\nrate of warm or cold Jupiter sized planets (4--20 R$_{\\oplus}$, 10 0.62. Finally we show with a high\nsignificance, that there is no orbital motion observed in the cases of the DH\nTau, HD 203030 and 1RXS J160929.1-210524 systems and give the most precise\nrelative astrometric measurement of the UScoCTIO 108 system to date.", "category": "astro-ph_EP" }, { "text": "Formation of Giant Planet Satellites: Recent analyses have shown that the concluding stages of giant planet\nformation are accompanied by the development of large-scale meridional flow of\ngas inside the planetary Hill sphere. This circulation feeds a circumplanetary\ndisk that viscously expels gaseous material back into the parent nebula,\nmaintaining the system in a quasi-steady state. Here we investigate the\nformation of natural satellites of Jupiter and Saturn within the framework of\nthis newly outlined picture. We begin by considering the long-term evolution of\nsolid material, and demonstrate that the circumplanetary disk can act as a\nglobal dust trap, where $s_{\\bullet}\\sim0.1-10\\,$mm grains achieve a\nhydrodynamical equilibrium, facilitated by a balance between radial updraft and\naerodynamic drag. This process leads to a gradual increase in the system's\nmetallicity, and eventually culminates in the gravitational fragmentation of\nthe outer regions of the solid sub-disk into $\\mathcal{R}\\sim100\\,$km\nsatellitesimals. Subsequently, satellite conglomeration ensues via pairwise\ncollisions, but is terminated when disk-driven orbital migration removes the\ngrowing objects from the satellitesimal feeding zone. The resulting satellite\nformation cycle can repeat multiple times, until it is brought to an end by\nphoto-evaporation of the parent nebula. Numerical simulations of the envisioned\nformation scenario yield satisfactory agreement between our model and the known\nproperties of the Jovian and Saturnian moons.", "category": "astro-ph_EP" }, { "text": "Eccentric Companions to Kepler-448b and Kepler-693b: Clues to the\n Formation of Warm Jupiters: I report the discovery of non-transiting close companions to two transiting\nwarm Jupiters (WJs), Kepler-448/KOI-12b (orbital period\n$P=17.9\\,\\mathrm{days}$, radius $R_{\\rm p}=1.23^{+0.06}_{-0.05}\\,R_{\\rm Jup}$)\nand Kepler-693/KOI-824b ($P=15.4\\,\\mathrm{days}$, $R_{\\rm\np}=0.91\\pm0.05\\,R_{\\rm Jup}$), via dynamical modeling of their transit timing\nand duration variations (TTVs and TDVs). The companions have masses of\n$22^{+7}_{-5}\\,M_{\\rm Jup}$ (Kepler-448c) and $150^{+60}_{-40}\\,M_{\\rm Jup}$\n(Kepler-693c), and both are on eccentric orbits ($e=0.65^{+0.13}_{-0.09}$ for\nKepler-448c and $e=0.47^{+0.11}_{-0.06}$ for Kepler-693c) with periastron\ndistances of $1.5\\,\\mathrm{au}$. Moderate eccentricities are detected for the\ninner orbits as well ($e=0.34^{+0.08}_{-0.07}$ for Kepler-448b and\n$e=0.2^{+0.2}_{-0.1}$ for Kepler-693b). In the Kepler-693 system, a large\nmutual inclination between the inner and outer orbits\n($53^{+7}_{-9}\\,\\mathrm{deg}$ or $134^{+11}_{-10}\\,\\mathrm{deg}$) is also\nrevealed by the TDVs. This is likely to induce a secular oscillation of the\ninner WJ's eccentricity that brings its periastron close enough to the host\nstar for tidal star-planet interactions to be significant. In the Kepler-448\nsystem, the mutual inclination is weakly constrained and such an eccentricity\noscillation is possible for a fraction of the solutions. Thus these WJs may be\nundergoing tidal migration to become hot Jupiters (HJs), although the migration\nvia this process from beyond the snow line is disfavored by the close-in and\nmassive nature of the companions. This may indicate that WJs can be formed in\nsitu and could even evolve into HJs via high-eccentricity migration inside the\nsnow line.", "category": "astro-ph_EP" }, { "text": "Planet-disc interaction on a freely moving mesh: General-purpose, moving-mesh schemes for hydrodynamics have opened the\npossibility of combining the accuracy of grid-based numerical methods with the\nflexibility and automatic resolution adaptivity of particle-based methods. Due\nto their supersonic nature, Keplerian accretion discs are in principle a very\nattractive system for applying such freely moving mesh techniques. However, the\nhigh degree of symmetry of simple accretion disc models can be difficult to\ncapture accurately by these methods, due to the generation of geometric grid\nnoise and associated numerical diffusion, which is absent in polar grids. To\nexplore these and other issues, in this work we study the idealized problem of\ntwo-dimensional planet-disc interaction with the moving-mesh code AREPO. We\nexplore the hydrodynamic evolution of discs with planets through a series of\nnumerical experiments that vary the planet mass, the disc viscosity and the\nmesh resolution, and compare the resulting surface density, vortensity field\nand tidal torque with results from the literature. We find that the performance\nof the moving-mesh code in this problem is in accordance with published\nresults, showing good consistency with grid codes written in polar coordinates.\nWe also conclude that grid noise and mesh distortions do not introduce\nexcessive numerical diffusion. Finally, we show how the moving-mesh approach\ncan naturally increase resolution in regions of high densityaround planets and\nplanetary wakes, while retaining the background flow at low resolution. This\nprovides an alternative to the difficult task of implementing adaptive mesh\nrefinement in conventional polar-coordinate codes.", "category": "astro-ph_EP" }, { "text": "Origin of Life Molecules in the Atmosphere After Big Impacts on the\n Early Earth: The origin of life on Earth would benefit from a prebiotic atmosphere that\nproduced nitriles, like HCN, which enable ribonucleotide synthesis. However,\ngeochemical evidence suggests that Hadean air was relatively oxidizing with\nnegligible photochemical production of prebiotic molecules. These paradoxes are\nresolved by iron-rich asteroid impacts that transiently reduced the entire\natmosphere, allowing nitriles to form in subsequent photochemistry. Here, we\ninvestigate impact-generated reducing atmospheres using new time-dependent,\ncoupled atmospheric chemistry and climate models, which account for gas-phase\nreactions and surface-catalysis. The resulting H$_2$-, CH$_4$- and NH$_3$-rich\natmospheres persist for millions of years, until hydrogen escapes to space. HCN\nand HCCCN production and rainout to the surface can reach $10^9$ molecules\ncm$^{-2}$ s$^{-1}$ in hazy atmospheres with a mole ratio of $\\mathrm{CH_4} /\n\\mathrm{CO_2} > 0.1$. Smaller $\\mathrm{CH_4} / \\mathrm{CO_2}$ ratios produce\nHCN rainout rates $< 10^5$ molecules cm$^{-2}$ s$^{-1}$, and negligible HCCCN.\nThe minimum impactor mass that creates atmospheric $\\mathrm{CH_4} /\n\\mathrm{CO_2} > 0.1$ is $4 \\times 10^{20}$ to $5 \\times 10^{21}$ kg (570 to\n1330 km diameter), depending on how efficiently iron reacts with a steam\natmosphere, the extent of atmospheric equilibration with an impact-induced melt\npond, and the surface area of nickel that catalyzes CH$_4$ production.\nAlternatively, if steam permeates and deeply oxidizes crust, impactors $\\sim\n10^{20}$ kg could be effective. Atmospheres with copious nitriles have $> 360$\nK surface temperatures, perhaps posing a challenge for RNA longevity, although\ncloud albedo can produce cooler climates. Regardless, post-impact cyanide can\nbe stockpiled and used in prebiotic schemes after hydrogen has escaped to\nspace.", "category": "astro-ph_EP" }, { "text": "Discovery of a young subfamily of the (221)~Eos asteroid family: In this work we report the discovery of a young cluster of asteroids that\noriginated by the breakup of an asteroid member of the (221)Eos family. By\napplying the Hierarchical clustering method to the catalog of proper elements\nwe have identified 26 members of this new small group of asteroids. We have\nestablished that the statistical significance of this cluster is $>99\\%$,\ntherefore it corresponds to a real asteroid family, named the (633)Zelima\ncluster, after its lowest numbered member. The orbits of its members are\ndynamically stable, a fact that enabled us to use the backward integration\nmethod, in two variants to identify potential interlopers and estimate its age.\nApplying it first on the orbits of the nominal family members we identified\nthree asteroids as interlopers. Then we applied it on a set of statistically\nequivalent clones of each member to determine the age of the cluster, with a\nresult of $2.9\\pm0.2$Myrs.", "category": "astro-ph_EP" }, { "text": "Scaling Relations for Terrestrial Exoplanet Atmospheres from Baroclinic\n Criticality: The macroturbulent atmospheric circulation of Earth-like planets mediates\ntheir equator-to-pole heat transport. For fast-rotating terrestrial planets,\nbaroclinic instabilities in the mid-latitudes lead to turbulent eddies that act\nto transport heat poleward. In this work, we derive a scaling theory for the\nequator-to-pole temperature contrast and bulk lapse rate of terrestrial\nexoplanet atmospheres. This theory is built on the work of Jansen & Ferrari\n(2013), and determines how unstable the atmosphere is to baroclinic instability\n(the baroclinic \"criticality\") through a balance between the baroclinic eddy\nheat flux and radiative heating/cooling. We compare our scaling theory to\nGeneral Circulation Model (GCM) simulations and find that the theoretical\npredictions for equator-to-pole temperature contrast and bulk lapse rate\nbroadly agree with GCM experiments with varying rotation rate and surface\npressure throughout the baroclincally unstable regime. Our theoretical results\nshow that baroclinic instabilities are a strong control of heat transport in\nthe atmospheres of Earth-like exoplanets, and our scalings can be used to\nestimate the equator-to-pole temperature contrast and bulk lapse rate of\nterrestrial exoplanets. These scalings can be tested by spectroscopic\nretrievals and full-phase light curves of terrestrial exoplanets with future\nspace telescopes.", "category": "astro-ph_EP" }, { "text": "'Oumuamua as a light sail -- evidence against artificial origin: `Oumuamua, the first detected interstellar visitor to the solar system,\nexhibits non-gravitational acceleration in its trajectory. Ruling out other\nmeans of propulsion, such as the evaporation of material via a cometary tail,\nit has been argued that radiation pressure is responsible for this\nacceleration. From this, the mass of the object must be approximately 40\ntonnes, and given its dimensions, `Oumuamua must have a thickness of ~1 mm if\nof a similar rock/iron composition as the Earth. This raises the much\npublicised possibility that `Oumuamua is artificial in origin, sent\nintentionally across interstellar space by an alien civilisation, This\nconclusion, however, relies upon the common misapprehension that light (solar)\nsails can accelerate to a considerable fraction of the speed of light,\npermitting rapid interstellar travel. We show that such speeds are unattainable\nfor conceptual man-made sails and that, based upon its observed parameters,\n`Oumuamua would require half a billion years just to travel to our solar system\nfrom its closest likely system of origin. These cosmological time-scales make\nit very unlikely that this is a probe sent by an alien civilisation.", "category": "astro-ph_EP" }, { "text": "Testing 2D temperature models in Bayesian retrievals of atmospheric\n properties from hot Jupiter phase curves: Spectroscopic phase curves of transiting hot Jupiters are spectral\nmeasurements at multiple orbital phases, giving a set of disc-averaged spectra\nthat probe multiple hemispheres. By fitting model phase curves to observations,\nwe can constrain the atmospheric properties of hot Jupiters such as molecular\nabundance, aerosol distribution and thermal structure, which offer insights\ninto their dynamics, chemistry, and formation. In this work, we propose a novel\n2D temperature scheme consisting of a dayside and a nightside to retrieve\ninformation from near-infrared phase curves, and apply the scheme to phase\ncurves of WASP-43b observed by HST/WFC3 and Spitzer/IRAC. In our scheme,\ntemperature is constant on isobars on the nightside and varies with\ncos$^n$(longitude/$\\epsilon$) on isobars on the dayside, where $n$ and\n$\\epsilon$ are free parameters. We fit all orbital phases simultaneously using\nthe radiative transfer package NEMESISPY coupled to a Bayesian inference code.\nWe first validate the performance of our retrieval scheme with synthetic phase\ncurves generated from a GCM, and find our 2D scheme can accurately retrieve the\nlatitudinally-averaged thermal structure and constrain the abundance of H$_2$O\nand CH$_4$. We then apply our 2D scheme to the observed phase curves of\nWASP-43b and find: (1) the dayside temperature-pressure profiles do not vary\nstrongly with longitude and are non-inverted; (2) the retrieved nightside\ntemperatures are extremely low, suggesting significant nightside cloud\ncoverage; (3) the H$_2$O volume mixing ratio is constrained to\n$5.6\\times10^{-5}$--$4.0\\times10^{-4}$, and we retrieve an upper bound for\nCH$_4$ at $\\sim$10$^{-6}$.", "category": "astro-ph_EP" }, { "text": "Feasibility of Passive Sounding of Uranian Moons using Uranian\n Kilometric Radiation: We present a feasibility study for passive sounding of Uranian icy moons\nusing Uranian Kilometric Radio (UKR) emissions in the 100 - 900 kHz band. We\nprovide a summary description of the observation geometry, the UKR\ncharacteristics, and estimate the sensitivity for an instrument analogous to\nthe Cassini Radio Plasma Wave Science (RPWS) but with a modified receiver\ndigitizer and signal processing chain. We show that the concept has the\npotential to directly and unambiguously detect cold oceans within Uranian\nsatellites and provide strong constraints on the interior structure in the\npresence of warm or no oceans. As part of a geophysical payload, the concept\ncould therefore have a key role in the detection of oceans within the Uranian\nsatellites. The main limitation of the concept is coherence losses attributed\nto the extended source size of the UKR and dependence on the illumination\ngeometry. These factors represent constraints on the tour design of a future\nUranus mission in terms of flyby altitudes and encounter timing.", "category": "astro-ph_EP" }, { "text": "Calibration of quasi-static aberrations in exoplanet direct-imaging\n instruments with a Zernike phase-mask sensor. II. Concept validation with\n ZELDA on VLT/SPHERE: Warm or massive gas giant planets, brown dwarfs, and debris disks around\nnearby stars are now routinely observed by dedicated high-contrast imaging\ninstruments on large, ground-based observatories. These facilities include\nextreme adaptive optics (ExAO) and state-of-the-art coronagraphy to achieve\nunprecedented sensitivities for exoplanet detection and spectral\ncharacterization. However, differential aberrations between the ExAO sensing\npath and the science path represent a critical limitation for the detection of\ngiant planets with a contrast lower than a few $10^{-6}$ at very small\nseparations (<0.3\\as) from their host star. In our previous work, we proposed a\nwavefront sensor based on Zernike phase contrast methods to circumvent this\nissue and measure these quasi-static aberrations at a nanometric level. We\npresent the design, manufacturing and testing of ZELDA, a prototype that was\ninstalled on VLT/SPHERE during its reintegration in Chile. Using the internal\nlight source of the instrument, we performed measurements in the presence of\nZernike or Fourier modes introduced with the deformable mirror. Our\nexperimental and simulation results are consistent, confirming the ability of\nour sensor to measure small aberrations (<50 nm rms) with nanometric accuracy.\nWe then corrected the long-lived non-common path aberrations in SPHERE based on\nZELDA measurements. We estimated a contrast gain of 10 in the coronagraphic\nimage at 0.2\\as, reaching the raw contrast limit set by the coronagraph in the\ninstrument. The simplicity of the design and its phase reconstruction algorithm\nmakes ZELDA an excellent candidate for the on-line measurements of quasi-static\naberrations during the observations. The implementation of a ZELDA-based\nsensing path on the current and future facilities (ELTs, future space missions)\ncould ease the observation of the cold gaseous or massive rocky planets around\nnearby stars.", "category": "astro-ph_EP" }, { "text": "The statistical reliability of 267 GHz JCMT observations of Venus: No\n significant evidence for phosphine absorption: In the light of the recent announcement of the discovery of the potential\nbiosignature phosphine in the atmosphere of Venus I present an independent\nreanalysis of the original JCMT data to assess the statistical reliability of\nthe detection. Two line detection methods are explored, low order polynomial\nfits and higher order multiple polynomial fits. A non-parametric bootstrap\nanalysis reveals that neither line detection method is able to recover a\nstatistically significant detection. Similar to the results of other reanalyses\nof ALMA Venus spectra, the polynomial fitting process results in false positive\ndetections in the JCMT spectrum. There is thus no significant evidence for\nphosphine absorption in the JCMT Venus spectra.", "category": "astro-ph_EP" }, { "text": "Observational and Theoretical study of the inner region of HH 30: HH 30 is a T Tauri star. In this thesis photometric and polarimetric\nobservations through the source are reported. The observations were carried out\nusing the 84cm telescope of the National Observatory of Mexico (OAN-SPM). This\nthesis also present a model of the brightness of the source using a Monte Carlo\ncode of Watson and Henney (2001) that solves the radiative transfer equation. I\nmodified this code in order to include the polarization. I used the parameters\nof Wood y Whitney (1998) to calculate the polarimetric variability observed in\nHH 30.", "category": "astro-ph_EP" }, { "text": "Dynamical Constraints on Mercury's Collisional Origin: Of the solar system's four terrestrial planets, the origin of Mercury is\nperhaps the most mysterious. Modern numerical simulations designed to model the\ndynamics of terrestrial planet formation systematically fail to replicate\nMercury; which possesses just 5% the mass of Earth and the highest orbital\neccentricity and inclination among the planets. However, Mercury's large\niron-rich core and low volatile inventory stand out among the inner planets,\nand seem to imply a violent collisional origin. Because most algorithms used\nfor simulating terrestrial accretion do not consider the effects of collisional\nfragmentation, it has been difficult to test these collisional hypotheses\nwithin the larger context of planet formation. Here, we analyze a large suite\nof terrestrial accretion models that account for the fragmentation of colliding\nbodies. We find that planets with core mass fractions boosted as a result of\nrepeated hit-and-run collisions are produced in 90% of our simulations. While\nmany of these planets are similar to Mercury in mass, they rarely lie on\nMercury-like orbits. Furthermore, we perform an additional batch of simulations\ndesigned to specifically test the single giant impact origin scenario. We find\nless than a 1% probability of simultaneously replicating the Mercury-Venus\ndynamical spacing and the terrestrial system's degree of orbital excitation\nafter such an event. While dynamical models have made great strides in\nunderstanding Mars' low mass, their inability to form accurate Mercury analogs\nremains a glaring problem.", "category": "astro-ph_EP" }, { "text": "A New M Dwarf Debris Disk Candidate in a Young Moving Group Discovered\n with Disk Detective: We used the Disk Detective citizen science project and the BANYAN II Bayesian\nanalysis tool to identify a new candidate member of a nearby young association\nwith infrared excess. WISE J080822.18-644357.3, an M5.5-type debris disk system\nwith significant excess at both 12 and 22 $\\mu$m, is a likely member ($\\sim\n90\\%$ BANYAN II probability) of the $\\sim 45$ Myr-old Carina association. Since\nthis would be the oldest M dwarf debris disk detected in a moving group, this\ndiscovery could be an important constraint on our understanding of M dwarf\ndebris disk evolution.", "category": "astro-ph_EP" }, { "text": "Evidence for 9 planets in the HD 10180 system: We re-analyse the HARPS radial velocities of HD 10180 and calculate the\nprobabilities of models with differing numbers of periodic signals in the data.\nWe test the significance of the seven signals, corresponding to seven\nexoplanets orbiting the star, in the Bayesian framework and perform comparisons\nof models with up to nine periodicities. We use posterior samplings and\nBayesian model probabilities in our analyses together with suitable prior\nprobability densities and prior model probabilities to extract all the\nsignificant signals from the data and to receive reliable uncertainties for the\norbital parameters of the six, possibly seven, known exoplanets in the system.\nAccording to our results, there is evidence for up to nine planets orbiting HD\n10180, which would make this this star a record holder in having more planets\nin its orbits than there are in the Solar system. We revise the uncertainties\nof the previously reported six planets in the system, verify the existence of\nthe seventh signal, and announce the detection of two additional statistically\nsignificant signals in the data. If of planetary origin, these two additional\nsignals would correspond to planets with minimum masses of 5.1$^{+3.1}_{-3.2}$\nand 1.9$^{+1.6}_{-1.8}$ M$_{\\oplus}$ on orbits with 67.55$^{+0.68}_{-0.88}$ and\n9.655$^{+0.022}_{-0.072}$ days periods (denoted using the 99% credibility\nintervals), respectively.", "category": "astro-ph_EP" }, { "text": "Survivor bias: divergent fates of the Solar System's ejected vs.\n persisting planetesimals: The orbital architecture of the Solar System is thought to have been sculpted\nby a dynamical instability among the giant planets. During the instability a\nprimordial outer disk of planetesimals was destabilized and ended up on\nplanet-crossing orbits. Most planetesimals were ejected into interstellar space\nbut a fraction were trapped on stable orbits in the Kuiper belt and Oort cloud.\nWe use a suite of N-body simulations to map out the diversity of planetesimals'\ndynamical pathways. We focus on two processes: tidal disruption from very close\nencounters with a giant planet, and loss of surface volatiles from repeated\npassages close to the Sun. We show that the rate of tidal disruption is more\nthan a factor of two higher for ejected planetesimals than for surviving\nobjects in the Kuiper belt or Oort cloud. Ejected planetesimals are\npreferentially disrupted by Jupiter and surviving ones by Neptune. Given that\nthe gas giants contracted significantly as they cooled but the ice giants did\nnot, taking into account the thermal evolution of the giant planets decreases\nthe disruption rate of ejected planetesimals. The frequency of volatile loss\nand extinction is far higher for ejected planetesimals than for surviving ones\nand is not affected by the giant planets' contraction. Even if all interstellar\nobjects were ejected from Solar System-like systems, our analysis suggests that\ntheir physical properties should be more diverse than those of Solar System\nsmall bodies as a result of their divergent dynamical histories. This is\nconsistent with the characteristics of the two currently-known interstellar\nobjects.", "category": "astro-ph_EP" }, { "text": "Laplace-like resonances with tidal effects: We generalize the Laplace resonance among three satellites, S1, S2 , and S3,\nby considering different ratios of the mean-longitude variations. These\nresonances, which we call Laplace-like, are classified as first order in the\ncases of the 2:1&2:1, 3:2&3:2, and 2:1&3:2 resonances, second order in the case\nof the 3:1&3:1 resonance, and mixed order in the case of the 2:1&3:1 resonance.\nWe consider a model that includes the gravitational interaction with the\ncentral body together with the effect due to its oblateness, the mutual\ngravitational influence of the satellites S1, S2, and S3 and the secular\ngravitational effect of a fourth satellite S 4 , which plays the role of\nCallisto in the Galilean system. In addition, we consider the dissipative\neffect due to the tidal torque between the inner satellite and the central\nbody. We investigate these Laplace-like resonances by studying different\naspects: (i) we study the survival of the resonances when the dissipation is\nincluded, taking two different expressions for the dissipative effect in the\ncase of a fast- or a slowly rotating central body, (ii) we investigate the\nbehavior of the Laplace-like resonances when some parameters are varied,\nspecifically, the oblateness coefficient, the semimajor axes, and the\neccentricities of the satellites, (iii) we analyze the linear stability of\nfirst-order resonances for different values of the parameters, and (iv) we also\ninclude the full gravitational interaction with S 4 to analyze its possible\ncapture into resonance. The results show a marked difference between first-,\nsecond-, and mixed-order resonances, which might find applications when the\nevolutionary history of the satellites in the Solar System are studied, and\nalso in possible actual configurations of extrasolar planetary systems.", "category": "astro-ph_EP" }, { "text": "Small Bodies of the Solar System Active at Large Heliocentric Distances:\n Studies with the 6-Meter Telescope of Sao Ras: A detailed study of comets active at large heliocentric distances (greater\nthan 4 au) which enter the Solar System for the first time and are composed of\nmatter in its elementary, unprocessed state, would help in our understanding of\nthe history and evolution of the Solar System. In particular, contemporary\ngiant planet formation models require the presence of accretion of volatile\nelements such as neon, argon, krypton, xenon and others, which initially could\nnot survive at the distances where giant planets were formed. Nevertheless, the\nvolatile components could be effectively delivered by the Kuiper-belt and\nOort-cloud bodies, which were formed at temperatures below 30 K. This review is\ndedicated to the results of a multi-year comprehensive study of small bodies of\nthe Solar System showing a comet-like activity at large heliocentric distances.\nThe data were obtained from observations with the 6-meter telescope of SAO RAS\nequipped with multi-mode focal reducers SCORPIO and SCORPIO-2.", "category": "astro-ph_EP" }, { "text": "The effect of varying atmospheric pressure upon habitability and\n biosignatures of Earth-like planets: Understanding the possible climatic conditions on rocky extrasolar planets,\nand thereby their potential habitability, is one of the major subjects of\nexoplanet research. Determining how the climate, as well as potential\natmospheric biosignatures, change under different conditions is a key aspect\nwhen studying Earth-like exoplanets. One important property is the atmospheric\nmass hence pressure and its influence on the climatic conditions. Therefore,\nthe aim of the present study is to understand the influence of atmospheric mass\non climate, hence habitability, and the spectral appearance of planets with\nEarth-like, that is, N2-O2 dominated, atmospheres orbiting the Sun at 1\nAstronomical Unit. This work utilizes a 1D coupled, cloud-free,\nclimate-photochemical atmospheric column model; varies atmospheric surface\npressure from 0.5 bar to 30 bar; and investigates temperature and key species\nprofiles, as well as emission and brightness temperature spectra in a range\nbetween 2{\\mu}m - 20{\\mu}m. Increasing the surface pressure up to 4 bar leads\nto an increase in the surface temperature due to increased greenhouse warming.\nAbove this point, Rayleigh scattering dominates and the surface temperature\ndecreases, reaching surface temperatures below 273K (approximately at ~34 bar\nsurface pressure). For ozone, nitrous oxide, water, methane, and carbon\ndioxide, the spectral response either increases with surface temperature or\npressure depending on the species. Masking effects occur, for example, for the\nbands of the biosignatures ozone and nitrous oxide by carbon dioxide, which\ncould be visible in low carbon dioxide atmospheres.", "category": "astro-ph_EP" }, { "text": "Mineralogical Characterization of Baptistina Asteroid Family:\n Implications for K/T Impactor Source: Bottke et al. (2007) linked the catastrophic formation of Baptistina Asteroid\nFamily (BAF) to the K/T impact event. This linkage was based on dynamical and\ncompositional evidence, which suggested the impactor had a composition similar\nto CM2 carbonaceous chondrites. However, our recent study (Reddy et al. 2009)\nsuggests that the composition of (298) Baptistina is similar to LL-type\nordinary chondrites rather than CM2 carbonaceous chondrites. This rules out any\npossibility of it being related to the source of the K/T impactor, if the\nimpactor was of CM-type composition. Mineralogical study of asteroids in the\nvicinity of BAF has revealed a plethora of compositional types suggesting a\ncomplex formation and evolution environment. A detailed compositional analysis\nof 16 asteroids suggests several distinct surface assemblages including\nordinary chondrites (Gaffey SIV subtype), primitive achondrites (Gaffey SIII\nsubtype), basaltic achondrites (Gaffey SVII subtype and V-type), and a\ncarbonaceous chondrite. Based on our mineralogical analysis we conclude that\n(298) Baptistina is similar to ordinary chondrites (LL-type) based on olivine\nand pyroxene mineralogy and moderate albedo. S-type and V-type in and around\nthe vicinity of BAF we characterized show mineralogical affinity to (8) Flora\nand (4) Vesta and could be part of their families. Smaller BAF asteroids with\nlower SNR spectra showing only a 'single' band are compositionally similar to\n(298) Baptistina and L/LL chondrites. It is unclear at this point why the\nsilicate absorption bands in spectra of asteroids with formal family definition\nseem suppressed relative to background population, despite having similar\nmineralogy.", "category": "astro-ph_EP" }, { "text": "Exoplanets: past, present, and future: Our understanding of extra-solar planet systems is highly driven by advances\nin observations in the past decade. Thanks to high precision spectrograph, we\nare able to reveal unseen companions to stars with the radial velocity method.\nHigh precision photometry from the space, especially with the Kepler mission,\nenables us to detect planets when they transit their stars and dim the stellar\nlight by merely one percent or smaller. Ultra wide-field, high cadence,\ncontinuous monitoring of the Galactic bulge from different sites around the\nsouthern hemisphere provides us the opportunity to observe microlensing effects\ncaused by planetary systems from the solar neighborhood, all the way to the\nMilky Way center. The exquisite AO imaging from ground-based large telescopes,\ncoupled with high-contrast coronagraph, captured the photons directly emitted\nby planets around other stars. In this article, I present a concise review of\nthe extra-solar planet discoveries, discussing the strengths and weaknesses of\nthe major planetary detection methods, providing an overview of our current\nunderstanding of planetary formation and evolution given the tremendous\nobservations delivered by various methods, as well as on-going and planned\nobservation endeavors to provide a clear picture of extra-solar planetary\nsystems.", "category": "astro-ph_EP" }, { "text": "Time-series photometry of Earth flyby asteroid 2012 DA14: Context. The object 2012 DA14 is a near-Earth asteroid with a size of several\ntens of meters. It had approached closely the Earth on 15 February, 2013 UT,\nproviding an opportunity for precise measurements of this tiny asteroid. Aims.\nThe solar phase angle of 2012 DA14 had varied widely around its closest\napproach but was almost constant during the following night. We performed\ntime-series photometric observations on those two nights to determine the\nrotational properties and phase effect. Methods. The observations were carried\nout using the 0.55-m telescope at Saitama University, Japan. The R-band images\nwere obtained continuously over a 2 hr period at the closest approach and for\nabout 5 hr on the next night. Results. The lightcurve data from the second\nnight indicates a rotational period of 11.0 +1.8/-0.6 hr and a peak-to-peak\namplitude of 1.59 +/- 0.02 mag. The brightness variation before and after the\nclosest approach was separated into two components that are derived from the\nrotation and phase effect. We found that the phase curve slope of this asteroid\nis significantly shallower than those of other L-type asteroids. Conclusions.\nWe suggest that 2012 DA14 is coated with a coarse surface that lacks fine\nregolith particles and/or a high albedo surface.", "category": "astro-ph_EP" }, { "text": "Growth of calcium-aluminum-rich inclusions by coagulation and\n fragmentation in a turbulent protoplanetary disk: observations and\n modelisation: Whereas it is generally accepted that calcium-aluminum-rich inclusions (CAIs)\nfrom chondritic meteorites formed in a hot environment in the solar\nprotoplanetary disk, the conditions of their formation remain debated. Recent\nlaboratory studies of CAIs have provided new kind of data: their size\ndistributions. We show that size distributions of CAIs measured in laboratory\nfrom sections of carbonaceous chondrites have a power law size distribution\nwith cumulative size exponent between -1.7 and -1.9, which translates into\ncumulative size exponent between -2.5 and -2.8 after correction for sectioning.\nTo explain these observations, numerical simulations were run to explore the\ngrowth of CAIs from micrometer to centimeter sizes, in a hot and turbulent\nprotoplanetary disk through the competition of coagulation and fragmentation.\nWe show that the size distributions obtained in growth simulations are in\nagreement with CAIs size distributions in meteorites. We explain the CAI sharp\ncut-off of their size distribution at centimeter sizes as the direct result\nfrom the famous fragmentation barrier, provided that CAI fragment for impact\nvelocities larger than 10 m/s. The growth/destruction timescales of millimeter-\nand centimeter-sized CAIs is inversely proportional to the local dust/gas ratio\nand is about 10 years at 1300 K and up to 104 years at 1670K. This implies that\nthe most refractory CAIs are expected to be smaller in size owing to their long\ngrowth timescale compared to less refractory CAIs. Conversely, the least\nrefractory CAIs could have been recycled many times during the CAI production\nera which may have profound consequences for their radiometric age.", "category": "astro-ph_EP" }, { "text": "DMPP-4: Candidate sub-Neptune mass planets orbiting a naked-eye star: We present radial velocity measurements of the very bright ($V\\sim5.7$)\nnearby F star, DMPP-4 (HD 184960). The anomalously low Ca II H&K emission\nsuggests mass loss from planets orbiting a low activity host star. Periodic\nradial velocity variability with $\\sim 10$ ms$^{-1}$ amplitude is found to\npersist over a $>4$ year timescale. Although the non-simultaneous photometric\nvariability in four TESS sectors supports the view of an inactive star, we\nidentify periodic photometric signals and also find spectroscopic evidence for\nstellar activity. We used a posterior sampling algorithm that includes the\nnumber of Keplerian signals, $N_\\textrm{p}$, as a free parameter to test and\ncompare (1) purely Keplerian models (2) a Keplerian model with linear activity\ncorrelation and (3) Keplerian models with Gaussian processes. A preferred\nmodel, with one Keplerian and quasi-periodic Gaussian process indicates a\nplanet with a period of $P_\\textrm{b} = 3.4982^{+0.0015}_{-0.0027}$ d and\ncorresponding minimum mass of $m_\\textrm{b}\\,\\textrm{sin}\\,i =\n12.2^{+1.8}_{-1.9}$ M$_\\oplus$. Without further high time resolution\nobservations over a longer timescale, we cannot definitively rule out the\npurely Keplerian model with 2 candidates planets with $P_\\textrm{b} =\n2.4570^{+0.0026}_{-0.0462}$ d, minimum mass $m_\\textrm{b}\\,\\textrm{sin}\\,i =\n8.0^{+1.1}_{-1.5}$ M$_\\oplus$ and $P_\\textrm{c} = 5.4196^{+0.6766}_{-0.0030}$ d\nand corresponding minimum mass of $m_\\textrm{b}\\,\\textrm{sin}\\,i =\n12.2^{+1.4}_{-1.6}$ M$_\\oplus$. The candidate planets lie in the region below\nthe lower-envelope of the Neptune Desert. Continued mass loss may originate\nfrom the highly irradiated planets or from an as yet undetected body in the\nsystem.", "category": "astro-ph_EP" }, { "text": "A re-assessment of the Kuiper belt size distribution for sub-kilometer\n objects, revealing collisional equilibrium at small sizes: We combine several constraints provided by the crater records on Arrokoth and\nthe worlds of the Pluto system to compute the size-frequency distribution (SFD)\nof the crater production function for craters with diameter D<10km. For this\npurpose, we use a Kuiper belt objects (KBO) population model calibrated on\ntelescopic surveys, that describes also the evolution of the KBO population\nduring the early Solar System. We further calibrate this model using the crater\nrecord on Pluto, Charon and Nix. Using this model, we compute the impact\nprobability on Arrokoth, integrated over the age of the Solar System. This\nprobability is then used together with other observational constraints to\ndetermine the slope of the crater-production function on Arrokoth. In addition,\nwe use our Kuiper belt model also to compare the impact rates and velocities of\nKBOs on Arrokoth with those on Charon, integrated over the crater retention\nages of their respective surfaces. This allows us to establish a relationship\nbetween the spatial density of sub-km craters on Arrokoth and of D~20km craters\non Charon. Together, all these considerations suggest the crater production\nfunction on these worlds has a cumulative power law slope of -1.5 100) microlensing events,\naccurate microlens parallaxes can be obtained from three or fewer photometric\nmeasurements from a small telescope on a satellite in solar orbit at ~1 AU from\nEarth. This is 1--2 orders of magnitude less observing resources than are\nrequired for standard space-based parallaxes. Such microlens parallax\nmeasurements would yield accurate mass and distance measurements to the lens\nfor all cases in which finite-source effects were observed from the ground over\npeak. This would include virtually all high-magnification events with detected\nplanets and a substantial fraction of those without. Hence it would permit\naccurate estimates of the Galactic distribution of planets.", "category": "astro-ph_EP" }, { "text": "C/O and Snowline Locations in Protoplanetary Disks: The Effect of Radial\n Drift and Viscous Gas Accretion: The C/O ratio is a defining feature of both gas giant atmospheric and\nprotoplanetary disk chemistry. In disks, the C/O ratio is regulated by the\npresence of snowlines of major volatiles at different distances from the\ncentral star. We explore the effect of radial drift of solids and viscous gas\naccretion onto the central star on the snowline locations of the main C and O\ncarriers in a protoplanetary disk, H2O, CO2 and CO, and their consequences for\nthe C/O ratio in gas and dust throughout the disk. We determine the snowline\nlocations for a range of fixed initial particle sizes and disk types. For our\nfiducial disk model, we find that grains with sizes ~0.5 cm < s < 7 m for an\nirradiated disk, and ~0.001 cm < s < 7 m for an evolving and viscous disk,\ndesorb at a size-dependent location in the disk, which is independent of the\nparticle's initial position. The snowline radius decreases for larger\nparticles, up to sizes of ~7 m. Compared to a static disk, we find that radial\ndrift and gas accretion in a viscous disk move the H2O snowline inwards by up\nto 40%, the CO2 snowline by up to 60%, and the CO snowline by up to 50%. We\nthus determine an inner limit on the snowline locations when radial drift and\ngas accretion are accounted for.", "category": "astro-ph_EP" }, { "text": "The CRIRES Search for Planets Around the Lowest-Mass Stars. I.\n High-Precision Near-Infrared Radial Velocities with an Ammonia Gas Cell: Radial velocities measured from near-infrared spectra are a potentially\npowerful tool to search for planets around cool stars and sub-stellar objects.\nHowever, no technique currently exists that yields near-infrared radial\nvelocity precision comparable to that routinely obtained in the visible. We\ndescribe a method for measuring high-precision relative radial velocities of\nthese stars from K-band spectra. The method makes use of a glass cell filled\nwith ammonia gas to calibrate the spectrograph response similar to the \"iodine\ncell\" technique that has been used very successfully in the visible. Stellar\nspectra are obtained through the ammonia cell and modeled as the product of a\nDoppler-shifted template spectrum of the object and a spectrum of the cell,\nconvolved with a variable instrumental profile model. A complicating factor is\nthat a significant number of telluric absorption lines are present in the\nspectral regions containing useful stellar and ammonia lines. The telluric\nlines are modeled simultaneously as well using spectrum synthesis with a\ntime-resolved model of the atmosphere over the observatory. The free parameters\nin the complete model are the wavelength scale of the spectrum, the\ninstrumental profile, adjustments to the water and methane abundances in the\natmospheric model, telluric spectrum Doppler shift, and stellar Doppler shift.\nTests of the method based on the analysis of hundreds of spectra obtained for\nlate M dwarfs over six months demonstrate that precisions of ~5 m/s are\nobtainable over long timescales, and precisions of better than 3 m/s can be\nobtained over timescales up to a week. The obtained precision is comparable to\nthe predicted photon-limited errors, but primarily limited over long timescales\nby the imperfect modeling of the telluric lines.", "category": "astro-ph_EP" }, { "text": "An advanced multipole model for (216) Kleopatra triple system: To interpret adaptive-optics observations of (216) Kleopatra, we need to\ndescribe an evolution of multiple moons, orbiting an extremely irregular body\nand including their mutual interactions. Such orbits are generally\nnon-Keplerian and orbital elements are not constants. Consequently, we use a\nmodified $N$-body integrator, which was significantly extended to include the\nmultipole expansion of the gravitational field up to the order $\\ell = 10$. Its\nconvergence was verified against the `brute-force' algorithm. We computed the\ncoefficients $C_{\\ell m},S_{\\!\\ell m}$ for Kleopatra's shape, assuming\na~constant bulk density. For solar-system applications, it was also necessary\nto implement a variable distance and geometry of observations. Our $\\chi^2$\nmetric then accounts for the absolute astrometry, the relative astrometry (2nd\nmoon with respect to 1st), angular velocities, and also silhouettes,\nconstraining the pole orientation. This allowed us to derive the orbital\nelements of Kleopatra's two moons. Using both archival astrometric data and new\nVLT/SPHERE observations (ESO LP 199.C-0074), we were able to identify the true\nperiods of the moons, $P_1 = (1.822359\\pm0.004156)\\,{\\rm d}$, $P_2 =\n(2.745820\\pm0.004820)\\,{\\rm d}$. They orbit very close to the 3:2 mean-motion\nresonance, but their osculating eccentricities are too small compared to other\nperturbations (multipole, mutual), so that regular librations of the critical\nargument are not present. The resulting mass of Kleopatra, $m_1 =\n(1.49\\pm0.16)\\cdot10^{-12}\\,M_\\odot$ or $2.97\\cdot10^{18}\\,{\\rm kg}$, is\nsignificantly lower than previously thought. An implication explained in the\naccompanying paper (Marchis et al.) is that (216) Kleopatra is a critically\nrotating body.", "category": "astro-ph_EP" }, { "text": "Long Term Evolution of Planet-Induced Vortices in Protoplanetary Disks: Recent observations of large-scale asymmetric features in protoplanetary\ndisks suggest that large-scale vortices exist in such disks. Massive planets\nare known to be able to produce deep gaps in protoplanetary disks. The gap\nedges could become hydrodynamically unstable to the Rossby wave/vortex\ninstability and form large-scale vortices. In this study we examine the long\nterm evolution of these vortices by carrying out high-resolution two\ndimensional hydrodynamic simulations that last more than $10^4$ orbits\n(measured at the planet's orbit). We find that the disk viscosity has a strong\ninfluence on both the emergence and lifetime of vortices. In the outer disk\nregion where asymmetric features are observed, our simulation results suggest\nthat the disk viscous $\\alpha$ needs to be low $\\sim 10^{-5 }$ - $10^{-4}$ to\nsustain vortices to thousands and up to $10^{4}$ orbits in certain cases. The\nchance of finding a vortex feature in a disk then decreases with smaller planet\norbital radius. For $\\alpha \\sim 10^{-3}$ or larger, even planets with masses\nof 5 Jupiter-masses will have difficulty either producing or sustaining\nvortices. We have also studied the effects of different disk temperatures and\nplanet masses. We discuss the implications of our findings on current and\nfuture protoplanetary disk observations.", "category": "astro-ph_EP" }, { "text": "Constraining the Radiation and Plasma Environment of the Kepler\n Circumbinary Habitable Zone Planets: The discovery of many planets using the Kepler telescope includes ten planets\norbiting eight binary stars. Three binaries, Kepler-16, Kepler-47, and\nKepler-453, have at least one planet in the circumbinary habitable-zone (BHZ).\nWe constrain the level of high-energy radiation and the plasma environment in\nthe BHZ of these systems. With this aim, BHZ limits in these Kepler binaries\nare calculated as a function of time, and the habitability lifetimes are\nestimated for hypothetical terrestrial planets and/or moons within the BHZ.\nWith the time-dependent BHZ limits established, a self-consistent model is\ndeveloped describing the evolution of stellar activity and radiation properties\nas proxies for stellar aggression toward planetary atmospheres. Modeling binary\nstellar rotation evolution, including the effect of tidal interaction between\nstars in binaries is key to establishing the environment around these systems.\nWe find that Kepler-16 and its binary analogs provide a plasma environment\nfavorable for the survival of atmospheres of putative Mars-sized planets and\nexomoons. Tides have modified the rotation of the stars in Kepler-47 making its\nradiation environment less harsh in comparison to the solar system. This is a\ngood example of the mechanism first proposed by Mason et al. Kepler-453 has an\nenvironment similar to that of the solar system with slightly better than Earth\nradiation conditions at the inner edge of the BHZ. These results can be\nreproduced and even reparametrized as stellar evolution and binary tidal models\nprogress, using our online tool http://bhmcalc.net.", "category": "astro-ph_EP" }, { "text": "Herschel celestial calibration sources: Four large main-belt asteroids\n as prime flux calibrators for the far-IR/sub-mm range: Celestial standards play a major role in observational astrophysics. They are\nneeded to characterise the performance of instruments and are paramount for\nphotometric calibration. During the Herschel Calibration Asteroid Preparatory\nProgramme approximately 50 asteroids have been established as far-IR/sub-mm/mm\ncalibrators for Herschel. The selected asteroids fill the flux gap between the\nsub-mm/mm calibrators Mars, Uranus and Neptune, and the mid-IR bright\ncalibration stars. All three Herschel instruments observed asteroids for\nvarious calibration purposes, including pointing tests, absolute flux\ncalibration, relative spectral response function, observing mode validation,\nand cross-calibration aspects. Here we present newly established models for the\nfour large and well characterized main-belt asteroids (1) Ceres, (2) Pallas,\n(4) Vesta, and (21) Lutetia which can be considered as new prime flux\ncalibrators. The relevant object-specific properties (size, shape,\nspin-properties, albedo, thermal properties) are well established. The seasonal\n(distance to Sun, distance to observer, phase angle, aspect angle) and daily\nvariations (rotation) are included in a new thermophysical model setup for\nthese targets. The thermophysical model predictions agree within 5% with the\navailable (and independently calibrated) Herschel measurements. The four\nobjects cover the flux regime from just below 1,000 Jy (Ceres at mid-IR\nN-/Q-band) down to fluxes below 0.1 Jy (Lutetia at the longest wavelengths).\nBased on the comparison with PACS, SPIRE and HIFI measurements and pre-Herschel\nexperience, the validity of these new prime calibrators ranges from\nmid-infrared to about 700 micron, connecting nicely the absolute stellar\nreference system in the mid-IR with the planet-based calibration at sub-mm/mm\nwavelengths.", "category": "astro-ph_EP" }, { "text": "Quadrupole and octupole order resonances in non-restricted hierarchical\n planetary systems: Nonrestricted hierarchical three-body configurations are common in various\nscales of astrophysical systems. Dynamical structures of the quadrupole-order\nresonance (the von Zeipel-Lidov-Kozai resonance) and the octupole-order\nresonance (the apsidal resonance) under the nonrestricted hierarchical\nplanetary systems are investigated in this work by taking advantage of\nperturbative treatments. Under the quadrupole-order Hamiltonian model, the\ndistribution of libration and circulation regions as well as the distribution\nof flipping region are analytically explored in the parameter space spanned by\nthe conserved quantities. The fundamental frequencies of system are produced\nand then the nominal location of octupole-order resonance is identified. From\nthe viewpoint of perturbative theory, the quadrupole-order Hamiltonian\ndetermines the unperturbed dynamical model and the octupole-order Hamiltonian\nplays an role of perturbation to the quadrupole-order dynamics. The resonant\nHamiltonian for octupole-order resonances is formulated by means of averaging\ntheory, giving rise to a new constant of motion. Phase portraits are produced\nto analyse dynamical structures of octupole-order resonance, including resonant\ncentres, saddle points, dynamical separatrices and islands of libration. By\nanalysing phase portraits, it is found that there are four branches of\nlibration centre and eight libration zones in the considered space.\nApplications to orbit flips show that there are five flipping regions.", "category": "astro-ph_EP" }, { "text": "Planet-Mediated Precision-Reconstruction of the Evolution of the\n Cataclysmic Variable HU Aquarius: Cataclysmic variables (CVs) are binaries in which a compact white dwarf\naccretes material from a low-mass companion star. The discovery of two planets\nin orbit around the CV HU Aquarii opens unusual opportunities for understanding\nthe formation and evolution of this system. In particular the orbital\nparameters of the planets constrains the past and enables us to reconstruct the\nevolution of the system through the common-envelope phase. During this dramatic\nevent the entire hydrogen envelope of the primary star is ejected, passing the\ntwo planets on the way. The observed eccentricities and orbital separations of\nthe planets in HU Aqr enable us to limit the common-envelope parameter $\\alpha\n\\lambda = 0.45\\pm 0.17$ or $\\gamma = 1.77\\pm0.02$ and measure the rate at which\nthe common envelope is ejected, which turns out to be copious. The mass in the\ncommon envelope is ejected from the binary system at a rate of ${\\dot m} =\n1.9\\pm 0.3\\,\\MSun/yr$. The reconstruction of the initial conditions for HU Aqr\nindicates that the primary star had a mass of $M_{\\rm ZAMS} =\n1.6\\pm0.2$\\,\\MSun\\, and a $m_{\\rm ZAMS} = 0.47\\pm 0.04$\\,\\MSun\\, companion in a\n$a=25$--160\\,\\RSun\\, (best value $a=97$\\,\\RSun) binary. The two planets were\nborn with an orbital separation of $a_a=541\\pm44$\\,\\RSun\\, and\n$a_b=750\\pm72$\\,\\Rsun\\, respectively. After the common envelope, the primary\nstar turns into a $0.52\\pm0.01$\\,\\MSun\\, helium white dwarf, which subsequently\naccreted $\\sim 0.30$\\,\\MSun\\, from its Roche-lobe filling companion star,\ngrinding it down to its current observed mass of $0.18\\,\\MSun$.", "category": "astro-ph_EP" }, { "text": "Systematic KMTNet Planetary Anomaly Search. X. Complete Sample of 2017\n Prime-Field Planets: We complete the analysis of planetary candidates found by the KMT\nAnomalyFinder for the 2017 prime fields that cover $\\sim 13\\,{\\rm deg}^2$. We\nreport 3 unambiguous planets: OGLE-2017-BLG-0640, OGLE-2017-BLG-1275, and\nOGLE-2017-BLG-1237. The first two of these were not previously identified,\nwhile the last was not previously published due to technical complications\ninduced by a nearby variable. We further report that a fourth anomalous event,\nthe previously recognized OGLE-2017-BLG-1777, is very likely to be planetary,\nalthough its light curve requires unusually complex modeling because the lens\nand source both have orbiting companions. One of the 3 unambiguous planets,\nOGLE-2017-BLG-1275 is the first AnomalyFinder discovery that has a {\\it\nSpitzer} microlens parallax measurement, $\\pi_E \\sim 0.045\\pm0.015$, implying\nthat this planetary system almost certainly lies in the Galactic bulge. In the\norder listed, the four planetary events have planet-host mass ratios $q$, and\nnormalized projected separations $s$, of $(\\log q,s)$ = $(-2.31,0.61)$,\n$(-2.06,0.63/1.09)$, $(-2.10,1.04)$, and $(-2.86,0.72)$. Combined with\npreviously published events, the 2017 AnomalyFinder prime fields contain 11\nunambiguous planets with well-measured $q$ and one very likely candidate, of\nwhich 3 are AnomalyFinder discoveries. In addition to these 12, there are three\nother unambiguous planets with large uncertainties in $q$.", "category": "astro-ph_EP" }, { "text": "Compositional Convection in the Deep Interior of Uranus: Uranus and Neptune share properties that are distinct from the other giant\nplanets in the solar system, but they are also distinct from one another,\nparticularly in their relative internal heat flux. Not only does Neptune emit\nabout ten times the amount of heat that emitted by Uranus, the relative amount\nof emitted heat to the energy they absorb from the sun also differs greatly,\nbeing comparable at Uranus and the largest of all giant planets at Neptune. As\na result, it is questionable whether thermal convection occurs within the\ninterior of Uranus. However, the presence of an intrinsic magnetic field\nimplies that interior fluid motions must exist. Here, we consider compositional\nconvection driven by the release of hydrogen associated with the formation of\nlarge organic networks or diamond precipitation in the deep interior. We test\nthis hypotheses using a set of numerical rotating convection models where the\nconvective driving is varied between thermal and compositional sources and is\nsufficiently vigorous to not be strongly constrained by rotation. In most\ncases, we find ice-giant-like zonal flows develop, with three bands\ncharacterized by a retrograde equatorial jet and prograde jets at higher\nlatitudes. Large-scale circulation cells also develop and lead to heat and mass\nfluxes that tend to exhibit local maxima along the equatorial plane. This\nsimilarity between convective flows driven by thermal and compositional\nbuoyancy therefore predict Uranus and Neptune to have similar interior dynamics\ndespite Uranus' minimal internal heat flow and may thus explain why both ice\ngiants have comparable magnetic fields.", "category": "astro-ph_EP" }, { "text": "Characterizing the WASP-4 system with TESS and radial velocity data:\n Constraints on the cause of the hot Jupiter's changing orbit and evidence of\n an outer planet: Orbital dynamics provide valuable insights into the evolution and diversity\nof exoplanetary systems. Currently, only one hot Jupiter, WASP-12b, is\nconfirmed to have a decaying orbit. Another, WASP-4b, exhibits hints of a\nchanging orbital period that could be caused by orbital decay, apsidal\nprecession, or the acceleration of the system towards the Earth. We have\nanalyzed all data sectors from NASA's Transiting Exoplanet Survey Satellite\ntogether with all radial velocity (RV) and transit data in the literature to\ncharacterize WASP-4b's orbit. Our analysis shows that the full RV data set is\nconsistent with no acceleration towards the Earth. Instead, we find evidence of\na possible additional planet in the WASP-4 system, with an orbital period of\n~7000 days and $M_{c}sin(i)$ of $5.47^{+0.44}_{-0.43} M_{Jup}$. Additionally,\nwe find that the transit timing variations of all of the WASP-4b transits\ncannot be explained by the second planet but can be explained with either a\ndecaying orbit or apsidal precession, with a slight preference for orbital\ndecay. Assuming the decay model is correct, we find an updated period of\n1.338231587$\\pm$0.000000022 days, a decay rate of -7.33$\\pm$0.71 msec/year, and\nan orbital decay timescale of 15.77$\\pm$1.57 Myr. If the observed decay results\nfrom tidal dissipation, we derive a modified tidal quality factor of\n$Q^{'}_{*}$ = 5.1$\\pm$0.9$\\times10^4$, which is an order of magnitude lower\nthan values derived for other hot Jupiter systems. However, more observations\nare needed to determine conclusively the cause of WASP-4b's changing orbit and\nconfirm the existence of an outer companion.", "category": "astro-ph_EP" }, { "text": "Semi-analytical near-Earth objects propagation: the orbit history of\n (35107) 1991 VH and (175706) 1996 FG3: The propagation of small bodies in the Solar system is driven by the\ncombination of planetary encounters that cause abrupt changes in their orbits\nand secular long-term perturbations. We propose a propagation strategy that\ncombines both of these effects into a single framework for long-term, rapid\npropagation of small bodies in the inner Solar System. The analytical secular\nperturbation of Jupiter is interrupted to numerically solve planetary\nencounters, which last a small fraction of the simulation time. The proposed\npropagation method is compared to numerical integrations in the Solar system,\neffectively capturing properties of the numerical solutions in a fraction of\nthe computational time. We study the orbital history of the Janus mission\ntargets: (35107) 1991 VH and (175706) 1996 FG3, obtaining a stochastic\nrepresentation of their long-term dynamics and frequencies of very close\nencounters. Over the last million years the probability of a strongly\nperturbing flyby is found to be small.", "category": "astro-ph_EP" }, { "text": "Benchmarking the ab initio hydrogen equations of state for the interior\n structure of Jupiter: As Juno is presently measuring Jupiter's gravitational moments to\nunprecedented accuracy, models for the interior structure of the planet are\nputted to the test. While equations of state based on first principles or ab\ninitio simulations have been available and used for the two most abundant\nelements constituting the envelope, hydrogen and helium, significant\ndiscrepancies remain regarding the predictions of the inner structure of\nJupiter. The differences are severe enough to clutter the analysis of Juno's\ndata and even cast doubts on the usefulness of these computationally expensive\nEOSs for the modeling of the interior of Jupiter and exoplanets at large. Using\nour newly developed equations of state for hydrogen and helium, we asses the ab\ninitio equations of state currently available and establish their efficiency at\npredicting the interior structure of Jupiter in a two-layers model. By\nadjusting our free energy parameterization to reproduce previous ab initio EOS\nbehavior, we identify the source of the disagreement previously reported for\nthe interior structure of Jupiter. We further point to area where care should\nbe taken when building EOS for the modeling of giant planets. This concerns the\ninterpolation between the ab initio results and the physical models used to\ncover the low density range as well as the interpolation of the {\\sl ab initio}\nsimulation results at high densities. This sensitivity falls well within the\nuncertainties of the ab initio simulations. This suggests that hydrogen EOS\nshould be carefully benchmarked using a simple planetary model before being\nused in the more advanced planetary models needed to interpret the Juno data.\nWe finally provide an updated version of our ab initio hydrogen EOS recently\npublished.", "category": "astro-ph_EP" }, { "text": "Phase Curves of Nine Trojan Asteroids over a Wide Range of Phase Angles: We have observed well-sampled phase curves for nine Trojan asteroids in B-,\nV-, and I-bands. These were constructed from 778 magnitudes taken with the\n1.3-m telescope on Cerro Tololo as operated by a service observer for the\nSMARTS consortium. Over our typical phase range of 0.2-10 deg, we find our\nphase curves to be adequately described by a linear model, for slopes of\n0.04-0.09 mag/deg with average uncertainty less than 0.02 mag/deg. (The one\nexception, 51378 (2001 AT33), has a formally negative slope of -0.02 +- 0.01\nmag/deg.) These slopes are too steep for the opposition surge mechanism to be\nshadow hiding (SH), so we conclude that the dominant surge mechanism must be\ncoherent backscattering (CB). In a detailed comparison of surface properties\n(including surge slope, B-R color, and albedo), we find that the Trojans have\nsurface properties similar to the P and C class asteroids prominent in the\nouter main belt, yet they have significantly different surge properties (at a\nconfidence level of 99.90%). This provides an imperfect argument against the\ntraditional idea that the Trojans were formed around Jupiter's orbit. We also\nfind no overlap in Trojan properties with either the main belt asteroids or\nwith the small icy bodies in the outer Solar System. Importantly, we find that\nthe Trojans are indistinguishable from other small bodies in the outer Solar\nSystem that have lost their surface ices (such as the gray Centaurs, gray\nScattered Disk Objects, and dead comets). Thus, we find strong support for the\nidea that the Trojans originally formed as icy bodies in the outer Solar\nSystem, were captured into their current orbits during the migration of the gas\ngiant planets, and subsequently lost all their surface ices.", "category": "astro-ph_EP" }, { "text": "Multiverse Predictions for Habitability: Fraction of Life that Develops\n Intelligence: Do mass extinctions affect the development of intelligence? If so, we may\nexpect to be in a universe that is exceptionally placid. We consider the\neffects of impacts, supervolcanoes, global glaciations, and nearby gamma ray\nbursts, and how their rates depend on fundamental constants. It is interesting\nthat despite the very disparate nature of these processes, each occurs on\ntimescales of 100 Myr-Gyr. We argue that this is due to a selection effect that\nfavors both tranquil locales within our universe, as well as tranquil\nuniverses. Taking gamma ray bursts to be the sole driver of mass extinctions is\ndisfavored in multiverse scenarios, as the rate is much lower for different\nvalues of the fundamental constants. In contrast, geological causes of\nextinction are very compatible with the multiverse. Various frameworks for the\neffects of extinctions are investigated, and the intermediate disturbance\nhypothesis is found to be most compatible with the multiverse.", "category": "astro-ph_EP" }, { "text": "A Near-coplanar Stellar Flyby of the Planet Host Star HD 106906: We present an investigation into the kinematics of HD 106906 using the newly\nreleased Gaia DR2 catalog to search for close encounters with other members of\nthe Scorpius-Centaurus (Sco-Cen) association. HD 106906 is an eccentric\nspectroscopic binary that hosts both a large asymmetric debris disk extending\nout to at least 500 au and a directly imaged planetary-mass companion at a\nprojected separation of 738 au. The cause of the asymmetry in the debris disk\nand the unusually wide separation of the planet is not currently known. Using a\ncombination of Gaia DR2 astrometry and ground-based radial velocities, we\nexplore the hypothesis that a close encounter with another cluster member\nwithin the last 15 Myr is responsible for the present configuration of the\nsystem. Out of 461 stars analyzed, we identified two candidate perturbers that\nhad a median closest approach (CA) distance within 1 pc of HD 106906: HIP 59716\nat $D_{\\rm CA}=0.65_{-0.40}^{+0.93}$ pc ($t_{\\rm CA}=-3.49_{-1.76}^{+0.90}$\nMyr) and HIP 59721 at $D_{\\rm CA}=0.71_{-0.11}^{+0.18}$ pc ($t_{\\rm\nCA}=-2.18_{-1.04}^{+0.54}$ Myr), with the two stars likely forming a wide\nphysical binary. The trajectories of both stars relative to HD 106906 are\nalmost coplanar with the inner disk ($\\Delta\\theta = 5.4\\pm1.7$ deg and\n$4.2_{-1.1}^{+0.9}$ deg). These two stars are the best candidates of the\ncurrently known members of Sco-Cen for having a dynamically important close\nencounter with HD 106906, which may have stabilized the orbit of HD 106906 b in\nthe scenario where the planet formed in the inner system and attained high\neccentricity by interaction with the central binary.", "category": "astro-ph_EP" }, { "text": "The emergence of relaxation-oscillator convection on Earth and Titan: In relaxation-oscillator (RO) climate states, short-lived convective storms\nwith torrential rainfall form and dissipate at regular, periodic intervals. RO\nstates have been demonstrated in two- and three-dimensional simulations of\nradiative-convective equilibrium (RCE), and it has been argued that the\nexistence of the RO state requires explicitly resolving moist convective\nprocesses. However, the exact nature and emergence mechanism of the RO state\nhave yet to be determined. Here, we show that (1) RO states exist in\nsingle-column-model simulations of RCE with parameterized convection, and (2)\nthe RO state can be understood as one that has no steady-state solutions of an\nanalytical model of RCE. As with model simulations with resolved convection,\nthese simpler, one-dimensional models of RCE clearly demonstrate RO states\nemerge at high surface temperatures and/or very moist atmospheres. Emergence\noccurs when atmospheric instability quantified by the convective available\npotential energy can no longer support the latent heat release of deep,\nentraining convective plumes. The proposed mechanism for RO emergence is\ngeneral to all moist planetary atmospheres, is agnostic of the condensing\ncomponent, and naturally leads to an understanding of Titan's bursty methane\nweather.", "category": "astro-ph_EP" }, { "text": "A Novel Solution for Resonant Scattering Using Self-Consistent Boundary\n Conditions: We present two novel additions to the semi-analytic solution of Lyman\n$\\alpha$ (Ly$\\alpha$) radiative transfer in spherical geometry: (1)\nimplementation of the correct boundary condition for a steady source, and (2)\nsolution of the time-dependent problem for an impulsive source. For the\nsteady-state problem, the solution can be represented as a sum of two terms: a\npreviously-known analytic solution of the equation with mean intensity $J=0$ at\nthe surface, and a novel, semi-analytic solution which enforces the correct\nboundary condition of zero-ingoing intensity at the surface. This solution is\ncompared to that of the Monte Carlo method, which is valid at arbitrary optical\ndepth. It is shown that the size of the correction is of order unity when the\nspectral peaks approach the Doppler core and decreases slowly with line center\noptical depth, specifically as $(a \\tau_0)^{-1/3}$, which may explain\ndiscrepancies seen in previous studies. For the impulsive problem, the time,\nspatial, and frequency dependence of the solution are expressed using an\neigenfunction expansion in order to characterize the escape time distribution\nand emergent spectra of photons. It is shown that the lowest-order\neigenfrequency agrees well with the decay rate found in the Monte Carlo escape\ntime distribution at sufficiently large line-center optical depths. The\ncharacterization of the escape-time distribution highlights the potential for a\nMonte Carlo acceleration method, which would sample photon escape properties\nfrom distributions rather than calculating every photon scattering, thereby\nreducing computational demand.", "category": "astro-ph_EP" }, { "text": "Thermal Wave Instability as an Origin of Gap and Ring Structures in\n Protoplanetary Disks: Recent millimeter and infrared observations have shown that gap and ring-like\nstructures are common in both dust thermal emission and scattered-light of\nprotoplanetary disks. We investigate the impact of the so-called Thermal Wave\nInstability (TWI) on the millimeter and infrared scattered-light images of\ndisks. We perform 1+1D simulations of the TWI and confirm that the TWI operates\nwhen the disk is optically thick enough for stellar light, i.e.,\nsmall-grain-to-gas mass ratio of $\\gtrsim0.0001$. The mid-plane temperature\nvaries as the waves propagate and hence gap and ring structures can be seen in\nboth millimeter and infrared emission. The millimeter substructures can be\nobserved even if the disk is fully optically thick since it is induced by the\ntemperature variation, while density-induced substructures would disappear in\nthe optically thick regime. The fractional separation between TWI-induced ring\nand gap is $\\Delta r/r \\sim$ 0.2-0.4 at $\\sim$ 10-50 au, which is comparable to\nthose found by ALMA. Due to the temperature variation, snow lines of volatile\nspecies move radially and multiple snow lines are observed even for a single\nspecies. The wave propagation velocity is as fast as $\\sim$ 0.6 ${\\rm\nau~yr^{-1}}$, which can be potentially detected with a multi-epoch observation\nwith a time separation of a few years.", "category": "astro-ph_EP" }, { "text": "The HARPS search for southern extra-solar planets XXXIV. Occurrence,\n mass distribution and orbital properties of super-Earths and Neptune-mass\n planets: We report on the results of an 8-year survey carried out at the La Silla\nObservatory with the HARPS spectrograph to detect and characterize planets in\nthe super-Earth and Neptune mass regime. The size of our star sample and the\nprecision achieved with HARPS have allowed the detection of a sufficiently\nlarge number of low-mass planets to study the statistical properties of their\norbital elements, the correlation of the host-star metallicity with the planet\nmasses, as well as the occurrence rate of planetary systems around solar-type\nstars. A robust estimate of the frequency of systems shows that more than 50%\nof solar-type stars harbor at least one planet of any mass and with period up\nto 100 days. Different properties are observed for the population of planets\nless massive than about 30M-Earth compared to the population of gaseous giant\nplanets. The mass distribution of Super-Earths and Neptune-mass planets (SEN)\nis strongly increasing between 30 and 15M-Earth. The SEN occurence rate does\nnot exhibit a preference for metal rich stars. Most of the SEN planets belong\nto multi-planetary systems. The orbital eccentricities of the SEN planets seems\nlimited to 0.45. At the opposite, the occurence rate of gaseous giant planets\nis growing with the logarithm of the period, and is strongly increasing with\nthe host-star metallicity. About 14% of solar-type stars have a planetary\ncompanion more massive than 50M-Earth? on an orbit with a period shorter than\n10 years. Orbital eccentricities of giant planets are observed up to 0.9 and\nbeyond. The precision of HARPS-type spectrographs opens the possibility to\ndetect planets in the habitable zone of solar-type stars. Identification of a\nsignificant number of super-Earths orbiting solar-type of the Sun vicinity is\nachieved by Doppler spectroscopy. 37 newly discovered planets are announced in\nthe Appendix of this paper, among which 15 Super-Earths.", "category": "astro-ph_EP" }, { "text": "Let the Great World Spin: Revealing the Stormy, Turbulent Nature of\n Young Giant Exoplanet Analogs with the Spitzer Space Telescope: We present a survey for photometric variability in young, low-mass brown\ndwarfs with the Spitzer Space Telescope. The 23 objects in our sample show\nrobust signatures of youth and share properties with directly-imaged\nexoplanets. We present three new young objects: 2MASS J03492367$+$0635078,\n2MASS J09512690 $-$8023553 and 2MASS J07180871$-$6415310. We detect variability\nin 13 young objects, and find that young brown dwarfs are highly likely to\ndisplay variability across the L2--T4 spectral type range. In contrast, the\nfield dwarf variability occurrence rate drops for spectral types $>$L9. We\nexamine the variability amplitudes of young objects and find an enhancement in\nmaximum amplitudes compared to field dwarfs. We speculate that the observed\nrange of amplitudes within a spectral type may be influenced by secondary\neffects such as viewing inclination and/or rotation period. We combine our new\nrotation periods with the literature to investigate the effects of mass on\nangular momentum evolution. While high mass brown dwarfs ($>30\nM_{\\mathrm{Jup}}$) spin up over time, the same trend is not apparent for lower\nmass objects ($<30 M_{\\mathrm{Jup}}$), likely due to the small number of\nmeasured periods for old, low-mass objects. The rotation periods of companion\nbrown dwarfs and planetary-mass objects are consistent with those of isolated\nobjects with similar ages and masses, suggesting similar angular momentum\nhistories. Within the AB Doradus group, we find a high variability occurrence\nrate and evidence for common angular momentum evolution. The results are\nencouraging for future variability searches in directly-imaged exoplanets with\nfacilities such as the James Webb Space Telescope and 30-meter telescopes.", "category": "astro-ph_EP" }, { "text": "Distant Comet C/2017 K2 and the Cohesion Bottleneck: Distant long-period comet C/2017 K2 has been outside the planetary region of\nthe solar system for 3 Myr, negating the possibility that heat retained from\nthe previous perihelion could be responsible for its activity. This inbound\ncomet is also too cold for water ice to sublimate and too cold for amorphous\nwater ice, if present, to crystallize. C/2017 K2 thus presents an ideal target\nin which to investigate the mechanisms responsible for activity in distant\ncomets. We have used Hubble Space Telescope to study the comet in the\npre-perihelion distance range 13.8 to 15.9 AU. The coma maintains a logarithmic\nsurface brightness gradient $m = -1.010\\pm$0.004, consistent with steady-state\nmass loss. The absence of a radiation pressure swept tail indicates that the\neffective particle size is large (0.1 mm) and the mass loss rate is $\\sim$200\nkg s$^{-1}$, remarkable for a comet still beyond the orbit of Saturn.\nExtrapolation of the photometry indicates that activity began in 2012.1, at\n25.9$\\pm$0.9 AU, where the blackbody temperature is only 55 K. This large\ndistance and low temperature suggest that cometary activity is driven by the\nsublimation of a super-volatile ice (e.g.~CO), presumably preserved by K2's\nlong-term residence in the Oort cloud. The mass loss rate can be sustained by\nCO sublimation from an area $\\lesssim 2$ km$^2$, if located near the hot\nsub-solar point on the nucleus. However, while the drag force from sublimated\nCO is sufficient to lift millimeter sized particles against the gravity of the\ncometary nucleus, it is 10$^2$ to 10$^3$ times too small to eject these\nparticles against inter-particle cohesion. Our observations thus require either\na new understanding of the physics of inter-particle cohesion or the\nintroduction of another mechanism to drive distant cometary mass loss. We\nsuggest thermal fracture and electrostatic supercharging in this context.", "category": "astro-ph_EP" }, { "text": "A dynamical study on the habitability of terrestrial exoplanets II: The\n super Earth HD 40307 g: HARPS and it Kepler results indicate that half of solar-type stars host\nplanets with periods P<100 d and masses M < 30 M_E. These super Earth systems\nare compact and dynamically cold. Here we investigate the stability of the\nsuper Earth system around the K-dwarf HD40307. It could host up to six planets,\nwith one in the habitable zone. We analyse the system's stability using\nnumerical simulations from initial conditions within the observational\nuncertainties. The most stable solution deviates 3.1 sigma from the published\nvalue, with planets e and f not in resonance and planets b and c apsidally\naligned. We study the habitability of the outer planet through the\nyearly-averaged insolation and black-body temperature at the pole. Both undergo\nlarge variations because of its high eccentricity and are much more intense\nthan on Earth. The insolation variations are precession dominated with periods\nof 40 kyr and 102 kyr for precession and obliquity if the rotation period is 3\nd. A rotation period of about 1.5 d could cause extreme obliquity variations\nbecause of capture in a Cassini state. For faster rotation rates the periods\nconverge to 10 kyr and 20 kyr. The large uncertainty in the precession period\ndoes not change the overall outcome.", "category": "astro-ph_EP" }, { "text": "Beyond Point Masses. II. Non-Keplerian Shape Effects are Detectable in\n Several TNO Binaries: About 40 transneptunian binaries (TNBs) have fully determined orbits with\nabout 10 others being solved except for breaking the mirror ambiguity. Despite\ndecades of study almost all TNBs have only ever been analyzed with a model that\nassumes perfect Keplerian motion (e.g., two point masses). In reality, all TNB\nsystems are non-Keplerian due to non-spherical shapes, possible presence of\nundetected system components, and/or solar perturbations. In this work, we\nfocus on identifying candidates for detectable non-Keplerian motion based on\nsample of 45 well-characterized binaries. We use MultiMoon, a non-Keplerian\nBayesian inference tool, to analyze published relative astrometry allowing for\nnon-spherical shapes of each TNB system's primary. We first reproduce the\nresults of previous Keplerian fitting efforts with MultiMoon, which serves as a\ncomparison for the non-Keplerian fits and confirms that these fits are not\nbiased by the assumption of a Keplerian orbit. We unambiguously detect\nnon-Keplerian motion in 8 TNB systems across a range of primary radii, mutual\norbit separations, and system masses. As a proof of concept for non-Keplerian\nfitting, we perform detailed fits for (66652) Borasisi-Pabu, possibly revealing\na $J_2 \\approx 0.44$, implying Borasisi (and/or Pabu) may be a contact binary\nor an unresolved compact binary. However, full confirmation of this result will\nrequire new observations. This work begins the next generation of TNB analyses\nthat go beyond the point mass assumption to provide unique and valuable\ninformation on the physical properties of TNBs with implications for their\nformation and evolution.", "category": "astro-ph_EP" }, { "text": "Galactic Punctuated Equilibrium: How to Undermine Carter's Anthropic\n Argument in Astrobiology: We investigate a new strategy which can defeat the (in)famous Carter's\n\"anthropic\" argument against extraterrestrial life and intelligence. In\ncontrast to those already considered by Wilson, Livio, and others, the present\napproach is based on relaxing hidden uniformitarian assumptions, considering\ninstead a dynamical succession of evolutionary regimes governed by both global\n(Galaxy-wide) and local (planet- or planetary system-limited) regulation\nmechanisms. This is in accordance with recent developments in both astrophysics\nand evolutionary biology. Notably, our increased understanding of the nature of\nsupernovae and gamma-ray bursts, as well as of strong coupling between the\nSolar System and the Galaxy on one hand, and the theories of \"punctuated\nequilibria\" of Eldredge and Gould and \"macroevolutionary regimes\" of Jablonski,\nValentine, et al. on the other, are in full accordance with the regulation-\nmechanism picture. The application of this particular strategy highlights the\nlimits of application of Carter's argument, and indicates that in the real\nuniverse its applicability conditions are not satisfied. We conclude that\ndrawing far-reaching conclusions about the scarcity of extraterrestrial\nintelligence and the prospects of our efforts to detect it on the basis of this\nargument is unwarranted.", "category": "astro-ph_EP" }, { "text": "Amino Acid Chiral Selection Via Weak Interactions in Stellar\n Environments: Implications for the Origin of Life: Magnetochiral phenomena may be responsible for the selection of chiral states\nof biomolecules in meteoric environments. For example, the Supernova Amino Acid\nProcessing (SNAAP) Model was proposed previously as a possible mode of\nmagnetochiral selection of amino acids by way of the weak interaction in strong\nmagnetic fields. In earlier work, this model was shown to produce an\nenantiomeric excess (ee) as high as 0.014% for alanine. In this paper we\npresent the results of molecular quantum chemistry calculations from which\n$ee$s are determined for the alpha-amino acids plus isovaline and norvaline,\nwhich were found to have positive ees in meteorites. Calculations are performed\nfor both isolated and aqueous states. In some cases, the aqueous state was\nfound to produce larger $ee$s reaching values as high as a few percent under\nplausible conditions.", "category": "astro-ph_EP" }, { "text": "Graze-and-Merge Collisions under External Perturbers: Graze-and-merge collisions (GMCs) are common multi-step mergers occurring in\nlow-velocity off-axis impacts between similar sized planetary bodies. The first\nimpact happens at somewhat faster than the mutual escape velocity; for typical\nimpact angles this does not result in immediate accretion, but the smaller body\nis slowed down so that it loops back around and collides again, ultimately\naccreting. The scenario changes in the presence of a third major body, i.e.\nplanets accreting around a star, or satellites around a planet. We find that\nwhen the loop-back orbit remains inside roughly 1/3 of the Hill radius from the\ntarget, then the overall process is not strongly affected. As the loop-back\norbit increases in radius, the return velocity and angle of the second\ncollision become increasingly random, with no record of the first collision's\norientation. When the loop-back orbit gets to about 3/4 of the Hill radius, the\npath of smaller body is disturbed up to the point that it will usually escape\nthe target.", "category": "astro-ph_EP" }, { "text": "Mass loading at 67P/Churyumov-Gerasimenko: a case study: We study the dynamics of the interaction between the solar wind ions and a\npartially ionized atmosphere around a comet, at a distance of 2.88 AU from the\nsun during a period of low nucleus activity. Comparing particle data and mag-\nnetic field data for a case study, we highlight the prime role of the solar\nwind electric field in the cometary ion dynamics. Cometary ion and solar wind\nproton flow directions evolve in a correlated manner, as expected from the\ntheory of mass loading. We find that the main component of the acceler- ated\ncometary ion flow direction is along the anti-sunward direction, and not along\nthe convective electric field direc- tion. This is interpreted as the effect of\nan anti-sunward polarisation electric field adding up to the solar wind con-\nvective electric field.", "category": "astro-ph_EP" }, { "text": "Cloud property trends in hot and ultra-hot giant gas planets (WASP-43b,\n WASP-103b, WASP-121b, HAT-P-7b, and WASP-18b): Ultra-hot Jupiters are the hottest exoplanets discovered so far. Observations\nbegin to provide insight into the composition of their extended atmospheres and\ntheir chemical day/night asymmetries. Both are strongly affected by cloud\nformation. We explore trends in cloud properties for a sample of five giant gas\nplanets: WASP-43b, WASP-18b, HAT-P-7b, WASP-103b, and WASP-121b. This provides\na reference frame for cloud properties for the JWST targets WASP-43b and\nWASP-121b. We further explore chemically inert tracers to observe geometrical\nasymmetries, and if the location of inner boundary of a 3D GCM matters for the\nclouds that form. The large day/night temperature differences of ultra-hot\nJupiters cause large chemical asymmetries: cloud-free days but cloudy nights,\natomic vs. molecular gases and respectively different mean molecular weights,\ndeep thermal ionospheres vs. low-ionised atmospheres, undepleted vs enhanced\nC/O. WASP-18b, as the heaviest planet in the sample, has the lowest global C/O.\nThe global climate may be considered as similar amongst ultra-hot Jupiters, but\ndifferent to that of hot gas giants. The local weather, however, is individual\nfor each planet since the local thermodynamic conditions, and hence the local\ncloud and gas properties, differ. The morning and the evening terminator of\nultra-hot Jupiters will carry signatures of their strong chemical asymmetry\nsuch that ingress/egress asymmetries can be expected. An increased C/O ratio is\na clear sign of cloud formation, making cloud modelling a necessity when\nutilizing C/O (or other mineral ratios) as tracer for planet formation. The\nchanging geometrical extension of the atmosphere from the day to the nightside\nmay be probed through chemically inert species like helium. Ultra-hot Jupiters\nare likely to develop deep atmospheric ionospheres which may impact the\natmosphere dynamics through MHD processes.", "category": "astro-ph_EP" }, { "text": "Trapping dust particles in the outer regions of protoplanetary disks: In order to explain grain growth to mm sized particles and their retention in\nouter regions of protoplanetary disks, as it is observed at sub-mm and mm\nwavelengths, we investigate if strong inhomogeneities in the gas density\nprofiles can slow down excessive radial drift and can help dust particles to\ngrow. We use coagulation/fragmentation and disk-structure models, to simulate\nthe evolution of dust in a bumpy surface density profile which we mimic with a\nsinusoidal disturbance. For different values of the amplitude and length scale\nof the bumps, we investigate the ability of this model to produce and retain\nlarge particles on million years time scales. In addition, we introduced a\ncomparison between the pressure inhomogeneities considered in this work and the\npressure profiles that come from magnetorotational instability. Using the\nCommon Astronomy Software Applications ALMA simulator, we study if there are\nobservational signatures of these pressure inhomogeneities that can be seen\nwith ALMA. We present the favorable conditions to trap dust particles and the\ncorresponding calculations predicting the spectral slope in the mm-wavelength\nrange, to compare with current observations. Finally we present simulated\nimages using different antenna configurations of ALMA at different frequencies,\nto show that the ring structures will be detectable at the distances of the\nTaurus Auriga or Ophiucus star forming regions.", "category": "astro-ph_EP" }, { "text": "Microbial Fuel Cells Applied to the Metabolically-Based Detection of\n Extraterrestrial Life: Since the 1970's, when the Viking spacecrafts carried out experiments aimed\nto the detection of microbial metabolism on the surface of Mars, the search for\nnonspecific methods to detect life in situ has been one of the goals of\nastrobiology. It is usually required that the methodology can detect life\nindependently from its composition or form, and that the chosen biological\nsignature points to a feature common to all living systems, as the presence of\nmetabolism. In this paper we evaluate the use of Microbial Fuel Cells (MFCs)\nfor the detection of microbial life in situ. MFCs are electrochemical devices\noriginally developed as power electrical sources, and can be described as fuel\ncells in which the anode is submerged in a medium that contains microorganisms.\nThese microorganisms, as part of their metabolic process, oxidize organic\nmaterial releasing electrons that contribute to the electric current, which is\ntherefore proportional to metabolic and other redox processes. We show that\npower and current density values measured in MFCs using microorganism cultures\nor soil samples in the anode are much larger than those obtained using a medium\nfree of microorganisms or sterilized soil samples, respectively. In particular,\nwe found that this is true for extremophiles, usually proposed to live in\nextraterrestrial environments. Therefore, our results show that MFCs have the\npotential to be used to detect microbial life in situ.", "category": "astro-ph_EP" }, { "text": "New constraints on the planetary system around the young active star AU\n Mic. Two transiting warm Neptunes near mean-motion resonance: AU Mic is a young, active star whose transiting planet was recently detected.\nWe report our analysis of its TESS data, where we modeled the BY Draconis type\nquasi-periodic rotational modulation by starspots simultaneously to the flaring\nactivity and planetary transits. We measured a flare occurrence rate of 6.35\nflares per day for flares with amplitudes in the range of $0.06\\% < f_{\\rm max}\n< 1.5\\%$ of the star flux. We employed a Bayesian MCMC analysis to model the\nfive transits of AU Mic b, improving the constraints on the planetary\nparameters. The planet radius of $4.07\\pm0.17$~R$_{\\oplus}$ and a mean density\nof $1.4\\pm0.4$~g~cm$^{-3}$ confirms that it is a Neptune-size moderately\ninflated planet. While a single feature possibly due to a second planet was\npreviously reported in the former TESS data, we report the detection of two\nadditional transit-like events in the new TESS observations of July 2020. This\nrepresents substantial evidence for a second planet (AU Mic c) in the system.\nWe analyzed its three transits and obtained an orbital period of\n$18.859019\\pm0.000016$~d and a planetary radius of $3.24\\pm0.16$~R$_{\\oplus}$,\nwhich defines it as a warm Neptune-size planet with an expected mass in the\nrange of 2.2~M$_{\\oplus}$~$< M_{\\rm c} < $25.0~M$_{\\oplus}$. The two planets in\nthe system are in near 9:4 mean-motion resonance. We show that this\nconfiguration is dynamically stable and should produce transit-timing\nvariations (TTV). Our non-detection of significant TTV in AU Mic b suggests an\nupper limit for the mass of AU Mic c of $<7$~M$_{\\oplus}$, indicating that this\nplanet is also likely to be inflated. As a young multi-planet system with at\nleast two transiting planets, AU Mic becomes a key system for the study of\natmospheres of infant planets and of planet-planet and planet-disk dynamics at\nthe early stages of planetary evolution.", "category": "astro-ph_EP" }, { "text": "Impacts of Dust Grains Accelerated by Supernovae on the Moon: There is evidence that ejecta from nearby supernovae have rained down on\nEarth in the past. Supernovae can accelerate pre-existing dust grains in the\ninterstellar medium to speeds of $\\sim 0.01 \\mathrm{\\;c}$. We investigate the\nsurvival and impact of dust grains from supernovae on the moon, finding that\nsupernova dust grains can form detectable tracks with widths of $\\sim 0.01 -\n0.07 \\mathrm{\\; \\mu m}$ and depths of $\\sim 0.1 - 0.7 \\mathrm{\\; mm}$ in lunar\nrocks. These tracks could potentially shed light on the timings, luminosities,\nand directions of nearby supernovae.", "category": "astro-ph_EP" }, { "text": "UKIRT microlensing surveys as a pathfinder for $WFIRST$: The detection\n of five highly extinguished low-$|b|$ events: Optical microlensing surveys are restricted from detecting events near the\nGalactic plane and center, where the event rate is thought to be the highest,\ndue to the high optical extinction of these fields. In the near-infrared (NIR),\nhowever, the lower extinction leads to a corresponding increase in event\ndetections and is a primary driver for the wavelength coverage of the $WFIRST$\nmicrolensing survey. During the 2015 and 2016 bulge observing seasons we\nconducted NIR microlensing surveys with UKIRT in conjunction with and in\nsupport of the $Spitzer$ and $Kepler$ microlensing campaigns. Here we report on\nfive highly extinguished ($A_H=0.81-1.97$), low-Galactic latitude ($-0.98\\le\nb\\le -0.36$) microlensing events discovered from our 2016 survey. Four of them\nwere monitored with an hourly cadence by optical surveys but were not reported\nas discoveries, likely due to the high extinction. Our UKIRT surveys and\nsuggested future NIR surveys enable the first measurement of the microlensing\nevent rate in the NIR. This wavelength regime overlaps with the bandpass of the\nfilter in which the $WFIRST$ microlensing survey will conduct its\nhighest-cadence observations, making this event rate derivation critically\nimportant for optimizing its yield.", "category": "astro-ph_EP" }, { "text": "Titan-Hyperion Resonance and the Tidal Q of Saturn: Lainey et al. (2012), by re-analyzing long-baseline astrometry of Saturn's\nmoons, have found that the moons' tidal evolution is much faster than\npreviously thought, implying an order of magnitude stronger tidal dissipation\nwithin Saturn. This result is controversial and implies recent formation of at\nleast some of the mid-sized icy moons of Saturn. Here we show that this more\nintensive tidal dissipation is in full agreement with the evolved state of the\nTitan-Hyperion resonance. This resonance was previously thought to be non-tidal\nin origin, as the amount of tidal evolution required for its assembly is beyond\nwhat is possible in models that assume that all the major moons are primordial.\nWe find that the survival of the Titan-Hyperion resonance is in agreement with\na past Titan-Iapetus 5:1 resonance, but not with unbroken tidal evolution of\nRhea from the rings to its current distance.", "category": "astro-ph_EP" }, { "text": "OGLE-2018-BLG-0567Lb and OGLE-2018-BLG-0962Lb: Two Microlensing Planets\n through Planetary-Caustic Channel: We present the analyses of two microlensing events, OGLE-2018-BLG-0567 and\nOGLE-2018-BLG-0962. In both events, the short-lasting anomalies were densely\nand continuously covered by two high-cadence surveys. The light-curve modeling\nindicates that the anomalies are generated by source crossings over the\nplanetary caustics induced by planetary companions to the hosts. The estimated\nplanet/host separation (scaled to the angular Einstein radius $\\theta_{\\rm E}$)\nand mass ratio are $(s, q) = (1.81, 1.24\\times10^{-3})$ and $(s, q) = (1.25,\n2.38\\times10^{-3})$, respectively. From Bayesian analyses, we estimate the host\nand planet masses as $(M_{\\rm h}, M_{\\rm p}) =\n(0.24_{-0.13}^{+0.16}\\,M_{\\odot}, 0.32_{-0.16}^{+0.34}\\,M_{\\rm J})$ and\n$(M_{\\rm h}, M_{\\rm p}) = (0.55_{-0.29}^{+0.32}\\,M_{\\odot},\n1.37_{-0.72}^{+0.80}\\,M_{\\rm J})$, respectively. These planetary systems are\nlocated at a distance of $7.07_{-1.15}^{+0.93}\\,{\\rm kpc}$ for\nOGLE-2018-BLG-0567 and $6.47_{-1.73}^{+1.04}\\,{\\rm kpc}$ for\nOGLE-2018-BLG-0962, suggesting that they are likely to be near the Galactic\nbulge. The two events prove the capability of current high-cadence surveys for\nfinding planets through the planetary-caustic channel. We find that most\npublished planetary-caustic planets are found in Hollywood events in which the\nsource size strongly contributes to the anomaly cross section relative to the\nsize of the caustic.", "category": "astro-ph_EP" }, { "text": "Asteroid 2014 OL339: yet another Earth quasi-satellite: Our planet has one permanently bound satellite -the Moon-, a likely large\nnumber of mini-moons or transient irregular natural satellites, and three\ntemporary natural retrograde satellites or quasi-satellites. These quasi-moons\n-(164207) 2004 GU9, (277810) 2006 FV35 and 2013 LX28- are unbound companions to\nthe Earth. The orbital evolution of quasi-satellites may transform them into\ntemporarily bound satellites of our planet. Here, we study the dynamical\nevolution of the recently discovered Aten asteroid 2014 OL339 to show that it\nis currently following a quasi-satellite orbit with respect to the Earth. This\nepisode started at least about 775 yr ago and it will end 165 yr from now. The\norbit of this object is quite chaotic and together with 164207 are the most\nunstable of the known Earth quasi-satellites. This group of minor bodies is,\ndynamically speaking, very heterogeneous but three of them exhibit Kozai-like\ndynamics: the argument of perihelion of 164207 oscillates around -90 degrees,\nthe one of 277810 librates around 180 degrees and that of 2013 LX28 remains\naround 0 degrees. Asteroid 2014 OL339 is not currently engaged in any\nKozai-like dynamics.", "category": "astro-ph_EP" }, { "text": "Long-Lived Dust Asymmetries at Dead Zone Edges in Protoplanetary Disks: A number of transition disks exhibit significant azimuthal asymmetries in\nthermal dust emission. One possible origin for these asymmetries is dust\ntrapping in vortices formed at the edges of dead zones. We carry out\nhigh-resolution, two-dimensional hydrodynamic simulations of this scenario,\nincluding the effects of dust feedback. We find that, although feedback weakens\nthe vortices and slows down the process of dust accumulation, the dust\ndistribution in the disk can nonetheless remain asymmetric for many thousands\nof orbits. We show that even after $10^4$ orbits, or $2.5$ Myr when scaled to\nthe parameters of Oph IRS 48 (a significant fraction of its age), the dust is\nnot dispersed into an axisymmetric ring, in contrast to the case of a vortex\nformed by a planet. This is because accumulation of mass at the dead zone edge\nconstantly replenishes the vortex, preventing it from being fully destroyed. We\nproduce synthetic dust emission images using our simulation results. We find\nthat multiple small clumps of dust may be distributed azimuthally. These\nclumps, if not resolved from one another, appear as a single large feature. A\ndefining characteristic of a disk with a dead zone edge is that an asymmetric\nfeature is accompanied by a ring of dust located about twice as far from the\ncentral star.", "category": "astro-ph_EP" }, { "text": "Seasonal Evolution of Saturn's Polar Temperatures and Composition: The seasonal evolution of Saturn's polar atmospheric temperatures and\nhydrocarbon composition is derived from a decade of Cassini Composite Infrared\nSpectrometer (CIRS) 7-16 $\\mu$m thermal infrared spectroscopy. We construct a\nnear-continuous record of atmospheric variability poleward of 60$^\\circ$ from\nnorthern winter/southern summer (2004, $L_s=293^\\circ$) through the equinox\n(2009, $L_s=0^\\circ$) to northern spring/southern autumn (2014,\n$L_s=56^\\circ$). The hot tropospheric polar cyclones and the hexagonal shape of\nthe north polar belt are both persistent features throughout the decade of\nobservations. The hexagon vertices rotated westward by $\\approx30^\\circ$\nlongitude between March 2007 and April 2013, confirming that they are not\nstationary in the Voyager-defined System III longitude system as previously\nthought. The extended region of south polar stratospheric emission has cooled\ndramatically poleward of the sharp temperature gradient near 75$^\\circ$S,\ncoinciding with a depletion in the abundances of acetylene and ethane, and\nsuggestive of stratospheric upwelling with vertical wind speeds of\n$w\\approx+0.1$ mm/s. This is mirrored by a general warming of the northern\npolar stratosphere and an enhancement in acetylene and ethane abundances that\nappears to be most intense poleward of 75$^\\circ$N, suggesting subsidence at\n$w\\approx-0.15$ mm/s. However, the sharp gradient in stratospheric emission\nexpected to form near 75$^\\circ$N by northern summer solstice (2017,\n$L_s=90^\\circ$) has not yet been observed, so we continue to await the\ndevelopment of a northern summer stratospheric vortex. North polar minima in\ntropospheric and stratospheric temperatures were detected in 2008-2010 (lagging\none season, or 6-8 years, behind winter solstice); south polar maxima appear to\nhave occurred before the start of the Cassini observations (1-2 years after\nsummer solstice). [Abridged]", "category": "astro-ph_EP" }, { "text": "The effect of Jupiter oscillations on Juno gravity measurements: Seismology represents a unique method to probe the interiors of giant\nplanets. Recently, Saturn's f-modes have been indirectly observed in its rings,\nand there is strong evidence for the detection of Jupiter global modes by means\nof ground-based, spatially-resolved, velocimetry measurements. We propose to\nexploit Juno's extremely accurate radio science data by looking at the gravity\nperturbations that Jupiter's acoustic modes would produce. We evaluate the\nperturbation to Jupiter's gravitational field using the oscillation spectrum of\na polytrope with index 1 and the corresponding radial eigenfunctions. We show\nthat Juno will be most sensitive to the fundamental mode ($n=0$), unless its\namplitude is smaller than 0.5 cm/s, i.e. 100 times weaker than the $n \\sim\\ 4 -\n11$ modes detected by spatially-resolved velocimetry. The oscillations yield\ncontributions to Juno's measured gravitational coefficients similar to or\nlarger than those expected from shallow zonal winds (extending to depths less\nthan 300 km). In the case of a strong f-mode (radial velocity $\\sim$ 30 cm/s),\nthese contributions would become of the same order as those expected from deep\nzonal winds (extending to 3000 km), especially on the low degree zonal\nharmonics, therefore requiring a new approach to the analysis of Juno data.", "category": "astro-ph_EP" }, { "text": "Episodic deluges in simulated hothouse climates: Earth's distant past and potentially its future include extremely warm\n\"hothouse\" climate states, but little is known about how the atmosphere behaves\nin such states. One distinguishing characteristic of hothouse climates is that\nthey feature lower-tropospheric radiative heating, rather than cooling, due to\nthe closing of the water vapor infrared window regions. Previous work has\nsuggested that this could lead to temperature inversions and significant\nchanges in cloud cover, but no previous modeling of the hothouse regime has\nresolved convective-scale turbulent air motions and cloud cover directly, thus\nleaving many questions about hothouse radiative heating unanswered. Here, we\nconduct simulations that explicitly resolve convection and find that\nlower-tropospheric radiative heating in hothouse climates causes the hydrologic\ncycle to shift from a quasi-steady regime to a \"relaxation oscillator\" regime,\nin which precipitation occurs in short and intense outbursts separated by\nmulti-day dry spells. The transition to the oscillatory regime is accompanied\nby strongly enhanced local precipitation fluxes, a significant increase in\ncloud cover, and a transiently positive (unstable) climate feedback parameter.\nOur results indicate that hothouse climates may feature a novel form of\n\"temporal\" convective self-organization, with implications for both cloud\ncoverage and erosion processes.", "category": "astro-ph_EP" }, { "text": "The first multi-dimensional view of mass loss from externally FUV\n irradiated protoplanetary discs: Computing the flow from externally FUV irradiated protoplanetary discs\nrequires solving complicated and expensive photodissociation physics\niteratively in conjunction with hydrodynamics. Previous studies have therefore\nbeen limited to 1D models of this process. In this paper we compare\n2D-axisymmetric models of externally photoevaporating discs with their 1D\nanalogues, finding that mass loss rates are consistent to within a factor four.\nThe mass loss rates in 2D are higher, in part because half of the mass loss\ncomes from the disc surface (which 1D models neglect). 1D mass loss rates used\nas the basis for disc viscous evolutionary calculations are hence expected to\nbe conservative. We study the anatomy of externally driven winds including the\nstreamline morphology, kinematic, thermal and chemical structure. A key\ndifference between the 1D and 2D models is in the chemical abundances. For\ninstance in the 2D models CO can be dissociated at smaller radial distances\nfrom the disc outer edge than in 1D calculations because gas is\nphotodissociated by radiation along trajectories that are assumed infinitely\noptically thick in 1D models. Multidimensional models will hence be critical\nfor predicting observable signatures of environmentally photoevaporating\nprotoplanetary discs.", "category": "astro-ph_EP" }, { "text": "In Search of Recent Disruption of (3200) Phaethon: Model Implication and\n Hubble Space Telescope Search: Near-Earth asteroid (3200) Phaethon is notable for its association to a\nstrong annual meteor shower, the Geminids, indicative of one or more episodes\nof mass ejection in the past. The mechanism of Phaethon's past activity is not\nyet understood. Here we present a Hubble Space Telescope (HST) search of\nmeter-sized fragments in the vicinity of Phaethon, carried out during\nPhaethon's historic approach to the Earth in mid-December of 2017. Numerical\nsimulation conducted to guide HST's pointing also show that the dynamical\nevolution of Phaethon-originated particles is quick, as ejected materials take\nno longer than $\\sim250$ yr to spread to the entire orbit of Phaethon. Our\nsearch was completed down to 4-meter-class limit (assuming Phaethon-like\nalbedo) and was expected to detect 0.035% particles ejected by Phaethon in the\nlast several decades. The negative result of our search capped the total mass\nloss of Phaethon over the past few dozen orbits to be $10^{12}$ kg at $3\\sigma$\nlevel, taking the best estimates of size power-law from meteor observations and\nspacecraft data. Our result also implies a millimeter-sized dust flux of\n$<10^{-12} \\mathrm{m^{-2} s^{-1}}$ within 0.1 au of Phaethon, suggesting that\nany Phaethon-bound mission is unlikely to encounter dense dust clouds.", "category": "astro-ph_EP" }, { "text": "Pre-perihelion photometric behavior of comet C/2012 S1 (ISON) and its\n future prospect: Comet C/2012 S1 (ISON) shows strange photometric behavior compared to many\npast comets. Shortly after its discovery, majority of astronomers expected its\nsurviving until perihelion passage. Unprecedented evolution of its photometric\nparameters nearly 2 AU from Sun, pushed this comet under survival line defined\nby formula of John. E. Bortle, where ~70% comets in his analysis disintegrated.\nHowever comparison with photometric behavior of group of past disintegrated\ncomets showing large differences and ISON doesn't seems to be typical member of\nthis group. In other hand, compared to surviving, dynamically new comets which\nwere observed far away from Sun and survived its perihelion passage, ISON\nshowing peculiar gradual decrease of its activity, probably caused by\nexhaustion of active fractions of its nucleus.", "category": "astro-ph_EP" }, { "text": "Atmospheric Rossiter-McLaughlin effect and transmission spectroscopy of\n WASP-121b with ESPRESSO: WASP-121b is one of the most studied Ultra-hot Jupiters: many recent analyses\nof its atmosphere report interesting features at different wavelength ranges.\nIn this paper we analyze one transit of WASP-121b acquired with the\nhigh-resolution spectrograph ESPRESSO at VLT in 1-telescope mode, and one\npartial transit taken during the commissioning of the instrument in 4-telescope\nmode. We investigate the anomalous in-transit radial velocity curve and study\nthe transmission spectrum of the planet. By analysing the in-transit radial\nvelocities we were able to infer the presence of the atmospheric\nRossiter-McLaughlin effect. We measured the height of the planetary atmospheric\nlayer that correlates with the stellar mask (mainly Fe) to be 1.052$\\pm$0.015\nRp and we also confirmed the blueshift of the planetary atmosphere. By\nexamining the planetary absorption signal on the stellar cross-correlation\nfunctions we confirmed the presence of a temporal variation of its blueshift\nduring transit, which could be investigated spectrum-by-spectrum. We detected\nsignificant absorption in the transmission spectrum for Na, H, K, Li, CaII, Mg,\nand we certified their planetary nature by using the 2D tomographic technique.\nParticularly remarkable is the detection of Li, with a line contrast of\n$\\sim$0.2% detected at the 6$\\sigma$ level. With the cross-correlation\ntechnique we confirmed the presence of FeI, FeII, CrI and VI. H$\\alpha$ and\nCaII are present up to very high altitudes in the atmosphere ($\\sim$1.44 Rp and\n$\\sim$2 Rp, respectively), and also extend beyond the transit-equivalent Roche\nlobe radius of the planet. These layers of the atmosphere have a large line\nbroadening that is not compatible with being caused by the tidally-locked\nrotation of the planet alone, and could arise from vertical winds or\nhigh-altitude jets in the evaporating atmosphere.", "category": "astro-ph_EP" }, { "text": "An extensive radial velocity survey toward NGC 6253: The old and metal rich open cluster NGC 6253 was observed with the FLAMES\nmulti-object spectrograph during an extensive radial velocity campaign\nmonitoring 317 stars with a median of 15 epochs per object. All the targeted\nstars are located along the upper main sequence of the cluster between 14.8 $<$\nV $<$ 16.5. Fifty nine stars are confirmed cluster members both by radial\nvelocities and proper motions and do not show evidence of variability. We\ndetected 45 variable stars among which 25 belong to NGC 6253. We were able to\nderive an orbital solution for 4 cluster members (and for 2 field stars)\nyielding minimum masses in between $\\sim$90 M$\\rm_J$ and $\\sim$460 M$\\rm_J$ and\nperiods between 3 and 220 days. Simulations demonstrated that this survey was\nsensitive to objects down to 30 M$\\rm_J$ at 10 days orbital periods with a\ndetection efficiency equal to 50%. On the basis of these results we concluded\nthat the observed frequency of binaries down to the hydrogen burning limit and\nup to 20 days orbital period is around (1.5$\\pm$1.3)% in NGC 6253. The overall\nobserved frequency of binaries around the sample of cluster stars is\n(13$\\pm$3)%. The median radial velocity precision achieved by the GIRAFFE\nspectrograph in this magnitude range was around $\\sim$240m$\\rm\\,s^{-1}$\n($\\sim$180 m$\\rm\\,s^{-1}$ for UVES). Based on a limited follow-up analysis of 7\nstars in our sample with the HARPS spectrograph we determined that a precision\nof 35 m $\\rm s^{-1}$ can be reached in this magnitude range, offering the\npossibility to further extend the variability analysis into the substellar\ndomain. Prospects are even more favourable once considering the upcoming\nESPRESSO spectrograph at VLT.", "category": "astro-ph_EP" }, { "text": "Gaia Data Release 3: Reflectance spectra of Solar System small bodies: The Gaia mission of the European Space Agency (ESA) has been routinely\nobserving Solar System objects (SSOs) since the beginning of its operations in\nAugust 2014. The Gaia data release three (DR3) includes, for the first time,\nthe mean reflectance spectra of a selected sample of 60 518 SSOs, primarily\nasteroids, observed between August 5, 2014, and May 28, 2017. Each reflectance\nspectrum was derived from measurements obtained by means of the Blue and Red\nphotometers (BP/RP), which were binned in 16 discrete wavelength bands. We\ndescribe the processing of the Gaia spectral data of SSOs, explaining both the\ncriteria used to select the subset of asteroid spectra published in Gaia DR3,\nand the different steps of our internal validation procedures. In order to\nfurther assess the quality of Gaia SSO reflectance spectra, we carried out\nexternal validation against SSO reflectance spectra obtained from ground-based\nand space-borne telescopes and available in the literature. For each selected\nSSO, an epoch reflectance was computed by dividing the calibrated spectrum\nobserved by the BP/RP at each transit on the focal plane by the mean spectrum\nof a solar analogue. The latter was obtained by averaging the Gaia spectral\nmeasurements of a selected sample of stars known to have very similar spectra\nto that of the Sun. Finally, a mean of the epoch reflectance spectra was\ncalculated in 16 spectral bands for each SSO. The agreement between Gaia mean\nreflectance spectra and those available in the literature is good for bright\nSSOs, regardless of their taxonomic spectral class. We identify an increase in\nthe spectral slope of S-type SSOs with increasing phase angle. Moreover, we\nshow that the spectral slope increases and the depth of the 1 um absorption\nband decreases for increasing ages of S-type asteroid families.", "category": "astro-ph_EP" }, { "text": "On possible life-dispersal patterns beyond the Earth: We model hypothetical bio-dispersal within a single Galactic region using the\nstochastic infection dynamics process, which is inspired by these local\nproperties of life dispersal on Earth. We split the population of stellar\nsystems into different categories regarding habitability and evolved them\nthrough time using probabilistic cellular automata rules analogous to the\nmodel. As a dynamic effect, we include the existence of natural dispersal\nvectors (e.g., dust, asteroids) in a way that avoids assumptions about their\nagency. By assuming that dispersal vectors have a finite velocity and range,\nthe model includes the parameter of 'optical depth of life spreading'. The\neffect of the oscillatory infection rate on the long-term behavior of the\ndispersal flux, which adds a diffusive component to its progression, is also\ntaken into account. We found that phase space is separated into subregions of\nlong-lasting transmission, rapidly terminated transmission, and a transition\nregion between the two. We observed that depending on the amplitude of the\noscillatory life spreading rate, life-transmission in the Galactic patch might\ntake on different geometrical shapes. Even if some host systems are\nuninhabited, life transmission has a certain threshold, allowing a patch to be\nsaturated with viable material over a long period. Although stochastic\nfluctuations in the local density of habitable systems allow for clusters that\ncan continuously infect one another, the spatial pattern disappears when life\ntransmission is below the observed threshold, so that transmission process is\nnot permanent in time. Both findings suggest that a habitable planet in a\ndensely populated region may remain uninfected.", "category": "astro-ph_EP" }, { "text": "The Shape of Saturn's Huygens Ringlet Viewed by Cassini ISS: A new model for the shape of the prominent eccentric ringlet in the gap\nexterior to Saturn's B-ring is developed based on Cassini imaging observations\ntaken over about 8 years. Unlike previous treatments, the new model treats each\nedge of the ringlet separately. The Keplerian component of the model is\nconsistent with results derived from Voyager observations, and $m=2$ modes\nforced by the nearby Mimas 2:1 Lindblad resonance are seen. Additionally, a\nfree $m=2$ mode is seen on the outer edge of the ringlet. Significant irregular\nstructure that cannot be described using normal-mode analysis is seen on the\nringlet edges as well. Particularly on the inner edge, that structure remains\ncoherent over multi-year intervals, moving at the local Keplerian rate. We\ninterpret the irregular structure as the signature of embedded massive bodies.\nThe long coherence time suggests the responsible bodies are concentrated near\nthe edge of the ringlet. Long wake-like structures originate from two locations\non the inner edge of the ringlet, revealing the locations of the two most\nmassive embedded bodies in that region. As with the Voyager observations, the\nCassini data sets showed no correlation between the width and the radius of the\nringlet as would be expected for a self-gravitating configuration, except for a\nbrief interval during late 2006, when the width-radius relation was similar to\nthose seen in most other narrow eccentric ringlets in the Solar System.", "category": "astro-ph_EP" }, { "text": "The Physical Origin of the Venus Low Atmosphere Chemical Gradient: Venus shares many similarities with the Earth, but concomitantly, some of its\nfeatures are extremely original. This is especially true for its atmosphere,\nwhere high pressures and temperatures are found at the ground level. In these\nconditions, carbon dioxide, the main component of Venus' atmosphere, is a\nsupercritical fluid. The analysis of VeGa-2 probe data has revealed the high\ninstability of the region located in the last few kilometers above the ground\nlevel. Recent works have suggested an explanation based on the existence of a\nvertical gradient of molecular nitrogen abundances, around 5 ppm per meter. Our\ngoal was then to identify which physical processes could lead to the\nestablishment of this intriguing nitrogen gradient, in the deep atmosphere of\nVenus. Using an appropriate equation of state for the binary mixture CO2-N2\nunder supercritical conditions, and also molecular dynamics simulations, we\nhave investigated the separation processes of N2 and CO2 in the Venusian\ncontext. Our results show that molecular diffusion is strongly inefficient, and\npotential phase separation is an unlikely mechanism. We have compared the\nquantity of CO2 required to form the proposed gradient with what could be\nreleased by a diffuse degassing from a low volcanic activity. The needed fluxes\nof CO2 are not so different from what can be measured over some terrestrial\nvolcanic systems, suggesting a similar effect at work on Venus.", "category": "astro-ph_EP" }, { "text": "Climate Modeling of a Potential ExoVenus: The planetary mass and radius sensitivity of exoplanet discovery capabilities\nhas reached into the terrestrial regime. The focus of such investigations is to\nsearch within the Habitable Zone where a modern Earth-like atmosphere may be a\nviable comparison. However, the detection bias of the transit and radial\nvelocity methods lies close to the host star where the received flux at the\nplanet may push the atmosphere into a runaway greenhouse state. One such\nexoplanet discovery, Kepler-1649b, receives a similar flux from its star as\nmodern Venus does from the Sun, and so was categorized as a possible exoVenus.\nHere we discuss the planetary parameters of Kepler-1649b with relation to Venus\nto establish its potential as a Venus analog. We utilize the general\ncirculation model ROCKE-3D to simulate the evolution of the surface temperature\nof Kepler-1649b under various assumptions, including relative atmospheric\nabundances. We show that in all our simulations the atmospheric model rapidly\ndiverges from temperate surface conditions towards a runaway greenhouse with\nrapidly escalating surface temperatures. We calculate transmission spectra for\nthe evolved atmosphere and discuss these spectra within the context of the\nJames Webb Space Telescope (JWST) Near-Infrared Spectrograph (NIRSpec)\ncapabilities. We thus demonstrate the detectability of the key atmospheric\nsignatures of possible runaway greenhouse transition states and outline the\nfuture prospects of characterizing potential Venus analogs.", "category": "astro-ph_EP" }, { "text": "An interstellar origin for Jupiter's retrograde co-orbital asteroid: Asteroid (514107) 2015 BZ509 was discovered recently in Jupiter's co-orbital\nregion with a retrograde motion around the Sun. The known chaotic dynamics of\nthe outer Solar System have so far precluded the identification of its origin.\nHere, we perform a high-resolution statistical search for stable orbits and\nshow that asteroid (514107) 2015 BZ509 has been in its current orbital state\nsince the formation of the Solar System. This result indicates that (514107)\n2015 BZ509 was captured from the interstellar medium 4.5 billion years in the\npast as planet formation models cannot produce such a primordial\nlarge-inclination orbit with the planets on nearly-coplanar orbits interacting\nwith a coplanar debris disk that must produce the low-inclination small-body\nreservoirs of the Solar System such as the asteroid and Kuiper belts. This\nresult also implies that more extrasolar asteroids are currently present in the\nSolar System on nearly-polar orbits.", "category": "astro-ph_EP" }, { "text": "Detection of Rotational Variability in Floofy Objects at Optical\n Wavelengths: Phase resolved observations of planetary bodies allow us to understand the\nlongitudinal and latitudinal variations that make each one unique. Rotational\nvariations have been detected in several types of astronomical bodies beyond\nthose of planetary mass, including asteroids, brown dwarfs, and stars.\nUnexpected rotational variations, such as those presented in this work, reminds\nus that the universe can be complicated, with more mysteries to uncover. In\nthis work we present evidence for a new class of astronomical objects we\nidentify as \"floofy\" with observational distinctions between several sub-types\nof these poorly understood objects. Using optical observations contributed by\nthe community, we have identified rotational variation in several of these\nfloofy objects, which suggests that they may have strong differences between\ntheir hemispheres, likely caused by differing reflectivity off their surfaces.\nAdditional sub-types show no rotational variability suggesting a uniform\ndistribution of reflective elements on the floofy object. While the work here\nis a promising step towards the categorization of floofy objects, further\nobservations with more strictly defined limits on background light,\nillumination angles, and companion objects are necessary to develop a better\nunderstanding of the many remaining mysteries of these astronomical objects.", "category": "astro-ph_EP" }, { "text": "Physical Characterization of ~2-meter Diameter Near-Earth Asteroid 2015\n TC25: A possible boulder from E-type Asteroid (44) Nysa: Small near-Earth asteroids (>20 meters) are interesting because they are\nprogenitors for meteorites in our terrestrial collection. Crucial to our\nunderstanding of the effectiveness of our atmosphere in filtering low-strength\nimpactors is the physical characteristics of these small near-Earth asteroids\n(NEAs). In the past, characterization of small NEAs has been a challenge\nbecause of the difficulty in detecting them prior to close Earth flyby. In this\nstudy we physically characterized the 2-meter diameter near-Earth asteroid 2015\nTC25 using ground-based optical, near-infrared and radar assets during a close\nflyby of the Earth (distance 69,000 miles) in Oct. 2015. Our observations\nsuggest that its surface composition is similar to aubrites, a rare class of\nhigh albedo differentiated meteorites. Aubrites make up only 0.14 % of all know\nmeteorites in our terrestrial meteorite collection. 2015 TC25 is also a very\nfast rotator with a rotation period of 133 seconds. We compared spectral and\ndynamical properties of 2015 TC25 and found the best candidate source body in\nthe inner main belt to be the 70-km diameter E-type asteroid (44) Nysa. We\nattribute difference in spectral slope between the two objects to the lack of\nregolith on the surface of 2015 TC25. Using the albedo of E-type asteroids\n(50-60%) we refine the diameter of 2015 TC25 to 2-meters making it one of the\nsmallest NEA ever to be characterized.", "category": "astro-ph_EP" }, { "text": "Super stellar abundances of alkali metals suggest significant migration\n for Hot Jupiters: We investigate the origin of the measured over-abundance of alkali metals in\nthe atmospheres of hot gas giants, relative to both their host stars and their\natmospheric water abundances. We show that formation exterior to the water snow\nline followed by inward disc-driven migration results in excess accretion of\noxygen-poor, refractory-rich material from within the snow-line. This naturally\nleads to enrichment of alkali metals in the planetary atmosphere relative to\nthe bulk composition of its host star but relative abundances of water that are\nsimilar to the stellar host. These relative abundances cannot be explained by\nin situ formation which places the refractory elements in the planetary deep\ninterior rather than the atmosphere. We therefore suggest that the measured\ncompositions of the atmospheres of hot Jupiters are consistent with significant\nmigration for at least a subset of hot gas giants. Our model makes robust\npredictions about atmospheric composition that can be confirmed with future\ndata from JWST and Ariel.", "category": "astro-ph_EP" }, { "text": "The Evolving Photometric Lightcurve of Comet 1P/Halley's Coma During the\n 1985/86 Apparition: We present new analyses of the photometric lightcurve of Comet 1P/Halley\nduring its 1985/86 apparition. As part of a world-wide campaign coordinated by\nthe International Halley Watch (IHW), narrowband photometry was obtained with\ntelescopes at 18 observatories. Following submissions to and basic reductions\nby the Photometry and Polarimetry Network of the IHW, we computed production\nrates and created composite lightcurves for each species. These were used to\nmeasure how the apparent rotational period (~7.35 day), along with its shape,\nevolved with time during the apparition. The lightcurve shape systematically\nvaried from double-peaked to triple-peaked and back again every 8-9 weeks, due\nto Halley's non-principal axis (complex) rotation and the associated component\nperiods. Unexpectedly, we found a phase shift of one-half cycle also took place\nduring this interval, and therefore the actual beat frequency between the\ncomponent periods is twice this interval or 16-18 weeks. Preliminary modeling\nsuggests that a single source might produce the entire post-perihelion\nlightcurve variability and associated evolution. The detailed evolution of the\napparent period varied in a non-smooth manner between 7.2 and 7.6 day, likely\ndue to a combination of synodic effects and the interaction of solar\nillumination with isolated source regions on a body in complex rotation. The\nneed to simultaneously reproduce each of these characteristics will provide\nvery strong additional constraints on Halley's component periods associated\nwith its complex rotation. To assist in these and future analyses, we created a\nsynthetic lightcurve based directly on the measured data. We unexpectedly\ndiscovered a strong correlation of ion tail disconnection event start times\nwith minima in the comet's gas production, implying that a decrease in\noutgassing is another cause of these events.", "category": "astro-ph_EP" }, { "text": "Electric charging of dust aggregates and its effect on dust coagulation\n in protoplanetary disks: Mutual sticking of dust aggregates is the first step toward planetesimal\nformation in protoplanetary disks. In spite that the electric charging of dust\nparticles is well recognized in some contexts, it has been largely ignored in\nthe current modeling of dust coagulation. In this study, we present a general\nanalysis of the dust charge state in protoplanetary disks, and then demonstrate\nhow the electric charging could dramatically change the currently accepted\nscenario of dust coagulation. First, we describe a new semianalytical method to\ncalculate the dust charge state and gas ionization state self-consistently.\nThis method is far more efficient than previous numerical methods, and provides\na general and clear description of the charge state of gas-dust mixture.\nSecond, we apply this analysis to early evolutionary stages where the dust has\nbeen thought to grow into fractal ($D \\sim 2$) aggregates with a\nquasi-monodisperse (i.e., narrow) size distribution. We find that, for a wide\nrange of model parameters, the fractal growth is strongly inhibited by the\nelectric repulsion between colliding aggregates and eventually \"freezes out\" on\nits way to the subsequent growth stage involving collisional compression.\nStrong disk turbulence would help the aggregates to overcome this growth\nbarrier, but then it would cause catastrophic collisional fragmentation in\nlater growth stages. These facts suggest that the combination of electric\nrepulsion and collisional fragmentation would impose a serious limitation on\ndust growth in protoplanetary disks. We propose a possible scenario of dust\nevolution after the freeze-out. Finally, we point out that the fractal growth\nof dust aggregates tends to maintain a low ionization degree and, as a result,\na large magnetorotationally stable region in the disk.", "category": "astro-ph_EP" }, { "text": "The Chicxulub Impactor: Comet or Asteroid?: A recent paper by Siraj & Loeb (2021) entitled \"Breakup of a long-period\ncomet as the origin of the dinosaur extinction\" attempts to revive the\nperennial debate about what type of body hit the Earth 66 million years ago,\ntriggering the end-Cretaceous extinction. Here we critique the paper and assess\nthe evidence it presents. To consider a comet more likely than an asteroid\nrequires extreme assumptions about how comets fragment, conflation of\ncarbonaceous chondrites with specific types of carbonaceous chondrites, and a\nblind eye to the evidence of the iridium layer.", "category": "astro-ph_EP" }, { "text": "TERMS Photometry of Known Transiting Exoplanets: The Transit Ephemeris Refinement and Monitoring Survey (TERMS) conducts\nradial velocity and photometric monitoring of known exoplanets in order to\nrefine planetary orbits and predictions of possible transit times. This effort\nis primarily directed towards planets not known to transit, but a small sample\nof our targets consist of known transiting systems. Here we present precision\nphotometry for 6 WASP planets acquired during their transit windows. We perform\na Markov Chain Monte Carlo (MCMC) analysis for each planet and combine these\ndata with previous measurements to redetermine the period and ephemerides for\nthese planets. These observations provide recent mid-transit times which are\nuseful for scheduling future observations. Our results improve the ephemerides\nof WASP-4b, WASP-5b and WASP-6b and reduce the uncertainties on the mid-transit\ntime for WASP-29b. We also confirm the orbital, stellar and planetary\nparameters of all 6 systems.", "category": "astro-ph_EP" }, { "text": "H-Atmospheres of Icy Super-Earths Formed in situ in the Outer Solar\n System: An Application to a Possible Planet Nine: We examine the possibility that icy super-Earth mass planets, formed over\nlong time scales (0.1--1~Gyr) at large distances ($\\sim$ 200--1000~AU) from\ntheir host stars, will develop massive H-rich atmospheres. Within the interior\nof these planets, high pressure converts CH$_4$ into ethane, butane, or diamond\nand releases H$_2$. Using simplified models which capture the basic physics of\nthe internal structure, we show that the physical properties of the atmosphere\ndepend on the outflux of H$_2$ from the mantle. When this outflux is $\\lesssim\n10^{10}$ [molec cm$^{-2}$ s$^{-1}$], the outgassed atmosphere has base pressure\n$\\lesssim$ 1 bar. Larger outflows result in a substantial atmosphere where the\nbase pressure may approach $10^3 - 10^4$ bar. For any pressure, the mean\ndensity of these planets, 2.4--3 [g cm$^{-3}$], is much larger than the mean\ndensity of Uranus and Neptune, 1.3--1.6 [g cm$^{-3}$]. Thus, observations can\ndistinguish between a Planet Nine with a primordial H/He-rich atmosphere\naccreted from the protosolar nebula and one with an atmosphere outgassed from\nthe core.", "category": "astro-ph_EP" }, { "text": "Properties and occurrence rates of $Kepler$ exoplanet candidates as a\n function of host star metallicity from the DR25 catalog: Correlations between the occurrence rate of exoplanets and their host star\nproperties provide important clues about the planet formation processes. We\nstudied the dependence of the observed properties of exoplanets (radius, mass,\nand orbital period) as a function of their host star metallicity. We analyzed\nthe planetary radii and orbital periods of over 2800 $Kepler$ candidates from\nthe latest $Kepler$ data release DR25 (Q1-Q17) with revised planetary radii\nbased on $Gaia$~DR2 as a function of host star metallicity (from the Q1-Q17\n(DR25) stellar and planet catalog). With a much larger sample and improved\nradius measurements, we are able to reconfirm previous results in the\nliterature. We show that the average metallicity of the host star increases as\nthe radius of the planet increases. We demonstrate this by first calculating\nthe average host star metallicity for different radius bins and then\nsupplementing these results by calculating the occurrence rate as a function of\nplanetary radius and host star metallicity. We find a similar trend between\nhost star metallicity and planet mass: the average host star metallicity\nincreases with increasing planet mass. This trend, however, reverses for masses\n$> 4.0\\, M_\\mathrm{J}$: host star metallicity drops with increasing planetary\nmass. We further examined the correlation between the host star metallicity and\nthe orbital period of the planet. We find that for planets with orbital periods\nless than 10 days, the average metallicity of the host star is higher than that\nfor planets with periods greater than 10 days.", "category": "astro-ph_EP" }, { "text": "The time evolution of $M_{\\mathrm{d}}/\\dot M$ in protoplanetary discs as\n a way to disentangle between viscosity and MHD winds: As the classic viscous paradigm for protoplanetary disk accretion is\nchallenged by the observational evidence of low turbulence, the alternative\nscenario of MHD disk winds is being explored as potentially able to reproduce\nthe same observed features traditionally explained with viscosity. Although the\ntwo models lead to different disk properties, none of them has been ruled out\nby observations - mainly due to instrumental limitations. In this work, we\npresent a viable method to distinguish between the viscous and MHD framework\nbased on the different evolution of the distribution in the disk mass\n($M_{\\mathrm{d}}$) - accretion rate ($\\dot M$) plane of a disk population. With\na synergy of analytical calculations and 1D numerical simulations, performed\nwith the population synthesis code \\texttt{Diskpop}, we find that both\nmechanisms predict the spread of the observed ratio $M_{\\mathrm{d}}/\\dot M$ in\na disk population to decrease over time; however, this effect is much less\npronounced in MHD-dominated populations as compared to purely viscous\npopulations. Furthermore, we demonstrate that this difference is detectable\nwith the current observational facilities: we show that convolving the\nintrinsic spread with the observational uncertainties does not affect our\nresult, as the observed spread in the MHD case remains significantly larger\nthan in the viscous scenario. While the most recent data available show a\nbetter agreement with the wind model, ongoing and future efforts to obtain\ndirect gas mass measurements with ALMA and ngVLA will cause a reassessment of\nthis comparison in the near future.", "category": "astro-ph_EP" }, { "text": "Segregation on small rubble bodies due to impact-induced seismic shaking: We present a framework to study regolith segregation on rubble-pile asteroids\n(self-gravitating granular aggregates) due to seismic shaking induced by\nimpacts sustained during their lifetimes. We first relate the amplitude and\nfrequency of surface vibrations to the location and severity of an impact, and\nthe rubble body's geometry and bulk properties. For clarity, the body is taken\nto be an ellipsoid with size and spin close to that of Itokawa, although other\nasteroids are also easily incorporated. We then model the body's collisional\nhistory stochastically given the variability in the impact activity on an\nasteroid. Finally, we utilize discrete element simulations to investigate the\nregolith's response to impacts. In these simulations, in any sample collisional\nhistory, every time an impact occurs, a bin filled with a grain mixture and\nlocated at the region of interest on the asteroid is vibrated at that impact's\nassociated amplitude and frequency. Utilizing this framework we find that\nimpact-driven seismicity is sufficient to drive size segregation on small\nrubble-piles, but the segregation quality depends on several aspects, e.g.\ntotal impact energy supplied, placement of the region of interest, bulk wave\nspeed, and seismic diffusivity.", "category": "astro-ph_EP" }, { "text": "Shellspec39 -- a tool for modelling the spectra, light curves, and\n images of interacting binaries and exoplanets: Program SHELLSPEC is designed to calculate light curves, spectra, and images\nof interacting binaries and extra-solar planets immersed in a moving gaseous or\ndusty circumstellar matter. It solves simple radiative transfer along the line\nof sight in 3D moving media. The Roche model and synthetic spectra from the\nstellar atmosphere models such as TLUSTY from Ivan Hubeny can be used as a\nboundary condition for the radiative transfer. The latest publicly available\nversion is Shellspec39. The code has been combined with other methods such as\nDoppler tomography and interferometry and used to analyze spectroscopic,\nphotometric, and interferometric observations of binary stars and transiting\nexoplanets. A few examples are briefly mentioned.", "category": "astro-ph_EP" }, { "text": "Gas and multi-species dust dynamics in viscous protoplanetary discs: the\n importance of the dust back-reaction: We study the dynamics of a viscous protoplanetary disc hosting a population\nof dust grains with a range of sizes. We compute steady-state solutions, and\nshow that the radial motion of both the gas and the dust can deviate\nsubstantially from those for a single-size dust population. Although the\naerodynamic drag from the dust on the gas is weaker than in the case where all\ngrains are optimally coupled to the gas, the cumulative \"back-reaction\" of the\ndust particles can still alter the gas dynamics significantly. In typical\nprotoplanetary discs, the net effect of the dust back-reaction decreases the\ngas accretion flow compared to the dust-free (viscous) case, even for\ndust-to-gas ratios of order $1\\%$. In the outer disc, where dust grains are\ntypically less strongly coupled to the gas and settle towards the midplane, the\ndust back-reaction can even drive outward gas flow. Moreover, the radial inward\ndrift of large grains is reduced below the gas motion in the inner disc\nregions, while small dust grains follow the gas dynamics over all the disc\nextent. The resulting dust and gas dynamics can give rise to observable\nstructures, such as gas and dust cavities. Our results show that the dust\nback-reaction can play a major role in both the dynamics and observational\nappearance of protoplanetary discs, and cannot be ignored in models of\nprotoplanetary disc evolution.", "category": "astro-ph_EP" }, { "text": "Multi-wavelength aperture polarimetry of debris disc host stars: Debris discs around main sequence stars have been extensively characterised\nfrom infrared to millimetre wavelengths through imaging, spectroscopic, and\ntotal intensity (scattered light and/or thermal emission) measurements.\nPolarimetric observations have only been used sparingly to interpret the\ncomposition, structure, and size of dust grains in these discs. Here we present\nnew multi-wavelength aperture polarisation observations with parts-per-million\nsensitivity of a sample of twelve bright debris discs, spanning a broad range\nof host star spectral types, and disc properties. These measurements were\nmostly taken with the HIgh Precision Polarimetric Instrument on the\nAnglo-Australian Telescope. We combine these polarisation observations with the\nknown disc architectures and geometries of the discs to interpret the\nmeasurements. We detect significant polarisation attributable to circumstellar\ndust from HD 377 and HD 39060, and find tentative evidence for HD 188228 and HD\n202628.", "category": "astro-ph_EP" }, { "text": "Multibeam Blind Search of Targeted SETI Observations toward 33 Exoplanet\n Systems with FAST: The search for extraterrestrial intelligence (SETI) is to search for\ntechnosignatures associated with extraterrestrial life, such as engineered\nradio signals. In this paper, we apply the multibeam coincidence matching\n(MBCM) strategy, and propose a new search mode based on the MBCM which we call\nMBCM blind search mode. In our recent targeted SETI research, 33 exoplanet\nsystems are observed by the Five-hundred-meter Aperture Spherical radio\nTelescope (FAST). With this blind search mode, we search for narrowband\ndrifting signals across $1.05-1.45$ GHz in two orthogonal linear polarization\ndirections separately. There are two special signals, one of which can only be\ndetected by the blind search mode while the other can be found by both blind\nand targeted search modes. This result reveals huge advantages of the new blind\nsearch mode. However, we eliminate the possibility of the special signals being\nETI signals based on much evidence, such as the polarization, drift, frequency\nand beam coverage characteristics. Our observations achieve an unprecedented\nsensitivity and our work provides a deeper understanding to the polarization\nanalysis of extraterrestrial signals.", "category": "astro-ph_EP" }, { "text": "Frequency of Close Companions among Kepler Planets - a TTV study: A transiting planet exhibits sinusoidal transit-time-variations (TTVs) if\nperturbed by a companion near a mean-motion-resonance (MMR). We search for\nsinusoidal TTVs in more than 2600 Kepler candidates, using the publicly\navailable Kepler light-curves (Q0-Q12). We find that the TTV fractions rise\nstrikingly with the transit multiplicity. Systems where four or more planets\ntransit enjoy roughly five times higher TTV fraction than those where a single\nplanet transits, and about twice higher than those for doubles and triples. In\ncontrast, models in which all transiting planets arise from similar dynamical\nconfigurations predict comparable TTV fractions among these different systems.\nOne simple explanation for our results is that there are at least two different\nclasses of Kepler systems, one closely packed and one more sparsely populated.", "category": "astro-ph_EP" }, { "text": "Planet formation in small separation binaries: not so excited after all: Existence of planets is binaries with relatively small separations (around 20\nAU), such as \\alpha Centauri or \\gamma Cephei poses severe challenges to\nstandard planet formation theories. The problem lies in the vigorous secular\nexcitation of planetesimal eccentricities at separations of several AU, where\nsome of the planets are found, by the massive, eccentric stellar companions.\nHigh relative velocities of planetesimals preclude their growth in mutual\ncollisions for a wide range of sizes, from below 1 km up to several hundred km,\nresulting in fragmentation barrier to planet formation. Here we show that rapid\napsidal precession of planetesimal orbits, caused by the gravity of the\ncircumstellar protoplanetary disk, acts to strongly reduce eccentricity\nexcitation, lowering planetesimal velocities by an order of magnitude or even\nmore at 1 AU. By examining the details of planetesimal dynamics we demonstrate\nthat this effect eliminates fragmentation barrier for in-situ growth of\nplanetesimals as small as < 10 km even at separations as wide as 2.6 AU\n(semi-major axis of the giant planet in HD 196885), provided that the\ncircumstellar protoplanetary disk is relatively massive, ~0.1 M_Sun.", "category": "astro-ph_EP" }, { "text": "Formation of recurring slope lineae on Mars by rarefied gas-triggered\n granular flows: Active dark flows known as recurring slope lineae have been observed on the\nwarmest slopes of equatorial Mars. The morphology, composition and seasonality\nof the lineae suggest a role of liquid water in their formation. However,\ninternal and atmospheric sources of water appear to be insufficient to sustain\nthe observed slope activity. Experimental evidence suggests that under the low\natmospheric pressure at the surface of Mars, gas can flow upwards through\nporous Martian soil due to thermal creep under surface regions heated by the\nSun, and disturb small particles. Here we present numerical simulations to\ndemonstrate that such a dry process involving the pumping of rarefied gas in\nthe Martian soil due to temperature contrasts can explain the formation of the\nrecurring slope lineae. In our simulations, solar irradiation followed by\nshadow significantly reduces the angle of repose due to the resulting temporary\ntemperature gradients over shaded terrain, and leads to flow at intermediate\nslope angles. The simulated flow locations are consistent with observed\nrecurring slope lineae that initiate in rough and bouldered terrains with local\nshadows over the soil. We suggest that this dry avalanche process can explain\nthe formation of the recurring slope lineae on Mars without requiring liquid\nwater or CO2 frost activity.", "category": "astro-ph_EP" }, { "text": "OGLE-2017-BLG-0173Lb: Low Mass-Ratio Planet in a \"Hollywood\"\n Microlensing Event: We present microlensing planet OGLE-2017-BLG-0173Lb, with planet-host mass\nratio either $q\\simeq 2.5\\times 10^{-5}$ or $q\\simeq 6.5\\times 10^{-5}$, the\nlowest or among the lowest ever detected. The planetary perturbation is\nstrongly detected, $\\Delta\\chi^2\\sim 10,000$, because it arises from a bright\n(therefore, large) source passing over and enveloping the planetary caustic: a\nso-called \"Hollywood\" event. The factor $\\sim 2.5$ offset in $q$ arises because\nof a previously unrecognized discrete degeneracy between Hollywood events in\nwhich the caustic is fully enveloped and those in which only one flank is\nenveloped, which we dub \"Cannae\" and \"von Schlieffen\", respectively. This\ndegeneracy is \"accidental\" in that it arises from gaps in the data.\nNevertheless, the fact that it appears in a $\\Delta\\chi^2=10,000$ planetary\nanomaly is striking. We present a simple formalism to estimate the sensitivity\nof other Hollywood events to planets and show that they can lead to detections\nclose to, but perhaps not quite reaching, the Earth/Sun mass ratio of $3\\times\n10^{-6}$. This formalism also enables an analytic understanding of the factor\n$\\sim 2.5$ offset in $q$ between the Cannae and von Schlieffen solutions. The\nBayesian estimates for the host-mass, system distance, and planet-host\nprojected separation are $M=0.39^{+0.40}_{-0.24}\\,M_\\odot$,\n$D_L=4.8^{+1.5}_{-1.8}\\,\\kpc$, and $a_\\perp=3.8\\pm 1.6\\,\\au$. The two estimates\nof the planet mass are $m_p=3.3^{+3.8}_{-2.1}\\,M_\\oplus$ and\n$m_p=8^{+11}_{-6}\\,M_\\oplus$. The measured lens-source relative proper motion\n$\\mu=6\\,\\masyr$ will permit imaging of the lens in about 15 years or at first\nlight on adaptive-optics imagers on next-generation telescopes. These will\nallow to measure the host mass but probably cannot resolve the planet-host\nmass-ratio degeneracy.", "category": "astro-ph_EP" }, { "text": "Planetary Entry Probe Dataset: Analysis and Rules of Thumb for Future\n Missions: Since the beginning of robotic interplanetary exploration nearly six decades\nago, successful atmospheric entry has been accomplished at Venus, Earth, Mars,\nJupiter, and Titan. More entry probe missions are planned to Venus, Titan, and\nUranus in the next decade. Atmospheric entry subjects the vehicle to rapid\ndeceleration and aerothermal loads which the vehicle must be designed for, to\ndeliver the robotic instruments inside the atmosphere. The design of planetary\nprobes and their mission architecture is complex, and involves various\nengineering constraints such as peak deceleration, heating rate, heating load,\nand communications which must be satisfied within the budget and schedule of\ncost constrained mission opportunities. Engineering design data from previous\nentry probe missions serve as a valuable reference for designing future\nmissions. The present study compiles an augmented version of the blue book\nentry probe dataset, performs a comparative analysis of the entry conditions,\nand provides engineering rules of thumb for design of future missions. Using\nthe dataset, the present study proposes a new empirical correlation which aims\nto more accurately predict the thermal protection system mass fraction for high\nheat load conditions during entry and aerocapture at Uranus and Neptune.", "category": "astro-ph_EP" }, { "text": "On the Habitable Lifetime of Terrestrial Worlds with High Radionuclide\n Abundances: The presence of a liquid solvent is widely regarded as an essential\nprerequisite for habitability. We investigate the conditions under which worlds\noutside the habitable zones of stars are capable of supporting liquid solvents\non their surface over geologically significant timescales via combined\nradiogenic and primordial heat. Our analysis suggests that super-Earths with\nradionuclide abundances that are $\\gtrsim 10^3$ times higher than Earth can\nhost long-lived water oceans. In contrast, the requirements for long-lived\nethane oceans, which have been explored in the context of alternative\nbiochemistries, are less restrictive: relative radionuclide abundances of\n$\\gtrsim 10^2$ could be sufficient. We find that this class of worlds might be\ndetectable ($10\\sigma$ detection over $\\sim 10$ days integration time at $12.8$\n$\\mu$m) in principle by the James Webb Space Telescope at distances of $\\sim\n10$ pc if their ages are $\\lesssim 1$ Gyr.", "category": "astro-ph_EP" }, { "text": "Solar XUV and ENA-driven water loss from early Venus' steam atmosphere: The influence of the hydrogen hydrodynamic upper atmosphere escape, driven by\nthe solar soft X-ray and extreme ultraviolet radiation (XUV) flux, on an\nexpected magma ocean outgassed steam atmosphere of early Venus is studied. By\nassuming that the young Sun was either a weak or moderate active young G star,\nwe estimated the water loss from a hydrogen dominated thermosphere due to the\nabsorption of the solar XUV flux and the precipitation of solar wind produced\nenergetic hydrogen atoms (ENAs). The production of ENAs and their interaction\nwith the hydrodynamic extended upper atmosphere, including collision-related\nfeedback processes, have been calculated by means of Monte Carlo models. ENAs\nthat collide in the upper atmosphere deposit their energy and heat the\nsurrounding gas mainly above the main XUV energy deposition layer. It is shown\nthat precipitating ENAs modify the thermal structure of the upper atmosphere,\nbut the enhancement of the thermal escape rates caused by these energetic\nhydrogen atoms is negligible. Our results also indicate that the majority of\noxygen arising from dissociated H$_2$O molecules is left behind during the\nfirst 100 Myr. It is thus suggested that the main part of the remaining oxygen\nhas been absorbed by crustal oxidation.", "category": "astro-ph_EP" }, { "text": "The impact of intrinsic magnetic field on the absorption signatures of\n elements probing the upper atmosphere of HD209458b: The signs of an expanding atmosphere of HD209458b have been observed with\nfar-ultraviolet transmission spectroscopy and in the measurements of transit\nabsorption by metastable HeI. These observations are interpreted using the\nhydrodynamic and Monte-Carlo numerical simulations of various degree of\ncomplexity and consistency. At the same time, no attempt has been made to model\natmospheric escape of a magnetized HD209458b, to see how the planetary magnetic\nfield might affect the measured transit absorption lines. This paper presents\nthe global 3D MHD self-consistent simulations of the expanding upper atmosphere\nof HD209458b interacting with the stellar wind, and models the observed HI\n(Lya), OI (1306 A), CII (1337 A), and HeI (10830 A) transit absorption\nfeatures. We find that the planetary dipole magnetic field with the equatorial\nsurface value of Bp = 1 G profoundly changes the character of atmospheric\nmaterial outflow and the related absorption. We also investigate the formation\nof planetary magnetosphere in the stellar wind and show that its size is more\ndetermined by the escaping atmosphere flow rather than by the strength of\nmagnetic field. Fitting of the simulation results to observations enables\nconstraining the stellar XUV flux and He abundance at ~10 erg cm2/s (at 1 a.u.)\nand He/H=0.02, respectively, as well as setting an upper limit for the dipole\nmagnetic field of Bp<0.1 G on the planetary surface at the equator. This\nimplies that the magnetic dipole moment of HD209458b should be less than 0.06\nof the Jovian value.", "category": "astro-ph_EP" }, { "text": "The determination of the trajectory of Chelyabinsk bolide according to\n the records of the drive cams and the simulation of the fragments motion in\n the atmosphere: The determination of the trajectory of Chelyabinsk bolide according to the\nvideo records is performed and the results of the simulation of the fragment\nmotion in the atmosphere are showed including its state at that moment. The\nmethods of distortion compensation and adjusting of the video images with the\ncalibration images and the iterative method of the trajectory improvement by\nazimuths and altitudes are developed. These methods allow improving the\nprecision of the trajectory tracing to the hundreds of meters in space and to\nthe tens of arc minutes in the angular measure.", "category": "astro-ph_EP" }, { "text": "Extrasolar planet population synthesis I: Method, formation tracks and\n mass-distance distribution: With the high number of extrasolar planets discovered by now, it becomes\npossible to constrain theoretical formation models in a statistical sense. This\npaper is the first in a series in which we carry out a large number of planet\npopulation synthesis calculations. We begin the series with a paper mainly\ndedicated to the presentation of our approach, but also the discussion of a\nrepresentative synthetic planetary population of solar like stars. Based as\ntightly as possible on observational data, we have derived probability\ndistributions for the most important initial conditions for the planetary\nformation process. We then draw sets of initial conditions from these\ndistributions and obtain the corresponding synthetic planets with our formation\nmodel. Although the main purpose of this paper is the description of our\nmethods, we present some key results: We find that the variation of the initial\nconditions in the limits occurring in nature leads to the formation of planets\nof large diversity. This formation process is best visualized in planetary\nformation tracks, where different phases of concurrent growth and migration can\nbe identified. These phases lead to the emergence of sub-populations of planets\ndistinguishable in a mass-semimajor axis diagram. The most important ones are\nthe \"failed cores\", a vast group of core-dominated low mass planets, the\n\"horizontal branch\", a sub-population of Neptune mass planets extending out to\n6 AU, and the \"main clump\", a concentration of giant gaseous giants planets at\naround 0.3-2 AU.", "category": "astro-ph_EP" }, { "text": "Spectral and orbital characterisation of the directly imaged giant\n planet HIP 65426 b: HIP 65426 b is a recently discovered exoplanet imaged during the course of\nthe SPHERE-SHINE survey. Here we present new $L'$ and $M'$ observations of the\nplanet from the NACO instrument at the VLT from the NACO-ISPY survey, as well\nas a new $Y-H$ spectrum and $K$-band photometry from SPHERE-SHINE. Using these\ndata, we confirm the nature of the companion as a warm, dusty planet with a\nmid-L spectral type. From comparison of its SED with the BT-Settl atmospheric\nmodels, we derive a best-fit effective temperature of $T_{\\text{eff}}=1618\\pm7$\nK, surface gravity $\\log g=3.78^{+0.04}_{-0.03}$ and radius $R=1.17\\pm0.04$\n$R_{\\text{J}}$ (statistical uncertainties only). Using the DUSTY and COND\nisochrones we estimate a mass of $8\\pm1$ $M_{\\text{J}}$. Combining the\nastrometric measurements from our new datasets and from the literature, we show\nthe first indications of orbital motion of the companion (2.6$\\sigma$\nsignificance) and derive preliminary orbital constraints. We find a highly\ninclined orbit ($i=107^{+13}_{-10}$ deg) with an orbital period of\n$800^{+1200}_{-400}$ yr. We also report SPHERE sparse aperture masking\nobservations that investigate the possibility that HIP 65426 b was scattered\nonto its current orbit by an additional companion at a smaller orbital\nseparation. From this data we rule out the presence of brown dwarf companions\nwith masses greater than 16 $M_{\\text{J}}$ at separations larger than 3 AU,\nsignificantly narrowing the parameter space for such a companion.", "category": "astro-ph_EP" }, { "text": "Detection of H2O and evidence for TiO/VO in an ultra hot exoplanet\n atmosphere: We present a primary transit observation for the ultra hot (Teq~2400K) gas\ngiant expolanet WASP-121b, made using the Hubble Space Telescope Wide Field\nCamera 3 in spectroscopic mode across the 1.12-1.64 micron wavelength range.\nThe 1.4 micron water absorption band is detected at high confidence (5.4 sigma)\nin the planetary atmosphere. We also reanalyze ground-based photometric\nlightcurves taken in the B, r', and z' filters. Significantly deeper transits\nare measured in these optical bandpasses relative to the near-infrared\nwavelengths. We conclude that scattering by high-altitude haze alone is\nunlikely to account for this difference, and instead interpret it as evidence\nfor titanium oxide and vanadium oxide absorption. Enhanced opacity is also\ninferred across the 1.12-1.3 micron wavelength range, possibly due to iron\nhydride absorption. If confirmed, WASP-121b will be the first exoplanet with\ntitanium oxide, vanadium oxide, and iron hydride detected in transmission. The\nlatter are important species in M/L dwarfs, and their presence is likely to\nhave a significant effect on the overall physics and chemistry of the\natmosphere, including the production of a strong thermal inversion.", "category": "astro-ph_EP" }, { "text": "The habitable zone for Earthlike exomoons orbiting Kepler-1625b: The recent announcement of a Neptune-sized exomoon candidate orbiting the\nJupiter-sized object Kepler-1625b has forced us to rethink our assumptions\nregarding both exomoons and their host exoplanets. In this paper I describe\ncalculations of the habitable zone for Earthlike exomoons in orbit of\nKepler-1625b under a variety of assumptions. I find that the candidate exomoon,\nKepler-1625b-i, does not currently reside within the exomoon habitable zone,\nbut may have done so when Kepler-1625 occupied the main sequence. If it were to\npossess its own moon (a \"moon-moon\") that was Earthlike, this could potentially\nhave been a habitable world. If other exomoons orbit Kepler-1625b, then there\nare a range of possible semimajor axes/eccentricities that would permit a\nhabitable surface during the main sequence phase, while remaining dynamically\nstable under the perturbations of Kepler-1625b-i. This is however contingent on\neffective atmospheric CO$_2$ regulation.", "category": "astro-ph_EP" }, { "text": "The Influence of Age on the Relative Frequency of Super-Earths and\n Sub-Neptunes: There is growing evidence that the population of close-in planets discovered\nby the Kepler mission was sculpted by atmospheric loss, though the typical\ntimescale for this evolution is not well-constrained. Among a highly complete\nsample of planet hosts of varying ages the age-dependence of the relative\nfraction of super-Earth and sub-Neptune detections can be used to constrain the\nrate at which some small planets lose their atmospheres. Using the\nCalifornia-Kepler Survey (CKS) sample, we find evidence that the ratio of\nsuper-Earth to sub-Neptune detections rises monotonically from 1-10 Gyr. Our\nresults are in good agreement with an independent study focused on stars hotter\nthan the Sun, as well as with forward modeling simulations incorporating the\neffects of photoevaporation and a CKS-like selection function. We find the\nobserved trend persists even after accounting for the effects of completeness\nor correlations between age and other fundamental parameters.", "category": "astro-ph_EP" }, { "text": "An Unprecedented Constraint on Water Content in the Sunlit Lunar\n Exosphere Seen by Lunar-Based Ultraviolet Telescope of Chang'e-3 Mission: The content of $\\mathrm{OH/H_2O}$ molecules in the tenuous exosphere of the\nMoon is still an open issue at present. We here report an unprecedented upper\nlimit of the content of the OH radicals, which is obtained from the in-situ\nmeasurements carried out \\rm by the Lunar-based Ultraviolet Telescope, a\npayload of Chinese Chang'e-3 mission. By analyzing the diffuse background in\nthe images taken by the telescope, the column density and surface concentration\nof the OH radicals are inferred to be $<10^{11}\\ \\mathrm{cm^{-2}}$ and\n$<10^{4}\\ \\mathrm{cm^{-3}}$ (by assuming a hydrostatic equilibrium with a scale\nheight of 100km), respectively, by assuming that the recorded background is\nfully contributed by their resonance fluorescence emission. The resulted\nconcentration is lower than the previously reported value by about two orders\nof magnitude, and is close to the prediction of the sputtering model. In\naddition, the same measurements and method allow us to derive a surface\nconcentration of $<10^{2}\\ \\mathrm{cm^{-3}}$ for the neutral magnesium, which\nis lower than the previously reported upper limit by about two orders of\nmagnitude. These results are the best known of the OH (MgI) content in the\nlunar exosphere to date.", "category": "astro-ph_EP" }, { "text": "Global Chemistry and Thermal Structure Models for the Hot Jupiter\n WASP-43b and Predictions for JWST: The James Webb Space Telescope (JWST) is expected to revolutionize the field\nof exoplanets. The broad wavelength coverage and the high sensitivity of its\ninstruments will allow characterization of exoplanetary atmospheres with\nunprecedented precision. Following the Call for the Cycle 1 Early Release\nScience Program, the Transiting Exoplanet Community was awarded time to observe\nseveral targets, including WASP-43b. The atmosphere of this hot Jupiter has\nbeen intensively observed but still harbors some mysteries, especially\nconcerning the day-night temperature gradient, the efficiency of the\natmospheric circulation, and the presence of nightside clouds. We will\nconstrain these properties by observing a full orbit of the planet and\nextracting its spectroscopic phase curve in the 5--12 $\\mu$m range with\nJWST/MIRI. To prepare for these observations, we performed an extensive\nmodeling work with various codes: radiative transfer, chemical kinetics, cloud\nmicrophysics, global circulation models, JWST simulators, and spectral\nretrieval. Our JWST simulations show that we should achieve a precision of 210\nppm per 0.1 $\\mu$m spectral bin on average, which will allow us to measure the\nvariations of the spectrum in longitude and measure the night-side emission\nspectrum for the first time. If the atmosphere of WASP-43b is clear, our\nobservations will permit us to determine if its atmosphere has an equilibrium\nor disequilibrium chemical composition, providing eventually the first\nconclusive evidence of chemical quenching in a hot Jupiter atmosphere. If the\natmosphere is cloudy, a careful retrieval analysis will allow us to identify\nthe cloud composition.", "category": "astro-ph_EP" }, { "text": "Pre-LHB Evolution of the Earth's Obliquity: The Earth's obliquity is stabilized by the Moon, which facilitates a rapid\nprecession of the Earth's spin-axis, de-tuning the system away from resonance\nwith orbital modulation. It is however, likely that the architecture of the\nSolar System underwent a dynamical instability-driven transformation, where the\nprimordial configuration was more compact. Hence, the characteristic\nfrequencies associated with orbital perturbations were likely faster in the\npast, potentially allowing for secular resonant encounters. In this work we\nexamine if at any point in the Earth's evolutionary history, the obliquity\nvaried significantly. Our calculations suggest that even though the orbital\nperturbations were different, the system nevertheless avoided resonant\nencounters throughout its evolution. This indicates that the Earth obtained its\ncurrent obliquity during the formation of the Moon.", "category": "astro-ph_EP" }, { "text": "TRAPPIST-1h as an Exo-Titan. I. The Role of Assumptions about\n Atmospheric Parameters in Understanding an Exoplanet Atmosphere: The TRAPPIST-1 system is home to at least seven terrestrial planets and is a\ntarget of interest for future James Webb Space Telescope (JWST) observations.\nAdditionally, these planets will be of interest to future missions making\nobservations in the ultraviolet (UV). Although several of these planets are\nlocated in the traditional habitable zone, where liquid water could exist on\nthe surface, TRAPPIST-1h is interesting to explore as a potentially habitable\nocean world analog. In this study, we evaluate the observability of a\nTitan-like atmosphere on TRAPPIST-1h. The ability of the JWST or a future UV\nmission to detect specific species in the atmosphere at TRAPPIST-1h will depend\non how far each species extends from the surface. In order to understand the\nconditions required for detection, we evaluate the input parameters used in\none-dimensional models to simulate the structure of Titan-like atmospheres.\nThese parameters include surface temperature and pressure, temperature profile\nas a function of distance from the surface, composition of the minor species\nrelative to N 2, and the eddy diffusion coefficient. We find that JWST\nsimulated spectra for cloud- and haze-free atmospheres are most sensitive to\nsurface temperature, temperature gradients with altitude, and surface pressure.\nThe importance of temperature gradients in JWST observations shows that a\nsimple isothermal scale height is not ideal for determining temperature or\natmospheric mean molecular mass in transit spectra from exoplanet atmospheres.\nWe demonstrate that UV transmission spectra are sensitive to the upper\natmosphere, where the exobase can be used to approximate the vertical extent of\nthe atmosphere.", "category": "astro-ph_EP" }, { "text": "Yearly and seasonal variations of low albedo surfaces on Mars in the\n OMEGA/MEx dataset: Constraints on aerosols properties and dust deposits: The time variations of spectral properties of dark martian surface features\nare investigated using the OMEGA near-IR dataset. The analyzed period covers\ntwo Mars years, spanning from early 2004 to early 2008 (includes the 2007\nglobal dust event). Radiative transfer modeling indicates that the apparent\nalbedo variations of low to mid-latitude dark regions are consistent with those\nproduced by the varying optical depth of atmospheric dust as measured\nsimultaneously from the ground by the Mars Exploration Rovers. We observe only\na few significant albedo changes that can be attributed to surface phenomena.\nThey are small-scaled and located at the boundaries between bright and dark\nregions. We then investigate the variations of the mean particle size of\naerosols using the evolution of the observed dark region spectra between 1 and\n2.5 {\\mu}m. Overall, we find that the observed changes in the spectral slope\nare consistent with a mean particle size of aerosols varying with time between\n1 and 2 {\\mu}m. Observations with different solar zenith angles make it\npossible to characterize the aerosol layer at different altitudes, revealing a\ndecrease of the particle size of aerosols as altitude increases.", "category": "astro-ph_EP" }, { "text": "Deep exploration of $\u03b5$ Eridani with Keck Ms-band vortex\n coronagraphy and radial velocities: mass and orbital parameters of the giant\n exoplanet: We present the most sensitive direct imaging and radial velocity (RV)\nexploration of $\\epsilon$ Eridani to date. $\\epsilon$ Eridani is an adolescent\nplanetary system, reminiscent of the early Solar system. It is surrounded by a\nprominent and complex debris disk which is likely stirred by one or several gas\ngiant exoplanets. The discovery of the RV signature of a giant exoplanet was\nannounced 15 years ago, but has met with scrutiny due to possible confusion\nwith stellar noise. We confirm the planet with a new compilation and analysis\nof precise RV data spanning 30 years, and combine it with upper limits from our\ndirect imaging search, the most sensitive ever performed. The deep images were\ntaken in the Ms band (4.7$\\mu$m) with the vortex coronagraph recently installed\nin W.M. Keck Observatory's infrared camera NIRC2, which opens a sensitive\nwindow for planet searches around nearby adolescent systems. The RV data and\ndirect imaging upper limit maps were combined in an innovative joint Bayesian\nanalysis, providing new constraints on the mass and orbital parameters of the\nelusive planet. $\\epsilon$ Eridani b has a mass of $0.78^{+0.38}_{-0.12}$\n$M_{Jup}$ and is orbiting $\\epsilon$ Eridani at about $3.48\\pm 0.02$ AU with a\nperiod of $7.37 \\pm 0.07$ years. The eccentricity of $\\epsilon$ Eridani b's\norbit is $0.07^{+0.06}_{-0.05}$, an order of magnitude smaller than early\nestimates and consistent with a circular orbit. We discuss our findings from\nthe standpoint of planet-disk interactions and prospects for future detection\nand characterization with the James Webb Space Telescope.", "category": "astro-ph_EP" }, { "text": "NEMESIS: Exoplanet Transit Survey of Nearby M-Dwarfs in TESS FFIs I: In this work, we present the analysis of 33,054 M-dwarf stars located within\n100 parsecs in the Transiting Exoplanet Survey Satellite (TESS) Full Frame\nImages (FFIs) of the observed sectors 1 to 5. We present a new pipeline called\nNEMESIS which was developed to extract detrended photometry and perform transit\nsearches of single sector data in TESS FFIs. As many M-dwarfs are faint and are\nnot observed with a 2 minute cadence by TESS, FFI transit surveys can give an\nempirical validation of how many planets are missed by using the 30 minute\ncadence data. In this work, we detected 183 threshold crossing events and\npresent 29 planet candidates for sectors 1 to 5, 24 of which are new\ndetections. Our sample contains orbital periods ranging from 1.25 to 6.84 days\nand planetary radii from 1.26 to 5.31 Earth radii. With the addition of our new\nplanet candidate detections along with previous detections observed in sectors\n1 to 5, we calculate an integrated occurrence rate of 2.49 +/- 1.58 planets per\nstar for the period range between [1,9] days and planet radius range between\n[0.5,11] Earth radii. We project an estimated yield of 122 +/- 11 transit\ndetections of nearby M-dwarfs. 23 of our new candidates have Signal to Noise\nratios > 7, Transmission Spectroscopy Metrics > 38 and Emission Spectroscopy\nMetrics > 10. We provide all of our data products for our planet candidates\nthrough the Filtergraph data visualization service located at\nhttps://filtergraph.com/NEMESIS.", "category": "astro-ph_EP" }, { "text": "H2-Induced Pressure Broadening and Pressure Shift in the P-Branch of the\n v3 Band of CH4 from 300 to 700 K: For accurate modelling of observations of exoplanet atmospheres,\nquantification of the pressure broadening of infrared absorption lines for and\nby a variety of gases at elevated temperatures is needed. High-resolution\nhigh-temperature H2-pressure-broadened spectra are recorded for the CH4 v3-band\nP-branch. Measured linewidths for 116 transitions between 2840 and 3000 cm^{-1}\nwith temperature and pressures ranging between 300 and 700 K, and 10 and 933\nTorr, respectively, were used to find rotation- and\ntetrahedral-symmetry-dependent coefficients for pressure and temperature\nbroadening and pressure-induced lineshifts. The new pressure-broadening data\nwill be useful in radiative-transfer models for retrieving the properties of\nobserved expolanet atmospheres.", "category": "astro-ph_EP" }, { "text": "High-resolution transmission spectroscopy of ultra-hot Jupiter WASP-33b\n with NEID: We report an attempt to detect molecular and atomic species in the atmosphere\nof the ultra-hot Jupiter WASP-33b using the high-resolution echelle\nspectrograph NEID with a wavelength coverage of 380$-$930 nm. By analyzing the\ntransmission spectrum of WASP-33b using the line-by-line technique and the\ncross-correlation technique, we confirm previous detection of H$\\alpha$,\nH$\\beta$, H$\\gamma$, and Ca II infrared triplets. We find no evidence for a\nsignificant day-to-night wind in WASP-33b, taking into account the effects of\nstellar pulsations using a relatively novel GP method and poorly constrained\nsystemic velocity measurements. We also detect the previously reported\npre-transit absorption signal, which may be a pulsation mode induced by the\nplanet. Combined with previous CARMENES and HARPS-N observations, we report the\nnon-detection of TiO, Ti I, and V I in the transmission spectrum, while they\nwere already detected in the dayside atmosphere of WASP-33b. This implies a\ndifference in the chemical compositions and abundances between the dayside and\nterminator atmospheres of WASP-33b, and certainly requires further improvements\nin the sensitivity of the detection methods.", "category": "astro-ph_EP" }, { "text": "Global Models of Runaway Accretion in White Dwarf Debris Disks: A growing sample of white dwarfs (WDs) with metal-enriched atmospheres are\naccompanied by excess infrared emission, indicating that they are encircled by\na compact dusty disk of solid debris. Such `WD debris disks' are thought to\noriginate from the tidal disruption of asteroids or other minor bodies, but the\nprecise mechanism(s) responsible for transporting matter to the WD surface\nremains unclear, especially in those systems with the highest inferred metal\naccretion rates dM_Z/dt ~ 1e8-1e10 g/s. Here we present global time-dependent\ncalculations of the coupled evolution of the gaseous and solid components of WD\ndebris disks. Solids transported inwards (initially due to PR drag) sublimate\nat tens of WD radii, producing a source of gas that accretes onto the WD\nsurface and viscously spreads outwards in radius, where it overlaps with the\nsolid disk. If the aerodynamic coupling between the solids and gaseous disks is\nsufficiently strong (and/or the gas viscosity sufficiently weak), then gas\nbuilds up near the sublimation radius faster than it can viscously spread away.\nSince the rate of drag-induced solid accretion increases with gas density, this\nresults in a runaway accretion process, during which the WD accretion rate\nreaches values orders of magnitude higher than can be achieved by PR drag\nalone. We explore the evolution of WD debris disks across a wide range of\nphysical conditions and calculate the predicted distribution of observed\naccretion rates dM_Z/dt, finding reasonable agreement with the current sample.\nAlthough the conditions necessary for runaway accretion are at best marginally\nsatisfied given the minimal level of aerodynamic drag between circular gaseous\nand solid disks, the presence of other stronger forms of solid-gas\ncoupling---such as would result if the gaseous disk is only mildly\neccentric---substantially increase the likelihood of runaway accretion.", "category": "astro-ph_EP" }, { "text": "EOS: Atmospheric Radiative Transfer in Habitable Worlds with HELIOS: We present EOS, a procedure for determining the Outgoing Longwave Radiation\n(OLR) and top-of-atmosphere (TOA) albedo for a wide range of conditions\nexpected to be present in the atmospheres of rocky planets with temperate\nconditions. EOS is based on HELIOS and HELIOS-K, which are novel and publicly\navailable atmospheric radiative transfer (RT) codes optimized for fast\ncalculations with GPU processors. These codes were originally developed for the\nstudy of giant planets. In this paper we present an adaptation for applications\nto terrestrial-type, habitable planets, adding specific physical recipes for\nthe gas opacity and vertical structure of the atmosphere. To test the\nreliability of the procedure we assessed the impact of changing line opacity\nprofile, continuum opacity model, atmospheric lapse rate and tropopause\nposition prescriptions on the OLR and the TOA albedo. The results obtained with\nEOS are in line with those of other RT codes running on traditional CPU\nprocessors, while being at least one order of magnitude faster. The adoption of\nOLR and TOA albedo data generated with EOS in a zonal and seasonal climate\nmodel correctly reproduce the fluxes of the present-day Earth measured by the\nCERES spacecraft. The results of this study disclose the possibility to\nincorporate fast RT calculations in climate models aimed at characterizing the\natmospheres of habitable exoplanets.", "category": "astro-ph_EP" }, { "text": "A Circumbinary Debris Disk in a Polluted White Dwarf System: Planetary systems commonly survive the evolution of single stars, as\nevidenced by terrestrial-like planetesimal debris observed orbiting and\npolluting the surfaces of white dwarfs. This letter reports the identification\nof a circumbinary dust disk surrounding a white dwarf with a substellar\ncompanion in a 2.27 hr orbit. The system bears the dual hallmarks of\natmospheric metal pollution and infrared excess, however the standard (flat and\nopaque) disk configuration is dynamically precluded by the binary. Instead, the\ndetected reservoir of debris must lie well beyond the Roche limit in an\noptically thin configuration, where erosion by stellar irradiation is\nrelatively rapid. This finding demonstrates that rocky planetesimal formation\nis robust around close binaries, even those with low mass ratios.", "category": "astro-ph_EP" }, { "text": "Jupiter's Ammonia Distribution Derived from VLA Maps at 3--37 GHz: We observed Jupiter four times over a full rotation (10 hrs) with the\nupgraded Karl G. Jansky Very Large Array (VLA) between December 2013 and\nDecember 2014. Preliminary results at 4-17 GHz were presented in de Pater et\nal. (2016); in the present paper we present the full data set at frequencies\nbetween 3 and 37 GHz. Major findings are: (i) the radio-hot belt at\n8.5--11$^\\circ$N latitude, near the interface between the North Equatorial Belt\n(NEB) and the Equatorial Zone (EZ) is prominent at all frequencies (3--37 GHz).\nIts location coincides with the southern latitudes of the NEB (7--17$^{\\circ}$\nN). (ii) Longitude-smeared maps reveal belts and zones at all frequencies at\nlatitudes $\\lesssim |20^\\circ|$. The lowest brightness temperature is in the EZ\nnear a latitude of 4$^\\circ$N, and the NEB has the highest brightness\ntemperature near 11$^\\circ$N. The bright part of the NEB increases in\nlatitudinal extent (spreads towards the north) with deceasing frequency, i.e.,\nwith depth into the atmosphere. In longitude-resolved maps, several belts, in\nparticular in the southern hemisphere, are not continuous along the latitude\nline, but broken into small segments as if caused by an underlying wave. (iii)\nModel fits to longitude-smeared spectra are obtained at each latitude. These\nshow a high NH$_3$ abundance (volume mixing ratio $\\sim 4 \\times 10^{-4}$) in\nthe deep ($P>8-10$ bar) atmosphere, decreasing at higher altitudes due to cloud\nformation (e.g., in zones), or dynamics in combination with cloud condensation\n(belts). In the NEB ammonia gas is depleted down to at least the 20 bar level\nwith an abundance of $1.75 \\times 10^{-4}$. (iv) Using the entire VLA dataset,\nwe confirm that the planet is extremely dynamic in the upper layers of the\natmosphere, at $P<$2--3 bar, i.e., at the altitudes where clouds form.\n[Abridged]", "category": "astro-ph_EP" }, { "text": "Titan-Hyperion Resonance and the Tidal Q of Saturn: Lainey et al. (2012), by re-analyzing long-baseline astrometry of Saturn's\nmoons, have found that the moons' tidal evolution is much faster than\npreviously thought, implying an order of magnitude stronger tidal dissipation\nwithin Saturn. This result is controversial and implies recent formation of at\nleast some of the mid-sized icy moons of Saturn. Here we show that this more\nintensive tidal dissipation is in full agreement with the evolved state of the\nTitan-Hyperion resonance. This resonance was previously thought to be non-tidal\nin origin, as the amount of tidal evolution required for its assembly is beyond\nwhat is possible in models that assume that all the major moons are primordial.\nWe find that the survival of the Titan-Hyperion resonance is in agreement with\na past Titan-Iapetus 5:1 resonance, but not with unbroken tidal evolution of\nRhea from the rings to its current distance.", "category": "astro-ph_EP" }, { "text": "An upper limit on late accretion and water delivery in the Trappist-1\n exoplanet system: The Trappist-1 system contains seven roughly Earth-sized planets locked in a\nmulti-resonant orbital configuration, which has enabled precise measurements of\nthe planets' masses and constrained their compositions. Here we use the\nsystem's fragile orbital structure to place robust upper limits on the planets'\nbombardment histories. We use N-body simulations to show how perturbations from\nadditional objects can break the multi-resonant configuration by either\ntriggering dynamical instability or simply removing the planets from resonance.\nThe planets cannot have interacted with more than ${\\sim 5\\%}$ of an Earth mass\n(${M_\\oplus}$) in planetesimals -- or a single rogue planet more massive than\nEarth's Moon -- without disrupting their resonant orbital structure. This\nimplies an upper limit of ${10^{-4}}$ to ${10^{-2} M_\\oplus}$ of late accretion\non each planet since the dispersal of the system's gaseous disk. This is\ncomparable to or less than the late accretion on Earth after the Moon-forming\nimpact, and demonstrates that the Trappist-1 planets' growth was complete in\njust a few million years, roughly an order of magnitude faster than Earth's.\nOur results imply that any large water reservoirs on the Trappist-1 planets\nmust have been incorporated during their formation in the gaseous disk.", "category": "astro-ph_EP" }, { "text": "Olivine-Carbonate Mineralogy of Jezero Crater: A well-preserved, ancient delta deposit, in combination with ample exposures\nof Mg-carbonate rich materials, make Jezero Crater in Nili Fossae a compelling\nastrobiological site and a top candidate for future landed missions to Mars. We\nuse CRISM observations to characterize the surface mineralogy of the crater and\nsurrounding watershed. We have identified a three- endmember sequence of\nolivine-bearing lithologies that we hypothesize are distinguished by their Mg\ncontent. We find that Mg-carbonates are consistently identified in association\nwith one of the olivine-bearing lithologies, although that lithology is not\nfully carbonatized. Surprisingly, this lithology contains relatively Fe-rich\nolivine. We address a range of formation scenarios, including the possibility\nthat these olivine and carbonate associations are indicators of\nserpentinization on early Mars. These deposits provide an opportunity for\ndeepening our understanding of early Mars by revealing the thermal history of\nthe martian interior and potentially changes in its tectonic regime with time.", "category": "astro-ph_EP" }, { "text": "The extrasolar planet Gliese 581 d: a potentially habitable planet?\n (Corrigendum to arXiv:1009.5814): We report here that the equation for H2O Rayleigh scattering was incorrectly\nstated in the original paper [arXiv:1009.5814]. Instead of a quadratic\ndependence on refractivity r, we accidentally quoted an r^4 dependence. Since\nthe correct form of the equation was implemented into the model, scientific\nresults are not affected.", "category": "astro-ph_EP" }, { "text": "Detection of water absorption in the day side atmosphere of HD 189733 b\n using ground-based high-resolution spectroscopy at 3.2 microns: We report a 4.8 sigma detection of water absorption features in the day side\nspectrum of the hot Jupiter HD 189733 b. We used high-resolution (R~100,000)\nspectra taken at 3.2 microns with CRIRES on the VLT to trace the\nradial-velocity shift of the water features in the planet's day side atmosphere\nduring 5 h of its 2.2 d orbit as it approached secondary eclipse. Despite\nconsiderable telluric contamination in this wavelength regime, we detect the\nsignal within our uncertainties at the expected combination of systemic\nvelocity (Vsys=-3 +5-6 km/s) and planet orbital velocity (Kp=154 +14-10 km/s),\nand determine a H2O line contrast ratio of (1.3+/-0.2)x10^-3 with respect to\nthe stellar continuum. We find no evidence of significant absorption or\nemission from other carbon-bearing molecules, such as methane, although we do\nnote a marginal increase in the significance of our detection to 5.1 sigma with\nthe inclusion of carbon dioxide in our template spectrum. This result\ndemonstrates that ground-based, high-resolution spectroscopy is suited to\nfinding not just simple molecules like CO, but also to more complex molecules\nlike H2O even in highly telluric contaminated regions of the Earth's\ntransmission spectrum. It is a powerful tool that can be used for conducting an\nimmediate census of the carbon- and oxygen-bearing molecules in the atmospheres\nof giant planets, and will potentially allow the formation and migration\nhistory of these planets to be constrained by the measurement of their\natmospheric C/O ratios.", "category": "astro-ph_EP" }, { "text": "An automated procedure for the detection of the Yarkovsky effect and\n results from the ESA NEO Coordination Centre: Context: The measurement of the Yarkovsky effect on near-Earth asteroids\n(NEAs) is common practice in orbit determination today, and the number of\ndetections will increase with the developments of new and more accurate\ntelescopic surveys. However, the process of finding new detections and\nidentifying spurious ones is not yet automated, and it often relies on personal\njudgment. Aims: We aim to introduce a more automated procedure that can search\nfor NEA candidates to measure the Yarkovsky effect, and that can identify\nspurious detections. Methods: The expected semi-major axis drift on an NEA\ncaused by the Yarkovsky effect was computed with a Monte Carlo method on a\nstatistical model of the physical parameters of the asteroid that relies on the\nmost recent NEA population models and data. The expected drift was used to\nselect candidates in which the Yarkovsky effect might be detected, according to\nthe current knowledge of their orbit and the length of their observational arc.\nThen, a nongravitational acceleration along the transverse direction was\nestimated through orbit determination for each candidate. If the detected\nacceleration was statistically significant, we performed a statistical test to\ndetermine whether it was compatible with the Yarkovsky effect model. Finally,\nwe determined the dependence on an isolated tracklet. Results: Among the known\nNEAs, our procedure automatically found 348 detections of the Yarkovsky effect\nthat were accepted. The results are overall compatible with the predicted trend\nwith the the inverse of the diameter, and the procedure appears to be efficient\nin identifying and rejecting spurious detections. This algorithm is now adopted\nby the ESA NEO Coordination Centre to periodically update the catalogue of NEAs\nwith a measurable Yarkovsky effect, and the results are automatically posted on\nthe web portal.", "category": "astro-ph_EP" }, { "text": "Water ice in the Kuiper belt: We examine a large collection of low resolution near-infrared spectra of\nKuiper belt objects and centaurs in an attempt to understand the presence of\nwater ice in the Kuiper belt. We find that water ice on the surface of these\nobjects occurs in three separate manners: (1) Haumea family members uniquely\nshow surfaces of nearly pure water ice, presumably a consequence of the\nfragmentation of the icy mantle of a larger differentiated proto-Haumea; (2)\nlarge objects with absolute magnitudes of $H<3$ (and a limited number to H=4.5)\nhave surface coverings of water ice - perhaps mixed with ammonia - that appears\nto be related to possibly ancient cryovolcanism on these large objects; and (3)\nsmaller KBOs and centaurs which are neither Haumea family members nor\ncold-classical KBOs appear to divide into two families (which we refer to as\n\"neutral\" and \"red\"), each of which is a mixture of a common nearly-neutral\ncomponent and either a slightly red or very red component that also includes\nwater ice. A model suggesting that the difference between neutral and red\nobjects is due to formation in an early compact solar system either inside or\noutside, respectively, of the ~20 AU methanol evaporation line is supported by\nthe observation that methanol is only detected on the reddest objects, which\nare those which would be expected to have the most of the methanol containing\nmixture.", "category": "astro-ph_EP" }, { "text": "The Sizes and Albedos of Centaurs 2014 YY $_{49}$ and 2013 NL $_{24}$\n from Stellar Occultation Measurements by RECON: In 2019, the Research and Education Collaborative Occultation Network (RECON)\nobtained multiple-chord occultation measurements of two centaur objects: 2014\nYY$_{49}$ on 2019 January 28 and 2013 NL$_{24}$ on 2019 September 4. RECON is a\ncitizen-science telescope network designed to observe high-uncertainty\noccultations by outer solar system objects. Adopting circular models for the\nobject profiles, we derive a radius $r=16^{+2}_{-1}$km and a geometric albedo\n$p_V=0.13^{+0.015}_{-0.024}$ for 2014 YY$_{49}$, and a radius $r=66\n^{+5}_{-5}$km and geometric albedo $p_V = 0.045^{+0.006}_{-0.008}$ for 2013\nNL$_{24}$. To the precision of these measurements, no atmosphere or rings are\ndetected for either object. The two objects measured here are among the\nsmallest distant objects measured with the stellar occultation technique. In\naddition to these geometric constraints, the occultation measurements provide\nastrometric constraints for these two centaurs at a higher precision than has\nbeen feasible by direct imaging. To supplement the occultation results, we also\npresent an analysis of color photometry from the Pan-STARRS surveys to\nconstrain the rotational light curve amplitudes and spectral colors of these\ntwo centaurs. We recommend that future work focus on photometry to more\ndeliberately constrain the objects' colors and light curve amplitudes, and on\nfollow-on occultation efforts informed by this astrometry.", "category": "astro-ph_EP" }, { "text": "Coupling between corotation and Lindblad resonances in the elliptic\n planar three-body problem: We investigate the dynamics of two satellites with masses $\\mu_s$ and\n$\\mu'_s$ orbiting a massive central planet in a common plane, near a first\norder mean motion resonance $m$+1:$m$ ($m$ integer). We consider only the\nresonant terms of first order in eccentricity in the disturbing potential of\nthe satellites, plus the secular terms causing the orbital apsidal precessions.\nWe obtain a two-degree of freedom system, associated with the two critical\nresonant angles $\\phi= (m+1)\\lambda' -m\\lambda - \\varpi$ and $\\phi'=\n(m+1)\\lambda' -m\\lambda - \\varpi'$, where $\\lambda$ and $\\varpi$ are the mean\nlongitude and longitude of periapsis of $\\mu_s$, respectively, and where the\nprimed quantities apply to $\\mu'_s$. We consider the special case where $\\mu_s\n\\rightarrow 0$ (restricted problem). The symmetry between the two angles $\\phi$\nand $\\phi'$ is then broken, leading to two different kinds of resonances,\nclassically referred to as Corotation Eccentric resonance (CER) and Lindblad\nEccentric Resonance (LER), respectively. We write the four reduced equations of\nmotion near the CER and LER, that form what we call the CoraLin model. This\nmodel depends upon only two dimensionless parameters that control the dynamics\nof the system: the distance $D$ between the CER and LER, and a forcing\nparameter $\\epsilon_L$ that includes both the mass and the orbital eccentricity\nof the disturbing satellite. Three regimes are found: for $D=0$ the system is\nintegrable, for $D$ of order unity, it exhibits prominent chaotic regions,\nwhile for $D$ large compared to 2, the behavior of the system is regular and\ncan be qualitatively described using simple adiabatic invariant arguments. We\napply this model to three recently discovered small Saturnian satellites\ndynamically linked to Mimas through first order mean motion resonances :\nAegaeon, Methone and Anthe.", "category": "astro-ph_EP" }, { "text": "Exoplanet Atmospheres at High Spectral Resolution: The spectrum of an exoplanet reveals the physical, chemical, and biological\nprocesses that have shaped its history and govern its future. However,\nobservations of exoplanet spectra are complicated by the overwhelming glare of\ntheir host stars. This review chapter focuses on high resolution spectroscopy\n(HRS; R=25,000-100,000), which helps to disentangle and isolate the exoplanet's\nspectrum. At high spectral resolution, molecular features are resolved into a\ndense forest of individual lines in a pattern that is unique for a given\nmolecule. For close-in planets, the spectral lines undergo large Doppler shifts\nduring the planet's orbit, while the host star and Earth's spectral features\nremain essentially stationary, enabling a velocity separation of the planet.\nFor slower-moving, wide-orbit planets, HRS aided by high contrast imaging\ninstead isolates their spectra using their spatial separation. The lines in the\nexoplanet spectrum are detected by comparing them with high resolution spectra\nfrom atmospheric modelling codes; essentially a form of fingerprinting for\nexoplanet atmospheres. This measures the planet's orbital velocity, and helps\ndefine its true mass and orbital inclination. Consequently, HRS can detect both\ntransiting and non-transiting planets. It also simultaneously characterizes the\nplanet's atmosphere due to its sensitivity to the depth, shape, and position of\nthe planet's spectral lines. These are altered by the planet's atmospheric\ncomposition, structure, clouds, and dynamics, including day-to-night winds and\nits rotation period. This chapter describes the HRS technique in detail,\nhighlighting its successes in exoplanet detection and characterization, and\nconcludes with the future prospects of using HRS to identify biomarkers on\nnearby rocky worlds, and map features in the atmospheres of giant exoplanets.", "category": "astro-ph_EP" }, { "text": "The timeline of the Lunar bombardment - revisited: The timeline of the lunar bombardment in the first Gy of the Solar System\nremains unclear. Some basin-forming impacts occurred 3.9-3.7Gy ago. Many other\nbasins formed before, but their exact ages are not precisely known. There are\ntwo possible interpretations of the data: in the cataclysm scenario there was a\nsurge in the impact rate approximately 3.9Gy ago, while in the accretion tail\nscenario the lunar bombardment declined since the era of planet formation and\nthe latest basins formed in its tail-end. Here, we revisit the work of\nMorbidelli et al.(2012) that examined which scenario could be compatible with\nboth the lunar crater record in the 3-4Gy period and the abundance of highly\nsiderophile elements (HSE) in the lunar mantle. We use updated numerical\nsimulations of the fluxes of impactors. Under the traditional assumption that\nthe HSEs track the total amount of material accreted by the Moon since its\nformation, we conclude that only the cataclysm scenario can explain the data.\nThe cataclysm should have started ~3.95Gy ago. However we show that HSEs could\nhave been sequestered from the lunar mantle due to iron sulfide exsolution\nduring magma ocean crystallization, followed by mantle overturn. Based on the\nhypothesis that the lunar magma ocean crystallized about 100-150My after Moon\nformation, and therefore that HSEs accumulated in the lunar mantle only after\nthis time, we show that the bombardment in the 3-4Gy period can be explained in\nthe accretion tail scenario. This hypothesis would also explain why the Moon\nappears so depleted in HSEs relative to the Earth. We also extend our analysis\nof the cataclysm and accretion tail scenarios to the case of Mars. The\naccretion tail scenario requires a global resurfacing event on Mars ~4.4Gy ago,\npossibly associated with the formation of the Borealis basin, and it is\nconsistent with the HSE budget of the planet.", "category": "astro-ph_EP" }, { "text": "Scattered light images of spiral arms in marginally gravitationally\n unstable discs with an embedded planet: Scattered light images of transition discs in the near-infrared often show\nnon-axisymmetric structures in the form of wide-open spiral arms in addition to\ntheir characteristic low-opacity inner gap region. We study self-gravitating\ndiscs and investigate the influence of gravitational instability on the shape\nand contrast of spiral arms induced by planet-disc interactions.\nTwo-dimensional non-isothermal hydrodynamical simulations including viscous\nheating and a cooling prescription are combined with three-dimensional dust\ncontinuum radiative transfer models for direct comparison to observations. We\nfind that the resulting contrast between the spirals and the surrounding disc\nin scattered light is by far higher for pressure scale height variations, i.e.\nthermal perturbations, than for pure surface density variations. Self-gravity\neffects suppress any vortex modes and tend to reduce the opening angle of\nplanet-induced spirals, making them more tightly wound. If the disc is only\nmarginally gravitationally stable with a Toomre parameter around unity, an\nembedded massive planet (planet-to-star mass ratio of $10^{-2}$) can trigger\ngravitational instability in the outer disc. The spirals created by this\ninstability and the density waves launched by the planet can overlap resulting\nin large-scale, more open spiral arms in the outer disc. The contrast of these\nspirals is well above the detection limit of current telescopes.", "category": "astro-ph_EP" }, { "text": "On the origin and composition of Theia: Constraints from new models of\n the Giant Impact: Knowing the isotopic composition of Theia, the proto-planet which collided\nwith the Earth in the Giant Impact that formed the Moon, could provide\ninteresting insights on the state of homogenization of the inner solar system\nat the late stages of terrestrial planet formation. We use the known isotopic\nand modeled chemical compositions of the bulk silicate mantles of Earth and\nMoon and combine them with different Giant Impact models, to calculate the\npossible ranges of isotopic composition of Theia in O, Si, Ti, Cr, Zr and W in\neach model. We compare these ranges to the isotopic composition of carbonaceous\nchondrites, Mars, and other solar system materials. In the absence of\npost-impact isotopic re-equilibration, the recently proposed high angular\nmomentum models of the Giant Impact (\"impact-fission\", Cuk & Stewart, 2012; and\n\"merger\", Canup, 2012) allow - by a narrow margin - for a Theia similar to\nCI-chondrites, and Mars. The \"hit-and-run\" model (Reufer et al., 2012) allows\nfor a Theia similar to enstatite-chondrites and other Earth-like materials. If\nthe Earth and Moon inherited their different mantle FeO contents from the bulk\nmantles of the proto-Earth and Theia, the high angular momentum models cannot\nexplain the observed difference. However, both the hit-and-run as well as the\nclassical or \"canonical\" Giant Impact model naturally explain this difference\nas the consequence of a simple mixture of two mantles with different FeO.\nTherefore, the simplest way to reconcile the isotopic similarity, and FeO\ndissimilarity, of Earth and Moon is a Theia with an Earth-like isotopic\ncomposition and a higher (~20%) mantle FeO content.", "category": "astro-ph_EP" }, { "text": "Planet Packing in Circumbinary Systems: The recent discovery of planets orbiting main sequence binaries will provide\ncrucial constraints for theories of binary and planet formation. The formation\npathway for these planets is complicated by uncertainties in the formation\nmechanism of the host stars. In this paper, we compare the dynamical states of\nsingle and binary star planetary systems. Specifically, we pose two questions:\n(1) What does it mean for a circumbinary system to be dynamically packed? (2)\nHow many systems are required to differentiate between a population of packed\nor sparse planets? We determine when circumbinary systems become dynamically\nunstable as a function of the separation between the host-stars and the inner\nplanet, and the first and second planets. We show that these represent unique\nstability constraints compared to single-star systems. We find that although\nthe existing Kepler data is insufficient to distinguish between a population of\npacked or sparse circumbinary systems, a more thorough study of circumbinary\nTTVs combined with an order of magnitude increase in the number of systems may\nprove conclusive. Future space missions such as TESS provide the best\nopportunity for increasing the sample size.", "category": "astro-ph_EP" }, { "text": "The vertical structure of Jupiter's equatorial zonal wind above the\n cloud deck, derived using mesoscale gravity waves: Data from the Galileo Probe, collected during its descent into Jupiter's\natmosphere, is used to obtain a vertical profile of the zonal wind from\n$\\mathbf{\\sim 0.5}$ bar (upper troposphere) to $\\mathbf{\\sim 0.1\\, \\mu{bar}}$\n(lower thermosphere) at the probe entry site. This is accomplished by\nconstructing a map of gravity wave Lomb-Scargle periodograms as a function of\naltitude. The profile obtained from the map indicates that the wind speed above\nthe visible cloud deck increases with height to $\\mathbf{\\sim 150}$\nm\\,s$\\mathbf{^{-1}}$ and then levels off at this value over a broad altitude\nrange. The location of the turbopause, as a region of wide wave spectrum, is\nalso identified from the map. In addition, a cross-equatorial oscillation of a\njet, which has previously been linked to the quasi-quadrennial oscillation in\nthe stratosphere, is suggested by the profile.", "category": "astro-ph_EP" }, { "text": "55 Cancri: A Coplanar Planetary System that is Likely Misaligned with\n its Star: Although the 55 Cnc system contains multiple, closely packed planets that are\npresumably in a coplanar configuration, we use numerical simulations to\ndemonstrate that they are likely to be highly inclined to their parent star's\nspin axis. Due to perturbations from its distant binary companion, this\nplanetary system precesses like a rigid body about its parent star.\nConsequently, the parent star's spin axis and the planetary orbit normal likely\ndiverged long ago. Because only the projected separation of the binary is\nknown, we study this effect statistically, assuming an isotropic distribution\nfor wide binary orbits. We find that the most likely projected spin-orbit angle\nis ~50 degrees, with a ~30% chance of a retrograde configuration. Transit\nobservations of the innermost planet - 55 Cnc e - may be used to verify these\nfindings via the Rossiter-McLaughlin effect. 55 Cancri may thus represent a new\nclass of planetary systems with well-ordered, coplanar orbits that are inclined\nwith respect to the stellar equator.", "category": "astro-ph_EP" }, { "text": "Observability of substructures in planet-forming disk in (sub)cm\n wavelength with SKA and ngVLA: Current imaging observations of protoplanetary disks using ALMA primarily\nfocus on the sub-millimeter wavelength, leaving a gap in effective\nobservational approaches for centimeter-sized dust, which is crucial to the\nissue of planet formation. The forthcoming SKA and ngVLA may rectify this\ndeficiency. In this paper, we employ multi-fluid hydrodynamic numerical\nsimulations and radiative transfer calculations to investigate the potential of\nSKA1-Mid, ngVLA, and SKA2 for imaging protoplanetary disks at sub-cm/cm\nwavelengths. We create mock images with ALMA/SKA/ngVLA at multi-wavelengths\nbased on the hydrodynamical simulation output, and test different sensitivity\nand spatial resolutions. We discover that both SKA and ngVLA will serve as\nexcellent supplements to the existing observational range of ALMA, and their\nhigh resolution enables them to image substructures in the disk's inner region\n($\\sim$ 5 au from the stellar). Our results indicate that SKA and ngVLA can be\nutilized for more extended monitoring programs in the centimeter waveband.\nWhile in the sub-centimeter range, ngVLA possesses the capability to produce\nhigh-fidelity images within shorter observation times ($\\sim$ 1 hour on source\ntime) than previous research, holding potential for future survey observations.\nWe also discuss for the first time the potential of SKA2 for observing\nprotoplanetary disks at a 0.7 cm wavelength.", "category": "astro-ph_EP" }, { "text": "Persephone: A Pluto-System Orbiter and Kuiper Belt Explorer: Persephone is a NASA concept mission study that addresses key questions\nraised by New Horizons' encounters with Kuiper Belt objects (KBOs), with\narguably the most important being \"Does Pluto have a subsurface ocean?\". More\nbroadly, Persephone would answer four significant science questions: (1) What\nare the internal structures of Pluto and Charon? (2) How have the surfaces and\natmospheres in the Pluto system evolved? (3) How has the KBO population\nevolved? (4) What are the particles and magnetic field environments of the\nKuiper Belt? To answer these questions, Persephone has a comprehensive payload,\nand would both orbit within the Pluto system and encounter other KBOs. The\nnominal mission is 30.7 years long, with launch in 2031 on a Space Launch\nSystem (SLS) Block 2 rocket with a Centaur kick stage, followed by a 27.6 year\ncruise powered by existing radioisotope electric propulsion (REP) and a Jupiter\ngravity assist to reach Pluto in 2058. En route to Pluto, Persephone would have\none 50- to 100-km-class KBO encounter before starting a 3.1 Earth-year orbital\ncampaign of the Pluto system. The mission also includes the potential for an\n8-year extended mission, which would enable the exploration of another KBO in\nthe 100- to 150-km-size class. The mission payload includes 11 instruments:\nPanchromatic and Color High-Resolution Imager; Low-Light Camera; Ultra-Violet\nSpectrometer; Near-Infrared (IR) Spectrometer; Thermal IR Camera; Radio\nFrequency Spectrometer; Mass Spectrometer; Altimeter; Sounding Radar;\nMagnetometer; and Plasma Spectrometer. The nominal cost of this mission is\n$3.0B, making it a large strategic science mission.", "category": "astro-ph_EP" }, { "text": "Chemical abundances of neutron capture elements in exoplanet-hosting\n stars: To understand the formation and composition of planetary systems it is\nimportant to study their host stars composition since both are formed in the\nsame stellar nebula. In this work we analyze the behaviour of chemical\nabundances of Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd and Eu in the large and homogeneous\nHARPS-GTO planet search sample ($R \\sim$ 115000). This sample is composed of\n120 stars hosting high-mass planets, 29 stars hosting exclusively Neptunians\nand Super-Earths and 910 stars without detected giant planets. We compare the\n[X/Fe] ratios of such elements in different metallicity bins and we find that\nplanet hosts present higher abundances of Zn for [Fe/H]$<$--0.1 dex. On the\nother hand, Ba, Sr, Ce and Zr abundances are underabundant in stars with\nplanets, with a bigger difference for stars only hosting low-mass planets.\nHowever, most of the offsets found can be explained by differences in stellar\nparameters and by the fact that planet hosts at low metallicity mostly belong\nto the Galactic thick disk. Only in the case of Ba we find a statistically\nsignificant (3$\\sigma$) underabundance of 0.03 dex for low-mass planet hosts.\nThe origin of these elements is quite complex due to their evolution during the\nhistory of the Galaxy. Therefore, it is necessary to understand and\ncharacterize the stellar populations to which planet hosts belong in order to\ndo a fair comparison with stars without detected planets. This work\ndemonstrates that the effects of Galactic chemical evolution and not the\npresence of planets mostly account for the differences we find.", "category": "astro-ph_EP" }, { "text": "Tidal dissipation in multi-planet systems and constraints to\n orbit-fitting: We present here in full details the linear secular theory with tidal damping\nthat was used to constraint the fit of the HD10180 planetary system in (Lovis\net al. 2011). The theory is very general and can provide some intuitive\nunderstanding of the final state of a planetary system when one or more planets\nare close to their central star. We globally recover the results of (Mardling\n2007), but we show that in the HD209458 planetary system, the consideration of\nthe tides raised by the central star on the planet lead to believe that the\neccentricity of HD209458b is most probably much smaller than 0.01.", "category": "astro-ph_EP" }, { "text": "Telling twins apart: Exo-Earths and Venuses with transit spectroscopy: The planned launch of the James Webb Space Telescope in 2018 will herald a\nnew era of exoplanet spectroscopy. JWST will be the first telescope sensitive\nenough to potentially characterize terrestrial planets from their transmission\nspectra. In this work, we explore the possibility that terrestrial planets with\nVenus-type and Earth-type atmospheres could be distinguished from each other\nusing spectra obtained by JWST. If we find a terrestrial planet close to the\nliquid water habitable zone of an M5 star within a distance of 10 parsecs, it\nwould be possible to detect atmospheric ozone if present in large enough\nquantities, which would enable an oxygen-rich atmosphere to be identified.\nHowever, the cloudiness of a Venus-type atmosphere would inhibit our ability to\ndraw firm conclusions about the atmospheric composition, making any result\nambiguous. Observing small, temperate planets with JWST requires significant\ninvestment of resources, with single targets requiring of order 100 transits to\nachieve sufficient signal to noise. The possibility of detecting a crucial\nfeature such as the ozone signature would need to be carefully weighed against\nthe likelihood of clouds obscuring gas absorption in the spectrum.", "category": "astro-ph_EP" }, { "text": "Obliquity evolution of the minor satellites of Pluto and Charon: New Horizons mission observations show that the small satellites Styx, Nix,\nKerberos and Hydra, of the Pluto-Charon system, have not tidally spun-down to\nnear synchronous spin states and have high obliquities with respect to their\norbit about the Pluto-Charon binary (Weaver et al. 2016). We use a damped\nmass-spring model within an N-body simulation to study spin and obliquity\nevolution for single spinning non-round bodies in circumbinary orbit.\nSimulations with tidal dissipation alone do not show strong obliquity\nvariations from tidally induced spin-orbit resonance crossing and this we\nattribute to the high satellite spin rates and low orbital eccentricities.\nHowever, a tidally evolving Styx exhibits intermittent obliquity variations and\nepisodes of tumbling. During a previous epoch where Charon migrated away from\nPluto, the minor satellites could have been trapped in orbital mean motion\ninclination resonances. An outward migrating Charon induces large variations in\nNix and Styx's obliquities. The cause is a commensurability between the mean\nmotion resonance frequency and the spin precession rate of the spinning body.\nAs the minor satellites are near mean motion resonances, this mechanism could\nhave lifted the obliquities of all four minor satellites. The high obliquities\nneed not be primordial if the minor satellites were at one time captured into\nmean motion resonances.", "category": "astro-ph_EP" }, { "text": "Growth and Evolution of Secondary Volcanic Atmospheres: II. The\n Importance of Kinetics: Volcanism is a major and long-term source of volatile elements such as C and\nH to Earth's atmosphere, likely has been to Venus's atmosphere, and may be for\nexoplanets. Models simulating volcanic growth of atmospheres often make one of\ntwo assumptions: either that atmospheric speciation is set by the\nhigh-temperature equilibrium of volcanism; or, that volcanic gases\nthermochemically re-equilibrate to the new, lower, temperature of the surface\nenvironment. In the latter case it has been suggested that volcanic atmospheres\nmay create biosignature false positives. Here, we test the assumptions\nunderlying such inferences by performing chemical kinetic calculations to\nestimate the relaxation timescale of volcanically-derived atmospheres to\nthermochemical equilibrium, in a simple 0D atmosphere neglecting photochemistry\nand reaction catalysis. We demonstrate that for planets with volcanic\natmospheres, thermochemical equilibrium over geological timescales can only be\nassumed if the atmospheric temperature is above ~700K. Slow chemical kinetics\nat lower temperatures inhibit the relaxation of redox-sensitive species to\nlow-temperature thermochemical equilibrium, precluding the production of two\nindependent biosignatures through thermochemistry alone: 1. ammonia, and 2. the\nco-occurrence of CO$_2$ and CH$_4$ in an atmosphere in the absence of CO. This\nsupports the use of both biosignatures for detecting life. Quenched at the high\ntemperature of their degassing, volcanic gases also have speciations\ncharacteristic of those produced from a more oxidized mantle, if interpreted as\nbeing at thermochemical equilibrium. This therefore complicates linking\natmospheres to the interiors of rocky exoplanets, even when their atmospheres\nare purely volcanic in origin.", "category": "astro-ph_EP" }, { "text": "A Gaussian process framework for modelling instrumental systematics:\n application to transmission spectroscopy: Transmission spectroscopy, which consists of measuring the\nwavelength-dependent absorption of starlight by a planet's atmosphere during a\ntransit, is a powerful probe of atmospheric composition. However, the expected\nsignal is typically orders of magnitude smaller than instrumental systematics,\nand the results are crucially dependent on the treatment of the latter. In this\npaper, we propose a new method to infer transit parameters in the presence of\nsystematic noise using Gaussian processes, a technique widely used in the\nmachine learning community for Bayesian regression and classification problems.\nOur method makes use of auxiliary information about the state of the\ninstrument, but does so in a non-parametric manner, without imposing a specific\ndependence of the systematics on the instrumental parameters, and naturally\nallows for the correlated nature of the noise. We give an example application\nof the method to archival NICMOS transmission spectroscopy of the hot Jupiter\nHD 189733, which goes some way towards reconciling the controversy surrounding\nthis dataset in the literature. Finally, we provide an appendix giving a\ngeneral introduction to Gaussian processes for regression, in order to\nencourage their application to a wider range of problems.", "category": "astro-ph_EP" }, { "text": "Physical Parameters of Asteroids Estimated from the WISE 3 Band Data and\n NEOWISE Post-Cryogenic Survey: Enhancements to the science data processing pipeline of NASA's Wide-field\nInfrared Explorer (WISE) mission, collectively known as NEOWISE, resulted in\nthe detection of $>$158,000 minor planets in four infrared wavelengths during\nthe fully cryogenic portion of the mission. Following the depletion of its\ncryogen, NASA's Planetary Science Directorate funded a four month extension to\ncomplete the survey of the inner edge of the Main Asteroid Belt and to detect\nand discover near-Earth objects (NEOs). This extended survey phase, known as\nthe NEOWISE Post-Cryogenic Survey, resulted in the detection of $\\sim$6500\nlarge Main Belt asteroids and 88 NEOs in its 3.4 and 4.6 $\\mu$m channels.\nDuring the Post-Cryogenic Survey, NEOWISE discovered and detected a number of\nasteroids co-orbital with the Earth and Mars, including the first known Earth\nTrojan. We present preliminary thermal fits for these and other NEOs detected\nduring the 3-Band Cryogenic and Post-Cryogenic Surveys.", "category": "astro-ph_EP" }, { "text": "Millimeter Gap Contrast as a Probe for Turbulence Level in\n Protoplanetary Disks: Turbulent motions are believed to regulate angular momentum transport and\ninfluence dust evolution in protoplanetary disks. Measuring the strength of\nturbulence is challenging through gas line observations because of the\nrequirement for high spatial and spectral resolution data, and an exquisite\ndetermination of the temperature. In this work, taking the well-known HD 163296\ndisk as an example, we investigated the contrast of gaps identified in high\nangular resolution continuum images as a probe for the level of turbulence.\nWith self-consistent radiative transfer models, we simultaneously analyzed the\nradial brightness profiles along the disk major and minor axes, and the\nazimuthal brightness profiles of the B67 and B100 rings. By fitting all the gap\ncontrasts measured from these profiles, we constrained the gas-to-dust scale\nheight ratio $\\Lambda$ to be $3.0_{-0.8}^{+0.3}$, $1.2_{-0.1}^{+0.1}$ and\n${\\ge}\\,6.5$ for the D48, B67 and B100 regions, respectively. The varying\ngas-to-dust scale height ratios indicate that the degree of dust settling\nchanges with radius. The inferred values for $\\Lambda$ translate into a\nturbulence level of $\\alpha_{\\rm turb}\\,{<}\\,3\\times10^{-3}$ in the D48 and\nB100 regions, which is consistent with previous upper limits set by gas line\nobservations. However, turbulent motions in the B67 ring are strong with\n$\\alpha_{\\rm turb}\\,{\\sim}1.2\\,{\\times}\\,10^{-2}$. Due to the degeneracy\nbetween $\\Lambda$ and the depth of dust surface density drops, the turbulence\nstrength in the D86 gap region is not constrained.", "category": "astro-ph_EP" }, { "text": "Common 0.1 bar Tropopause in Thick Atmospheres Set by Pressure-Dependent\n Infrared Transparency: A minimum atmospheric temperature, or tropopause, occurs at a pressure of\naround 0.1 bar in the atmospheres of Earth, Titan, Jupiter, Saturn, Uranus and\nNeptune, despite great differences in atmospheric composition, gravity,\ninternal heat and sunlight. In all these bodies, the tropopause separates a\nstratosphere with a temperature profile that is controlled by the absorption of\nshortwave solar radiation, from a region below characterised by convection,\nweather, and clouds. However, it is not obvious why the tropopause occurs at\nthe specific pressure near 0.1 bar. Here we use a physically-based model to\ndemonstrate that, at atmospheric pressures lower than 0.1 bar, transparency to\nthermal radiation allows shortwave heating to dominate, creating a\nstratosphere. At higher pressures, atmospheres become opaque to thermal\nradiation, causing temperatures to increase with depth and convection to ensue.\nA common dependence of infrared opacity on pressure, arising from the shared\nphysics of molecular absorption, sets the 0.1 bar tropopause. We hypothesize\nthat a tropopause at a pressure of approximately 0.1 bar is characteristic of\nmany thick atmospheres, including exoplanets and exomoons in our galaxy and\nbeyond. Judicious use of this rule could help constrain the atmospheric\nstructure, and thus the surface environments and habitability, of exoplanets.", "category": "astro-ph_EP" }, { "text": "Submillimeter Array Observations of the RX J1633.9-2442 Transition Disk:\n Evidence for Multiple Planets in the Making: We present continuum high resolution Submillimeter Array (SMA) observations\nof the transition disk object RX J1633.9-2442, which is located in the\nOphiuchus molecular cloud and has recently been identified as a likely site of\nongoing giant planet formation. The observations were taken at 340 GHz (880\nmicron) with the SMA in its most extended configuration, resulting in an\nangular resolution of 0.3\" (35 AU at the distance of the target). We find that\nthe disk is highly inclined (i ~50 deg) and has an inner cavity ~25 AU in\nradius, which is clearly resolved by our observations. We simultaneously model\nthe entire optical to millimeter wavelength spectral energy distribution (SED)\nand SMA visibilities of RX J1633.9-2442 in order to constrain the structure of\nits disk. We find that an empty cavity ~25 AU in radius is inconsistent with\nthe excess emission observed at 12, 22, and 24 micron. Instead, the mid-IR\nexcess can be modeled by either a narrow, optically thick ring at ~10 AU or an\noptically thin region extending from ~7 AU to ~25 AU. The inner disk (r < 5 AU)\nis mostly depleted of small dust grains as attested by the lack of detectable\nnear-IR excess. We also present deep Keck aperture masking observations in the\nnear-IR, which rule out the presence of a companion up to 500 times fainter\nthan the primary star (in K-band) for projected separations in the 5-20 AU\nrange. We argue that the complex structure of the RX J1633.9-2442 disk is best\nexplained by multiple planets embedded within the disk. We also suggest that\nthe properties and incidence of objects such as RX J1633.9-2442, T Cha, and\nLkCa 15 (and those of the companions recently identified to these two latter\nobjects) are most consistent with the runaway gas accretion phase of the core\naccretion model, when giant planets gain their envelopes and suddenly become\nmassive enough to open wide gaps in the disk.", "category": "astro-ph_EP" }, { "text": "Combining high-dispersion spectroscopy (HDS) with high contrast imaging\n (HCI): Probing rocky planets around our nearest neighbors: Aims: In this work, we discuss a way to combine High Dispersion Spectroscopy\nand High Contrast Imaging (HDS+HCI). For a planet located at a resolvable\nangular distance from its host star, the starlight can be reduced up to several\norders of magnitude using adaptive optics and/or coronography. In addition, the\nremaining starlight can be filtered out using high-dispersion spectroscopy,\nutilizing the significantly different (or Doppler shifted) high-dispersion\nspectra of the planet and star. In this way, HDS+HCI can in principle reach\ncontrast limits of ~1e-5 x 1e-5, although in practice this will be limited by\nphoton noise and/or sky-background.\n Methods: We present simulations of HDS+HCI observations with the E-ELT, both\nprobing thermal emission from a planet at infrared wavelengths, and starlight\nreflected off a planet atmosphere at optical wavelengths. For the infrared\nsimulations we use the baseline parameters of the E-ELT and METIS instrument,\nwith the latter combining extreme adaptive optics with an R=100,000 IFS. We\ninclude realistic models of the adaptive optics performance and atmospheric\ntransmission and emission. For the optical simulation we also assume R=100,000\nIFS with adaptive optics capabilities at the E-ELT.\n Results: One night of HDS+HCI observations with the E-ELT at 4.8 um (d_lambda\n= 0.07 um) can detect a planet orbiting alpha Cen A with a radius of R=1.5\nR_earth and a twin-Earth thermal spectrum of T_eq=300 K at a signal-to-noise\n(S/N) of 5. In the optical, with a Strehl ratio performance of 0.3, reflected\nlight from an Earth-size planet in the habitable zone of Proxima Centauri can\nbe detected at a S/N of 10 in the same time frame. Recently, first HDS+HCI\nobservations have shown the potential of this technique by determining the\nspin-rotation of the young massive exoplanet beta Pictoris b. [abridged]", "category": "astro-ph_EP" }, { "text": "High-precision photometry by telescope defocussing. I. The transiting\n planetary system WASP-5: We present high-precision photometry of two transit events of the extrasolar\nplanetary system WASP-5, obtained with the Danish 1.54m telescope at ESO La\nSilla. In order to minimise both random and flat-fielding errors, we defocussed\nthe telescope so its point spread function approximated an annulus of diameter\n40 pixels (16 arcsec). Data reduction was undertaken using standard aperture\nphotometry plus an algorithm for optimally combining the ensemble of comparison\nstars. The resulting light curves have point-to-point scatters of 0.50 mmag for\nthe first transit and 0.59 mmag for the second. We construct detailed signal to\nnoise calculations for defocussed photometry, and apply them to our\nobservations. We model the light curves with the JKTEBOP code and combine the\nresults with tabulated predictions from theoretical stellar evolutionary models\nto derive the physical properties of the WASP-5 system. We find that the planet\nhas a mass of M_b = 1.637 +/- 0.075 +/- 0.033 Mjup, a radius of R_b = 1.171 +/-\n0.056 +/- 0.012 Rjup, a large surface gravity of g_b = 29.6 +/- 2.8 m/s2 and a\ndensity of rho_b = 1.02 +/- 0.14 +/- 0.01 rhojup (statistical and systematic\nuncertainties). The planet's high equilibrium temperature of T_eq = 1732 +/- 80\nK makes it a good candidate for detecting secondary eclipses.", "category": "astro-ph_EP" }, { "text": "A LOOK at Outbursts of Comet C/2014 UN$_{271}$ (Bernardinelli-Bernstein)\n Near 20 au: Cometary activity may be driven by ices with very low sublimation\ntemperatures, such as carbon monoxide ice, which can sublimate at distances\nwell beyond 20 au. This point is emphasized by the discovery of Oort cloud\ncomet C/2014 UN$_{271}$ (Bernardinelli-Bernstein), and its observed activity\nout to $\\sim$26 au. Through observations of this comet's optical brightness and\nbehavior, we can potentially discern the drivers of activity in the outer solar\nsystem. We present a study of the activity of comet Bernardinelli-Bernstein\nwith broad-band optical photometry taken at 19-20 au from the Sun (2021 June to\n2022 February) as part of the LCO Outbursting Objects Key (LOOK) Project. Our\nanalysis shows that the comet's optical brightness during this period was\ninitially dominated by cometary outbursts, stochastic events that ejected\n$\\sim10^7$ to $\\sim10^8$ kg of material on short (< 1 day) timescales. We\npresent evidence for three such outbursts occurring in 2021 June and September.\nThe nominal nuclear volumes excavated by these events are similar to the 10-100\nm pit-shaped voids on the surfaces of short-period comet nuclei, as imaged by\nspacecraft. Two out of three Oort cloud comets observed at large pre-perihelion\ndistances exhibit outburst behavior near 20 au, suggesting such events may be\ncommon in this population. In addition, quiescent CO-driven activity may\naccount for the brightness of the comet in 2022 January to February, but that\nvariations in the cometary active area (i.e., the amount of sublimating ice)\nwith heliocentric distance are also possible.", "category": "astro-ph_EP" }, { "text": "Constraints on Planet Occurrence around Nearby Mid-to-Late M Dwarfs from\n the MEarth Project: The MEarth Project is a ground-based photometric survey to find planets\ntransiting the closest and smallest main-sequence stars. In its first four\nyears, MEarth discovered one transiting exoplanet, the 2.7 Earth radius planet\nGJ1214b. Here, we answer an outstanding question: in light of the bounty of\nsmall planets transiting small stars uncovered by the Kepler mission, should\nMEarth have found more than just one planet so far? We estimate MEarth's\nensemble sensitivity to exoplanets by performing end-to-end simulations of 1.25\nmillion observations of 988 nearby mid-to-late M dwarfs, gathered by MEarth\nbetween October 2008 and June 2012. For 2-4 Earth radius planets, we compare\nthis sensitivity to results from Kepler and find that MEarth should have found\nplanets at a rate of 0.05 - 0.36 planets/year in its first four years. As part\nof this analysis, we provide new analytic fits to the Kepler early M dwarf\nplanet occurrence distribution. When extrapolating between Kepler's early M\ndwarfs and MEarth's mid-to-late M dwarfs, we find that assuming the planet\noccurrence distribution stays fixed with respect to planetary equilibrium\ntemperature provides a good match to our detection of a planet with GJ1214b's\nobserved properties. For larger planets, we find that the warm (600-700K),\nNeptune-sized (4 Earth radius) exoplanets that transit early M dwarfs like\nGl436 and GJ3470 occur at a rate of <0.15/star (at 95% confidence) around\nMEarth's later M dwarf targets. We describe a strategy with which MEarth can\nincrease its expected planet yield by 2.5X without new telescopes, by shifting\nits sensitivity toward the smaller and cooler exoplanets that Kepler has\ndemonstrated to be abundant.", "category": "astro-ph_EP" }, { "text": "Formation of giant planets with large metal masses and metal fractions\n via giant impacts in a rapidly dissipating disk: According to planetary interior models, some giant planets contain large\nmetal masses with large metal-mass fractions. HD 149026b and TOI-849b are\ncharacteristic examples of these giant planets. It has been suggested that the\nenvelope mass loss during giant impacts plays a key role in the formation of\nsuch giant planets. The aim of the present letter is to propose a mechanism\nthat can explain the origin of such giant planets. We investigate the formation\nof giant planets in a rapidly dissipating disk using N-body simulations that\nconsider pebble accretion. The results show that although the pebble isolation\nmass is smaller than the metal mass (> 30 Earth masses) in some giant planets,\nthe interior metal mass can be increased by giant impacts between planets with\nthe isolation mass. Regarding the metal fraction, the cores accrete massive\nenvelopes by runaway gas accretion during the disk-dissipation phase of 1-10\nMyr in a disk that evolves without photoevaporation. Although a large fraction\nof the envelope can be lost during giant impacts, the planets can reaccrete the\nenvelope after impacts in a slowly dissipating disk. Here, we demonstrate that,\nby photoevaporation in a rapidly dissipating disk, the runaway gas accretion is\nquenched in the middle, resulting in the formation of giant planets with large\nmetal-mass fractions. The origins of HD 149026b and TOI-849b, which are\ncharacterized by their large metal-mass fractions, can be naturally explained\nby a model that considers a disk evolving with photoevaporation.", "category": "astro-ph_EP" }, { "text": "The Hubble PanCET program: An extensive search for metallic ions in the\n exosphere of GJ 436 b: (Abridged) The quiet M2.5 star GJ 436 hosts a warm Neptune that displays an\nextended atmosphere that dwarfs its own host star. Predictions of atmospheric\nescape in such planets state that H atoms escape from the upper atmosphere in a\ncollisional regime and that the flow can drag heavier atoms to the upper\natmosphere. It is unclear, however, what astrophysical mechanisms drive the\nprocess. Our objective is to leverage the extensive coverage of HST/COS\nobservations of the far-ultraviolet (FUV) spectrum of GJ 436 to search for\nsignals of metallic ions in the upper atmosphere of GJ 436 b. We analyzed flux\ntime-series of species present in the FUV spectrum of GJ 436, as well as the\nLyman-$\\alpha$ line. GJ 436 displays FUV flaring events with a rate of $\\sim$10\nd$^{-1}$. There is evidence for a possibly long-lived active region or\nlongitude that modulates the FUV metallic lines of the star with amplitudes up\nto 20%. Despite the strong geocoronal contamination in the COS spectra, we\ndetected in-transit excess absorption signals of $\\sim$50% and $\\sim$30% in the\nblue and red wings, respectively, of the Lyman-$\\alpha$ line. We rule out a\nwide range of excess absorption levels in the metallic lines of the star during\nthe transit. The large atmospheric loss of GJ 436 b observed in Lyman-$\\alpha$\ntransmission spectra is stable over the timescale of a few years, and the red\nwing signal supports the presence of a variable hydrogen absorption source\nbesides the stable exosphere. The previously claimed in-transit absorption in\nthe Si III line is likely an artifact resulting from the stellar magnetic\ncycle. The non-detection of metallic ions in absorption could indicate that the\nescape is not hydrodynamic or that the atmospheric mixing is not efficient in\ndragging metals high enough for sublimation to produce a detectable escape rate\nof ions to the exosphere.", "category": "astro-ph_EP" }, { "text": "Five Special Types of Orbits Around Mars: The abstract is additional with repect to the paper published in JGCD.\nOrdinary Earth satellites are usually placed into five categories of special\norbits: sun-synchronous orbits, orbits at the critical inclination, frozen\norbits, repeating ground track orbits, and geostationary orbits. This paper\ninvestigates their counterparts around Mars and examines the basic nature of\nthese orbits, which are of special interest for missions conducted around Mars,\nincluding Mars reconnaissance. Mars' gravity field is much more complicated,\nwith relatively smaller J2, compared to Earth's, which makes the behaviors of\nthese Martian orbits different from those of Earth. Analytical formulations and\nnumerical simulations are used to analyze these Martian orbits and compare them\nwith their Earth counterparts. First, mean element theory is employed to\ndescribe variations of orbital elements and give the constraint conditions for\nachieving these special orbits. Then, numerical verifications based on the\nPSODE algorithm (particle swarm optimization combined with differential\nevolution) are adopted to provide more accurate conditions for achieving these\norbits when considering an Mars gravity field. Using the numerical method can\nsignificantly improve the design in the full gravity field, and it is therefore\npossible to select these usable orbits for Mars that can reduce or eliminate\nthe need for stationkeeping.", "category": "astro-ph_EP" }, { "text": "Wind-Enhanced Interaction of Radiation and Dust (WEIRD) and the Growth\n and Maintenance of Local Dust Storms on Mars: A radiative-dynamic positive feedback mechanism (Wind Enhanced Interaction of\nRadiation and Dust: WEIRD) for localized Mars dust disturbances was previously\nfound to operate in highly idealized numerical experiments. Numerical\nsimulations are used to test for the presence and quantitative effect of the\nradiative-dynamic WEIRD feedback mechanism under more realistic conditions.\nComparisons between cases where lifted dust is radiatively active and\nradiatively passive elucidate the importance of the dust radiative forcing on\nthe thermodynamic and kinematic structure of the atmosphere. The WEIRD feedback\nmechanism does operate under realistic conditions, although it can be masked\nand diminished by a variety of other forcing mechanisms. Globally increased\ndust loading is found to accelerate the local winds while simultaneously\ndiminishing the impact of local physiographical forcing. Local enhancements of\ndust produce a thermal and dynamical response that resembles many of the\nessential features seen in the idealized experiments. The development of a warm\ncore low, rotational wind tendencies and convergence boundaries intersecting at\nthe center of the strongest dust storms are consistent with WEIRD. Local and\nregional storms are effective at producing elevated dust layers above the\nboundary layer aided by the radiative forcing of the dust. Ubiquitous and\npersistent thermal circulations associated with topography can also inject dust\ninto the free atmosphere above the planetary boundary layer, but they are less\nefficient than the dust storms. High concentrations of dust in the lowest\nlevels of the atmosphere produce a significant and dramatic heating of the\nground and the near-surface air despite greatly reduced insolation at the\nsurface.", "category": "astro-ph_EP" }, { "text": "Deserts and pile-ups in the distribution of exoplanets due to\n photoevaporative disc clearing: We present models of giant planet migration in evolving protoplanetary discs.\nWe show that disc clearing by EUV photoevaporation can have a strong effect on\nthe distribution of giant planet semi-major axes. During disc clearing planet\nmigration is slowed or accelerated in the region where photoevaporation opens a\ngap in the disc, resulting in \"deserts\" where few giant planets are found and\ncorresponding \"pile-ups\" at smaller and larger radii. However, the precise\nlocations and sizes of these features are strong functions of the efficiency of\nplanetary accretion, and therefore also strongly dependent on planet mass. We\nsuggest that photoevaporative disc clearing may be responsible for the pile-up\nof ~Jupiter-mass planets at ~1AU seen in exoplanet surveys, and show that\nobservations of the distribution of exoplanet semi-major axes can be used to\ntest models of both planet migration and disc clearing.", "category": "astro-ph_EP" }, { "text": "Long-Term Cycling of Kozai-Lidov Cycles: Extreme Eccentricities and\n Inclinations Excited by a Distant Eccentric Perturber: Kozai-Lidov oscillations of Jupiter-mass planets, excited by comparable\nplanetary or brown dwarf mass perturbers were recently shown in numerical\nexperiments to be slowly modulated and to exhibit striking features, including\nextremely high eccentricities and the generation of retrograde orbits with\nrespect to the perturber. Here we solve this problem analytically for the case\nof a test particle orbiting a host star and perturbed by a distant companion\nwhose orbit is eccentric and highly inclined. We give analytic expressions for\nthe conditions that produce retrograde orbits and high eccentricities. This\nmechanism likely operates in various systems thought to involve Kozai-Lidov\noscillations such as tight binaries, mergers of compact objects, irregular\nmoons of planets and many others. In particular, it could be responsible for\nexciting eccentricities and inclinations of exo-planetary orbits and be\nimportant for understanding the spin-orbit (mis)alignment of hot Jupiters.", "category": "astro-ph_EP" }, { "text": "Refined Parameters of Chelyabinsk and Tunguska Meteoroids and their\n Explosion Modes: This paper describes application of mathematical model that establishes\nrelationship between parameters of celestial bodies motion in the spheres of\nactivity of the Sun and the Earth with mass-energy characteristics of these\nobjects and their explosion modes during destruction in the Earth atmosphere,\nthat in turn are linked with phenomena observed on underlying surface. This\nmodel was used to calculate the characteristics of objects that caused the\nChelyabinsk and Tunguska explosions with using of its trajectory parameters\ndescribed in recent scientific publications (late 2013 - early 2014). It turned\nout that the size of Chelyabinsk meteoroid was equal to 180 - 185 meters, and\nits mass was close to 1.8 megatons. Energy of its explosion was equal to 57\nmegatons of TNT, size of Tunguska meteoroid was equal to 105 m, mass - 0.35\nmegatons, while energy of explosion was about of 14.5 megatons of TNT. Due to\nthe common origin of these two celestial bodies their average density was equal\n- about of 570 kg/m^3.", "category": "astro-ph_EP" }, { "text": "Elimination of a virtual impactor of 2006 QV89 via deep non-detection: As a consequence of the large (and growing) number of near-Earth objects\ndiscovered, some of them are lost before their orbit can be firmly established\nto ensure long-term recovery. A fraction of these present non-negligible\nchances of impact with the Earth. We present a method of targeted observations\nthat allowed us to eliminate that risk by obtaining deep images of the area\nwhere the object would be, should it be on a collision orbit. 2006 QV89 was one\nof these objects, with a chance of impact with the Earth on 2019 September 9.\nIts position uncertainty (of the order of 1 degree) and faintness (below\nV$\\sim$24) made it a difficult candidate for a traditional direct recovery.\nHowever, the position of the virtual impactors could be determined with\nexcellent accuracy. In July 2019, the virtual impactors of 2006 QV89 were\nparticularly well placed, with a very small uncertainty region, and an expected\nmagnitude of V$<$26. The area was imaged using ESO's Very Large Telescope, in\nthe context of the ESA/ESO collaboration on Near-Earth Objects, resulting in\nvery constraining a non-detection. This resulted in the elimination of the\nvirtual impactor, even without effectively recovering 2006 QV89, indicating\nthat it did not represent a threat. This method of deep non-detection of\nvirtual impactors demonstrated a large potential to eliminate the threat of\nother-wise difficult to recover near-Earth objects", "category": "astro-ph_EP" }, { "text": "Misaligned And Alien Planets From Explosive Death Of Stars: Exoplanets whose orbit is misaligned with the spin of their host star could\nhave originated from high-speed gas blobs, which are observed in multitudes in\nnearby supernova remnants and planetary nebulae. These blobs grow in mass and\nslow down in the interstellar medium (ISM) by mass accretion and cool by\nradiation. If their mass exceeds the Jeans mass, they collapse into hot giant\ngas planets. Most of the 'missing baryons' in galaxies could have been swept\ninto such free-floating objects, which could perturb stellar planetary systems,\nkick bound planets into misaligned orbits or be captured themselves into\nmisaligned orbits. The uncollapsed ones can then collapse or be tidally\ndisrupted into a tilted gas disk where formation of misaligned planets can take\nplace. Giant gas planets free floating in the Galactic ISM may be detected by\ntheir microlensing effects or by deep photometry if they are hot. The\nuncollapsed gas blobs may produce the observed radio scintillations of comact\nextragalactic radio sources such as quasars and gamma ray bursts.", "category": "astro-ph_EP" }, { "text": "Dust Formation in Astrophysical Environments: The Importance of Kinetics: Astronomical observations and analysis of stardust isolated from meteorites\nhave revealed a highly diverse interstellar and circumstellar grain inventory,\nincluding a wide range of amorphous materials and crystalline compounds\n(silicates and carbon). This diversity reflects the wide range of stellar\nsources injecting solids into the interstellar medium each with its own\nphysical characteristics such as density, temperature and elemental composition\nand highlights the importance of kinetics rather than thermodynamics in the\nformation of these compounds. Based upon the extensive literature on soot\nformation in terrestrial settings, detailed kinetic pathways have been\nidentified for the formation of carbon dust in C-rich stellar ejecta. These\nhave been incorporated in astronomical models for these environments. In recent\nyears, the chemical routes in the nucleation of oxides and silicates have been\nthe focus of much astronomical research. These aspects of stardust formation\nwill be reviewed and lessons for dust formation in planetary atmospheres will\nbe drawn with the emphasis on the influence of kinetics on the characteristics\nand structure of dust in these environments.", "category": "astro-ph_EP" }, { "text": "Tidal dissipation and the formation of Kepler near-resonant planets: Multi-planetary systems detected by the Kepler mission present an excess of\nplanets close to first-order mean-motion resonances (2:1 and 3:2) but with a\nperiod ratio slightly higher than the resonant value. Several mechanisms have\nbeen proposed to explain this observation. Here we provide some clues that\nthese near-resonant systems were initially in resonance and reached their\ncurrent configuration through tidal dissipation. The argument that has been\nopposed to this scenario is that it only applies to the close-in systems and\nnot to the farthest ones for which the tidal effect is too weak. Using the\ncatalog of KOI of the Kepler mission, we show that the distributions of period\nratio among the most close-in planetary systems and the farthest ones differ\nsignificantly. This distance dependent repartition is a strong argument in\nfavor of the tidal dissipation scenario.", "category": "astro-ph_EP" }, { "text": "29P/Schwassmann-Wachmann: A Rosetta Stone for Amorphous Water Ice and CO\n <-> CO2 Conversion in Centaurs and Comets?: Centaur 29P/Schwassmann-Wachmann 1 (SW1) is a highly active object orbiting\nin the transitional Gateway region (Sarid et al. 2019) between the Centaur and\nJupiter Family Comet regions. SW1 is unique among the Centaurs in that it\nexperiences quasi-regular major outbursts and produces CO emission\ncontinuously; however, the source of the CO is unclear. We argue that due to\nits very large size (approx. 32 km radius), SW1 is likely still responding, via\namorphous water ice (AWI) conversion to crystalline water ice (CWI), to the\nrapid change in its external thermal environment produced by its dynamical\nmigration from the Kuiper belt to the Gateway Region at the inner edge of the\nCentaur region at 6 au. It is this conversion process that is the source of the\nabundant CO and dust released from the object during its quiescent and outburst\nphases. If correct, these arguments have a number of important predictions\ntestable via remote sensing and in situ spacecraft characterization, including:\nthe quick release on Myr timescales of CO from AWI conversion for any few\nkm-scale scattered disk KBO transiting into the inner system; that to date SW1\nhas only converted between 50 to 65% of its nuclear AWI to CWI; that volume\nchanges upon AWI conversion could have caused subsidence and cave-ins, but not\nsignificant mass wasting or crater loss on SW1; that SW1s coma should contain\nabundant amounts of CWI CO2-rich icy dust particles; and that when SW1 transits\ninto the inner system within the next 10,000 years, it will be a very different\nkind of JFC comet.", "category": "astro-ph_EP" }, { "text": "Using Deep Neural Networks to compute the mass of forming planets: Computing the mass of planetary envelopes and the critical mass beyond which\nplanets accrete gas in a runaway fashion is important when studying planet\nformation, in particular for planets up to the Neptune mass range. This\ncomputation requires in principle solving a set of differential equations, the\ninternal structure equations, for some boundary conditions (pressure,\ntemperature in the protoplanetary disk where a planet forms, core mass and\naccretion rate of solids by the planet). Solving these equations in turn proves\nbeing time consuming and sometimes numerically unstable. We developed a method\nto approximate the result of integrating the internal structure equations for a\nvariety of boundary conditions. We compute a set of planet internal structures\nfor a very large number (millions) of boundary conditions, considering two\nopacities,(ISM and reduced). This database is then used to train Deep Neural\nNetworks in order to predict the critical core mass as well as the mass of\nplanetary envelopes as a function of the boundary conditions. We show that our\nneural networks provide a very good approximation (at the level of percents) of\nthe result obtained by solving interior structure equations, but with a much\nsmaller required computer time. The difference with the real solution is much\nsmaller than the one obtained using some analytical formulas available in the\nliterature which at best only provide the correct order of magnitude. We\ncompare the results of the DNN with other popular machine learning methods\n(Random Forest, Gradient Boost, Support Vector Regression) and show that the\nDNN outperforms these methods by a factor of at least two. We show that some\nanalytical formulas that can be found in various papers can severely\noverestimate the mass of planets, therefore predicting the formation of planets\nin the Jupiter-mass regime instead of the Neptune-mass regime.", "category": "astro-ph_EP" }, { "text": "Determination of the Interior Structure of Transiting Planets in\n Multiple-Planet Systems: Tidal dissipation within a short-period transiting extrasolar planet\nperturbed by a companion object can drive orbital evolution of the system to a\nso-called tidal fixed point, in which the apsidal lines of the transiting\nplanet and its perturber are aligned, and for which variations in the orbital\neccentricities of both planet and perturber are damped out. Significant\ncontributions to the apsidal precession rate are made by the secular\nplanet-planet interaction, by general relativity, and by the gravitational\nquadropole fields created by the transiting planet's tidal and rotational\ndistortions. The fixed-point orbital eccentricity of the inner planet is\ntherefore a strong function of the planet's interior structure. We illustrate\nthese ideas in the specific context of the recently discovered HAT-P-13\nexo-planetary system, and show that one can already glean important insights\ninto the physical properties of the inner transiting planet. We present\nstructural models of the planet, which indicate that its observed radius can be\nmaintained for a one-parameter sequence of models that properly vary core mass\nand tidal energy dissipation in the interior. We use an octopole-order secular\ntheory of the orbital dynamics to derive the dependence of the inner planet's\neccentricity, on its tidal Love number. We find that the currently measured\neccentricity, implies 0.116 < k2_{b} < 0.425, 0 M_{Earth}5\\sigma$ confidence. This discrepancy may\nbe due to magnetic effects in the planet's highly ionized atmosphere.", "category": "astro-ph_EP" }, { "text": "Polarimetric and Photometric Observations of NEAs; (422699) 2000 PD3 and\n (3200) Phaethon with the 1.6m Pirka Telescope: We report on optical polarimetric observations of two Apollo type near-Earth\nasteroids, (422699) 2000 PD3 and (3200) Phaethon, and BVRI photometric\nobservations of 2000 PD3 using the 1.6m Pirka telescope in 2017. We derived the\ngeometric albedo of pv = 0.22 +- 0.06 and the color indices (B-V = 0.282 +-\n0.072, V-R = 0.198 +- 0.035 and V-I = 0.203 +- 0.022) for 2000 PD3 which are\nconsistent with those of S-type asteroids (including Q-types). The effective\ndiameter of 2000 PD3 was derived as 0.69 +- 0.15 km using our derived geometric\nalbedo. We found that our polarimetric data of Phaethon in 2017 is deviated\nfrom the polarimetric profile taken at different epoch of 2016 using the\nidentical instrument setting (Ito et al., 2018). This result suggests that\nPhaethon would have a regional heterogeneity in grain size and/or albedo on its\nsurface.", "category": "astro-ph_EP" }, { "text": "Orbital evolution under the action of fast interstellar gas flow with\n non-constant drag coefficient: The acceleration of a spherical dust particle caused by an interstellar gas\nflow depends on the drag coefficient which is, for the given particle and flow\nof interstellar gas, a specific function of the relative speed of the dust\nparticle with respect to the interstellar gas. We investigate the motion of a\ndust particle in the case when the acceleration caused by the interstellar gas\nflow represent a small perturbation to the gravity of a central star. We\npresent the secular time derivatives of the Keplerian orbital elements of the\ndust particle under the action of the acceleration from the interstellar gas\nflow for arbitrary orbit orientation. The semimajor axis of the dust particle\nis a decreasing function of time for an interstellar gas flow acceleration with\nconstant drag coefficient and also for such an acceleration with the linearly\nvariable drag coefficient. The decrease of the semimajor axis is slower for the\ninterstellar gas flow acceleration with the variable drag coefficient. The\nminimal and maximal values of the decrease of the semimajor axis are\ndetermined. In the planar case, when the interstellar gas flow velocity lies in\nthe orbital plane of the particle, the orbit always approaches the position\nwith the maximal value of the transversal component of the interstellar gas\nflow velocity vector measured at perihelion.\n The properties of the orbital evolution derived from the secular time\nderivatives are consistent with numerical integrations of the equation of\nmotion. If the interstellar gas flow speed is much larger than the speed of the\ndust particle, then the linear approximation of dependence of the drag\ncoefficient on the relative speed of the dust particle with respect to the\ninterstellar gas is usable for practically arbitrary (no close to zero) values\nof the molecular speed ratios (Mach numbers).", "category": "astro-ph_EP" }, { "text": "Tilting Uranus via Secular Spin-Orbit Resonance with Planet 9: Uranus' startlingly large obliquity of 98 degrees has yet to admit a\nsatisfactory explanation. The most widely accepted hypothesis involving a giant\nimpactor that tipped Uranus onto its side encounters several difficulties with\nregards to the Uranus' spin rate and its prograde satellite system. An\nobliquity increase that was driven by capture of Uranus into a secular\nspin-orbit resonance remains a possible alternative hypothesis that avoids many\nof the issues associated with a giant impact. We propose that secular\nspin-orbit resonance could have excited Uranus' obliquity to its present day\nvalue if it was driven by the outward migration of an as-yet undetected outer\nSolar System body commonly known as Planet Nine. We draw support for our\nhypothesis from an analysis of 123 N-body simulations with varying parameters\nfor Planet Nine and its migration. We find that in multiple instances, a\nsimulated Planet Nine drives Uranus' obliquity past 98 degrees, with a\nsignificant number falling within 10 percent of this value. We note a\nsignificant caveat to our results in that a much faster than present-day\nspin-axis precession rate for Uranus is required in all cases for it to reach\nhigh obliquities. We conclude that while it was in principle possible for\nPlanet Nine (if it exists) to have been responsible for Uranus' obliquity, the\nfeasibility of such a result hinges on Uranus' primordial precession rate.", "category": "astro-ph_EP" }, { "text": "Prospects for detecting decreasing exoplanet frequency with main\n sequence age using PLATO: The space mission PLATO will usher in a new era of exoplanetary science by\nexpanding our current inventory of transiting systems and constraining host\nstar ages, which are currently highly uncertain. This capability might allow\nPLATO to detect changes in planetary system architecture with time,\nparticularly because planetary scattering due to Lagrange instability may be\ntriggered long after the system was formed. Here, we utilize previously\npublished instability timescale prescriptions to determine PLATO's capability\nto detect a trend of decreasing planet frequency with age for systems with\nequal-mass planets. For two-planet systems, our results demonstrate that PLATO\nmay detect a trend for planet masses which are at least as massive as\nsuper-Earths. For systems with three or more planets, we link their initial\ncompactness to potentially detectable frequency trends in order to aid future\ninvestigations when these populations will be better characterized.", "category": "astro-ph_EP" }, { "text": "Higher Martian atmospheric temperatures at all altitudes increase the\n D/H fractionation factor and water loss: Much of the water that once flowed on the surface of Mars was lost to space\nlong ago, and the total amount lost remains unknown. Clues to the amount lost\ncan be found by studying hydrogen (H) and its isotope deuterium (D), which are\nproduced when atmospheric water molecules H$_2$O and HDO dissociate. The\ndifference in escape efficiencies of H and D (which leads to} an enhanced D/H\nratio) is referred to as the fractionation factor $f$. Both the D/H ratio and\n$f$ are necessary to estimate water loss; thus, if we can constrain the range\nof $f$ and understand what controls it, we will be able to estimate water loss\nmore accurately. In this study, we use a 1D photochemical model of the neutral\nMartian atmosphere to determine how $f$ depends on assumed temperature and\nwater vapor profiles. We find that the exobase temperature most strongly\ncontrols the value of $f$ for thermal escape processes. When we include\nestimates of non-thermal escape from other studies, we find that the tropopause\ntemperature is also important. Overall, for the standard Martian atmosphere,\n$f=0.002$ for thermal escape, and $f=0.06$ for thermal + non-thermal escape. We\nestimate that Mars has lost at minimum 66-122 m GEL of water. Importantly, our\nresults demonstrate that the value of $f$ depends critically on non-thermal\nescape of D, and that modeling studies that include D/H fractionation must\nmodel both neutral and ion processes throughout the atmosphere.", "category": "astro-ph_EP" }, { "text": "Investigating Thermal Contrasts Between Jupiter's Belts, Zones, and\n Polar Vortices with VLT/VISIR: Using images at multiple mid-infrared wavelengths, acquired in May 2018 using\nthe VISIR instrument on ESO's Very Large Telescope (VLT), we study Jupiter's\npole-to-pole thermal, chemical and aerosol structure in the troposphere and\nstratosphere. We confirm that the pattern of cool and cloudy anticyclonic zones\nand warm cloud-free cyclonic belts persists throughout the mid-latitudes, up to\nthe polar boundaries, and evidence a strong correlation with the vertical\nmaximum windshear and the locations of Jupiter's zonal jets. At high latitudes,\nVISIR images reveal a large region of mid-infrared cooling poleward\n$\\sim$64$^{\\circ}$N and $\\sim$67$^{\\circ}$S extending from the upper\ntroposphere to the stratosphere, co-located with the reflective aerosols\nobserved by JunoCam, and suggesting that aerosols play a key role in the\nradiative cooling at the poles. Comparison of zonal-mean thermal properties and\nhigh-resolution visible imaging from Juno allows us to study the variability of\natmospheric properties as a function of altitude and jet boundaries,\nparticularly in the cold southern polar vortex. However, the southern\nstratospheric polar vortex is partly masked by a warm mid-infrared signature of\nthe aurora. Co-located with the southern main auroral oval, this warming\nresults from the auroral precipitation and/or joule heating which heat the\natmosphere and thus cause a significant stratospheric emission. This high\nemission results from a large enhancement of both ethane and acetylene in the\npolar region, reinforcing the evidence of enhanced ion-related chemistry in\nJupiter's auroral regions.", "category": "astro-ph_EP" }, { "text": "The Direct Detectability of Giant Exoplanets in the Optical: Motivated by the possibility that a coronagraph will be put on WFIRST/AFTA,\nwe explore the direct detectability of extrasolar giant planets (EGPs) in the\noptical. We quantify a planet's detectability by the fraction of its orbit for\nwhich it is in an observable configuration ($f_\\mathrm{obs}$). Using a suite of\nMonte Carlo experiments, we study the dependence of $f_\\mathrm{obs}$ upon the\ninner working angle (IWA) and minimum achievable contrast ($C_\\mathrm{min}$) of\nthe direct-imaging observatory; the planet's phase function, geometric albedo,\nsingle-scattering albedo, radius, and distance from Earth; and the semi-major\naxis distribution of EGPs. We calculate phase functions for a given geometric\nor single-scattering albedo, assuming various scattering mechanisms. We find\nthat the Lambertian phase function can predict significantly larger\n$f_\\mathrm{obs}$'s with respect to the more realistic Rayleigh phase function.\nFor observations made with WFIRST/AFTA's baseline capabilities\n($C_\\mathrm{min}\\sim10^{-9}$, $\\mathrm{IWA}\\sim0.2''$), Jupiter-like planets\norbiting stars within 10, 30, and 50 parsecs of Earth have volume-averaged\nobservability fractions of ${\\sim}$12%, 3%, and 0.5%, respectively. At 10\nparsecs, such observations yield $f_\\mathrm{obs}>1\\%$ for low- to\nmodest-eccentricity planets with semi-major axes in the range ${\\sim}2 - 10$\nAU. If $C_\\mathrm{min}=10^{-10}$, this range extends to ${\\sim}35$ AU. We find\nthat, in all but the most optimistic configurations, the probability for\ndetection in a blind search is low (${<}\\,5\\%$). However, with orbital\nparameter constraints from long-term radial-velocity campaigns and Gaia\nastrometry, the tools we develop in this work can be used to determine both the\nmost promising systems to target and when to observe them.", "category": "astro-ph_EP" }, { "text": "Tidal Distortions as a Bottleneck on Constraining Exoplanet Compositions: Improvements in the number of confirmed planets and the precision of\nobservations imply a need to better understand subtle effects that may bias\ninterpretations of exoplanet observations. One such effect is the distortion of\na short period planet by its host star, affecting its derived density. We\nextend the work of Burton et al., Correia, and others, using a gravitational\npotential formulation to a sample of nearly 200 planets with periods less than\n3 days. We find five planets exhibiting density variations of >10% and as many\nas 20 planets with deviations >5%. We derive an analytic approximation for this\ndeviation as a function of the orbital period, transit depth, and mass ratio\nbetween the planet and host star, allowing for rapid determination of such\ntidal effects. We find that current density error bars are typically larger\nthan tidal deviations but that reducing the uncertainty on transit depth and\nradial velocity (RV) amplitude by a factor of 3 causes tidal effects to\ndominate density errors (>50%) in >40% of planets in our sample, implying that\nin the near future upgraded observational precision will cause shape deviations\nto become a bottleneck with regards to analysis of exoplanet compositions.\nThese two parameters are found to dominate uncertainties compared to errors on\nstellar mass and radius. We identify a group of eight planets (including\nWASP-19 b, HAT-P-7 b, and WASP-12 b) for which current density uncertainties\nare as much as 4x smaller than the potential shift due to tides, implying a\npossible 4{\\sigma} bias on their density estimates.", "category": "astro-ph_EP" }, { "text": "Space based microlensing planet searches: The discovery of extra-solar planets is arguably the most exciting\ndevelopment in astrophysics during the past 15 years, rivalled only by the\ndetection of dark energy. Two projects unite the communities of exoplanet\nscientists and cosmologists: the proposed ESA M class mission EUCLID and the\nlarge space mission WFIRST, top ranked by the Astronomy 2010 Decadal Survey\nreport. The later states that: \"Space-based microlensing is the optimal\napproach to providing a true statistical census of planetary systems in the\nGalaxy, over a range of likely semi-major axes\". They also add: \"This census,\ncombined with that made by the Kepler mission, will determine how common\nEarth-like planets are over a wide range of orbital parameters\". We will\npresent a status report of the results obtained by microlensing on exoplanets\nand the new objectives of the next generation of ground based wide field imager\nnetworks. We will finally discuss the fantastic prospect offered by space based\nmicrolensing at the horizon 2020-2025.", "category": "astro-ph_EP" }, { "text": "Comparison of different exoplanet mass detection limit methods using a\n sample of main-sequence intermediate-type stars: The radial velocity (RV) technique is a powerful tool for detecting\nextrasolar planets and deriving mass detection limits that are useful for\nconstraining planet pulsations and formation models. Detection limit methods\nmust take into account the temporal distribution of power of various origins in\nthe stellar signal. These methods must also be able to be applied to large\nsamples of stellar RV time series We describe new methods for providing\ndetection limits. We compute the detection limits for a sample of ten main\nsequence stars, which are of G-F-A type, in general active, and/or with\ndetected planets, and various properties. We use them to compare the\nperformances of these methods with those of two other methods used in the\nlitterature. We obtained detection limits in the 2-1000 day period range for\nten stars. Two of the proposed methods, based on the correlation between\nperiodograms and the power in the periodogram of the RV time series in specific\nperiod ranges, are robust and represent a significant improvement compared to a\nmethod based on the root mean square of the RV signal. We conclude that two of\nthe new methods (correlation-based method and local power analysis, i.e. LPA,\nmethod) provide robust detection limits, which are better than those provided\nby methods that do not take into account the temporal sampling.", "category": "astro-ph_EP" }, { "text": "Equilibrium Configurations of Synchronous Binaries: Numerical Solutions\n and Application to Kuiper-Belt Binary 2001 QG298: We present numerical computations of the equilibrium configurations of\ntidally-locked homogeneous binaries, rotating in circular orbits. Unlike the\nclassical Roche approximations, we self-consistently account for the tidal and\nrotational deformations of both components, and relax the assumptions of\nellipsoidal configurations and Keplerian rotation. We find numerical solutions\nfor mass ratios q between 1e-3 and 1, starting at a small angular velocity for\nwhich tidal and rotational deformations are small, and following a sequence of\nincreasing angular velocities. Each series terminates at an appropriate ``Roche\nlimit'', above which no equilibrium solution can be found. Even though the\nRoche limit is crossed before the ``Roche lobe'' is filled, any further\nincrease in the angular velocity will result in mass-loss. For close,\ncomparable-mass binaries, we find that local deviations from ellipsoidal forms\nmay be as large as 10-20%, and departures from Keplerian rotation are\nsignificant. We compute the light curves that arise from our equilibrium\nconfigurations, assuming their distance is >>1 AU (e.g. in the Kuiper Belt). We\nconsider both backscatter (proportional to the projected area) and diffuse\n(Lambert) reflections. Backscatter reflection always yields two minima of equal\ndepths. Diffuse reflection, which is sensitive to the surface curvature,\ngenerally gives rise to unequal minima. We find detectable intensity\ndifferences of up to 10% between our light curves and those arising from the\nRoche approximations. Finally, we apply our models to Kuiper Belt binary 2001\nQG298, and find a nearly edge-on binary with a mass ratio q = 0.93\n^{+0.07}_{-0.03}, angular velocity Omega^2/G rho = 0.333+/-0.001 (statistical\nerrors only), and pure diffuse reflection. For the observed period of 2001\nQG298, these parameters imply a bulk density, rho = 0.72 +/- 0.04 g cm^-3.", "category": "astro-ph_EP" }, { "text": "Origin of craters on Phoebe: comparison with Cassini's data: Phoebe is one of the irregular satellites of Saturn; the images taken by\nCassini-Huygens spacecraft allowed us to analyze its surface and the craters on\nit. We study the craters on Phoebe produced by Centaur objects from the\nScattered Disk (SD) and plutinos escaped from the 3:2 mean motion resonance\nwith Neptune and compare our results with the observations by Cassini. We use\nprevious simulations on trans-Neptunian Objects and a method that allows us to\nobtain the number of craters and the cratering rate on Phoebe. We obtain the\nnumber of craters and the greatest crater on Phoebe produced by Centaurs in the\npresent configuration of the Solar System. Moreover, we obtain a present\nnormalized rate of encounters of Centaurs with Saturn of $\\dot F = 7.1 \\times\n10^{-11}$ per year, from which we can infer the current cratering rate on\nPhoebe for each crater diameter. Our study and the comparison with the\nobservations suggest that the main crater features on Phoebe are unlikely to\nhave been produced in the present configuration of the Solar System and that\nthey must have been acquired when the SD were depleted in the early Solar\nSystem. If this is what happened and the craters were produced when Phoebe was\na satellite of Saturn, then it had to be captured, very early in the evolution\nof the Solar System.", "category": "astro-ph_EP" }, { "text": "Probing the Protosolar Disk Using Dust Filtering at Gaps in the Early\n Solar System: Jupiter and Saturn formed early, before the gas disk dispersed. The presence\nof gap-opening planets affects the dynamics of the gas and embedded solids and\nhalts the inward drift of grains above a certain size. A drift barrier can\nexplain the absence of calcium aluminium rich inclusions (CAIs) in chondrites\noriginating from parent bodies that accreted in the inner solar system.\nEmploying an interdisciplinary approach, we use a $\\mu$-X-Ray-fluorescence\nscanner to search for large CAIs and a scanning electron microscope to search\nfor small CAIs in the ordinary chondrite NWA 5697. We carry out long-term,\ntwo-dimensional simulations including gas, dust, and planets to characterize\nthe transport of grains within the viscous $\\alpha$-disk framework exploring\nthe scenarios of a stand-alone Jupiter, Jupiter and Saturn \\textit{in situ}, or\nJupiter and Saturn in a 3:2 resonance. In each case, we find a critical grain\nsize above which drift is halted as a function of the physical conditions in\nthe disk. From the laboratory search we find four CAIs with a largest size of\n$\\approx$200$\\,\\mu$m. \\Combining models and data, we provide an estimate for\nthe upper limit of the $\\alpha$-viscosity and the surface density at the\nlocation of Jupiter, using reasonable assumptions about the stellar accretion\nrate during inward transport of CAIs, and assuming angular momentum transport\nto happen exclusively through viscous effects. Moreover, we find that the\ncompound gap structure in the presence of Saturn in a 3:2 resonance favors\ninward transport of grains larger than CAIs currently detected in ordinary\nchondrites.", "category": "astro-ph_EP" }, { "text": "Giant planets around two intermediate-mass evolved stars and\n confirmation of the planetary nature of HIP67851 c: Precision radial velocities are required to discover and characterize planets\norbiting nearby stars. Optical and near infrared spectra that exhibit many\nhundreds of absorption lines can allow the m/s precision levels required for\nsuch work. However, this means that studies have generally focused on\nsolar-type dwarf stars. After the main-sequence, intermediate-mass stars\n(former A-F stars) expand and rotate slower than their progenitors, thus\nthousands of narrow absorption lines appear in the optical region, permitting\nthe search for planetary Doppler signals in the data for these types of stars.\nWe present the discovery of two giant planets around the intermediate-mass\nevolved star HIP65891 and HIP107773. The best Keplerian fit to the HIP65891 and\nHIP107773 radial velocities leads to the following orbital parameters: P=1084.5\nd; m$_b$sin$i$ = 6.0 M$_{jup}$; $e$=0.13 and P=144.3 d; m$_b$sin$i$ = 2.0\nM$_{jup}$; $e$=0.09, respectively. In addition, we confirm the planetary nature\nof the outer object orbiting the giant star HIP67851. The orbital parameters of\nHIP67851c are: P=2131.8 d, m$_c$sin$i$ = 6.0 M$_{jup}$ and $e$=0.17. With\nmasses of 2.5 M$_\\odot$ and 2.4 M$_\\odot$ HIP65891 and HIP107773 are two of the\nmost massive stars known to host planets. Additionally, HIP67851 is one of five\ngiant stars that are known to host a planetary system having a close-in planet\n($a <$ 0.7 AU). Based on the evolutionary states of those five stars, we\nconclude that close-in planets do exist in multiple systems around subgiants\nand slightly evolved giants stars, but probably they are subsequently destroyed\nby the stellar envelope during the ascent of the red giant branch phase. As a\nconsequence, planetary systems with close-in objects are not found around\nhorizontal branch stars.", "category": "astro-ph_EP" }, { "text": "A JWST NIRSpec Phase Curve for WASP-121b: Dayside Emission Strongest\n Eastward of the Substellar Point and Nightside Conditions Conducive to Cloud\n Formation: We present the first exoplanet phase curve measurement made with the JWST\nNIRSpec instrument, highlighting the exceptional stability of this\nnewly-commissioned observatory for exoplanet climate studies. The target,\nWASP-121b, is an ultrahot Jupiter with an orbital period of 30.6 hr. We analyze\ntwo broadband light curves generated for the NRS1 and NRS2 detectors, covering\nwavelength ranges of 2.70-3.72 micron and 3.82-5.15 micron, respectively. Both\nlight curves exhibit minimal systematics, with approximately linear drifts in\nthe baseline flux level of 30 ppm/hr (NRS1) and 10 ppm/hr (NRS2). Assuming a\nsimple brightness map for the planet described by a low-order spherical\nharmonic dipole, our light curve fits suggest that the phase curve peaks\ncoincide with orbital phases $3.36 \\pm 0.11$ deg (NRS1) and $2.66 \\pm 0.12$ deg\n(NRS2) prior to mid-eclipse. This is consistent with the strongest dayside\nemission emanating from eastward of the substellar point. We measure\nplanet-to-star emission ratios of $3,924 \\pm 7$ ppm (NRS1) and $4,924 \\pm 9$\nppm (NRS2) for the dayside hemisphere, and $136 \\pm 8$ ppm (NRS1) and $630 \\pm\n10$ ppm (NRS2) for the nightside hemisphere. The latter nightside emission\nratios translate to planetary brightness temperatures of $926 \\pm 12$ K (NRS1)\nand $1,122 \\pm 10$ K (NRS2), which are low enough for a wide range of\nrefractory condensates to form, including enstatite and forsterite. A nightside\ncloud deck may be blocking emission from deeper, hotter layers of the\natmosphere, potentially helping to explain why cloud-free 3D general\ncirculation model simulations systematically over-predict the nightside\nemission for WASP-121b.", "category": "astro-ph_EP" }, { "text": "Phosphine on Venus Cannot be Explained by Conventional Processes: The recent candidate detection of ~1 ppb of phosphine in the middle\natmosphere of Venus is so unexpected that it requires an exhaustive search for\nexplanations of its origin. Phosphorus-containing species have not been\nmodelled for Venus' atmosphere before and our work represents the first attempt\nto model phosphorus species in the Venusian atmosphere. We thoroughly explore\nthe potential pathways of formation of phosphine in a Venusian environment,\nincluding in the planet's atmosphere, cloud and haze layers, surface, and\nsubsurface. We investigate gas reactions, geochemical reactions,\nphotochemistry, and other non-equilibrium processes. None of these potential\nphosphine production pathways are sufficient to explain the presence of ppb\nphosphine levels on Venus. If PH3's presence in Venus' atmosphere is confirmed,\nit therefore is highly likely to be the result of a process not previously\nconsidered plausible for Venusian conditions. The process could be unknown\ngeochemistry, photochemistry, or even aerial microbial life, given that on\nEarth phosphine is exclusively associated with anthropogenic and biological\nsources. The detection of phosphine adds to the complexity of chemical\nprocesses in the Venusian environment and motivates in situ follow up sampling\nmissions to Venus. Our analysis provides a template for investigation of\nphosphine as a biosignature on other worlds.", "category": "astro-ph_EP" }, { "text": "HATS-19b, HATS-20b, HATS-21b: Three Transiting Hot-Saturns Discovered by\n the HATSouth Survey: We report the discovery by the HATSouth exoplanet survey of three hot-Saturn\ntransiting exoplanets: HATS-19b, HATS-20b, and HATS-21b. The planet host\nHATS-19 is a slightly evolved V = 13.0 G0 star with [Fe/H] = 0.240, a mass of\n1.303 Msun, and a radius of 1.75 Rsun. HATS-19b is in an eccentric orbit (e =\n0.30) around this star with an orbital period of 4.5697 days and has a mass of\n0.427 Mjup and a highly inflated radius of 1.66 Rjup. The planet HATS-20b has a\nSaturn-like mass and radius of 0.273 Mjup and 0.776 Rjup respectively. It\norbits the V = 13.8 G9V star HATS-20 (Ms = 0.910 Msun; Rs = 0.892 Rsun) with a\nperiod of 3.7993 days. Finally, HATS-21 is a V = 12.2 G4V star with [Fe/H] =\n0.300, a mass of 1.080 Msun, and a radius of 1.021 Rsun. Its accompanying\nplanet HATS-21b has a 3.5544-day orbital period, a mass of 0.332 Mjup, and a\nmoderately inflated radius of 1.123 Rjup. With the addition of these three very\ndifferent planets to the growing sample of hot-Saturns, we re-examine the\nrelations between the observed giant planet radii, stellar irradiation, and\nhost metallicity. We find a significant positive correlation between planet\nequilibrium temperature and radius, and a weak negative correlation between\nhost metallicity and radius. To assess the relative influence of various\nphysical parameters on observed planet radii, we train and fit models using\nRandom Forest regression. We find that for hot-Saturns (0.1 < Mp < 0.5 Mjup),\nthe planetary mass and equilibrium temperature play dominant roles in\ndetermining radii. For hot-Jupiters (0.5 < Mp < 2.0 Mjup), the most important\nparameter is equilibrium temperature alone. Finally, for irradiated higher-mass\nplanets (Mp > 2.0 Mjup), we find that equilibrium temperature dominates in\ninfluence, with smaller contributions from planet mass and host metallicity.", "category": "astro-ph_EP" }, { "text": "Light Curve Analysis of Ground-Based Data from Exoplanets Transit\n Database: Photometric observations of exoplanet transits can be used to derive the\norbital and physical parameters of an exoplanet. We analyzed several transit\nlight curves of exoplanets that are suitable for ground-based observations\nwhose complete information is available on the Exoplanet Transit Database\n(ETD). We analyzed transit data of planets including HAT-P-8 b, HAT-P-16 b,\nHAT-P-21 b, HAT-P-22 b, HAT-P-28 b and HAT-P-30 b using the AstroImageJ (AIJ)\nsoftware package. In this paper, we investigated 82 transit light curves from\nETD, deriving their physical parameters as well as computing their mid-transit\ntimes for future Transit Timing Variation (TTV) analyses. The Precise values of\nthe parameters show that using AIJ as a fitting tool for follow-up observations\ncan lead to results comparable to the values at the NASA Exoplanet Archive (the\nNEA). Such information will be invaluable considering the numbers of future\ndiscoveries from the ground and space-based exoplanet surveys.", "category": "astro-ph_EP" }, { "text": "GJ 1252b: A Hot Terrestrial Super-Earth With No Atmosphere: The increasing numbers of rocky, terrestrial exoplanets known to orbit nearby\nstars (especially M dwarfs) has drawn increased attention to the possibility of\nstudying these planets' surface properties, and atmospheric compositions &\nescape histories. Here we report the detection of the secondary eclipse of the\nterrestrial exoplanet GJ1252b using the Spitzer Space Telescope's IRAC2 4.5\nmicron channel. We measure an eclipse depth of 149(+25/-32) ppm, corresponding\nto a day-side brightness temperature of 1410(+91/-125) K and consistent with\nthe prediction for no atmosphere. Comparing our measurement to atmospheric\nmodels indicates that GJ1252b has a surface pressure of <10 bar, substantially\nless than Venus. Assuming energy-limited escape, even a 100 bar atmosphere\nwould be lost in <1 Myr, far shorter than estimated age of 3.9+/-0.4 Gyr. The\nexpected mass loss could be overcome by mantle outgassing, but only if the\nmantle's carbon content were >7% by mass - over two orders of magnitude greater\nthan that found in Earth. We therefore conclude that GJ1252b has no significant\natmosphere. Model spectra with granitoid or feldspathic surface composition,\nbut with no atmosphere, are disfavored at >2 sigma. The eclipse occurs just\n+1.4(+2.8/-1.0) min after orbital phase 0.5, indicating e cos\nomega=+0.0025(+0.0049/-0.0018), consistent with a circular orbit. Tidal heating\nis therefore likely to be negligible to GJ1252b's global energy budget.\nFinally, we also analyze additional, unpublished TESS transit photometry of\nGJ1252b which improves the precision of the transit ephemeris by a factor of\nten, provides a more precise planetary radius of 1.180+/-0.078 R_E, and rules\nout any transit timing variations with amplitudes <1 min.", "category": "astro-ph_EP" }, { "text": "The role of planetary formation and evolution in shaping the composition\n of exoplanetary atmospheres: Over the last twenty years, the search for extrasolar planets revealed us the\nrich diversity of the outcomes of the formation and evolution of planetary\nsystems. In order to fully understand how these extrasolar planets came to be,\nhowever, the orbital and physical data we possess are not enough, and they need\nto be complemented with information on the composition of the exoplanets.\nGround-based and space-based observations provided the first data on the\natmospheric composition of a few extrasolar planets, but a larger and more\ndetailed sample is required before we can fully take advantage of it. The\nprimary goal of the Exoplanet Characterization Observatory (EChO) is to fill\nthis gap, expanding the limited data we possess by performing a systematic\nsurvey of hundreds of extrasolar planets. The full exploitation of the data\nthat EChO and other space-based and ground-based facilities will provide in the\nnear future, however, requires the knowledge of what are the sources and sinks\nof the chemical species and molecules that will be observed. Luckily, the study\nof the past history of the Solar System provides several indications on the\neffects of processes like migration, late accretion and secular impacts, and on\nthe time they occur in the life of planetary systems. In this work we will\nreview what is already known about the factors influencing the composition of\nplanetary atmospheres, focusing on the case of gaseous giant planets, and what\ninstead still need to be investigated.", "category": "astro-ph_EP" }, { "text": "Planetesimal fragmentation and giant planet formation: the role of\n planet migration: In the standard model of core accretion, the cores of the giant planets form\nby the accretion of planetesimals. In this scenario, the evolution of the\nplanetesimal population plays an important role in the formation of massive\ncores. Recently, we studied the role of planetesimal fragmentation in the in\nsitu formation of a giant planet. However, the exchange of angular momentum\nbetween the planet and the gaseous disk causes the migration of the planet in\nthe disk. In this new work, we incorporate the migration of the planet and\nglobally study the role of planet migration in the formation of a massive core\nwhen the population of planetesimals evolves by planet accretion, migration due\nto the nebular drag, and fragmentation due to planetesimal collisions.", "category": "astro-ph_EP" }, { "text": "OSSOS: IV. Discovery of a dwarf planet candidate in the 9:2 resonance\n with Neptune: We report the discovery and orbit of a new dwarf planet candidate, 2015\nRR$_{245}$, by the Outer Solar System Origins Survey (OSSOS). 2015 RR$_{245}$'s\norbit is eccentric ($e=0.586$), with a semi-major axis near 82 au, yielding a\nperihelion distance of 34 au. 2015 RR$_{245}$ has $g-r = 0.59 \\pm 0.11$ and\nabsolute magnitude $H_{r} = 3.6 \\pm 0.1$; for an assumed albedo of $p_V = 12$%\nthe object has a diameter of $\\sim670$ km. Based on astrometric measurements\nfrom OSSOS and Pan-STARRS1, we find that 2015 RR$_{245}$ is securely trapped on\nten-Myr timescales in the 9:2 mean-motion resonance with Neptune. It is the\nfirst TNO identified in this resonance. On hundred-Myr timescales, particles in\n2015 RR$_{245}$-like orbits depart and sometimes return to the resonance,\nindicating that 2015 RR$_{245}$ likely forms part of the long-lived metastable\npopulation of distant TNOs that drift between resonance sticking and actively\nscattering via gravitational encounters with Neptune. The discovery of a 9:2\nTNO stresses the role of resonances in the long-term evolution of objects in\nthe scattering disk, and reinforces the view that distant resonances are\nheavily populated in the current Solar System. This object further motivates\ndetailed modelling of the transient sticking population.", "category": "astro-ph_EP" }, { "text": "A New Desalination Pump Help Define the pH of Ocean Worlds: We study ocean exoplanets, for which the global surface ocean is separated\nfrom the rocky interior by a high-pressure ice mantle. We describe a mechanism\nthat can pump salts out of the ocean, resulting in oceans of very low salinity.\nHere we focus on the H2O-NaCl system, though we discuss the application of this\npump to other salts as well. We find our ocean worlds to be acidic, with a pH\nin the range of 2-4. We discuss and compare between the conditions found within\nour studied oceans and the conditions in which polyextremophiles were\ndiscovered. This work focuses on exoplanets in the super-Earth mass range (2\nM_Earth), with water composing at least a few percent of their mass. Although,\nthe principal of the desalination pump may extend beyond this mass range.", "category": "astro-ph_EP" }, { "text": "On the Need for a Classification System for Consistent Characterization\n of the Composition of Planetary Bodies: A classification system is presented for characterizing the composition of\nplanetary bodies. From mass-radius and mass-density relationships, planets may\nbe broadly grouped into five composition classes identified as: Gas Giant,\nRock-Ice Giant, gas-rich Terrestrial, Rock Terrestrial, and Rock-Ice\nTerrestrial based upon the mass fractions of H-He gas, rock, and ice. For each\nof these broad composition classes, specific bulk composition classes are\ndefined and characterized with Solar System analog names. The classification\nsystem allows for both general and detailed characterization of exoplanets\nbased upon planetary mass-radius-composition models and provides rationale for\ndistinguishing gas-rich super-Earths from mini-Neptunes.", "category": "astro-ph_EP" }, { "text": "A shortcut to calculate SPAM limb-darkening coefficients: We release a new grid of stellar limb-darkening coefficients (LDCs, using the\nquadratic, power-2 and claret-4 laws) and intensity profiles for the Kepler, U,\nB, V and R passbands, based on STAGGER model atmospheres. The data can be\ndownloaded from Zenodo (doi:10.5281/zenodo.5593162). We compare the\nnewly-released LDCs, computed by ExoTETHyS, with previously published values,\nbased on the same atmospheric models using a so-called \"SPAM\" procedure. The\nSPAM method relies on synthetic light curves in order to compute the LDCs that\nbest represent the photometry of exoplanetary transits. We confirm that\nExoTETHyS achieves the same objective with a much simpler algorithm.", "category": "astro-ph_EP" }, { "text": "The Oblique Orbit of WASP-107b from K2 Photometry: Observations of nine transits of WASP-107 during the {\\it K2} mission reveal\nthree separate occasions when the planet crossed in front of a starspot. The\ndata confirm the stellar rotation period to be 17 days --- approximately three\ntimes the planet's orbital period --- and suggest that large spots persist for\nat least one full rotation. If the star had a low obliquity, at least two\nadditional spot crossings should have been observed. They were not observed,\ngiving evidence for a high obliquity. We use a simple geometric model to show\nthat the obliquity is likely in the range 40-140$^\\circ$, i.e., both spin-orbit\nalignment and anti-alignment can be ruled out. WASP-107 thereby joins the small\ncollection of relatively low-mass stars hosting a giant planet with a high\nobliquity. Most such stars have been observed to have low obliquities; all the\nexceptions, including WASP-107, involve planets with relatively wide orbits\n(\"warm Jupiters\", with $a_{\\rm min}/R_\\star \\gtrsim 8$). This demonstrates a\nconnection between stellar obliquity and planet properties, in contradiction to\nsome theories for obliquity excitation.", "category": "astro-ph_EP" }, { "text": "Shape models and spin states of Jupiter Trojans: Testing the streaming\n instability formation scenario: The leading theory for the origin of Jupiter Trojans (JTs) assumes that JTs\nwere captured to their orbits near the Lagrangian points of Jupiter during the\nearly reconfiguration of the giant planets. The natural source region for the\nmajority of JTs would then be the population of planetesimals born in a massive\ntrans-Neptunian disk. If true, JTs represent the most accessible stable\npopulation of small Solar System bodies that formed in the outer regions of the\nSolar System. For this work, we compiled photometric datasets for about 1000\nJTs and applied the convex inversion technique in order to assess their shapes\nand spin states. We obtained full solutions for $79$ JTs, and partial solutions\nfor an additional $31$ JTs. We found that the observed distribution of the pole\nobliquities of JTs is broadly consistent with expectations from the streaming\ninstability, which is the leading mechanism for the formation of planetesimals\nin the trans-Neptunian disk. The observed JTs' pole distribution has a slightly\nsmaller prograde vs. retrograde asymmetry (excess of obliquities $>130^\\circ$)\nthan what is expected from the existing streaming instability simulations.\nHowever, this discrepancy can be plausibly reconciled by the effects of the\npost-formation collisional activity. Our numerical simulations of the\npost-capture spin evolution indicate that the JTs' pole distribution is not\nsignificantly affected by dynamical processes such as the eccentricity\nexcitation in resonances, close encounters with planets, or the effects of\nnongravitational forces. However, a few JTs exhibit large latitude variations\nof the rotation pole and may even temporarily transition between prograde- and\nretrograde-rotating categories.", "category": "astro-ph_EP" }, { "text": "Debris disks as signposts of terrestrial planet formation: Circumstantial evidence suggests that most known extra-solar planetary\nsystems are survivors of violent dynamical instabilities. Here we explore how\ngiant planet instabilities affect the formation and survival of terrestrial\nplanets. We simulate planetary system evolution around Sun-like stars from\ninitial conditions that comprise: an inner disk of planetesimals and planetary\nembryos, three giant planets at Jupiter-Saturn distances, and a massive outer\nplanetesimal disk. We then calculate dust production rates and debris disk SEDs\nassuming that each planetesimal particle represents an ensemble of smaller\nbodies in collisional equilibrium. We predict a strong correlation between the\npresence of terrestrial planets and debris disks, mediated by the giant\nplanets. Strong giant planet instabilities destroy all rocky material -\nincluding fully-formed terrestrial planets if the instabilities occur late -\nalong with the icy planetesimals. Stable or weakly unstable systems allow\nterrestrial planets to accrete and significant dust to be produced in their\nouter regions. Stars older than ~100 Myr with bright cold dust emission (at ~70\nmicrons) signpost the dynamically calm environments conducive to efficient\nterrestrial accretion. We predict that while the typical eccentricities of\nterrestrial planets are small, there should exist a novel class of terrestrial\nplanet system whose single planet undergoes large amplitude oscillations in\neccentricity and inclination. By scaling to the observed semimajor axis\ndistribution of giant exoplanets, we estimate that terrestrial exoplanets in\nthe same systems should be a few times more abundant at 0.5 AU than giant or\nterrestrial exoplanets at 1 AU. Finally, we discuss the Solar System, which\nappears to be unusual in combining a rich terrestrial planet system with a low\ndust content.", "category": "astro-ph_EP" }, { "text": "Radial Transport of Large-Scale Magnetic Fields in Accretion Disks. I.\n Steady Solutions and an Upper Limit on the Vertical Field Strength: Large-scale magnetic fields are key ingredients of magnetically driven disk\naccretion. We study how large-scale poloidal fields evolve in accretion disks,\nwith the primary aim of quantifying the viability of magnetic accretion\nmechanisms in protoplanetary disks. We employ a kinematic mean-field model for\npoloidal field transport and focus on steady states where inward advection of a\nfield balances with outward diffusion due to effective resistivities. We\nanalytically derive the steady-state radial distribution of poloidal fields in\nhighly conducting accretion disks. The analytic solution reveals an upper limit\non the strength of large-scale vertical fields attainable in steady states. Any\nexcess poloidal field will be diffused away within a finite time, and we\ndemonstrate this with time-dependent numerical calculations of the mean-field\nequations. We apply this upper limit to large-scale vertical fields threading\nprotoplanetary disks. We find that the maximum attainable strength is about 0.1\nG at 1 AU, and about 1 mG at 10 AU from the central star. When combined with\nrecent magnetic accretion models, the maximum field strength translates into\nthe maximum steady-state accretion rate of $\\sim 10^{-7} M_\\odot {\\rm\nyr}^{-1}$, in agreement with observations. We also find that the maximum field\nstrength is ~ 1 kG at the surface of the central star provided that the disk\nextends down to the stellar surface. This implies that any excess stellar\npoloidal field of strength >~ kG can be transported to the surrounding disk.\nThis might in part resolve the magnetic flux problem in star formation.", "category": "astro-ph_EP" }, { "text": "Composition of Massive Giant Planets: The two current models for giant planet formation are core accretion and disk\ninstability. We discuss the core masses and overall planetary enrichment in\nheavy elements predicted by the two formation models, and show that both models\ncould lead to a large range of final compositions. For example, both can form\ngiant planets with nearly stellar compositions. However, low-mass giant\nplanets, enriched in heavy elements compared to their host stars, are more\neasily explained by the core accretion model. The final structure of the\nplanets, i.e., the distribution of heavy elements, is not firmly constrained in\neither formation model.", "category": "astro-ph_EP" }, { "text": "3D shape of asteroid (6)~Hebe from VLT/SPHERE imaging: Implications for\n the origin of ordinary H chondrites: Context. The high-angular-resolution capability of the new-generation\nground-based adaptive-optics camera SPHERE at ESO VLT allows us to assess, for\nthe very first time, the cratering record of medium-sized (D~100-200 km)\nasteroids from the ground, opening the prospect of a new era of investigation\nof the asteroid belt's collisional history. Aims. We investigate here the\ncollisional history of asteroid (6) Hebe and challenge the idea that Hebe may\nbe the parent body of ordinary H chondrites, the most common type of meteorites\nfound on Earth (~34% of the falls). Methods. We observed Hebe with SPHERE as\npart of the science verification of the instrument. Combined with earlier\nadaptive-optics images and optical light curves, we model the spin and\nthree-dimensional (3D) shape of Hebe and check the consistency of the derived\nmodel against available stellar occultations and thermal measurements. Results.\nOur 3D shape model fits the images with sub-pixel residuals and the light\ncurves to 0.02 mag. The rotation period (7.274 47 h), spin (343 deg,+47 deg),\nand volume-equivalent diameter (193 +/- 6km) are consistent with previous\ndeterminations and thermophysical modeling. Hebe's inferred density is 3.48 +/-\n0.64 g.cm-3 , in agreement with an intact interior based on its H-chondrite\ncomposition. Using the 3D shape model to derive the volume of the largest\ndepression (likely impact crater), it appears that the latter is significantly\nsmaller than the total volume of close-by S-type H-chondrite-like asteroid\nfamilies. Conclusions. Our results imply that (6) Hebe is not the most likely\nsource of H chondrites. Over the coming years, our team will collect similar\nhigh-precision shape measurements with VLT/SPHERE for ~40 asteroids covering\nthe main compositional classes, thus providing an unprecedented dataset to\ninvestigate the origin and collisional evolution of the asteroid belt.", "category": "astro-ph_EP" }, { "text": "Binary planetesimals and their role in planet formation: One of the main evolutionary stages of planet formation is the dynamical\nevolution of planetesimal disks. These disks are thought to evolve through\ngravitational encounters and physical collisions between single planetesimals.\nIn recent years, many binary planetesimals have been observed in the Solar\nsystem, indicating that the binarity of planetesimals is high. However, current\nstudies of planetesimal disks formation and evolution do not account for the\nrole of binaries. Here we point out that gravitational encounters of binary\nplanetesimals can have an important role in the evolution of planetesimal\ndisks. Binary planetesimals catalyze close encounters between planetesimals,\nand can strongly enhance their collision rate. Binaries may also serve as\nadditional heating source of the planetesimal disk, through the exchange of the\nbinaries gravitational potential energy into the kinetic energy of\nplanetesimals in the disk.", "category": "astro-ph_EP" }, { "text": "Growth and Evolution of Secondary Volcanic Atmospheres: II. The\n Importance of Kinetics: Volcanism is a major and long-term source of volatile elements such as C and\nH to Earth's atmosphere, likely has been to Venus's atmosphere, and may be for\nexoplanets. Models simulating volcanic growth of atmospheres often make one of\ntwo assumptions: either that atmospheric speciation is set by the\nhigh-temperature equilibrium of volcanism; or, that volcanic gases\nthermochemically re-equilibrate to the new, lower, temperature of the surface\nenvironment. In the latter case it has been suggested that volcanic atmospheres\nmay create biosignature false positives. Here, we test the assumptions\nunderlying such inferences by performing chemical kinetic calculations to\nestimate the relaxation timescale of volcanically-derived atmospheres to\nthermochemical equilibrium, in a simple 0D atmosphere neglecting photochemistry\nand reaction catalysis. We demonstrate that for planets with volcanic\natmospheres, thermochemical equilibrium over geological timescales can only be\nassumed if the atmospheric temperature is above ~700K. Slow chemical kinetics\nat lower temperatures inhibit the relaxation of redox-sensitive species to\nlow-temperature thermochemical equilibrium, precluding the production of two\nindependent biosignatures through thermochemistry alone: 1. ammonia, and 2. the\nco-occurrence of CO$_2$ and CH$_4$ in an atmosphere in the absence of CO. This\nsupports the use of both biosignatures for detecting life. Quenched at the high\ntemperature of their degassing, volcanic gases also have speciations\ncharacteristic of those produced from a more oxidized mantle, if interpreted as\nbeing at thermochemical equilibrium. This therefore complicates linking\natmospheres to the interiors of rocky exoplanets, even when their atmospheres\nare purely volcanic in origin.", "category": "astro-ph_EP" }, { "text": "The DEdicated MONitor of EXotransits (DEMONEX): Seven Transits of XO-4b: The DEdicated MONitor of EXotransits (DEMONEX) was a 20 inch robotic and\nautomated telescope to monitor bright stars hosting transiting exoplanets to\ndiscover new planets and improve constraints on the properties of known\ntransiting planetary systems. We present results for the misaligned hot Jupiter\nXO-4b containing 7 new transits from the DEMONEX telescope, including 3 full\nand 4 partial transits. We combine these data with archival light curves and\narchival radial velocity measurements to derive the host star mass\n$M_{*}=1.293_{-0.029}^{+0.030} M_\\odot$ and radius\n$R_{*}=1.554_{-0.030}^{+0.042} R_\\odot$ as well as the planet mass\n$M_{P}=1.615_{-0.099}^{+0.10} M_{\\rm J}$ and radius\n$R_{P}=1.317_{-0.029}^{+0.040} R_{\\rm J}$ and a refined ephemeris of\n$P=4.1250687\\pm0.0000024$ days and $T_{0}=2454758.18978\\pm0.00024 \\rm\n{BJD_{TDB}}$. We include archival Rossiter-McLaughlin measurements of XO-4 to\ninfer the stellar spin-planetary orbit alignment $\\lambda=-40.0_{-7.5}^{+8.8}$\ndegrees.\n We test the effects of including various detrend parameters, theoretical and\nempirical mass-radius relations, and Rossiter-McLaughlin models. We infer that\ndetrending against CCD position and time or airmass can improve data quality,\nbut can have significant effects on the inferred values of many parameters ---\nmost significantly $R_{P}/R_{*}$ and the observed central transit times\n$T_{C}$. In the case of $R_{P}/R_{*}$ we find that the systematic uncertainty\ndue to detrending can be three times that of the quoted statistical\nuncertainties. The choice of mass-radius relation has little effect on our\ninferred values of the system parameters. The choice of Rossiter-McLaughlin\nmodels can have significant effects of the inferred values of $v\\sin{I_{*}}$\nand the stellar spin-planet orbit angle $\\lambda$.", "category": "astro-ph_EP" }, { "text": "Collisional Charging in the Low Pressure Range of Protoplanetary Disks: In recent years, collisional charging has been proposed to promote the growth\nof pebbles in early phases of planet formation. Ambient pressure in\nprotoplanetary disks spans a wide range from below $10^{-9}$ mbar up to way\nbeyond mbar. Yet, experiments on collisional charging of same material surfaces\nhave only been conducted under Earth atmospheric pressure, Martian pressure and\nmore generally down to $10^{-2}$ mbar thus far. This work presents first\npressure dependent charge measurements of same material collisions between\n$10^{-8}$ and $10^3$ mbar. Strong charging occurs down to the lowest pressure.\nIn detail, our observations show a strong similarity to the pressure dependence\nof the breakdown voltage between two electrodes and we suggest that breakdown\nalso determines the maximum charge on colliding grains in protoplanetary disks.\nWe conclude that collisional charging can occur in all parts of protoplanetary\ndisks relevant for planet formation.", "category": "astro-ph_EP" }, { "text": "Near-Ultraviolet Absorption Distribution of Primitive Asteroids from\n Spectrophotometric Surveys: Aims: Our objectives were first to evaluate the possibility for using the NUV\nabsorption as diagnostics of hydrated minerals based on the recent datasets of\nprimitive asteroids and hydrated carbonaceous chondrites, and second to\ninvestigate the reflectance spectrophotometry of the primitive asteroids in the\nNUV as functions of heliocentric distance and size. Methods: The NUV and\nvisible reflectance spectrophotometry of more than 9,000 primitive asteroids\nwas investigated using two spectrophotometric surveys, the Eight Color Asteroid\nSurvey (ECAS) and the Sloan Digital Sky Survey (SDSS), which cover wavelengths\ndown to 0.32 um and 0.36 um, respectively. We classified asteroids from the\nmain asteroid belt, the Cybele and Hilda zones, and Jupiter Trojans based on\nTholen's taxonomy and described the statistical distribution of primitive\nasteroid types. We also examined the relationship of the NUV, 0.7 um, and 2.7\num absorptions among primitive asteroids and hydrous carbonaceous chondrites CI\nand CM. Results: We found strong correlations between the NUV and the OH-band\n(2.7 um) absorptions for primitive asteroids and hydrated meteorites,\nsuggesting the NUV absorption can be indicative of hydrated silicates.\nMoreover, there is a great difference in the NUV absorption between the large\nasteroids (diameter d > 50 km) and small asteroids (d < 10 km) in the taxonomic\ndistribution. The taxonomic distribution of asteroids differs between the inner\nmain belt and middle-outer main belt. Notably, the C types are dominating large\nmembers through the main belt and the F types are dominating small asteroids of\nthe inner main belt. The asteroids beyond the main belt consist mostly of P and\nD types, although P types are common everywhere in the main belt. The peculiar\ndistribution of F types might indicate a different formation reservoir or\ndisplacement process of F types in the early Solar System.", "category": "astro-ph_EP" }, { "text": "Coplanar circumbinary planets can be unstable to large tilt oscillations\n in the presence of an inner polar planet: Mutually misaligned circumbinary planets may form in a warped or broken gas\ndisc or from later planet-planet interactions. With numerical simulations and\nanalytic estimates we explore the dynamics of two circumbinary planets with a\nlarge mutual inclination. A coplanar inner planet causes prograde apsidal\nprecession of the binary and the stationary inclination for the outer planet is\nhigher for larger outer planet orbital radius. In this case a coplanar outer\nplanet always remains coplanar. On the other hand, a polar inner planet causes\nretrograde apsidal precession of the binary orbit and the stationary\ninclination is smaller for larger outer planet orbital radius. For a range of\nouter planet semi-major axes, an initially coplanar orbit is librating meaning\nthat the outer planet undergoes large tilt oscillations. Circumbinary planets\nthat are highly inclined to the binary are difficult to detect -- it is\nunlikely for a planet to have an inclination below the transit detection limit\nin the presence of a polar inner planet. These results suggest that there could\nbe a population of circumbinary planets that are undergoing large tilt\noscillations.", "category": "astro-ph_EP" }, { "text": "Transmission spectroscopy of the inflated exoplanet WASP-52b, and\n evidence for a bright region on the stellar surface: We have measured the transmission spectrum of the extremely inflated hot\nJupiter WASP-52b using simultaneous photometric observations in SDSS u', g' and\na filter centred on the sodium doublet (NaI) with the ULTRACAM instrument\nmounted on the 4.2m William Herschel Telescope. We find that Rayleigh\nscattering is not the dominant source of opacity within the planetary\natmosphere and find a transmission spectrum more consistent with\nwavelength-independent opacity such as from clouds. We detect an in-transit\nanomaly that we attribute to the presence of stellar activity and find that\nthis feature can be more simply modelled as a bright region on the stellar\nsurface akin to Solar faculae rather than spots. A spot model requires a\nsignificantly larger planet/star radius ratio than that found in previous\nstudies. Our results highlight the precision that can be achieved by\nground-based photometry with errors in the scaled planetary radii of less than\none atmospheric scale height, comparable to HST observations.", "category": "astro-ph_EP" }, { "text": "HATS-4b: A Dense Hot-Jupiter Transiting a Super Metal-Rich G Star: We report the discovery by the HATSouth survey of HATS-4b, an extrasolar\nplanet transiting a V=13.46 mag G star. HATS-4b has a period of P = 2.5167 d,\nmass of Mp = 1.32 Mj, radius of Rp = 1.02 Rj and density of rho_p = 1.55 +-\n0.16 g/cm^3 ~ 1.24 rhoj. The host star has a mass of 1.00 Msun, a radius of\n0.92 Rsun and a very high metallicity [Fe/H]= 0.43 +- 0.08. HATS-4b is among\nthe densest known planets with masses between 1-2 Mj and is thus likely to have\na significant content of heavy elements of the order of 75 Mearth. In this\npaper we present the data reduction, radial velocity measurement and stellar\nclassification techniques adopted by the HATSouth survey for the CORALIE\nspectrograph. We also detail a technique to estimate simultaneously vsini and\nmacroturbulence using high resolution spectra.", "category": "astro-ph_EP" }, { "text": "WASP-180Ab: Doppler tomography of an hot Jupiter orbiting the primary\n star in a visual binary: We report the discovery and characterisation of WASP-180Ab, a hot Jupiter\nconfirmed by the detection of its Doppler shadow and by measuring its mass\nusing radial velocities. We find the 0.9 $\\pm$ 0.1 $M_{\\rm Jup}$, 1.24 $\\pm$\n0.04 $R_{\\rm Jup}$ planet to be in a misaligned, retrograde orbit around an F7\nstar with $T_{\\rm eff}$ = 6500K and a moderate rotation speed of vsini = 19.9\nkm s$^{-1}$. The host star is the primary of a $V$ = 10.7 binary, where a\nsecondary separated by 5$''$ ($\\sim$1200 AU) contributes $\\sim$30% of the\nlight. WASP-180Ab therefore adds to a small sample of transiting hot Jupiters\nknown in binary systems. A 4.6-day modulation seen in the WASP data is likely\nto be the rotational modulation of the companion star, WASP-180B.", "category": "astro-ph_EP" }, { "text": "Kepler's Earth-like Planets Should Not Be Confirmed Without Independent\n Detection: The Case of Kepler-452b: We show that the claimed confirmed planet Kepler-452b (a.k.a. K07016.01, KIC\n8311864) can not be confirmed using a purely statistical validation approach.\nKepler detects many more periodic signals from instrumental effects than it\ndoes from transits, and it is likely impossible to confidently distinguish the\ntwo types of event at low signal-to-noise. As a result, the scenario that the\nobserved signal is due to an instrumental artifact can't be ruled out with 99\\%\nconfidence, and the system must still be considered a candidate planet. We\ndiscuss the implications for other confirmed planets in or near the habitable\nzone.", "category": "astro-ph_EP" }, { "text": "Interior Models of Saturn: Including the Uncertainties in Shape and\n Rotation: The accurate determination of Saturn's gravitational coefficients by Cassini\ncould provide tighter constrains on Saturn's internal structure. Also,\noccultation measurements provide important information on the planetary shape\nwhich is often not considered in structure models. In this paper we explore how\nwind velocities and internal rotation affect the planetary shape and the\nconstraints on Saturn's interior. We show that within the geodetic approach\n(Lindal et al., 1985, ApJ, 90, 1136) the derived physical shape is insensitive\nto the assumed deep rotation. Saturn's re-derived equatorial and polar radii at\n100 mbar are found to be 54,445 $\\pm$10 km and 60,365$\\pm$10 km, respectively.\nTo determine Saturn's interior we use {\\it 1 D} three-layer hydrostatic\nstructure models, and present two approaches to include the constraints on the\nshape. These approaches, however, result in only small differences in Saturn's\nderived composition. The uncertainty in Saturn's rotation period is more\nsignificant: with Voyager's 10h39mns period, the derived mass of heavy elements\nin the envelope is 0-7 M$_{\\oplus}$. With a rotation period of 10h32mns, this\nvalue becomes $<4$ $M_{\\oplus}$, below the minimum mass inferred from\nspectroscopic measurements. Saturn's core mass is found to depend strongly on\nthe pressure at which helium phase separation occurs, and is estimated to be\n5-20 M$_{\\oplus}$. Lower core masses are possible if the separation occurs\ndeeper than 4 Mbars. We suggest that the analysis of Cassini's radio\noccultation measurements is crucial to test shape models and could lead to\nconstraints on Saturn's rotation profile and departures from hydrostatic\nequilibrium.", "category": "astro-ph_EP" }, { "text": "The Exomoon Corridor: Half of all exomoons exhibit TTV frequencies\n within a narrow window due to aliasing: Exomoons are expected to produce potentially detectable transit timing\nvariations (TTVs) upon their parent planet. Unfortunately, distinguishing\nmoon-induced TTVs from other sources, in particular planet-planet interactions,\nhas severely impeded its usefulness as a tool for identifying exomoon\ncandidates. A key feature of exomoon TTVs is that they will always be\nundersampled, due to the simple fact that we can only observe the TTVs once per\ntransit/planetary period. We show that it is possible to analytically express\nthe aliased TTV periodicity as a function of planet and moon period. Further,\nwe show that inverting an aliased TTV period back to a true moon period is\nfraught with hundreds of harmonic modes. However, a unique aspect of these TTV\naliases is that they are predicted to occur at consistently short periods,\nirrespective of what model one assumes for the underlying moon population.\nSpecifically, 50% of all exomoons are expected to induce TTVs with a period\nbetween 2 to 4 cycles, a range that planet-planet interactions rarely manifest\nat. This provides an exciting and simple tool for quickly identifying exomoons\ncandidates and brings the TTV method back to the fore as an exomoon hunting\nstrategy. Applying this method to the candidate, Kepler-1625b i, reveals that\nits TTV periodicity centers around the median period expected for exomoons.", "category": "astro-ph_EP" }, { "text": "Can Ground-based Telescopes Detect The Oxygen 1.27 Micron Absorption\n Feature as a Biomarker in Exoplanets ?: The oxygen absorption line imprinted in the scattered light from the\nEarth-like planets has been considered the most promising metabolic biomarker\nof the exo-life. We examine the feasibility of the detection of the 1.27 micron\noxygen band from habitable exoplanets, in particular, around late- type stars\nobserved with a future instrument on a 30 m class ground-based telescope. We\nanalyzed the night airglow around 1.27 micron with IRCS/echelle spectrometer on\nSubaru and found that the strong telluric emission from atmospheric oxygen\nmolecules declines by an order of magnitude by midnight. By compiling nearby\nstar catalogs combined with the sky background model, we estimate the\ndetectability of the oxygen absorption band from an Earth twin, if it exists,\naround nearby stars. We find that the most dominant source of photon noise for\nthe oxygen 1.27 micron band detection comes from the night airglow if the\ncontribution of the stellar PSF halo is suppressed enough to detect the planet.\nWe conclude that the future detectors for which the detection contrast is\nlimited by photon noise can detect the oxygen 1.27 micron absorption band of\nthe Earth twins for ~50 candidates of the late type star. This paper\ndemonstrates the importance of deploying small inner working angle efficient\ncoronagraph and extreme adaptive optics on extremely large telescopes, and\nclearly shows that doing so will enable study of potentially habitable planets.", "category": "astro-ph_EP" }, { "text": "Dusty tails of evaporating exoplanets. II. Physical modelling of the KIC\n 12557548b light curve: Evaporating rocky exoplanets, such as KIC 12557548b, eject large amounts of\ndust grains, which can trail the planet in a comet-like tail. When such objects\noccult their host star, the resulting transit signal contains information about\nthe dust in the tail. We aim to use the detailed shape of the Kepler light\ncurve of KIC 12557548b to constrain the size and composition of the dust grains\nthat make up the tail, as well as the mass loss rate of the planet. Using a\nself-consistent numerical model of the dust dynamics and sublimation, we\ncalculate the shape of the tail by following dust grains from their ejection\nfrom the planet to their destruction due to sublimation. From this dust cloud\nshape, we generate synthetic light curves (incorporating the effects of\nextinction and angle-dependent scattering), which are then compared with the\nphase-folded Kepler light curve. We explore the free-parameter space thoroughly\nusing a Markov chain Monte Carlo method. Our physics-based model is capable of\nreproducing the observed light curve in detail. Good fits are found for initial\ngrain sizes between 0.2 and 5.6 micron and dust mass loss rates of 0.6 to 15.6\nM_earth/Gyr (2-sigma ranges). We find that only certain combinations of\nmaterial parameters yield the correct tail length. These constraints are\nconsistent with dust made of corundum (Al2O3), but do not agree with a range of\ncarbonaceous, silicate, or iron compositions. Using a detailed, physically\nmotivated model, it is possible to constrain the composition of the dust in the\ntails of evaporating rocky exoplanets. This provides a unique opportunity to\nprobe to interior composition of the smallest known exoplanets.", "category": "astro-ph_EP" }, { "text": "Gamma Ray Bursts: Not so Much Deadlier than We Thought: We analyze the additional effect on planetary atmospheres of recently\ndetected gamma-ray burst afterglow photons in the range up to 1 TeV. For an\nEarth-like atmosphere we find that there is a small additional depletion in\nozone versus that modeled for only prompt emission. We also find a small\nenhancement of muon flux at the planet surface. Overall, we conclude that the\nadditional afterglow emission, even with TeV photons, does not result in a\nsignificantly larger impact over that found in past studies.", "category": "astro-ph_EP" }, { "text": "Accretion onto a binary from a polar circumbinary disc: We present hydrodynamical simulations to model the accretion flow from a\npolar circumbinary disc onto a high eccentricity ($e=0.78$) binary star system\nwith near unity mass ratio ($q=0.83$), as a model for binary HD 98800 BaBb. We\ncompare the polar circumbinary disc accretion flow with the previously studied\ncoplanar case. In the coplanar case, the circumbinary disc becomes eccentric\nand the accretion alternates from being dominant onto one binary member to the\nother. For the polar disc case involving a highly eccentric binary, we find\nthat the circumbinary disc retains its initially low eccentricity and that the\nprimary star accretion rate is always about the same as the secondary star\naccretion rate. Recent observations of the binary HD 98800 BaBb, which has a\npolar circumbinary disc, have been used to determine the value of the $\\rm\nH\\alpha$ flux from the brighter component. From this value, we infer that the\naccretion rate is much lower than for typical T Tauri stars. The eccentric\norbit of the outer companion HD 98800 A increases the accretion rate onto HD\n98800 B by $\\sim 20$ per cent after each periastron passage. Our hydrodynamical\nsimulations are unable to explain such a low accretion rate unless the disc\nviscosity parameter is very small, $\\alpha < 10^{-5}$. Additional observations\nof this system would be useful to check on this low accretion rate.", "category": "astro-ph_EP" }, { "text": "Analytical determination of orbital elements using Fourier analysis. II.\n Gaia astrometry and its combination with radial velocities: The ESA global astrometry space mission Gaia has been monitoring the position\nof a billion stars since 2014. The analysis of such a massive dataset is\nchallenging in terms of the data processing involved. In particular, the blind\ndetection and characterization of single or multiple companions to stars\n(planets, brown dwarfs, or stars) using Gaia astrometry requires highly\nefficient algorithms. In this article, we present a set of analytical methods\nto detect and characterize companions in scanning space astrometric time series\nas well as via a combination of astrometric and radial velocity time series. We\npropose a general linear periodogram framework and we derive analytical\nformulas for the false alarm probability (FAP) of periodogram peaks. Once a\nsignificant peak has been identified, we provide analytical estimates of all\nthe orbital elements of the companion based on the Fourier decomposition of the\nsignal. The periodogram, FAP, and orbital elements estimates can be computed\nfor the astrometric and radial velocity time series separately or in tandem.\nThese methods are complementary with more accurate and more computationally\nintensive numerical algorithms (e.g., least-squares minimization, Markov chain\nMonte Carlo, genetic algorithms). In particular, our analytical approximations\ncan be used as an initial condition to accelerate the convergence of numerical\nalgorithms. Our formalism has been partially implemented in the Gaia exoplanet\npipeline for the third Gaia data release. Since the Gaia astrometric time\nseries are not yet publicly available, we illustrate our methods on the basis\nof Hipparcos data, together with on-ground CORALIE radial velocities, for three\ntargets known to host a companion: HD 223636 (HIP 117622), HD 17289 (HIP\n12726), and HD 3277 (HIP 2790).", "category": "astro-ph_EP" }, { "text": "The Atmosphere: These notes contain everything necessary to run a flipped course on \"The\nAtmosphere\" at an introductory undergraduate level. There are notes for the\nstudents to read before each course meeting and problems for them to work on in\nsmall groups during course meetings. Topics include (1) atmospheric\ncomposition, structure, and thermodynamics; (2) solar and terrestrial radiation\nin the atmospheric energy balance; (3) atmospheric dynamics and circulation. I\ninclude 10 problem sets, six practice midterms, and three practice finals.\nProblems are drawn from the atmospheres of modern and past Earth, solar system\nplanets, and extrasolar planets. I can provide solutions to the in-class\nproblems and problem sets to teachers upon request. You are free to use these\nnotes in your classes, and to expand them as you please. If you catch any typos\nor errors, please send them to me. Enjoy!", "category": "astro-ph_EP" }, { "text": "A Near-coplanar Stellar Flyby of the Planet Host Star HD 106906: We present an investigation into the kinematics of HD 106906 using the newly\nreleased Gaia DR2 catalog to search for close encounters with other members of\nthe Scorpius-Centaurus (Sco-Cen) association. HD 106906 is an eccentric\nspectroscopic binary that hosts both a large asymmetric debris disk extending\nout to at least 500 au and a directly imaged planetary-mass companion at a\nprojected separation of 738 au. The cause of the asymmetry in the debris disk\nand the unusually wide separation of the planet is not currently known. Using a\ncombination of Gaia DR2 astrometry and ground-based radial velocities, we\nexplore the hypothesis that a close encounter with another cluster member\nwithin the last 15 Myr is responsible for the present configuration of the\nsystem. Out of 461 stars analyzed, we identified two candidate perturbers that\nhad a median closest approach (CA) distance within 1 pc of HD 106906: HIP 59716\nat $D_{\\rm CA}=0.65_{-0.40}^{+0.93}$ pc ($t_{\\rm CA}=-3.49_{-1.76}^{+0.90}$\nMyr) and HIP 59721 at $D_{\\rm CA}=0.71_{-0.11}^{+0.18}$ pc ($t_{\\rm\nCA}=-2.18_{-1.04}^{+0.54}$ Myr), with the two stars likely forming a wide\nphysical binary. The trajectories of both stars relative to HD 106906 are\nalmost coplanar with the inner disk ($\\Delta\\theta = 5.4\\pm1.7$ deg and\n$4.2_{-1.1}^{+0.9}$ deg). These two stars are the best candidates of the\ncurrently known members of Sco-Cen for having a dynamically important close\nencounter with HD 106906, which may have stabilized the orbit of HD 106906 b in\nthe scenario where the planet formed in the inner system and attained high\neccentricity by interaction with the central binary.", "category": "astro-ph_EP" }, { "text": "Formation of Regular Satellites from Ancient Massive Rings in the Solar\n System: When a planetary tidal disk -like Saturn's rings- spreads beyond the Roche\nradius (inside which planetary tides prevent aggregation), satellites form and\nmigrate away. Here, we show that most regular satellites in the solar system\nprobably formed in this way. According to our analytical model, when the\nspreading is slow, a retinue of satellites appear with masses increasing with\ndistance to the Roche radius, in excellent agreement with Saturn's, Uranus',\nand Neptune's satellite systems. This suggests that Uranus and Neptune used to\nhave massive rings that disappeared to give birth to most of their regular\nsatellites. When the spreading is fast, only one large satellite forms, as was\nthe case for Pluto and Earth. This conceptually bridges the gap between\nterrestrial and giant planet systems.", "category": "astro-ph_EP" }, { "text": "Planetesimals Around Stars with TESS (PAST): I. Transient Dimming of a\n Binary Solar Analog at the End of the Planet Accretion Era: We report detection of quasi-periodic (1.5 day) dimming of HD 240779, the\nsolar-mass primary in a 5\" visual binary (also TIC 284730577), by the\nTransiting Exoplanet Survey Satellite. This dimming, as has been shown for\nother \"dipper\" stars, is likely due to occultation by circumstellar dust. The\nbarycentric space motion, lithium abundance, rotation, and chromospheric\nemission of the stars in this system point to an age of ~125 Myr, and possible\nmembership in the AB Doradus moving group. As such it occupies an important but\npoorly explored intermediate regime of stars with transient dimming between\nyoung stellar objects in star forming regions and main sequence stars, and\nbetween UX Orionis-type Ae/Be stars and M-type \"dippers\". HD 240779, but not\nits companion BD+10714B, has WISE-detected excess infrared emission at 12 and\n22 microns indicative of circumstellar dust. We propose that infrared emission\nis produced by collisions of planetesimals during clearing of a residual disk\nat the end of rocky planet formation, and that quasi-periodic dimming is\nproduced by the rapid disintegration of a 100 km planetesimal near the silicate\nevaporation radius. Further studies of this and similar systems will illuminate\na poorly understood final phase of rocky planet formation like that which\nproduced the inner Solar System.", "category": "astro-ph_EP" }, { "text": "What are little worlds made of? Stellar abundances and the building\n blocks of planets: If the photospheres of solar-type stars represent the composition of\ncircumstellar disks from which any planets formed, spectroscopic determinations\nof stellar elemental abundances offer information on the composition of those\nplanets, including smaller, rocky planets. In particular, the C/O ratio is\nproposed to be a key determinant of the composition of solids that condense\nfrom disk gas and are incorporated into planets. Also, planets may leave\nchemical signatures on the photospheres of their host stars by sequestering\nheavy elements, or by being accreted by the stars. The presence, absence, and\ncomposition of planets could be revealed by small differences in the relative\nabundances between stars. I critically examine these scenarios and show that\n(i) a model of Galactic chemical evolution predicts that the C/O ratio is\nexpected to be close to the solar value and vary little between dwarf stars in\nthe solar neighborhood; (ii) spectroscopic surveys of M dwarf stars limit the\noccurrence of stars with C/O $\\gtrsim 1$ to $<10^{-3}$; and (iii) planetesimal\nchemistry will be controlled by the composition of oxygen-rich dust inherited\nfrom the molecular cloud and processed in a dust-rich environment, not a gas\nwith the stellar composition. A second generation of more reduced planetesimals\ncould be produced by re-equilibration of some material with dust-depleted gas.\nFinally, I discuss how minor differences in relative abundances between stars\nthat correlate with condensation temperature can be explained by dust-gas\nsegregation, perhaps in circumstellar disks, rather than planet formation.", "category": "astro-ph_EP" }, { "text": "Condensation of Rocky Material in Astrophysical Environments: Volatility-dependent fractionation of the rock-forming elements at high\ntemperatures is an early, widespread process during formation of the earliest\nsolids in protoplanetary disks. Equilibrium condensation calculations allow\nprediction of the identities and compositions of mineral and liquid phases\ncoexisting with gas under presumed bulk chemical, pressure and temperature\nconditions. A graphical survey of such results is presented for systems of\nsolar and non-solar bulk composition. Chemical equilibrium was approached to\nvarying degrees in the local regions where meteoritic chondrules, Ca-Al-rich\ninclusions, matrix and other components formed. Early, repeated vapor-solid\ncycling and homogenization, followed by hierarchical accretion in dust-rich\nregions, is hypothesized for meteoritic inclusions. Disequilibrium chemical\neffects appear to have been common at all temperatures, but increasingly so in\nless refractory meteoritic components. Work is needed to better model\nhigh-temperature solid solutions, indicators of these processes.", "category": "astro-ph_EP" }, { "text": "The effect of Poynting-Robertson drag on the triangular Lagrangian\n points: We investigate the stability of motion close to the Lagrangian equilibrium\npoints L4 and L5 in the framework of the spatial, elliptic, restricted three-\nbody problem, subject to the radial component of Poynting-Robertson drag. For\nthis reason we develop a simplified resonant model, that is based on averaging\ntheory, i.e. averaged over the mean anomaly of the perturbing planet. We find\ntemporary stability of particles displaying a tadpole motion in the 1:1\nresonance. From the linear stability study of the averaged simplified resonant\nmodel, we find that the time of temporary stability is proportional to beta a1\nn1 , where beta is the ratio of the solar radiation over the gravitational\nforce, and a1, n1 are the semi-major axis and the mean motion of the perturbing\nplanet, respectively. We extend previous results (Murray (1994)) on the\nasymmetry of the stability indices of L4 and L5 to a more realistic force\nmodel. Our analytical results are supported by means of numerical simulations.\nWe implement our study to Jupiter-like perturbing planets, that are also found\nin extra-solar planetary systems.", "category": "astro-ph_EP" }, { "text": "Neptune's resonances in the Scattered Disk: The Scattered Disk Objects (SDOs) are thought to be a small fraction of the\nancient population of leftover planetesimals in the outer solar system that\nwere gravitationally scattered by the giant planets and have managed to survive\nprimarily by capture and sticking in Neptune's exterior mean motion resonances\n(MMRs). In order to advance understanding of the role of MMRs in the dynamics\nof the SDOs, we investigate the phase space structure of a large number of\nNeptune's MMRs in the semi-major axis range 33--140~au by use of Poincar\\'e\nsections of the circular planar restricted three body model for the full range\nof particle eccentricity pertinent to SDOs. We find that, for eccentricities\ncorresponding to perihelion distances near Neptune's orbit, distant MMRs have\nstable regions with widths that are surprisingly large and of similar size to\nthose of the closer-in MMRs. We identify a phase-shifted second resonance zone\nthat exists in the phase space at planet-crossing eccentricities but not at\nlower eccentricities; this second resonance zone plays an important role in the\ndynamics of SDOs in lengthening their dynamical lifetimes. Our non-perturbative\nmeasurements of the sizes of the stable resonance zones confirm previous\nresults and provide an additional explanation for the prominence of the $N$:1\nsequence of MMRs over the $N$:2, $N$:3 sequences and other MMRs in the\npopulation statistics of SDOs; our results also provide a tool to more easily\nidentify resonant objects.", "category": "astro-ph_EP" }, { "text": "Cooling Requirements for the Vertical Shear Instability in\n Protoplanetary Disks: The vertical shear instability (VSI) offers a potential hydrodynamic\nmechanism for angular momentum transport in protoplanetary disks (PPDs). The\nVSI is driven by a weak vertical gradient in the disk's orbital motion, but\nmust overcome vertical buoyancy, a strongly stabilizing influence in cold\ndisks, where heating is dominated by external irradiation. Rapid radiative\ncooling reduces the effective buoyancy and allows the VSI to operate. We\nquantify the cooling timescale $t_c$ needed for efficient VSI growth, through a\nlinear analysis of the VSI with cooling in vertically global, radially local\ndisk models. We find the VSI is most vigorous for rapid cooling with\n$t_c<\\Omega_\\mathrm{K}^{-1}h|q|/(\\gamma -1)$ in terms of the Keplerian orbital\nfrequency, $\\Omega_\\mathrm{K}$; the disk's aspect-ratio, $h\\ll1$; the radial\npower-law temperature gradient, $q$; and the adiabatic index, $\\gamma$. For\nlonger $t_c$, the VSI is much less effective because growth slows and shifts to\nsmaller length scales, which are more prone to viscous or turbulent decay. We\napply our results to PPD models where $t_c$ is determined by the opacity of\ndust grains. We find that the VSI is most effective at intermediate radii, from\n$\\sim5$AU to $\\sim50$AU with a characteristic growth time of $\\sim30$ local\norbital periods. Growth is suppressed by long cooling times both in the opaque\ninner disk and the optically thin outer disk. Reducing the dust opacity by a\nfactor of 10 increases cooling times enough to quench the VSI at all disk\nradii. Thus the formation of solid protoplanets, a sink for dust grains, can\nimpede the VSI.", "category": "astro-ph_EP" }, { "text": "Predicting Exoplanets Mass and Radius: A Nonparametric Approach: A fundamental endeavor in exoplanetary research is to characterize the bulk\ncompositions of planets via measurements of their masses and radii. With future\nsample sizes of hundreds of planets to come from TESS and PLATO, we develop a\nstatistical method that can flexibly yet robustly characterize these\ncompositions empirically, via the exoplanet M-R relation. Although the M-R\nrelation has been explored in many prior works, they mostly use a power-law\nmodel, with assumptions that are not flexible enough to capture important\nfeatures in current and future M-R diagrams. To address these shortcomings, a\nnonparametric approach is developed using a sequence of Bernstein polynomials.\nWe demonstrate the benefit of taking the nonparametric approach by benchmarking\nour findings with previous work and showing that a power-law can only\nreasonably describe the M-R relation of the smallest planets and that the\nintrinsic scatter can change non-monotonically with different values of a\nradius. We then apply this method to a larger dataset, consisting of all the\nKepler observations in the NASA Exoplanet Archive. Our nonparametric approach\nprovides a tool to estimate the M-R relation by incorporating heteroskedastic\nmeasurement errors into the model. As more observations will be obtained in the\nnear future, this approach can be used with the provided R code to analyze a\nlarger dataset for a better understanding of the M-R relation.", "category": "astro-ph_EP" }, { "text": "Normal forms for the Laplace resonance: We describe a comprehensive model for systems locked in the Laplace\nresonance. The framework is based on the simplest possible dynamical structure\nprovided by the Keplerian problem perturbed by the resonant coupling truncated\nat second order in the eccentricities. The reduced Hamiltonian, constructed by\na transformation to resonant coordinates, is then submitted to a suitable\nordering of the terms and to the study of its equilibria. Henceforth, resonant\nnormal forms are computed. The main result is the identification of two\ndifferent classes of equilibria. In the first class, only one kind of stable\nequilibrium is present: the paradigmatic case is that of the Galilean system.\nIn the second class, three kinds of stable equilibria are possible and at least\none of them is characterised by a high value of the forced eccentricity for the\n`first planet': here the paradigmatic case is the exo-planetary system GJ-876,\nin which the combination of libration centers admits triple conjunctions\notherwise not possible in the Galilean case. The normal form obtained by\naveraging with respect to the free eccentricity oscillations, describes the\nlibration of the Laplace argument for arbitrary amplitudes and allows us to\ndetermine the libration width of the resonance. The agreement of the analytic\npredictions with the numerical integration of the toy models is very good.", "category": "astro-ph_EP" }, { "text": "Spin Axes and Shape Models of Asteroid Pairs: Fingerprints of YORP and a\n Path to the Density of Rubble Piles: An asteroid pair consists of two unbound objects with almost identical\nheliocentric orbital elements that were formed when a single \"rubble pile\"\nasteroid failed to remain bound against an increasing rotation rate. Models\nsuggest that the pairs' progenitors gained the fast rotation due to the YORP\neffect. Since it was shown that the spin axis vector can be aligned by the YORP\neffect, such a behavior should be seen on asteroid pairs, if they were indeed\nformed by the described mechanism. Alternatively, if the pairs were formed by a\ncollision, the spin axes should have a random direction and small or young\nbodies might have a tumbling rotation.\n Here I apply the lightcurve inversion method on self-obtained photometric\ndata, in order to derive the rotation axis vectors and shape models of the\nasteroid pairs 2110, 3749, 5026, 6070, 7343 and 44612. Three asteroids resulted\nwith polar-directed spin axes and three objects with ambiguous results. In\naddition, the secondary member 44612 presents the same sense of rotation as its\nprimary member 2110, and its spin is not tumbling. Finally, I use a rotational\nfission model, based on the assumption of an angular momentum conservation, and\nmatch it to the measured spin, shape, and mass ratio parameters in order to\nconstrain the density of the primary members in the pairs. Using this method,\nlow density values that are expected from a \"rubble pile\" are derived. All\nthese results lead to the conclusion that the disruption of these asteroid\npairs was most likely the outcome of the YORP effect that spun-up \"rubble pile\"\nasteroids.", "category": "astro-ph_EP" }, { "text": "Extreme Climate Variations from Milankovitch-like Eccentricity\n Oscillations in Extrasolar Planetary Systems: Although our solar system features predominantly circular orbits, the\nexoplanets discovered so far indicate that this is the exception rather than\nthe rule. This could have crucial consequences for exoplanet climates, both\nbecause eccentric terrestrial exoplanets could have extreme seasonal variation,\nand because giant planets on eccentric orbits could excite Milankovitch-like\nvariations of a potentially habitable terrestrial planet,\\\"A\\^os eccentricity,\non timescales of thousands-to-millions of years. A particularly interesting\nimplication concerns the fact that the Earth is thought to have gone through at\nleast one globally frozen, \"snowball\" state in the last billion years that it\npresumably exited after several million years of buildup of greenhouse gases\nwhen the ice-cover shut off the carbonate-silicate cycle. Water-rich extrasolar\nterrestrial planets with the capacity to host life might be at risk of falling\ninto similar snowball states. Here we show that if a terrestrial planet has a\ngiant companion on a sufficiently eccentric orbit, it can undergo\nMilankovitch-like oscillations of eccentricity of great enough magnitude to\nmelt out of a snowball state.", "category": "astro-ph_EP" }, { "text": "Modeling Self-Subtraction in Angular Differential Imaging: Application\n to the HD 32297 Debris Disk: We present a new technique for forward-modeling self-subtraction of spatially\nextended emission in observations processed with angular differential imaging\n(ADI) algorithms. High-contrast direct imaging of circumstellar disks is\nlimited by quasi-static speckle noise and ADI is commonly used to suppress\nthose speckles. However, the application of ADI can result in self-subtraction\nof the disk signal due to the disk's finite spatial extent. This signal\nattenuation varies with radial separation and biases measurements of the disk's\nsurface brightness, thereby compromising inferences regarding the physical\nprocesses responsible for the dust distribution. To compensate for this\nattenuation, we forward-model the disk structure and compute the form of the\nself-subtraction function at each separation. As a proof of concept, we apply\nour method to 1.6 and 2.2 micron Keck AO NIRC2 scattered-light observations of\nthe HD 32297 debris disk reduced using a variant of the \"locally optimized\ncombination of images\" (LOCI) algorithm. We are able to recover disk surface\nbrightness that was otherwise lost to self-subtraction and produce simplified\nmodels of the brightness distribution as it appears with and without\nself-subtraction. From the latter models, we extract radial profiles for the\ndisk's brightness, width, midplane position, and color that are unbiased by\nself-subtraction. Our analysis of these measurements indicates a break in the\nbrightness profile power law at r~110 AU and a disk width that increases with\nseparation from the star. We also verify disk curvature that displaces the\nmidplane by up to 30 AU towards the northwest relative to a straight fiducial\nmidplane.", "category": "astro-ph_EP" }, { "text": "Using HCO$^+$ isotopologues as tracers of gas depletion in\n protoplanetary disk gaps: The widespread rings and gaps seen in the dust continuum in protoplanetary\ndisks are sometimes accompanied by similar substructures seen in molecular line\nemission. One example is the outer gap at 100 au in AS 209, which shows that\nthe H$_{13}$CO$^+$ and C$_{18}$O emission intensities decrease along with the\ncontinuum in the gap, while the DCO$^+$ emission increases inside the gap.\n We aim to study the behavior of DCO$^+$/H$_{13}$CO$^+$ and DCO$^+$/HCO$^+$\nratios in protoplanetary disk gaps assuming the two scenarios: the gas\ndepletion follows the dust depletion and only the dust is depleted.\n We first modeled the physical disk structure using the thermo-chemical model\nANDES. This 1+1D steady-state disk model calculates the thermal balance of gas\nand dust and includes the FUV, X-rays, cosmic rays, and other ionization\nsources together with the reduced chemical network for molecular coolants.\nAfterward, this physical structure was adopted for calculations of molecular\nabundances with the extended gas-grain chemical network with deuterium\nfractionation. Ideal synthetic spectra and 0th-moment maps were produced with\nLIME.\n We are able to qualitatively reproduce the increase in the DCO$^+$ intensity\nand the decrease in the H$_{13}$CO$^+$ and C$_{18}$O intensities inside the\ndisk gap, which is qualitatively similar to what is observed in the outer AS\n209 gap. The corresponding disk model assumes that both the gas and dust are\ndepleted in the gap. The model with the gas-rich gap, where only the dust is\ndepleted, produces emission that is too bright in all HCO$^+$ isotopologues and\nC$_{18}$O.\n The DCO$^+$/H$_{13}$CO$^+$ line ratio can be used to probe gas depletion in\ndust continuum gaps outside of the CO snow line. The DCO$^+$/C$_{18}$O line\nratio shows a similar, albeit weaker, effect; however, these species can be\nobserved simultaneously with a single ALMA or NOEMA setup.", "category": "astro-ph_EP" }, { "text": "A Methane Extension to the Classical Habitable Zone: The habitable zone (HZ) is the circumstellar region where standing bodies of\nliquid water could exist on the surface of a rocky planet. Conventional\ndefinitions assume that CO2 and H2O are the only greenhouse gases. The outer\nedge of this classical N2-CO2-H2O HZ extends out to nearly 1.7 AU in our solar\nsystem, beyond which condensation and scattering by CO2 outstrip its greenhouse\ncapacity. We use a single column radiative-convective climate model to assess\nthe greenhouse effect of CH4 (10 to about 100,000 ppm) on the classical\nhabitable zone (N2-CO2-H2O) for main-sequence stars with stellar temperatures\nbetween 2,600 to 10,000 K (about A3 to M8). Assuming N2-CO2-H2O atmospheres,\nprevious studies have shown that cooler stars more effectively heat terrestrial\nplanets. However, we find that the addition of CH4 produces net greenhouse\nwarming (tens of degrees) in planets orbiting stars hotter than a mid-K (about\n4500K), whereas a prominent anti-greenhouse effect is noted for planets around\ncooler stars. We show that 10% CH4 can increase the width of the classical HZ\nof the hottest stars (TEFF = 10,000 K) by over 20%. In contrast, the CH4\nanti-greenhouse can shrink the HZ for the coolest stars (TEFF = 2,600 K) by a\nsimilar percentage. We find that dense CO2-CH4 atmospheres near the outer edge\nof hotter stars may suggest inhabitance, highlighting the importance of\nincluding secondary greenhouse gases in alternative definitions of the HZ. We\nparameterize the limits of this N2-CO2-H2O-CH4 habitable zone and discuss\nimplications in the search for extraterrestrial life.", "category": "astro-ph_EP" }, { "text": "Observational evidence for a metal rich atmosphere on the super-Earth\n GJ1214b: We report observations of two consecutive transits of the warm super-Earth\nexoplanet GJ1214b at 3.6 and 4.5 microns with the Infrared Array Camera\ninstrument on-board the Spitzer Space Telescope. The two transit light curves\nallow for the determination of the transit parameters for this system. We find\nthese paremeters to be consistent with the previously determined values and no\nevidence for transit timing variations. The main investigation consists of\nmeasuring the transit depths in each bandpass to constrain the planet's\ntransmission spectrum. Fixing the system scale and impact parameters, we\nmeasure R_p/R_star=0.1176 (+0.0008/-0.0009) and 0.1163 (+0.0010/-0.0008) at 3.6\nand 4.5 microns, respectively. Combining these data with the previously\nreported MEarth Observatory measurements in the red optical yields constraints\non the GJ1214b's transmission spectrum and allows us to rule-out a cloud-free,\nsolar composition (i.e., hydrogen-dominated) atmosphere at 4.5 sigma\nconfidence. This independently confirms a recent finding that was based on a\nmeasurement of the planet's transmission spectrum using the VLT. The Spitzer,\nMEarth, and VLT observations together yield a remarkably flat transmission\nspectrum over the large wavelength domain spanned by the data. Consequently,\ncloud-free atmospheric models require more than 30% metals (assumed to be in\nthe form of H2O by volume to be consistent with all the observations.", "category": "astro-ph_EP" }, { "text": "The Effect of Composition on the Evolution of Giant and\n Intermediate-Mass Planets: We model the evolution of planets with various masses and compositions. We\ninvestigate the effects of the composition and its depth dependence on the\nlong-term evolution of the planets. The effects of opacity and stellar\nirradiation are also considered. It is shown that the change in radius due to\nvarious compositions can be significantly smaller than the change in radius\ncaused by the opacity. Irradiation also affects the planetary contraction but\nis found to be less important than the opacity effects. We suggest that the\nmass-radius relationship used for characterization of observed extrasolar\nplanets should be taken with great caution since different physical conditions\ncan result in very different mass-radius relationships.", "category": "astro-ph_EP" }, { "text": "Model atmospheres of irradiated exoplanets: The influence of stellar\n parameters, metallicity, and the C/O ratio: Many parameters constraining the spectral appearance of exoplanets are still\npoorly understood. We therefore study the properties of irradiated exoplanet\natmospheres over a wide parameter range including metallicity, C/O ratio and\nhost spectral type. We calculate a grid of 1-d radiative-convective atmospheres\nand emission spectra. We perform the calculations with our new\nPressure-Temperature Iterator and Spectral Emission Calculator for Planetary\nAtmospheres (PETIT) code, assuming chemical equilibrium. The atmospheric\nstructures and spectra are made available online. We find that atmospheres of\nplanets with C/O ratios $\\sim$ 1 and $T_{\\rm eff}$ $\\gtrsim$ 1500 K can exhibit\ninversions due to heating by the alkalis because the main coolants CH$_4$,\nH$_2$O and HCN are depleted. Therefore, temperature inversions possibly occur\nwithout the presence of additional absorbers like TiO and VO. At low\ntemperatures we find that the pressure level of the photosphere strongly\ninfluences whether the atmospheric opacity is dominated by either water (for\nlow C/O) or methane (for high C/O), or both (regardless of the C/O). For hot,\ncarbon-rich objects this pressure level governs whether the atmosphere is\ndominated by methane or HCN. Further we find that host stars of late spectral\ntype lead to planetary atmospheres which have shallower, more isothermal\ntemperature profiles. In agreement with prior work we find that for planets\nwith $T_{\\rm eff}$ $<$ 1750 K the transition between water or methane dominated\nspectra occurs at C/O $\\sim$ 0.7, instead of $\\sim$ 1, because condensation\npreferentially removes oxygen.", "category": "astro-ph_EP" }, { "text": "Detection of Earth-mass and Super-Earth Trojan Planets Using Transit\n Timing Variation Method: We have carried out an extensive study of the possibility of the detection of\nEarth-mass and super-Earth Trojan planets using transit timing variation method\nwith the Kepler space telescope. We have considered a system consisting of a\ntransiting Jovian-type planet in a short period orbit, and determined the\ninduced variations in its transit timing due to an Earth-mass/super-Earth\nTrojan planet. We mapped a large section of the phase space around the 1:1\nmean-motion resonance and identified regions corresponding to several other\nmean-motion resonances where the orbit of the planet would be stable. We\ncalculated TTVs for different values of the mass and orbital elements of the\ntransiting and perturbing bodies as well as the mass of central star, and\nidentified orbital configurations of these objects (ranges of their orbital\nelements and masses) for which the resulted TTVs would be within the range of\nthe variations of the transit timing of Kepler's planetary candidates. Results\nof our study indicate that in general, the amplitudes of the TTVs fall within\nthe detectable range of timing precision obtained from the Kepler's\nlong-cadence data, and depending on the parameters of the system, their\nmagnitudes may become as large as a few hours. The probability of detection is\nhigher for super-Earth Trojans with slightly eccentric orbits around\nshort-period Jovian-type planets with masses slightly smaller than Jupiter. We\npresent the details of our study and discuss the implications of its results.", "category": "astro-ph_EP" }, { "text": "New Nomenclature Rules for Meteor Showers Adopted: The Shower Database (SD) of the Meteor Data Center (MDC) had been operating\non the basis of stream-naming rules which were too complex and insufficiently\nprecise for 15 years. With a gradual increase in the number of discovered\nmeteor showers, the procedure for submitting new showers to the database and\nnaming them lead to situations that were inconsistent with the fundamental role\nof the SD - the disambiguation of stream names in the scientific literature.\nOur aim is to simplify the meteor shower nomenclature rules. We propose a much\nsimpler set of meteor shower nomenclature rules, based on a two-stage approach,\nsimilar to those used in the case of asteroids. The first stage applies to a\nnew shower just after its discovery. The second stage concerns the repeatedly\nobserved shower, the existence of which no longer raises any doubts. Our\nproposed new procedure was approved by a vote of the commission F1 of the IAU\nin July 2022.", "category": "astro-ph_EP" }, { "text": "The weird and the wonderful in our Solar System: Searching for\n serendipity in the Legacy Survey of Space and Time: We present a novel method for anomaly detection in Solar System object data,\nin preparation for the Legacy Survey of Space and Time. We train a deep\nautoencoder for anomaly detection and use the learned latent space to search\nfor other interesting objects. We demonstrate the efficacy of the autoencoder\napproach by finding interesting examples, such as interstellar objects, and\nshow that using the autoencoder, further examples of interesting classes can be\nfound. We also investigate the limits of classic unsupervised approaches to\nanomaly detection through the generation of synthetic anomalies and evaluate\nthe feasibility of using a supervised learning approach. Future work should\nconsider expanding the feature space to increase the variety of anomalies that\ncan be uncovered during the survey using an autoencoder.", "category": "astro-ph_EP" }, { "text": "A Comprehensive Dust Model Applied to the Resolved Beta Pictoris Debris\n Disk from Optical to Radio Wavelengths: We investigate whether varying the dust composition (described by the optical\nconstants) can solve a persistent problem in debris disk modeling--the\ninability to fit the thermal emission without over-predicting the scattered\nlight. We model five images of the beta Pictoris disk: two in scattered light\nfrom HST/STIS at 0.58 microns and HST/WFC3 at 1.16 microns, and three in\nthermal emission from Spitzer/MIPS at 24 microns, Herschel/PACS at 70 microns,\nand ALMA at 870 microns. The WFC3 and MIPS data are published here for the\nfirst time. We focus our modeling on the outer part of this disk, consisting of\na parent body ring and a halo of small grains. First, we confirm that a model\nusing astronomical silicates cannot simultaneously fit the thermal and\nscattered light data. Next, we use a simple, generic function for the optical\nconstants to show that varying the dust composition can improve the fit\nsubstantially. Finally, we model the dust as a mixture of the most plausible\ndebris constituents: astronomical silicates, water ice, organic refractory\nmaterial, and vacuum. We achieve a good fit to all datasets with grains\ncomposed predominantly of silicates and organics, while ice and vacuum are, at\nmost, present in small amounts. This composition is similar to one derived from\nprevious work on the HR 4796A disk. Our model also fits the thermal SED,\nscattered light colors, and high-resolution mid-IR data from T-ReCS for this\ndisk. Additionally, we show that sub-blowout grains are a necessary component\nof the halo.", "category": "astro-ph_EP" }, { "text": "TEM analyses of in situ presolar grains from unequilibrated ordinary\n chondrite LL3.0 Semarkona: We investigated six presolar grains from very primitive regions of the matrix\nin the unequilibrated ordinary chondrite Semarkona with TEM. These grains\ninclude one SiC, one oxide (Mg-Al spinel), and four silicates. Structural and\nelemental compositional studies of presolar grains located within their\nmeteorite hosts have the potential to provide information on conditions and\nprocesses throughout the grains' histories. Our analyses show that the SiC and\nspinel grains are stoichiometric and well crystallized. In contrast, the\nmajority of the silicate grains are non-stoichiometric and poorly crystallized.\nThese findings are consistent with previous TEM studies of presolar grains from\ninterplanetary dust particles and chondritic meteorites. We interpret the\npoorly crystalline nature, non-stoichiometry, more Fe- rather than Mg-rich\ncompositions, and/or compositional heterogeneities as features of the formation\nby condensation under non-equilibrium conditions. Evidence for parent body\nalteration includes rims with mobile elements (S or Fe) on the SiC grain and\none silicate grain. Other features characteristic of secondary processing in\nthe interstellar medium, the solar nebula, and/or on parent bodies, were not\nobserved or are better explained by processes operating in circumstellar\nenvelopes. In general, there was very little overprinting of primary features\nof the presolar grains by secondary processes (e.g., ion irradiation,\ngrain-grain collisions, thermal metamorphism, aqueous alteration). This finding\nunderlines the need for additional TEM studies of presolar grains located in\nthe primitive matrix regions of Semarkona, to address gaps in our knowledge of\npresolar grain populations accreted to ordinary chondrites.", "category": "astro-ph_EP" }, { "text": "Synergies between Asteroseismology and Exoplanetary Science: Over the past decade asteroseismology has become a powerful method to\nsystematically characterize host stars and dynamical architectures of exoplanet\nsystems. In this contribution I review current key synergies between\nasteroseismology and exoplanetary science such as the precise determination of\nplanet radii and ages, the measurement of orbital eccentricities, stellar\nobliquities and their impact on hot Jupiter formation theories, and the\nimportance of asteroseismology on spectroscopic analyses of exoplanet hosts. I\nalso give an outlook on future synergies such as the characterization of\nsub-Neptune-size planets orbiting solar-type stars, the study of planet\npopulations orbiting evolved stars, and the determination of ages of\nintermediate-mass stars hosting directly imaged planets.", "category": "astro-ph_EP" }, { "text": "Studying wave optics in the light curve of exoplanet microlensing: We study the wave optics features of gravitational microlensing by a binary\nlens composed of a planet and a parent star. In this system, the source star\nnear the caustic line produces a pair of images in which they can play the role\nof secondary sources for the observer. This optical system is similar to the\nYoung double-slit experiment. The coherent wave fronts from a source on the\nlens plane can form diffraction pattern on the observer plane. This diffraction\npattern has two modes from the close- and wide-pair images. From the\nobservational point of view, we study the possibility of detecting this effect\nthrough the Square Kilometer Array (SKA) project in the resonance and high\nmagnification channels of binary lensing. While the red giant sources do not\nseem satisfy the spatial coherency condition, during the caustic crossing, a\nsmall part of source traversing the caustic line can produce coherent pair\nimages. Observations of wave optics effect in the longer wavelengths\naccompanied by optical observations of a microlensing event provide extra\ninformation from the parameter space of the planet. These observations can\nprovide a new basis for study of exoplanets.", "category": "astro-ph_EP" }, { "text": "Finding Long Lost Lexell's Comet: The Fate of the First Discovered\n Near-Earth Object: Jupiter-family Comet D/1770 L1 (Lexell) was the first discovered Near-Earth\nObject (NEO), and passed the Earth on 1770 Jul 1 at a recorded distance of\n0.015 au. The comet was subsequently lost due to unfavorable observing\ncircumstances during its next apparition followed by a close encounter with\nJupiter in 1779. Since then, the fate of D/Lexell has attracted interest from\nthe scientific community, and now we revisit this long-standing question. We\ninvestigate the dynamical evolution of D/Lexell based on a set of orbits\nrecalculated using the observations made by Charles Messier, the comet's\ndiscoverer, and find that there is a $98\\%$ chance that D/Lexell remains in the\nSolar System by the year of 2000. This finding remains valid even if a moderate\nnon-gravitational effect is imposed. Messier's observations also suggest that\nthe comet is one of the largest known near-Earth comets, with a nucleus of\n$\\gtrsim 10$ km in diameter. This implies that the comet should have been\ndetected by contemporary NEO surveys regardless of its activity level if it has\nremained in the inner Solar System. We identify asteroid 2010 JL$_{33}$ as a\npossible descendant of D/Lexell, with a $0.8\\%$ probability of chance\nalignment, but a direct orbital linkage of the two bodies has not been\nsuccessfully accomplished. We also use the recalculated orbit to investigate\nthe meteors potentially originating from D/Lexell. While no associated meteors\nhave been unambiguously detected, we show that meteor observations can be used\nto better constrain the orbit of D/Lexell despite the comet being long lost.", "category": "astro-ph_EP" }, { "text": "A Wideband Self-Consistent Disk-Averaged Spectrum of Jupiter Near 30 GHz\n and Its Implications for NH$_{3}$ Saturation in the Upper Troposphere: We present a new set of measurements obtained with the Combined Array for\nResearch in Millimeter-wave Astronomy (CARMA) of Jupiter's microwave thermal\nemission near the 1.3 cm ammonia (NH$_{3}$) absorption band. We use these\nobservations to investigate the ammonia mole fraction in the upper troposphere,\nnear $0.3 < P < 2$ bar, based on radiative transfer modeling. We find that the\nammonia mole fraction must be $\\sim2.4\\times 10^{-4}$ below the NH$_{3}$ ice\ncloud, i.e., at $0.8 < P < 8$ bar, in agreement with results by de Pater et al.\n(2001, 2016a). We find the NH$_{3}$ cloud-forming region between $0.3 < P <\n0.8$ bar to be globally sub-saturated by 55% on average, in accordance with the\nresult in Gibson et al. (2005). Although our data are not very sensitive to the\nregion above the cloud layer, we are able to set an upper limit of $2.4\\times\n10^{-7}$ on the mole fraction here, a factor of $\\sim$10 above the saturated\nvapor curve.", "category": "astro-ph_EP" }, { "text": "Astrometry of the main satellites of Uranus: 18 years of observations: We determine accurate positions of the main satellites of Uranus: Miranda,\nAriel, Umbriel, Titania, and Oberon. Positions of Uranus, as derived from those\nof these satellites, are also determined. The observational period spans from\n1992 to 2011. All runs were made at the Pico dos Dias Observatory, Brazil.\n We used the software called Platform for Reduction of Astronomical Images\nAutomatically (PRAIA) to minimise (digital coronography) the influence of the\nscattered light of Uranus on the astrometric measurements and to determine\naccurate positions of the main satellites. The positions of Uranus were then\nindirectly determined by computing the mean differences between the observed\nand ephemeris positions of these satellites. A series of numerical filters was\napplied to filter out spurious data. These filters are mostly based on the\ncomparison between the positions of Oberon with those of the other satellites\nand on the offsets as given by the differences between the observed and\nephemeris positions of all satellites.\n We have, for the overall offsets of the five satellites, -29 (+/-63) mas in\nright ascension and -27 (+/-46) mas in declination. For the overall difference\nbetween the offsets of Oberon and those of the other satellites, we have +3\n(+/-30) mas in right ascension and -2 (+/-28) mas in declination. Ephemeris\npositions for the satellites were determined from DE432+ura111. Comparisons\nusing other modern ephemerides for the solar system -INPOP13c- and for the\nmotion of the satellites -NOE-7-2013- were also made. They confirm that the\nlargest contribution to the offsets we find comes from the motion of the\nbarycenter of the Uranus system around the barycenter of the solar system, as\ngiven by the planetary ephemerides. Catalogues with the observed positions are\nprovided.", "category": "astro-ph_EP" }, { "text": "HADES RV program with HARPS-N at TNG. IX. A super-Earth around the M\n dwarf Gl686: The HArps-n red Dwarf Exoplanet Survey is providing a major contribution to\nthe widening of the current statistics of low-mass planets, through the\nin-depth analysis of precise radial velocity measurements in a narrow range of\nspectral sub-types. As part of that program, we obtained radial velocity\nmeasurements of Gl 686, an M1 dwarf at d = 8.2 pc. The analysis of data\nobtained within an intensive observing campaign demonstrates that the excess\ndispersion is due to a coherent signal, with a period of 15.53 d. Almost\nsimultaneous photometric observations were carried out within the APACHE and\nEXORAP programs to characterize the stellar activity and to distinguish\nperiodic variations related to activity from signals due to the presence of\nplanetary companions, complemented also with ASAS photometric data. We took\nadvantage of the available radial velocity measurements for this target from\nother observing campaigns. The analysis of the radial velocity composite time\nseries from the HIRES, HARPS and HARPS-N spectrographs, consisting of 198\nmeasurements taken over 20 years, enabled us to address the nature of periodic\nsignals and also to characterize stellar physical parameters (mass,\ntemperature, and rotation). We report the discovery of a super-Earth orbiting\nat a distance of 0.092 AU from the host star Gl 686. Gl 686 b has a minimum\nmass of 7.1 +/- 0.9 MEarth and an orbital period of 15.532 +/- 0.002 d. The\nanalysis of the activity indexes, correlated noise through a Gaussian process\nframework and photometry, provides an estimate of the stellar rotation period\nat 37 d, and highlights the variability of the spot configuration during the\nlong timespan covering 20 yrs. The observed periodicities around 2000 d likely\npoint to the existence of an activity cycle.", "category": "astro-ph_EP" }, { "text": "Imaging polarimetry of Comet C/2012 L2 (LINEAR): We present the polarimetric results and analysis of comet C/2012 L2 (LINEAR)\nobserved at 31$^\\circ$.1 phase angle before perihelion passage. The\nobservations of the comet were carried out using ARIES Imaging Polarimeter\n(AIMPOL) mounted on the 1.04-m Sampurnanand telescope of ARIES, Nainital, India\non 11 and 12 March, 2013 using R photometric band ($\\lambda$ = 630 nm,\n$\\Delta$$\\lambda$ =120nm). The extended coma of the comet ($\\sim65000$ km)\nshows a significant variation in the intensity as well as polarization profile\nin all considered directions which suggest that the dust particles originate\nfrom the active areas of the nucleus. The elongation of the coma is prominent\nalong the Sun-comet position angle. The polarization of Comet C/2012 L2\n(LINEAR) does not show steep radial dependence on the aperture size during both\nthe nights of observation. A jet extended in the antisolar direction is well\nobserved in both intensity and polarization map.", "category": "astro-ph_EP" }, { "text": "Bouncing on Titan: Motion of the Huygens Probe in the Seconds After\n Landing: While landing on Titan, several instruments onboard Huygens acquired\nmeasurements that indicate the probe did not immediately come to rest. Detailed\nknowledge of the probe's motion can provide insight into the nature of Titan's\nsurface. Combining accelerometer data from the Huygens Atmospheric Structure\nInstrument (HASI) and the Surface Science Package (SSP) with photometry data\nfrom the Descent Imager/Spectral Radiometer (DISR) we develop a quantitative\nmodel to describe motion of the probe, and its interaction with the surface.\nThe most likely scenario is the following. Upon impact, Huygens created a 12 cm\ndeep hole in the surface of Titan. It bounced back, out of the hole onto the\nflat surface, after which it commenced a 30-40 cm long slide in the southward\ndirection. The slide ended with the probe out of balance, tilted in the\ndirection of DISR by around 10 degrees. The probe then wobbled back and forth\nfive times in the north-south direction, during which it probably encountered a\n1-2 cm sized pebble. The SSP provides evidence for movement up to 10 s after\nimpact. This scenario puts the following constraints on the physical properties\nof the surface. For the slide over the surface we determine a friction\ncoefficient of 0.4. While this value is not necessarily representative for the\nsurface itself due to the presence of protruding structures on the bottom of\nthe probe, the dynamics appear to be consistent with a surface consistency of\ndamp sand. Additionally, we find that spectral changes observed in the first\nfour seconds after landing are consistent with a transient dust cloud, created\nby the impact of the turbulent wake behind the probe on the surface. The\noptical properties of the dust particles are consistent with those of Titan\naerosols from Tomasko et al. (P&SS 56, 669). We suggest that the surface at the\nlanding site was covered by a dust layer, possibly the 7 mm layer of...", "category": "astro-ph_EP" }, { "text": "Detection of acoustic-gravity waves in lower ionosphere by VLF radio\n waves: We present a new method to study harmonic waves in the low ionosphere (60 -\n90 km) by detecting their effects on reflection of very low frequency (VLF)\nradio waves. Our procedure is based on amplitude analysis of reflected VLF\nradio waves recorded in real time, which yields an insight into the dynamics of\nthe ionosphere at heights where VLF radio waves are being reflected. The method\nwas applied to perturbations induced by the solar terminator motions at\nsunrises and sunsets. The obtained results show that typical perturbation\nfrequencies found to exist in higher regions of the atmosphere are also present\nin the lower ionosphere, which indicates a global nature of the considered\noscillations. In our model atmosphere, they turn out to be the acoustic and\ngravity waves with comparatively short and long periods, respectively.", "category": "astro-ph_EP" }, { "text": "Proton and antiproton modulation in the heliosphere for different solar\n conditions and AMS-02 measurements prediction: Galactic Cosmic Rays (GCRs) are mainly protons confined in the galactic\nmagnetic field to form an isotropic flux inside the galaxy. Before reaching the\nEarth orbit they enter the Heliosphere and undergo diffusion, convection,\nmagnetic drift and adiabatic energy loss. The result is a reduction of\nparticles flux at low energy (below 10 GeV), called solar modulation. We\nrealized a quasi time-dependent 2D Stochastic Simulation of Solar Modulation\nthat is able to reproduce CR spectra once known the Local Interstellar Spectrum\n(LIS). We were able to estimate the different behaviors associated to the\npolarity dependence of the Heliospheric modulation for particles as well as for\nantiparticles. We show a good agreement with the antiproton/proton ratio\nmeasured by AMS-01, Pamela, BESS, Heat and Caprice and we performed a\nprediction for the AMS-02 Experiment.", "category": "astro-ph_EP" }, { "text": "Particle-Particle Particle-Tree: A Direct-Tree Hybrid Scheme for\n Collisional N-Body Simulations: In this paper, we present a new hybrid algorithm for the time integration of\ncollisional N-body systems. In this algorithm, gravitational force between two\nparticles is divided into short-range and long-range terms, using a\ndistance-dependent cutoff function. The long-range interaction is calculated\nusing the tree algorithm and integrated with the constant-timestep leapfrog\nintegrator. The short-range term is calculated directly and integrated with the\nhigh-order Hermite scheme. We can reduce the calculation cost per orbital\nperiod from O(N^2) to O(N log N), without significantly increasing the\nlong-term integration error. The results of our test simulations show that\nclose encounters are integrated accurately. Long-term errors of the total\nenergy shows random-walk behaviour, because it is dominated by the error caused\nby tree approximation.", "category": "astro-ph_EP" }, { "text": "Hydrodynamic outcomes of planet scattering in transitional discs: A significant fraction of unstable multiple planet systems likely scatter\nduring the transitional disc phase as gas damping becomes ineffectual. Using an\nensemble of FARGO hydrodynamic simulations and MERCURY n-body integrations, we\ndirectly follow planet-disc and planet-planet interactions through the clearing\nphase and on through 50 Myr of dynamical evolution. Disc clearing occurs via\nX-ray driven photoevaporation. The hydrodynamic evolution of individual\nscattering systems is complex, and involves phases in which massive planets\norbit within eccentric gaps, or accrete directly from the disc without a gap.\nComparing the results to a gas-free model, we find that the n-body dynamics and\nhydrodynamics of scattering into one- and two-planet final states are almost\nidentical. The eccentricity distributions in these channels are almost\nunaltered by the presence of gas. The hydrodynamic simulations, however, also\nform low eccentricity three-planet systems in long-term stable configurations,\nand the admixture of these systems results in modestly lower eccentricities in\nhydrodynamic as opposed to gas-free simulations. The incidence of these\nthree-planet systems is likely a function of the initial conditions; different\nplanet setups (number or spacing) may change the character of this result. We\nanalyze the properties of surviving multiple planet systems, and show that only\na small fraction (a few percent) enter mean-motion resonances after scattering,\nwhile a larger fraction form stable resonant chains and avoid scattering\nentirely. Our results remain consistent with the hypothesis that exoplanet\neccentricity results from scattering, though the detailed agreement between\nobservations and gas-free simulation results is likely coincidental. We discuss\nthe prospects for testing scattering models by observing planets or\nnon-axisymmetric gas structure in transitional discs.", "category": "astro-ph_EP" }, { "text": "Apsidal asymmetric-alignment of Jupiter Trojans: The most distant Kuiper belt objects exhibit the clustering in their orbits,\nand this anomalous architecture could be caused by Planet 9 with large\neccentricity and high inclination. We then suppose that the orbital clustering\nof minor planets may be observed somewhere else in the solar system. In this\npaper, we consider the over 7000 Jupiter Trojans from the Minor Planet Center,\nand find that they are clustered in the longitude of perihelion $\\varpi$,\naround the locations $\\varpi_{\\mbox{{J}}}+60^{\\circ}$ and\n$\\varpi_{\\mbox{{J}}}-60^{\\circ}$ ($\\varpi_{\\mbox{{J}}}$ is the longitude of\nperihelion of Jupiter) for the L4 and L5 swarms, respectively. Then we build a\nHamiltonian system to describe the associated dynamical aspects for the\nco-orbital motion. The phase space displays the existence of the apsidally\naligned islands of libration centered on\n$\\Delta\\varpi=\\varpi-\\varpi_{\\mbox{{J}}}\\approx\\pm60^{\\circ}$, for the\nTrojan-like orbits with eccentricities $e<0.1$. Through a detailed analysis, we\nhave shown that the observed Jupiter Trojans with proper eccentricities\n$e_p<0.1$ spend most of their time in the range of\n$|\\Delta\\varpi|=0-120^{\\circ}$, while the more eccentric ones with $e_p>0.1$\nare too few to affect the orbital clustering within this $\\Delta\\varpi$ range\nfor the entire Trojan population. Our numerical results further prove that,\neven starting from a uniform $\\Delta\\varpi$ distribution, the apsidal alignment\nof simulated Trojans similar to the observation can appear on the order of the\nage of the solar system. We conclude that the apsidal asymmetric-alignment of\nJupiter Trojans is robust, and this new finding can be helpful to design the\nsurvey strategy in the future.", "category": "astro-ph_EP" }, { "text": "K2-106, a system containing a metal-rich planet and a planet of lower\n density: Planets in the mass range from 2 to 15 MEarth are very diverse. Some of them\nhave low densities, while others are very dense. By measuring the masses and\nradii, the mean densities, structure, and composition of the planets are\nconstrained. These parameters also give us important information about their\nformation and evolution, and about possible processes for atmospheric loss.We\ndetermined the masses, radii, and mean densities for the two transiting planets\norbiting K2-106. The inner planet has an ultra-short period of 0.57 days. The\nperiod of the outer planet is 13.3 days.Although the two planets have similar\nmasses, their densities are very different. For K2-106b we derive\nMb=8.36-0.94+0.96 MEarh, Rb=1.52+/-0.16 REarth, and a high density of\n13.1-3.6+5.4 gcm-3. For K2-106c, we find Mc=5.8-3.0+3.3 MEarth,\nRc=2.50-0.26+0.27 REarth and a relatively low density of 2.0-1.1+1.6\ngcm-3.Since the system contains two planets of almost the same mass, but\ndifferent distances from the host star, it is an excellent laboratory to study\natmospheric escape. In agreement with the theory of atmospheric-loss processes,\nit is likely that the outer planet has a hydrogen-dominated atmosphere. The\nmass and radius of the inner planet is in agreement with theoretical models\npredicting an iron core containing 80+20-30% of its mass. Such a high metal\ncontent is surprising, particularly given that the star has an ordinary (solar)\nmetal abundance. We discuss various possible formation scenarios for this\nunusual planet.", "category": "astro-ph_EP" }, { "text": "Molecular abundances and C/O ratios in chemically evolving\n planet-forming disk midplanes: (Abridged) Exoplanet atmospheres are thought be built up from accretion of\ngas as well as pebbles and planetesimals in the midplanes of planet-forming\ndisks. The chemical composition of this material is usually assumed to be\nunchanged during the disk lifetime. However, chemistry can alter the relative\nabundances of molecules in this planet-building material. To assess the impact\nof disk chemistry during the era of planet formation, an extensive kinetic\nchemistry gas-grain reaction network is utilised to evolve the abundances of\nchemical species over time. Given a high level of ionisation, chemical\nevolution in protoplanetary disk midplanes becomes significant after a few\ntimes $10^{5}$ yrs, and is still ongoing by 7 Myr between the H$_{2}$O and the\nO$_{2}$ icelines. Importantly, the changes in the abundances of the major\nelemental carbon and oxygen-bearing molecules imply that the traditional\n\"stepfunction\" for the C/O ratios in gas and ice in the disk midplane (as\ndefined by sharp changes at icelines of H$_{2}$O, CO$_{2}$ and CO) evolves over\ntime, and cannot be assumed fixed. In addition, at lower temperatures (< 29 K),\ngaseous CO colliding with the grains gets converted into CO$_{2}$ and other\nmore complex ices, lowering the CO gas abundance between the O$_{2}$ and CO\nthermal icelines. This effect can mimic a CO iceline at a higher temperature\nthan suggested by its binding energy. Chemistry in the disk midplane is\nionisation-driven, and evolves over time. In order to reliably predict the\natmospheric compositions of forming planets, as well as to relate observed\natmospheric C/O ratios of exoplanets to where and how the atmospheres have\nformed in a disk midplane, chemical evolution needs to be considered and\nimplemented into planet formation models.", "category": "astro-ph_EP" }, { "text": "Ephemeris Updates for Seven Selected HATNet Survey Transiting Exoplanets: We refined the ephemeris of seven transiting exoplanets HAT-P-6b, HAT-P-12b,\nHAT-P-18b, HAT-P-22b, HAT-P-32b, HAT-P-33b, and HAT-P-52b. We observed 11\ntransits from eight observatories in different filters for HAT-P-6b and\nHAT-P-32b. Also, the Exoplanet Transit Database (ETD) observations for each of\nthe seven exoplanets were analyzed, and the light curves of five systems were\nstudied using Transiting light Exoplanet Survey Satellite (TESS) data. We used\nExofast-v1 to simulate these ground- and space-based light curves and estimate\nmid-transit times. We obtained a total of 11, 175 and 67 mid-transit times for\nthese seven exoplanets from our observations, ETD and TESS data, respectively,\nalong with 155 mid-transit times from the literature. Then, we generated\ntransit timing variation (TTV) diagrams for each using derived mid-transit\ntimes as well as those found in the literature. The systems' linear ephemeris\nwas then refined and improved using the Markov Chain Monte Carlo (MCMC) method.\nAll of the studied exoplanets, with the exception of the HAT-P-12b system,\ndisplayed an increasing trend in the orbital period in the TTV diagrams.", "category": "astro-ph_EP" }, { "text": "Turbulence-Induced Relative Velocity of Dust particles IV: the Collision\n Kernel: Motivated by its importance for modeling dust particle growth in\nprotoplanetary disks, we study turbulence-induced collision statistics of\ninertial particles as a function of the particle friction time, tau_p. We show\nthat turbulent clustering significantly enhances the collision rate for\nparticles of similar sizes with tau_p corresponding to the inertial range of\nthe flow. If the friction time, tau_p,h, of the larger particle is in the\ninertial range, the collision kernel per unit cross section increases with\nincreasing friction time, tau_p,l, of the smaller particle, and reaches the\nmaximum at tau_p,l = tau_p,h, where the clustering effect peaks. This feature\nis not captured by the commonly-used kernel formula, which neglects the effect\nof clustering. We argue that turbulent clustering helps alleviate the bouncing\nbarrier problem for planetesimal formation. We also investigate the collision\nvelocity statistics using a collision-rate weighting factor to account for\nhigher collision frequency for particle pairs with larger relative velocity.\nFor tau_p,h in the inertial range, the rms relative velocity with\ncollision-rate weighting is found to be invariant with tau_p,l and scales with\ntau_p,h roughly as ~ tau_p,h^(1/2). The weighting factor favors collisions with\nlarger relative velocity, and including it leads to more destructive and less\nsticking collisions. We compare two collision kernel formulations based on\nspherical and cylindrical geometries. The two formulations give consistent\nresults for the collision rate and the collision-rate weighted statistics,\nexcept that the spherical formulation predicts more head-on collisions than the\ncylindrical formulation.", "category": "astro-ph_EP" }, { "text": "Formation of the warped debris disc around $\u03b2$ Pictoris: In light of the recent confirmation of an eccentric orbit giant planet,\n$\\beta$ Pic c, I revisit the formation and evolution of the warped debris disc\nin the system. $\\beta$ Pic c is interior to $\\beta$ Pic b, and the debris disc\nis exterior to both planets. Previous $N$-body simulations have shown that\n$\\beta$ Pic b is responsible for exciting the inclination of the debris disc.\nWith hydrodynamical simulations, I model a protoplanetary gas disc misaligned\nwith the planets. I find that the gas disc does not exhibit significant long\nlasting inclination excitation from the planets even for the observed disc\nsize. The warp that is excited by the planets propagates through the entire\ndisc with a timescale much less than the gas disc lifetime. Therefore, the\nobserved warp in the debris disc must be produced after the gas disc has\ndispersed. With analytical secular theory calculations, I show that two secular\nresonances are exterior to $\\beta$ Pic b, located at $\\sim 20\\, \\rm au$ and\n$\\sim 25\\, \\rm au$. This agrees with my $N$-body simulations that show that\nthese secular resonances shape the inner edge of the $\\beta$ Pic debris disc at\na radius that agrees with observations.", "category": "astro-ph_EP" }, { "text": "Corotation torques experienced by planets embedded in weakly magnetized\n turbulent discs: The migration of low-mass planets is driven by the differential Lindblad\ntorque and the corotation torque in non-magnetic viscous models of\nprotoplanetary discs. The corotation torque has recently received detailed\nattention as it may slow down, stall, or reverse migration. In laminar viscous\ndisc models, the long-term evolution of the corotation torque is intimately\nrelated to viscous and thermal diffusion processes in the planet's horseshoe\nregion. This paper examines the properties of the corotation torque in discs\nwhere MHD turbulence develops as a result of the magnetorotational instability,\nconsidering a weak initial toroidal magnetic field. We present results of 3D\nMHD simulations carried out with two different codes. Non-ideal MHD effects and\nthe disc's vertical stratification are neglected, and locally isothermal disc\nmodels are considered. The running time-averaged torque exerted by the disc on\na fixed planet is evaluated in three disc models. We first present results with\nan inner disc cavity (planet trap). As in viscous disc models, the planet is\nfound to experience a positive running time-averaged torque over several\nhundred orbits, which highlights the existence of an unsaturated corotation\ntorque maintained in the long term in MHD turbulent discs. Two disc models with\ninitial power-law density and temperature profiles are also adopted, in which\nthe time-averaged torque is found to be in decent agreement with its\ncounterpart in laminar viscous disc models with similar viscosity at the planet\nlocation. Detailed analysis of the averaged torque density distributions\nindicates that the differential Lindblad torque takes very similar values in\nMHD turbulent and laminar viscous discs, and there exists an unsaturated\ncorotation torque in MHD turbulent discs. This analysis also reveals the\nexistence of an additional corotation torque in weakly magnetized discs.", "category": "astro-ph_EP" }, { "text": "Formation and dynamics of water clouds on temperate sub-Neptunes: The\n example of K2-18b: Hubble (HST) spectroscopic transit observations of the temperate sub-Neptune\nK2-18b were interpreted as the presence of water vapour with potential water\nclouds. 1D modelling studies also predict the formation of water clouds at some\nconditions. However, such models cannot predict the cloud cover, driven by\natmospheric dynamics and thermal contrasts, and thus their real impact on\nspectra. The main goal of this study is to understand the formation,\ndistribution and observational consequences of water clouds on K2-18b and other\ntemperate sub-Neptunes. We simulated the atmospheric dynamics, water cloud\nformation and spectra of K2-18b for H2-dominated atmosphere using a 3D GCM. We\nanalysed the impact of atmospheric composition (with metallicity from 1*solar\nto 1000*solar), concentration of cloud condensation nuclei and planetary\nrotation rate. Assuming that K2-18b has a synchronous rotation, we show that\nthe atmospheric circulation in the upper atmosphere essentially corresponds to\na symmetric day-to-night circulation. This regime preferentially leads to cloud\nformation at the substellar point or at the terminator. Clouds form for\nmetallicity >100*solar with relatively large particles. For 100-300*solar\nmetallicity, the cloud fraction at the terminators is small with a limited\nimpact on transit spectra. For 1000*solar metallicity, very thick clouds form\nat the terminator. The cloud distribution appears very sensitive to the\nconcentration of CCN and to the planetary rotation rate. Fitting HST transit\ndata with our simulated spectra suggests a metallicity of ~100-300*solar. In\naddition, we found that the cloud fraction at the terminator can be highly\nvariable, leading to a potential variability in transit spectra. This effect\ncould be common on cloudy exoplanets and could be detectable with multiple\ntransit observations.", "category": "astro-ph_EP" }, { "text": "Precise Dynamical Masses and Orbital Fits for $\u03b2$ Pic b and $\u03b2$\n Pic c: We present a comprehensive orbital analysis to the exoplanets $\\beta$\nPictoris b and c that resolves previously reported tensions between the\ndynamical and evolutionary mass constraints on $\\beta$ Pic b. We use the MCMC\norbit code orvara to fit fifteen years of radial velocities and relative\nastrometry (including recent GRAVITY measurements), absolute astrometry from\nHipparcos and Gaia, and a single relative radial velocity measurement between\n$\\beta$ Pic A and b. We measure model-independent masses of\n$9.3^{+2.6}_{-2.5}\\, M_{\\rm Jup}$ for $\\beta$ Pic b and $8.3\\pm 1.0\\,M_{\\rm\nJup}$ for $\\beta$ Pic c. These masses are robust to modest changes to the input\ndata selection. We find a well-constrained eccentricity of $0.119 \\pm 0.008$\nfor $\\beta$ Pic b, and an eccentricity of $0.21^{+0.16}_{-0.09}$ for $\\beta$\nPic c, with the two orbital planes aligned to within $\\sim$0.5$^\\circ$. Both\nplanets' masses are within $\\sim$1$\\sigma$ of the predictions of hot-start\nevolutionary models and exclude cold starts. We validate our approach on\n$N$-body synthetic data integrated using REBOUND. We show that orvara can\naccount for three-body effects in the $\\beta$ Pic system down to a level\n$\\sim$5 times smaller than the GRAVITY uncertainties. Systematics in the masses\nand orbital parameters from orvara's approximate treatment of multiplanet\norbits are a factor of $\\sim$5 smaller than the uncertainties we derive here.\nFuture GRAVITY observations will improve the constraints on $\\beta$ Pic c's\nmass and (especially) eccentricity, but improved constraints on the mass of\n$\\beta$ Pic b will likely require years of additional RV monitoring and\nimproved precision from future Gaia data releases.", "category": "astro-ph_EP" }, { "text": "Molecules with ALMA at Planet-forming Scales (MAPS) V: CO gas\n distributions: Here we present high resolution (15-24 au) observations of CO isotopologue\nlines from the Molecules with ALMA on Planet-forming Scales (MAPS) ALMA Large\nProgram. Our analysis employs $^{13}$CO and C$^{18}$O ($J$=2-1), (1-0), and\nC$^{17}$O (1-0) line observations of five protoplanetary disks. We retrieve CO\ngas density distributions, using three independent methods: (1) a\nthermo-chemical modeling framework based on the CO data, the broadband spectral\nenergy distribution, and the mm-continuum emission; (2) an empirical\ntemperature distribution based on optically thick CO lines; and (3) a direct\nfit to the C$^{17}$O hyperfine lines. Results from these methods generally show\nexcellent agreement. The CO gas column density profiles of the five disks show\nsignificant variations in the absolute value and the radial shape. Assuming a\ngas-to-dust mass ratio of 100, all five disks have a global CO-to-H$_2$\nabundance of 10-100 times lower than the ISM ratio. The CO gas distributions\nbetween 150-400 au match well with models of viscous disks, supporting the\nlong-standing theory. CO gas gaps appear to be correlated with continuum gap\nlocations, but some deep continuum gaps do not have corresponding CO gaps. The\nrelative depths of CO and dust gaps are generally consistent with predictions\nof planet-disk interactions, but some CO gaps are 5-10 times shallower than\npredictions based on dust gaps. This paper is part of the MAPS special issue of\nthe Astrophysical Journal Supplement.", "category": "astro-ph_EP" }, { "text": "The Formation of the Cold Classical Kuiper Belt by a Short Range\n Transport Mechanism: The Classical Kuiper Belt is populated by a group of objects with low\ninclination orbits, reddish colors and usually belonging to a binary system.\nThis so called Cold Classical Kuiper Belt is considered to have been formed in\nsitu from primordial ice pebbles that coagulated into planetesimals hundreds of\nkilometers in diameter. According to this scenario, the accretion of pebbles\ninto large planetesimals would have occurred through the streaming instability\nmechanism that would be effective in the primordial Solar System disk of gas\nand solids. Nevertheless other objects with the same color characteristics as\nthose found in the Cold Classical Kuiper Belt can be encountered also past the\n2:1 mean motion resonance with Neptune as scattered or detached objects. Here I\npropose a mechanism that can account for both the cold Classical Kuiper Belt\nobjects and other reddish objects outside the Classical Kuiper Belt. According\nto the proposed scenario, reddish objects were primordially in the outer\nportion of the planetesimal disk which was however truncated somewhere below 42\nau. In this manner the cold Classical Kuiper Belt and its scattered / detached\ncounterpart were respectively transported outwards by a short range or slightly\nscattered to their present locations. Resonant objects were also formed by the\nsame process. This mechanism is aimed at explaining the distribution of all\nobjects that share the same color characteristics as coming from a common\norigin in the outer borders of the primordial planetesimal disk. According to\nthe scenario here proposed the Cold Classical Kuiper Belt would have been\nformed around 4 au inside its present location with a total mass 20 to 100\ntimes as large as its present value.", "category": "astro-ph_EP" }, { "text": "Star Hoppers: Planet Instability and Capture in Evolving Binary Systems: Many planets are observed in stellar binary systems, and their frequency may\nbe comparable to that of planetary systems around single stars. Binary stellar\nevolution in such systems influences the dynamical evolution of the resident\nplanets. Here we study the evolution of a single planet orbiting one star in an\nevolving binary system. We find that stellar evolution can trigger dynamical\ninstabilities that drive planets into chaotic orbits. This instability leads to\nplanet-star collisions, exchange of the planet between the binary stars\n(\"star-hoppers\"), and ejection of the planet from the system. The means by\nwhich planets can be recaptured is similar to the pull-down capture mechanism\nfor irregular solar system satellites. Because planets often suffer close\nencounters with the primary on the asymptotic giant branch, captures during a\ncollision with the stellar envelope are also possible. Such capture could\npopulate the habitable zone around white dwarfs.", "category": "astro-ph_EP" }, { "text": "The future lifespan of Earth's oxygenated Atmosphere: Earth's modern atmosphere is highly oxygenated and is a remotely detectable\nsignal of its surface biosphere. However, the lifespan of oxygen-based\nbiosignatures in Earth's atmosphere remains uncertain, particularly for the\ndistant future. Here we use a combined biogeochemistry and climate model to\nexamine the likely timescale of oxygen-rich atmospheric conditions on Earth.\nUsing a stochastic approach, we find that the mean future lifespan of Earth's\natmosphere with oxygen levels more than 1% of the present atmospheric level is\n1.08+-0.14 billion years. The model projects that a deoxygenation of the\natmosphere, with atmospheric oxygen dropping sharply to levels reminiscnet of\nthe Archaean Earth, will most probably be triggered before the inception of\nmoist greenhouse conditions in Earth's climate system and before the extensive\nloss of surface water from the atmosphere. We find that future deoxygenation is\nan inevitable consequence of increasing solar fluxes, whereas its precise\ntiming is modulated by the exchange flux of reducing power between the mantle\nand the ocean-atmosphere-crust system. Our results suggest that the planetary\ncarbonate-silicate cycle will tend to lead to terminally CO2-limited biospheres\nand rapid atmospheric deoxygenation, emphasizing the need for robust\natmospheric biosignatures applicable to weakly oxygenated and anoxic exoplanet\natmospheres and highlighting the potential importance of atmospheric organic\nhaze during the terminal stages of planetary habitability.", "category": "astro-ph_EP" }, { "text": "Effects of primitive photosynthesis on Earth's early climate system: The evolution of different forms of photosynthetic life has profoundly\naltered the activity level of the biosphere, radically reshaping the\ncomposition of Earth's oceans and atmosphere over time. However, the\nmechanistic impacts of a primitive photosynthetic biosphere on Earth's early\natmospheric chemistry and climate are poorly understood. Here, we use a global\nredox balance model to explore the biogeochemical and climatological effects of\ndifferent forms of primitive photosynthesis. We find that a hybrid ecosystem of\nH2-based and Fe-based anoxygenic photoautotrophs - organisms that perform\nphotosynthesis without producing oxygen - gives rise to a strong nonlinear\namplification of Earth's methane (CH4) cycle, and would thus have represented a\ncritical component of Earth's early climate system before the advent of\noxygenic photosynthesis. Using a Monte Carlo approach, we find that a hybrid\nphotosynthetic biosphere widens the range of geochemical conditions that allow\nfor warm climate states well beyond either of these metabolic processes acting\nin isolation. Our results imply that Earth's early climate was governed by a\nnovel and poorly explored set of regulatory feedbacks linking the anoxic\nbiosphere and the coupled H, C and Fe cycles. We suggest that similar processes\nshould be considered when assessing the potential for sustained habitability on\nEarth-like planets with reducing atmospheres.", "category": "astro-ph_EP" }, { "text": "Observability of molecular species in a nitrogen dominated atmosphere\n for 55 Cancri e: One of the key goals of exoplanet science is the atmospheric characterisation\nof super-Earths. Atmospheric abundances provide insight on the formation and\nevolution of those planets and help to put our own rocky planets in context.\nObservations on 55 Cancri e point towards a N-dominated atmosphere. In this\npaper we explore this possibility, showing which will be the most abundant\ngases and observable species in emission and transmission spectroscopy of such\nan atmosphere. We use analytical arguments and observed parameters to estimate\nthe possible thermal profile of the atmosphere and test three different extreme\npossibilities. The chemistry is calculated using equilibrium calculations and\nadopting Titan's elemental abundances as a potential N-dominated atmospheric\ncomposition. We also test the effect of different N/O ratios in the atmosphere.\nEmission and transmission spectra are computed and showed with a resolution\nrelevant to future missions suitable to observe super-Earths (e.g. JWST,\nARIEL). We find that even though N$_2$ is the most abundant molecule in the\natmosphere followed by H$_2$ and CO, the transmission spectra shows strong\nfeatures of NH3 and HCN, and CO and HCN dominate emission spectra. We also show\nthat a decrease in the N/O ratio leads to stronger H2O, CO and CO2 and weaker\nNH3 and HCN features. A larger N/O is also more consistent with observations.\nOur exploration of a N-atmosphere for 55 Cancri e serve as a guide to\nunderstand such atmospheres and provide a reference for future observations.", "category": "astro-ph_EP" }, { "text": "Detectability of biosignatures in anoxic atmospheres with the James Webb\n Space Telescope: A TRAPPIST-1e case study: The James Webb Space Telescope (JWST) may be capable of finding biogenic\ngases in the atmospheres of habitable exoplanets around low mass stars.\nConsiderable attention has been given to the detectability of biogenic oxygen,\nwhich could be found using an ozone proxy, but ozone detection with JWST will\nbe extremely challenging, even for the most favorable targets. Here, we\ninvestigate the detectability of biosignatures in anoxic atmospheres analogous\nto those that likely existed on the early Earth. Arguably, such anoxic\nbiosignatures could be more prevalent than oxygen biosignatures if life exists\nelsewhere. Specifically, we simulate JWST retrievals of TRAPPIST-1e to\ndetermine whether the methane plus carbon dioxide disequilibrium biosignature\npair is detectable in transit transmission. We find that ~10 transits using the\nNear InfraRed Spectrograph (NIRSpec) prism instrument may be sufficient to\ndetect carbon dioxide and constrain methane abundances sufficiently well to\nrule out known, non-biological CH$_{4}$ production scenarios to ~90%\nconfidence. Furthermore, it might be possible to put an upper limit on carbon\nmonoxide abundances that would help rule out non-biological methane-production\nscenarios, assuming the surface biosphere would efficiently drawdown\natmospheric CO. Our results are relatively insensitive to high altitude clouds\nand instrument noise floor assumptions, although stellar heterogeneity and\nvariability may present challenges.", "category": "astro-ph_EP" }, { "text": "Can Moons Have Moons?: Each of the giant planets within the Solar System has large moons but none of\nthese moons have their own moons (which we call ${\\it submoons}$). By analogy\nwith studies of moons around short-period exoplanets, we investigate the\ntidal-dynamical stability of submoons. We find that 10 km-scale submoons can\nonly survive around large (1000 km-scale) moons on wide-separation orbits.\nTidal dissipation destabilizes the orbits of submoons around moons that are\nsmall or too close to their host planet; this is the case for most of the Solar\nSystem's moons. A handful of known moons are, however, capable of hosting\nlong-lived submoons: Saturn's moons Titan and Iapetus, Jupiter's moon Callisto,\nand Earth's Moon. Based on its inferred mass and orbital separation, the\nnewly-discovered exomoon candidate Kepler-1625b-I can in principle host a large\nsubmoon, although its stability depends on a number of unknown parameters. We\ndiscuss the possible habitability of submoons and the potential for\nsubsubmoons. The existence, or lack thereof, of submoons, may yield important\nconstraints on satellite formation and evolution in planetary systems.", "category": "astro-ph_EP" }, { "text": "On the observed clustering of major bodies in solar and extrasolar\n subsystems: Major (exo)planetary and satellite bodies seem to concentrate at intermediate\nareas of the radial distributions of all the objects present in each\n(sub)system. We prove rigorously that the secular evolution of (exo)planets and\nsatellites necessarily results in the observed intermediate accumulation of the\nmassive objects in all such subsystems. We quantify a \"middle\" as the mean of\nmean motions (orbital angular velocities) of three or more massive objects\ninvolved. Orbital evolution is expected to be halted or severely diminished\nwhen the survivors settle near mean-motion resonances and substantial\nangular-momentum transfer between bodies ceases to occur (gravitational Landau\ndamping). The dynamics is opposite in direction to what has been theorized for\nviscous and magnetized accretion disks in which gas spreads out and away from\neither side of any conceivable intermediate area. The results are bound to\nchange the way we think about planet and moon formation and evolution.", "category": "astro-ph_EP" }, { "text": "Bouncing on Titan: Motion of the Huygens Probe in the Seconds After\n Landing: While landing on Titan, several instruments onboard Huygens acquired\nmeasurements that indicate the probe did not immediately come to rest. Detailed\nknowledge of the probe's motion can provide insight into the nature of Titan's\nsurface. Combining accelerometer data from the Huygens Atmospheric Structure\nInstrument (HASI) and the Surface Science Package (SSP) with photometry data\nfrom the Descent Imager/Spectral Radiometer (DISR) we develop a quantitative\nmodel to describe motion of the probe, and its interaction with the surface.\nThe most likely scenario is the following. Upon impact, Huygens created a 12 cm\ndeep hole in the surface of Titan. It bounced back, out of the hole onto the\nflat surface, after which it commenced a 30-40 cm long slide in the southward\ndirection. The slide ended with the probe out of balance, tilted in the\ndirection of DISR by around 10 degrees. The probe then wobbled back and forth\nfive times in the north-south direction, during which it probably encountered a\n1-2 cm sized pebble. The SSP provides evidence for movement up to 10 s after\nimpact. This scenario puts the following constraints on the physical properties\nof the surface. For the slide over the surface we determine a friction\ncoefficient of 0.4. While this value is not necessarily representative for the\nsurface itself due to the presence of protruding structures on the bottom of\nthe probe, the dynamics appear to be consistent with a surface consistency of\ndamp sand. Additionally, we find that spectral changes observed in the first\nfour seconds after landing are consistent with a transient dust cloud, created\nby the impact of the turbulent wake behind the probe on the surface. The\noptical properties of the dust particles are consistent with those of Titan\naerosols from Tomasko et al. (P&SS 56, 669). We suggest that the surface at the\nlanding site was covered by a dust layer, possibly the 7 mm layer of...", "category": "astro-ph_EP" }, { "text": "A statistical search for a population of Exo-Trojans in the Kepler\n dataset: Trojans are small bodies in planetary Lagrangian points. In our solar system,\nJupiter has the largest number of such companions. Their existence is assumed\nfor exoplanetary systems as well, but none has been found so far. We present an\nanalysis by super-stacking $\\sim4\\times10^4$ Kepler planets with a total of\n$\\sim9\\times10^5$ transits, searching for an average trojan transit dip. Our\nresult gives an upper limit to the average Trojan transiting area (per planet)\ncorresponding to one body of radius $<460$km at $2\\sigma$ confidence. We find a\nsignificant Trojan-like signal in a sub-sample for planets with more (or\nlarger) Trojans for periods $>$60 days. Our tentative results can and should be\nchecked with improved data from future missions like PLATO2.0, and can guide\nplanetary formation theories.", "category": "astro-ph_EP" }, { "text": "A Detailed Investigation of the Proposed NN Serpentis Planetary System: The post-main sequence eclipsing binary NN Serpentis was recently announced\nas the potential host of at least two massive planetary companions. In that\nwork, the authors put forward two potential architectures that fit the\nobservations of the eclipsing binary with almost identical precision. In this\nwork, we present the results of a dynamical investigation of the orbital\nstability of both proposed system architectures, finding that they are only\nstable for scenarios in which the planets are locked in mutual mean motion\nresonance. In the discovery work, the authors artificially fixed the orbital\neccentricity of the more massive planet, NN Ser(AB) c, at 0. Here, we reanalyse\nthe observational data on NN Serpentis without this artificial constraint, and\nderive a new orbital solution for the two proposed planets. We detail the\nresults of further dynamical simulations investigating the stability of our new\norbital solution, and find that allowing a small non-zero eccentricity for the\nouter planet renders the system unstable. We conclude that, although the\noriginal orbits proposed for the NN Serpentis planetary system prove\ndynamically feasible, further observations of the system are vital in order to\nbetter constrain the system's true architecture.", "category": "astro-ph_EP" }, { "text": "Planets Around Low-Mass Stars (PALMS). IV. The Outer Architecture of M\n Dwarf Planetary Systems: We present results from a high-contrast adaptive optics imaging search for\ngiant planets and brown dwarfs (>1 MJup) around 122 newly identified nearby\n(<40 pc) young M dwarfs. Half of our targets are younger than 135 Myr and 90%\nare younger than the Hyades (620 Myr). Our H- and K-band coronagraphic\nobservations with Keck/NIRC2 and Subaru/HiCIAO achieve typical contrasts of\n12-14 mag and 9-13 mag at 1\", respectively, which corresponds to limiting\nplanet masses of 0.5-10 MJup at 5-33 AU for 85% of our sample. We discovered\nfour young brown dwarf companions: 1RXS J235133.3+312720 B (32 $\\pm$ 6 MJup;\nL0$^{+2}_{-1}$; 120 $\\pm$ 20 AU), GJ 3629 B (64$^{+30}_{-23}$ MJup; M7.5 $\\pm$\n0.5; 6.5 $\\pm$ 0.5 AU), 1RXS J034231.8+121622 B (35 $\\pm$ 8 MJup; L0 $\\pm$ 1;\n19.8 $\\pm$ 0.9 AU), and 2MASS J15594729+4403595 B (43 $\\pm$ 9 MJup; M8.0 $\\pm$\n0.5; 190 $\\pm$ 20 AU). Over 150 candidate planets were identified; we obtained\nfollow-up imaging for 56% of these but all are consistent with background\nstars. Our null detection of planets enables strong statistical constraints on\nthe occurrence rate of long-period giant planets around single M dwarfs. We\ninfer an upper limit (at the 95% confidence level) of 10.3% and 16.0% for 1-13\nMJup planets between 10-100 AU for hot-start and cold-start (Fortney)\nevolutionary models, respectively. Fewer than 6.0% (9.9%) of M dwarfs harbor\nmassive gas giants in the 5-13 MJup range like those orbiting HR 8799 and\n$\\beta$ Pictoris between 10-100 AU for a hot-start (cold-start) formation\nscenario. Although the first directly imaged planets were found around massive\nstars, there is currently no statistical evidence for a trend of giant planet\nfrequency with stellar host mass at large separations as predicted by the disk\ninstability model of giant planet formation.", "category": "astro-ph_EP" }, { "text": "Determination of uncertainty profiles in neutral atmospheric properties\n measured by radio occultation experiments: Radio occultations are commonly used to assess remotely the thermodynamic\nproperties of planets or satellites' atmospheres within the solar system. The\ndata processing usually involves the so-called Abel inversion method or the\nnumerical ray-tracing technique. Both these approaches are now well\nestablished, however, they do not allow to easily determine the uncertainty\nprofiles in the atmospheric properties, and this makes the results difficult to\ninterpret statistically. Recently, a purely analytical approach based on the\ntime transfer functions formalism was proposed for modeling radio occultation\ndata. Using this formulation, we derive uncertainty relationships between the\nfrequency shift and the thermodynamic properties of the neutral atmosphere such\nas the temperature, pressure, and neutral number density. These expressions are\nimportant for interpreting previous results from past radio occultation\nexperiments. They are especially relevant for deriving the system requirements\nfor future missions in a rigorous manner and consistently with the scientific\nrequirements about the atmospheric properties retrieval.", "category": "astro-ph_EP" }, { "text": "Hints on the origins of particle traps in protoplanetary disks given by\n the $M_{\\rm{dust}}-M_{\\star}$ relation: Demographic surveys of protoplanetary disks, carried out mainly with ALMA,\nhave provided access to a large range of disk dust masses ($M_{\\rm{dust}}$)\naround stars with different stellar types and in different star-forming\nregions. These surveys found a power-law relation between $M_{\\rm{dust}}$ and\n$M_{\\star}$ that steepens in time, but which is also flatter for transition\ndisks (TDs). We performed dust evolution models, which included perturbations\nto the gas surface density with different amplitudes to investigate the effect\nof particle trapping on the $M_{\\rm{dust}}-M_{\\star}$ relation. These\nperturbations were aimed at mimicking pressure bumps that originated from\nplanets. We focused on the effect caused by different stellar and disk masses\nbased on exoplanet statistics that demonstrate a dependence of planet mass on\nstellar mass and metallicity. Models of dust evolution can reproduce the\nobserved $M_{\\rm{dust}}-M_{\\star}$ relation in different star-forming regions\nwhen strong pressure bumps are included and when the disk mass scales with\nstellar mass (case of $M_{\\rm{disk}}=0.05\\,M_\\star$ in our models). This result\narises from dust trapping and dust growth beyond centimeter-sized grains inside\npressure bumps. However, the flatter relation of $M_{\\rm{dust}}-M_{\\star}$ for\nTDs and disks with substructures cannot be reproduced by the models unless the\nformation of boulders is inhibited inside pressure bumps. In the context of\npressure bumps originating from planets, our results agree with current\nexoplanet statistics on giant planet occurrence increasing with stellar mass,\nbut we cannot draw a conclusion about the type of planets needed in the case of\nlow-mass stars. This is attributed to the fact that for $M_\\star<1\\,M_\\odot$,\nthe observed $M_{\\rm{dust}}$ obtained from models is very low due to the\nefficient growth of dust particles beyond centimeter-sizes inside pressure\nbumps.", "category": "astro-ph_EP" }, { "text": "The Atmospheres of Earth-like Planets after Giant Impact Events: It is now understood that the accretion of terrestrial planets naturally\ninvolves giant collisions, the moon-forming impact being a well known example.\nIn the aftermath of such collisions the surface of the surviving planet is very\nhot and potentially detectable. Here we explore the atmospheric chemistry,\nphotochemistry, and spectral signatures of post-giant-impact terrestrial\nplanets enveloped by thick atmospheres consisting predominantly of CO2, and\nH2O. The atmospheric chemistry and structure are computed self-consistently for\natmospheres in equilibrium with hot surfaces with composition reflecting either\nthe bulk silicate Earth (which includes the crust, mantle, atmosphere and\noceans) or Earth's continental crust. We account for all major molecular and\natomic opacity sources including collision-induced absorption. We find that\nthese atmospheres are dominated by H2O and CO2, while the formation of CH4, and\nNH3 is quenched due to short dynamical timescales. Other important constituents\nare HF, HCl, NaCl, and SO2. These are apparent in the emerging spectra, and can\nbe indicative that an impact has occurred. The use of comprehensive opacities\nresults in spectra that are a factor of 2 lower in surface brightness in the\nspectral windows than predicted by previous models. The estimated luminosities\nshow that the hottest post-giant-impact planets will be detectable with\nnear-infrared coronagraphs on the planned 30m-class telescopes. The 1-4um\nregion will be most favorable for such detections, offering bright features and\nbetter contrast between the planet and a potential debris disk. We derive\ncooling timescales on the order of 10^5-10^6 Myrs, based on the modeled\neffective temperatures. This leads to the possibility of discovering tens of\nsuch planets in future surveys.", "category": "astro-ph_EP" }, { "text": "Habitable Zones with Stable Orbits for Planets around Binary Systems: A general formulation to compute habitable zones (HZ) around binary stars is\npresented. A HZ in this context must satisfy two separate conditions: a\nradiative one and one of dynamical stability. For the case of single stars, the\nusual concept of circumstellar habitable zone is based on the radiative\ncondition only, as the dynamical stability condition is taken for granted. For\nthe radiative condition, we extend the simple formulation of the circumstellar\nhabitable zone for single stars, to the case of eccentric stellar binary\nsystems, where two sources of luminosity at different orbital phases contribute\nto the irradiance of their planetary circumstellar and circumbinary regions.\nOur approach considers binaries with eccentric orbits and guarantees that\norbits in the computed habitable zone remain within it at all orbital phases.\nFor the dynamical stability condition, we use the approach of invariant loops\ndeveloped by Pichardo et al. 2005 to find regions of stable, non-intersecting\norbits, which is a robust method to find stable regions in binary stars, as it\nis based in the existence of integrals of motion. We apply the combined\ncriteria to calculate HZ for 64 binary stars in the solar neighborhood with\nknown orbital parameters, including some with discovered planets. Formulae and\ninterpolating tables are provided, so the reader can compute the boundaries of\nthe HZ for an arbitrary binary system, using the stellar flux limits they\nprefer. Together with the formulae provided for stable zones, these allow the\ncomputation of both regions of stability and habitability around any binary\nstellar system. We found 56% of the cases we consider can satisfy both\nrestrictions, this is a very important constriction to binary systems.\nNevertheless, we conclude that these systems where a dynamical and radiative\nsafe zone exists, must be considered strong candidates in the search for\nhabitable planets", "category": "astro-ph_EP" }, { "text": "The Dynamics of Dust Grains in the Outer Solar System: We study the dynamics of large dust grains >1 micron with orbits outside of\nthe heliosphere (beyond 250 AU). Motion of the Solar System through the\ninterstellar medium (ISM) at a velocity of 26 km/s subjects these particles to\ngas and Coulomb drag (grains are expected to be photoelectrically charged) as\nwell as the Lorentz force and the electric force caused by the induction\nelectric field. We show that to zeroth order the combined effect of these\nforces can be well described in the framework of the classical Stark problem:\nparticle motion in a Keplerian potential subject to an additional constant\nforce. Based on this analogy, we elucidate the circumstances in which the\nmotion becomes unbound, and show that under local ISM conditions dust grains\nsmaller than ~100 microns originating in the Oort Cloud (e.g. in collisions of\ncomets) beyond 10000 AU are ejected from the Solar System under the action of\nthe electric force. Orbital motion of larger, bound grains is described\nanalytically using the orbit-averaged Hamiltonian approach and consists of\norbital plane precession at a fixed semi-major axis, accompanied by the\nperiodic variations of the inclination and eccentricity (the latter may\napproach unity in some cases). A more detailed analysis of the combined effect\nof gas and Coulomb drag shows it is possible to reduce particle semi-major\naxes, but that the degree of orbital decay is limited (a factor of several at\nbest) by passages through atomic and molecular clouds, which easily eject small\nparticles.", "category": "astro-ph_EP" }, { "text": "ALMA constraints on assembly of Core Accretion planets: Resolved dust continuum and CO line ALMA imaging, and in some cases detection\nof H$\\alpha$ emission, hint that young massive planets are abundant at wide\nseparations in protoplanetary discs. Here, we show how these observations can\nprobe the runaway phase of planetary growth in the Core Accretion theory.\nPlanets in this phase have the right range of masses to account for the\npredominantly moderate contrast gaps and rings seen in ALMA observations.\nHowever, we find that these planets gain mass and migrate inward very rapidly.\nAs a result, the phase when they could produce gaps with properties similar to\nthose observed is very short, i.e., $t_{\\rm gap} \\lesssim 0.1$~Myr,\nindependently of the disc viscosity parameter. This would require many tens to\nhundreds of gas giant planets to be born per ALMA system, violating the\navailable mass budget of solids in realistic discs. This also predicts\npreponderance of discs with very wide gaps or complete inner disc holes, which\nis not observed. We show that suppression of both planet accretion and\nmigration by a factor of at least ten is a possible solution to these serious\nproblems. Future population synthesis models of planet formation should aim to\naddress both exoplanetary data of older discless planetary systems and ALMA\ndiscs with embedded planets in one framework.", "category": "astro-ph_EP" }, { "text": "Evolution of the Dust Coma in Comet 67P/Churyumov-Gerasimenko Before\n 2009 Perihelion: Comet 67P/Churyumov-Gerasimenko is the main target of ESA's Rosetta mission\nand will be encountered in May 2014. As the spacecraft shall be in orbit the\ncomet nucleus before and after release of the lander {\\it Philae}, it is\nnecessary necessary to know the conditions in the coma. Study the dust\nenvironment, including the dust production rate and its variations along its\npreperihelion orbit. The comet was observed during its approach to the Sun on\nfour epochs between early-June 2008 and mid-January 2009, over a large range of\nheliocentric distances that will be covered by the mission in 2014. An\nanomalous enhancement of the coma dust density was measured towards the comet\nnucleus. The scalelength of this enhancement increased with decreasing\nheliocentric distance of the comet. This is interpreted as a result of an\nunusually slow expansion of the dust coma. Assuming a spherical symmetric coma,\nthe average amount of dust as well as its ejection velocity have been derived.\nThe latter increases exponentially with decreasing heliocentric distance (\\rh),\nranging from about 1 m/s at 3 AU to about 25-35 m/s at 1.4 AU. Based on these\nresults we describe the dust environment at those nucleocentric distances at\nwhich the spacecraft will presumably be in orbit.\n Astronomy and Astrophysics, in press", "category": "astro-ph_EP" }, { "text": "The periodic and chaotic regimes of motion in the exoplanet 2/1\n mean-motion resonance: We present the dynamical structure of the phase space of the planar planetary\n2/1 mean-motion resonance (MMR). Inside the resonant domain, there exist two\nfamilies of periodic orbits, one associated to the librational motion of the\ncritical angle ($\\sigma$-family) and the other related to the circulatory\nmotion of the angle between the pericentres ($\\Delta\\varpi$-family). The\nwell-known apsidal corotation resonances (ACR) appear at the intersections of\nthese families. A complex web of secondary resonances exists also for low\neccentricities, whose strengths and positions are dependent on the individual\nmasses and spatial scale of the system.\n Depending on initial conditions, a resonant system is found in one of the two\ntopologically different states, referred to as \\textit{internal} and\n\\textit{external} resonances. The internal resonance is characterized by\nsymmetric ACR and its resonant angle is $2\\,\\lambda_2-\\lambda_1-\\varpi_1$,\nwhere $\\lambda_i$ and $\\varpi_i$ stand for the planetary mean longitudes and\nlongitudes of pericentre, respectively. In contrast, the external resonance is\ncharacterized by asymmetric ACR and the resonant angle is\n$2\\,\\lambda_2-\\lambda_1-\\varpi_2$. We show that systems with more massive outer\nplanets always envolve inside internal resonances. The limit case is the\nwell-known asteroidal resonances with Jupiter. At variance, systems with more\nmassive inner planets may evolve in either internal or external resonances; the\ninternal resonances are typical for low-to-moderate eccentricity\nconfigurations, whereas the external ones for high eccentricity configurations\nof the systems. In the limit case, analogous to Kuiper belt objects in\nresonances with Neptune, the systems are always in the external resonances\ncharacterized by asymmetric equilibria.", "category": "astro-ph_EP" }, { "text": "The Rossiter-McLaughlin effect of CoRoT-3b & HD189733b: We present radial-velocity sequences acquired during three transits of the\nexoplanet HD 189733b and one transit of the CoRoT-3b. We applied a combined\nMarkov-Chain Monte Carlo analysis of spectroscopic and photometric data on\nthese stars, to determine a full set of system parameters including the project\nspin-orbit misalignement angle of HD 189733b to an unprecedented precision via\nthe Rossiter-McLaughlin effect: beta = 0.85 degrees (+0.32 -0.28) . This small\nbut non-zero inclination of the planetary orbit is important to understand the\norigin of the system. On CoRoT-3b, results seem to point towards a non-zero\ninclination as well with beta = 37.6 degrees (+10.0 -22.3), but this remains\nmarginal. Systematic effects due to non-gaussian cross-correlation functions\nappear to be the main cause of significant residuals that prevent an accurate\ndetermination of the projected stellar rotation velocity V sin(I) for both\nstars.", "category": "astro-ph_EP" }, { "text": "Planetary Orbital Equations in Externally-Perturbed Systems: Position\n and Velocity-Dependent Forces: The increasing number and variety of extrasolar planets illustrates the\nimportance of characterizing planetary perturbations. Planetary orbits are\ntypically described by physically intuitive orbital elements. Here, we\nexplicitly express the equations of motion of the unaveraged perturbed two-body\nproblem in terms of planetary orbital elements by using a generalized form of\nGauss' equations. We consider a varied set of position and velocity-dependent\nperturbations, and also derive relevant specific cases of the equations: when\nthey are averaged over fast variables (the \"adiabatic\" approximation), and in\nthe prograde and retrograde planar cases. In each instance, we delineate the\nproperties of the equations. As brief demonstrations of potential applications,\nwe consider the effect of Galactic tides. We measure the effect on the\nwidest-known exoplanet orbit, Sedna-like objects, and distant scattered disk\nobjects, particularly with regard to where the adiabatic approximation breaks\ndown. The Mathematica code which can help derive the equations is freely\navailable upon request.", "category": "astro-ph_EP" }, { "text": "BEAST detection of a brown dwarf and a low-mass stellar companion around\n the young bright B star HIP 81208: Recent observations from B-star Exoplanet Abundance Study (BEAST) have\nillustrated the existence of sub-stellar companions around very massive stars.\nIn this paper, we present the detection of two lower mass companions to a\nrelatively nearby ($148.7^{+1.5}_{-1.3}$ pc), young ($17^{+3}_{-4}$ Myr),\nbright (V=$6.632\\pm0.006$ mag), $2.58\\pm0.06~ M_{\\odot}$ B9V star HIP 81208\nresiding in the Sco-Cen association, using the Spectro-Polarimetric\nHigh-contrast Exoplanet REsearch (SPHERE) instrument at the Very Large\nTelescope (VLT) in Chile. Analysis of the photometry obtained gives mass\nestimates of $67^{+6}_{-7}~M_J$ for the inner companion and\n$0.135^{+0.010}_{-0.013}~M_{\\odot}$ for the outer companion, indicating the\nformer to be most likely a brown dwarf and the latter to be a low-mass star.\nThe system is compact but unusual, as the orbital planes of the two companions\nare likely close to orthogonal. The preliminary orbital solutions we derived\nfor the system indicate that the star and the two companions are likely in a\nKozai resonance, rendering the system dynamically very interesting for future\nstudies.", "category": "astro-ph_EP" }, { "text": "Discovery of the first Earth-sized planets orbiting a star other than\n our Sun in the Kepler-20 system: Discovering other worlds the size of our own has been a long-held dream of\nastronomers. The transiting planets Kepler-20e and Kepler-20f, which belong to\na multi-planet system, hold a very special place among the many groundbreaking\ndiscoveries of the Kepler mission because they finally realized that dream. The\nradius of Kepler-20f is essentially identical to that of the Earth, while\nKepler-20e is even smaller (0.87 R[Earth]), and was the first exoplanet to earn\nthat distinction. Their masses, however, are too light to measure with current\ninstrumentation, and this has prevented their confirmation by the usual Doppler\ntechnique that has been used so successfully to confirm many other larger\nplanets. To persuade themselves of the planetary nature of these tiny objects,\nastronomers employed instead a statistical technique to \"validate\" them,\nshowing that the likelihood they are planets is orders of magnitude larger than\na false positive. Kepler-20e and 20f orbit their Sun-like star every 6.1 and\n19.6 days, respectively, and are most likely of rocky composition. Here we\nreview the history of how they were found, and present an overview of the\nmethodology that was used to validate them.", "category": "astro-ph_EP" }, { "text": "Incomplete cooling down of Saturn's A ring at solar equinox: Implication\n for seasonal thermal inertia and internal structure of ring particles: At the solar equinox in August 2009, the Composite Infrared Spectrometer\n(CIRS) onboard Cassini showed the lowest Saturn's ring temperatures ever\nobserved. Detailed radiative transfer models show that the observed equinox\ntemperatures of Saturn's A ring are much higher than model predictions as long\nas only the flux from Saturn is taken into account. This indicates that the A\nring was not completely cooled down at the equinox. We develop a simple\nseasonal model for ring temperatures and first assume that the internal density\nand the thermal inertia of a ring particle are uniform with depth. The particle\nsize is estimated to be 1-2 m. The seasonal thermal inertia is found to be\n30-50 Jm$^{-2}$K$^{-1}$s$^{-1/2}$ in the middle A ring whereas it is $\\sim$ 10\nJm$^{-2}$K$^{-1}$s$^{-1/2}$ or as low as the diurnal thermal inertia in the\ninner and outermost regions of the A ring. An additional internal structure\nmodel, in which a particle has a high density core surrounded by a fluffy\nregolith mantle, shows that the core radius relative to the particle radius is\nabout 0.9 for the middle A ring and is much less for the inner and outer\nregions of the A ring. This means that the radial variation of the internal\ndensity of ring particles exists across the A ring. Some mechanisms may be\nconfining dense particles in the middle A ring against viscous diffusion.\nAlternatively, the (middle) A ring might have recently formed ($<$ 10$^{8}$ yr)\nby destruction of an icy satellite, so that dense particles have not yet\ndiffused over the A ring and regolith mantles of particles have not grown\nthick. Our model results also indicate that the composition of the core is\npredominantly water ice, not rock.", "category": "astro-ph_EP" }, { "text": "Extrasolar planets and brown dwarfs around A--F type stars. VIII. A\n giant planet orbiting the young star HD113337: In the frame of the search for extrasolar planets and brown dwarfs around\nearly-type main-sequence stars, we present the detection of a giant planet\naround the young F-type star HD113337. We estimated the age of the system to be\n150 +100/-50 Myr. Interestingly, an IR excess attributed to a cold debris disk\nwas previously detected on this star. The SOPHIE spectrograph on the 1.93m\ntelescope at Observatoire de Haute-Provence was used to obtain ~300 spectra\nover 6 years. We used our SAFIR tool, dedicated to the spectra analysis of A\nand F stars, to derive the radial velocity variations. The data reveal a 324.0\n+1.7/-3.3 days period that we attribute to a giant planet with a minimum mass\nof 2.83 +- 0.24 Mjup in an eccentric orbit with e=0.46 +- 0.04. A long-term\nquadratic drift, that we assign to be probably of stellar origin, is\nsuperimposed to the Keplerian solution.", "category": "astro-ph_EP" }, { "text": "Transit least-squares survey IV. Earth-like transiting planets expected\n from the PLATO mission: In its long-duration observation phase, the PLATO satellite will observe two\nnon-overlapping fields for a total of 4 yr. The exact duration of each pointing\nwill be determined 2 yr before launch. Previous estimates of PLATO's yield of\nEarth-sized planets in the habitable zones (HZs) around solar-type stars ranged\nbetween 6 and 280. We use the PLATO Solar-like Light curve Simulator (PSLS) to\nsimulate light curves with transiting planets around bright (m_V > 11) Sun-like\nstars at a cadence of 25 s, roughly representative of the >15,000 targets in\nPLATO's high-priority P1 sample (mostly F5-K7 dwarfs and sub-dwarfs). Our study\nincludes light curves generated from synchronous observations of 6, 12, 18, and\n24 of PLATO's 12 cm aperture cameras over both 2 yr and 3 yr of continuous\nobservations. Automated detrending is done with the Wotan software and\npost-detrending transit detection is performed with the Transit Least Squares\n(TLS) algorithm. We scale the true positive rates (TPRs) with the expected\nnumber of stars in the P1 sample and with modern estimates of the exoplanet\noccurrence rates and predict the detection of planets with 0.5 R_E <= R_p <=\n1.5 R_E in the HZs around F5-K7 dwarf stars. For the (2 yr + 2 yr)\nlong-duration observation phase strategy we predict 11-34 detections, for the\n(3 yr + 1 yr) strategy we predict 8-25 discoveries. Our study of the effects of\nstellar variability on shallow transits of Earth-like planets illustrates that\nour estimates of PLATO's planet yield, which we derive using a photometrically\nquiet star like the Sun, must be seen as upper limits. In conclusion, PLATO's\ndetection of about a dozen Earth-sized planets in the HZs around solar-type\nstars will mean a major contribution to this yet poorly sampled part of the\nexoplanet parameter space with Earth-like planets.", "category": "astro-ph_EP" }, { "text": "Hydrodynamics of Embedded Planets' First Atmospheres. II. A Rapid\n Recycling of Atmospheric Gas: Following Paper I we investigate the properties of atmospheres that form\naround small protoplanets embedded in a protoplanetary disc by conducting\nhydrodynamical simulations. These are now extended to three dimensions,\nemploying a spherical grid centred on the planet. Compression of gas is shown\nto reduce rotational motions. Contrasting the 2D case, no clear boundary\ndemarcates bound atmospheric gas from disc material; instead, we find an open\nsystem where gas enters the Bondi sphere at high latitudes and leaves through\nthe midplane regions, or, vice versa, when the disc gas rotates sub-Keplerian.\nThe simulations do not converge to a time-independent solution; instead, the\natmosphere is characterized by a time-varying velocity field. Of particular\ninterest is the timescale to replenish the atmosphere by nebular gas,\n$t_\\mathrm{replenish}$. It is shown that the replenishment rate,\n$M_\\mathrm{atm}/t_\\mathrm{replenish}$, can be understood in terms of a modified\nBondi accretion rate,\n$\\sim$$R_\\mathrm{Bondi}^2\\rho_\\mathrm{gas}v_\\mathrm{Bondi}$, where\n$v_\\mathrm{Bondi}$ is set by the Keplerian shear or the magnitude of the\nsub-Keplerian motion of the gas, whichever is larger. In the inner disk, the\natmosphere of embedded protoplanets replenishes on a timescale that is shorter\nthan the Kelvin-Helmholtz contraction (or cooling) timescale. As a result,\natmospheric gas can no longer contract and the growth of these atmospheres\nterminates. Future work must confirm whether these findings continue to apply\nwhen the (thermodynamical) idealizations employed in this study are relaxed.\nBut if shown to be broadly applicable, replenishment of atmospheric gas\nprovides a natural explanation for the preponderance of gas-rich but\nrock-dominant planets like super-Earths and mini-Neptunes.", "category": "astro-ph_EP" }, { "text": "The optical transmission spectrum of the hot Jupiter HAT-P-32b: clouds\n explain the absence of broad spectral features?: We report Gemini-North GMOS observations of the inflated hot Jupiter\nHAT-P-32b during two primary transits. We simultaneously observed two\ncomparison stars and used differential spectro-photometry to produce\nmulti-wavelength light curves. 'White' light curves and 29 'spectral' light\ncurves were extracted for each transit and analysed to refine the system\nparameters and produce transmission spectra from 520-930nm in ~14nm bins. The\nlight curves contain time-varying white noise as well as time-correlated noise,\nand we used a Gaussian process model to fit this complex noise model. Common\nmode corrections derived from the white light curve fits were applied to the\nspectral light curves which significantly improved our precision, reaching\ntypical uncertainties in the transit depth of ~2x10^-4, corresponding to about\nhalf a pressure scale height. The low resolution transmission spectra are\nconsistent with a featureless model, and we can confidently rule out broad\nfeatures larger than about one scale height. The absence of Na/K wings or\nprominent TiO/VO features is most easily explained by grey absorption from\nclouds in the upper atmosphere, masking the spectral features. However, we\ncannot confidently rule out clear atmosphere models with low abundances (~10^-3\nsolar) of TiO, VO or even metal hydrides masking the Na and K wings. A smaller\nscale height or ionisation could also contribute to muted spectral features,\nbut alone are unable to to account for the absence of features reported here.", "category": "astro-ph_EP" }, { "text": "The Origin of Chondrules: Constraints from Matrix-Chondrule\n Complementarity: One of the major unresolved problems in cosmochemistry is the origin of\nchondrules, once molten, spherical silicate droplets with diameters of 0.2 to 2\nmm. Chondrules are an essential component of primitive meteorites and perhaps\nof all early solar system materials including the terrestrial planets. Numerous\nhypotheses have been proposed for their origin. Many carbonaceous chondrites\nare composed of about equal amounts of chondrules and fine-grained matrix.\nRecent data confirm that matrix in carbonaceous chondrites has high Si/Mg and\nFe/Mg ratios when compared to bulk carbonaceous chondrites with solar abundance\nratios. Chondrules have the opposite signature, low Si/Mg and Fe/Mg ratios. In\nsome carbonaceous chondrites chondrules have low Al/Ti ratios, matrix has the\nopposite signature and the bulk is chondritic. It is shown in detail that these\ncomplementary relationships cannot have evolved on the parent asteroid(s) of\ncarbonaceous chondrites. They reflect preaccretionary processes. Both\nchondrules and matrix must have formed from a single, solar-like reservoir.\nConsequences of complementarity for chondrule formation models are discussed.\nAn independent origin and/or random mixing of chondrules and matrix can be\nexcluded. Hence, complementarity is a strong constraint for all\nastrophysical-cosmochemical models of chondrule formation. Although chondrules\nand matrix formed from a single reservoir, the chondrule-matrix system was open\nto the addition of oxygen and other gaseous components.", "category": "astro-ph_EP" }, { "text": "Binary planetesimals and their role in planet formation: One of the main evolutionary stages of planet formation is the dynamical\nevolution of planetesimal disks. These disks are thought to evolve through\ngravitational encounters and physical collisions between single planetesimals.\nIn recent years, many binary planetesimals have been observed in the Solar\nsystem, indicating that the binarity of planetesimals is high. However, current\nstudies of planetesimal disks formation and evolution do not account for the\nrole of binaries. Here we point out that gravitational encounters of binary\nplanetesimals can have an important role in the evolution of planetesimal\ndisks. Binary planetesimals catalyze close encounters between planetesimals,\nand can strongly enhance their collision rate. Binaries may also serve as\nadditional heating source of the planetesimal disk, through the exchange of the\nbinaries gravitational potential energy into the kinetic energy of\nplanetesimals in the disk.", "category": "astro-ph_EP" }, { "text": "AKARI/IRC Near-Infrared Asteroid Spectroscopic Survey: AcuA-spec: Knowledge of water in the solar system is important for understanding of a\nwide range of evolutionary processes and the thermal history of the solar\nsystem. To explore the existence of water in the solar system, it is\nindispensable to investigate hydrated minerals and/or water ice on asteroids.\nThese water-related materials show absorption features in the 3-$\\micron$ band\n(wavelengths from 2.7 to 3.1 $\\micron$). We conducted a spectroscopic survey of\nasteroids in the 3-$\\micron$ band using the Infrared Camera (IRC) on board the\nJapanese infrared satellite AKARI. In the warm mission period of AKARI, 147\npointed observations were performed for 66 asteroids in the grism mode for\nwavelengths from 2.5 to 5 $\\micron$. According to these observations, most\nC-complex asteroids have clear absorption features ($> 10\\%$ with respect to\nthe continuum) related to hydrated minerals at a peak wavelength of\napproximately 2.75 $\\micron$, while S-complex asteroids have no significant\nfeature in this wavelength range. The present data are released to the public\nas the Asteroid Catalog using AKARI Spectroscopic Observations (AcuA-spec).", "category": "astro-ph_EP" }, { "text": "Transit of Exomoon Plasma Tori: New Diagnosis: In the solar system, moons largely exceed planets in number. The Kepler\ndatabase has been shown to be sensitive to exomoon detection down to the mass\nof Mars, but the first search has been unsuccessful. Here, we use a\nparticles-in-cell code to predict the transit of the plasma torus produced by a\nsatellite. Despite the small size of a moon, the spatial extent of its plasma\ntorus can be large enough to produce substantial transit absorptions. The model\nis used for the interpretation of Hubble Space Telescope early ingress\nabsorptions apparently observed during WASP-12b and HD 189733b UV transits for\nwhich no consistent explanation exists. For HD 189733b an exomoon transiting\n$\\sim 16$ $R_p$ ahead of the planet and loading $\\sim 10^{29}$ C II ions/s into\nspace is required to explain the tentative early ingress absorption observed\nfor C II. For WASP-12b, a moon transiting $\\sim 6$ $R_p$ ahead from the planet\nand ejecting $\\sim 10^{28}$ Mg II ions per second is required to explain the\nNUV early ingress absorption feature. Interestingly, both HD 189733b and\nWASP-12b predicted satellites are outside the Hill sphere of their planets, an\nindication that the moons, if present, were not formed in situ but probably\ncaptured later. Finally, our simulations show a strong electromagnetic coupling\nbetween the polar regions of planets and the orbital position of the moons, an\nexpected outcome of the unipolar induction DC circuit model. Future\nobservations should test our predictions with a potential opportunity to\nunambiguously detect the first exomoon plasma torus.", "category": "astro-ph_EP" }, { "text": "Tidal spin down rates of homogeneous triaxial viscoelastic bodies: We use numerical simulations to measure the sensitivity of the tidal spin\ndown rate of a homogeneous triaxial ellipsoid to its axis ratios by comparing\nthe drift rate in orbital semi-major axis to that of a spherical body with the\nsame mass, volume and simulated rheology. We use a mass-spring model\napproximating a viscoelastic body spinning around its shortest body axis, with\nspin aligned with orbital spin axis, and in circular orbit about a point mass.\nThe torque or drift rate can be estimated from that predicted for a sphere with\nequivalent volume if multiplied by $0.5 (1 + b^4/a^4)(b/a)^{-4/3}\n(c/a)^{-\\alpha_c}$ where $b/a$ and $c/a$ are the body axis ratios and index\n$\\alpha_c \\approx 1.05$ is consistent with the random lattice mass spring model\nsimulations but $\\alpha_c = 4/3$ suggested by scaling estimates.\n A homogeneous body with axis ratios 0.5 and and 0.8, like Haumea, has orbital\nsemi-major axis drift rate about twice as fast as a spherical body with the\nsame mass, volume and material properties. A simulation approximating a mostly\nrocky body but with 20\\% of its mass as ice concentrated at its ends has a\ndrift rate 10 times faster than the equivalent homogeneous rocky sphere.\nHowever, this increase in drift rate is not enough to allow Haumea's satellite,\nHi'iaka, to have tidally drifted away from Haumea to its current orbital\nsemi-major axis.", "category": "astro-ph_EP" }, { "text": "The secondary eclipse of the transiting exoplanet CoRoT-2b: We present a study of the light curve of the transiting exoplanet CoRoT-2b,\naimed at detecting the secondary eclipse and measuring its depth. The data were\nobtained with the CoRoT satellite during its first run of more than 140 days.\nAfter filtering the low frequencies with a pre-whitening technique, we detect a\n0.0060$\\pm$0.0020% secondary eclipse centered on the orbital phase\n0.494$\\pm$0.006. Assuming a black-body emission of the planet, we estimate a\nsurface brightness temperature of T$_{\\rm p,CoRoT}$=1910$^{+90}_{-100}$ K. We\nprovide the planet's equilibrium temperature and re-distribution factors as a\nfunction of the unknown amount of reflected light. The upper limit for the\ngeometric albedo is 0.12. The detected secondary is the shallowest ever found.", "category": "astro-ph_EP" }, { "text": "Extreme asteroids in the Pan-STARRS 1 Survey: Using the first 18 months of the Pan-STARRS 1 survey we have identified 33\ncandidate high-amplitude objects for follow-up observations and carried out\nobservations of 22 asteroids. 4 of the observed objects were found to have\nobserved amplitude $A_{obs}\\geq 1.0$ mag. We find that these high amplitude\nobjects are most simply explained by single rubble pile objects with some\ndensity-dependent internal strength, allowing them to resist mass shedding even\nat their highly elongated shapes. 3 further objects although below the cut-off\nfor 'high-amplitude' had a combination of elongation and rotation period which\nalso may require internal cohesive strength, depending on the density of the\nbody. We find that none of the 'high-amplitude asteroids' identified here\nrequire any unusual cohesive strengths to resist rotational fission. 3\nasteroids were sufficiently observed to allow for shape and spin pole models to\nbe determined through light curve inversion. 45864 was determined to have\nretrograde rotation with spin pole axes $\\lambda=218\\pm 10^{\\circ},\n\\beta=-82\\pm 5^{\\circ}$ and asteroid 206167 was found to have best fit spin\npole axes $\\lambda= 57 \\pm 5^{\\circ}$, $\\beta=-67 \\pm 5^{\\circ}$. An additional\nobject not initially measured with $A_{obs}>1.0$ mag, 49257, was determined to\nhave a shape model which does suggest a high-amplitude object. Its spin pole\naxes were best fit for values $\\lambda=112\\pm 6^{\\circ}, \\beta=6\\pm 5^{\\circ}$.\nIn the course of this project to date no large super-fast rotators ($P_{rot} <\n2.2$ h) have been identified.", "category": "astro-ph_EP" }, { "text": "The late accretion and erosion of Vesta's crust recorded by eucrites and\n diogenites as an astrochemical window into the formation of Jupiter and the\n early evolution of the Solar System: For decades the limited thickness of Vesta's basaltic crust, revealed by the\nlink between the asteroid and the howardite-eucrite-diogenite family of\nmeteorites, and its survival to collisional erosion offered an important\nconstraint for the study of the early evolution of the Solar System. Some\nresults of the Dawn mission, however, cast doubts on our understanding of\nVesta's interior composition and of the characteristics of its basaltic crust,\nweakening this classical constraint. In this work we investigate the late\naccretion and erosion experienced by Vesta's crust after its differentiation\nand recorded in the composition of eucrites and diogenites and show that it\noffers an astrochemical window into the earliest evolution of the Solar System.\nIn our proof-of-concept case study focusing on the late accretion and erosion\nof Vesta's crust during the growth and migration of Jupiter, the water\nenrichment of eucrites appears to be a sensitive function of Jupiter's\nmigration while the enrichment in highly-siderophile elements of diogenites\nappears to be particularly sensitive to the size-frequency distribution of the\nplanetesimals. The picture depicted by the enrichments created by late\naccretion in eucrites and diogenites is not qualitatively affected by the\nuncertainty on the primordial mass of Vesta. Crustal erosion, instead, is more\nsignificantly affected by said uncertainty and Vesta's crust survival appears\nto be mainly useful to study violent collisional scenarios where highly\nenergetic impacts can strip significant amounts of vestan material while\nlimitedly contributing to Vesta's late accretion. Our results suggest that the\nastrochemical record of the late accretion and erosion of Vesta's crust\nprovided by eucrites and diogenites can be used as a tool to investigate any\nprocess or scenario associated to the evolution of primordial Vesta and of the\nearly Solar System.", "category": "astro-ph_EP" }, { "text": "Turbulence in the TW Hya Disk: Turbulence is a fundamental parameter in models of grain growth during the\nearly stages of planet formation. As such, observational constraints on its\nmagnitude are crucial. Here we self-consistently analyze ALMA CO(2-1), SMA\nCO(3-2), and SMA CO(6-5) observations of the disk around TW Hya and find an\nupper limit on the turbulent broadening of $<$0.08c$_s$ ($\\alpha<$0.007 for\n$\\alpha$ defined only within 2-3 pressure scale heights above the midplane),\nlower than the tentative detection previously found from an analysis of the\nCO(2-1) data. We examine in detail the challenges of image plane fitting vs\ndirectly fitting the visibilities, while also considering the role of the\nvertical temperature gradient, systematic uncertainty in the amplitude\ncalibration, and assumptions about the CO abundance, as potential sources of\nthe discrepancy in the turbulence measurements. These tests result in\nvariations of the turbulence limit between $<$0.04c$_s$ and $<$0.13c$_s$,\nconsistently lower than the 0.2-0.4c$_s$ found previously. Having ruled out\nnumerous factors, we restrict the source of the discrepancy to our assumed\ncoupling between temperature and density through hydrostatic equilibrium in the\npresence of a vertical temperature gradient and/or the confinement of CO to a\nthin molecular layer above the midplane, although further work is needed to\nquantify the influence of these prescriptions. Assumptions about hydrostatic\nequilibrium and the CO distribution are physically motivated, and may have a\nsmall influence on measuring the kinematics of the gas, but they become\nimportant when constraining small effects such as the strength of the\nturbulence within a protoplanetary disk.", "category": "astro-ph_EP" }, { "text": "A Substellar Companion in a 1.3 yr Nearly-circular Orbit of HD 16760: We report the detection of a substellar companion orbiting the G5 dwarf HD\n16760 from the N2K sample. Precise Doppler measurements of the star from Subaru\nand Keck revealed a Keplerian velocity variation with a period of 466.47+-0.35\nd, a semiamplitude of 407.71+-0.84 m/s, and an eccentricity of 0.084+-0.003.\nAdopting a stellar mass of 0.78+-0.05 M_Sun, we obtain a minimum mass for the\ncompanion of 13.13+-0.56 M_JUP, which is close to the planet/brown-dwarf\ntransition, and the semimajor axis of 1.084+-0.023 AU. The nearly circular\norbit despite the large mass and intermediate orbital period makes this\ncompanion unique among known substellar companions.", "category": "astro-ph_EP" }, { "text": "Performance of near-infrared high-contrast imaging methods with JWST\n from commissioning: The James Webb Space Telescope (JWST) will revolutionize the field of\nhigh-contrast imaging and enable both the direct detection of Saturn-mass\nplanets and the characterization of substellar companions in the mid-infrared.\nWhile JWST will feature unprecedented sensitivity, angular resolution will be\nthe key factor when competing with ground-based telescopes. Here, we aim to\ncharacterize the performance of several extreme angular resolution imaging\ntechniques available with JWST in the 3-5 micron regime based on data taken\nduring commissioning. Firstly, we introduce custom tools to simulate, reduce,\nand analyze NIRCam and MIRI coronagraphy data and use these tools to extract\ncompanion detection limits from on-sky NIRCam round and bar mask coronagraphy\nobservations. Secondly, we present on-sky NIRISS aperture masking\ninterferometry (AMI) and kernel phase imaging (KPI) observations from which we\nextract companion detection limits using the publicly available fouriever tool.\nScaled to a total integration time of one hour and a target of the brightness\nof AB Dor, we find that NIRISS AMI and KPI reach contrasts of $\\sim$7-8 mag at\n$\\sim$70 mas and $\\sim$9 mag at $\\sim$200 mas. Beyond $\\sim$250 mas, NIRCam\ncoronagraphy reaches deeper contrasts of $\\sim$13 mag at $\\sim$500 mas and\n$\\sim$15 mag at $\\sim$2 arcsec. While the bar mask performs $\\sim$1 mag better\nthan the round mask at small angular separations $\\lesssim$0.75 arcsec, it is\nthe other way around at large angular separations $\\gtrsim$1.5 arcsec.\nMoreover, the round mask gives access to the full 360 deg field-of-view which\nis beneficial for the search of new companions. We conclude that already during\nthe instrument commissioning, JWST high-contrast imaging in the L- and M-bands\nperforms close to its predicted limits.", "category": "astro-ph_EP" }, { "text": "The secondary eclipse of CoRoT-1b: The transiting planet CoRoT-1b is thought to belong to the pM-class of\nplanets, in which the thermal emission dominates in the optical wavelengths. We\npresent a detection of its secondary eclipse in the CoRoT white channel data,\nwhose response function goes from ~400 to ~1000 nm. We used two different\nfiltering approaches, and several methods to evaluate the significance of a\ndetection of the secondary eclipse. We detect a secondary eclipse centered\nwithin 20 min at the expected times for a circular orbit, with a depth of\n0.016+/-0.006%. The center of the eclipse is translated in a 1-sigma upper\nlimit to the planet's eccentricity of ecosomega<0.014. Under the assumption of\na zero Bond Albedo and blackbody emission from the planet, it corresponds to a\nT_{CoRoT}=2330 +120-140 K. We provide the equilibrium temperatures of the\nplanet as a function of the amount of reflected light. If the planet is in\nthermal equilibrium with the incident flux from the star, our results imply an\ninefficient transport mechanism of the flux from the day to the night sides.", "category": "astro-ph_EP" }, { "text": "A Lyman-alpha transit left undetected: the environment and atmospheric\n behavior of K2-25b: K2-25b is a Neptune-sized exoplanet (3.45 Earth radii) that orbits its M4.5\nhost with a period of 3.48 days. Due to its membership in the Hyades Cluster,\nthe system has a known age (727 +/- 75 Myr). K2-25b's youth and its\nsimilarities with Gl 436b suggested that K2-25b could be undergoing strong\natmospheric escape. We observed two transits of K2-25b at Lyman-alpha using\nHST/STIS in order to search for escaping neutral hydrogen. We were unable to\ndetect an exospheric signature, but placed an upper limit of (R_p/R_s) < 0.56\nat 95% confidence by fitting the light curve of the Lyman-alpha red-wing, or <\n1.20 in the blue-wing. We reconstructed the intrinsic Lyman-alpha profile of\nK2-25 to determine its Lyman-alpha flux, and analyzed XMM-Newton observations\nto determined its X-ray flux. Based on the total X-ray and extreme ultraviolet\nirradiation of the planet (8763 +/- 1049 erg/s/cm^2), we estimated the maximum\nenergy-limited mass loss rate of K2-25b to be 10.6 x 10^10 g/s (0.56 Earth\nmasses per 1 Gyr), five times larger than the similarly estimated mass loss\nrate of Gl 436b (2.2 x 10^10 g/s). The photoionization time is about 3 hours,\nsignificantly shorter than Gl 436b's 14 hours. A non-detection of a Lyman-alpha\ntransit could suggest K2-25b is not significantly losing its atmosphere, or\nfactors of the system are resulting in the mass loss being unobservable (e.g.,\natmosphere composition or the system's large high energy flux). Further\nobservations could provide more stringent constraints.", "category": "astro-ph_EP" }, { "text": "Vital Signs: Seismology of ocean worlds: Ice-covered ocean worlds possess diverse energy sources and associated\nmechanisms that are capable of driving significant seismic activity, but to\ndate no measurements of their seismic activity have been obtained. Such\ninvestigations could probe their transport properties and radial structures,\nwith possibilities for locating and characterizing trapped liquids that may\nhost life and yielding critical constraints on redox fluxes, and thus on\nhabitability. Modeling efforts have examined seismic sources from tectonic\nfracturing and impacts. Here, we describe other possible seismic sources, their\nassociations with science questions constraining habitability, and the\nfeasibility of implementing such investigations. We argue, by analogy with the\nMoon, that detectable seismic activity on tidally flexed ocean worlds should\noccur frequently. Their ices fracture more easily than rocks, and dissipate\nmore tidal energy than the <1 GW of the Moon and Mars. Icy ocean worlds also\nshould create less thermal noise for a due to their greater distance and\nconsequently smaller diurnal temperature variations. They also lack substantial\natmospheres (except in the case of Titan) that would create additional noise.\nThus, seismic experiments could be less complex and less susceptible to noise\nthan prior or planned planetary seismology investigations of the Moon or Mars.", "category": "astro-ph_EP" }, { "text": "Seismometer Detection of Dust Devil Vortices by Ground Tilt: We report seismic signals on a desert playa caused by convective vortices and\ndust devils. The long-period (10-100s) signatures, with tilts of ~10$^{-7}$\nradians, are correlated with the presence of vortices, detected with nearby\nsensors as sharp temporary pressure drops (0.2-1 mbar) and solar obscuration by\ndust. We show that the shape and amplitude of the signals, manifesting\nprimarily as horizontal accelerations, can be modeled approximately with a\nsimple quasi-static point-load model of the negative pressure field associated\nwith the vortices acting on the ground as an elastic half space. We suggest the\nload imposed by a dust devil of diameter D and core pressure {\\Delta}Po is\n~({\\pi}/2){\\Delta}PoD$^2$, or for a typical terrestrial devil of 5 m diameter\nand 2 mbar, about the weight of a small car. The tilt depends on the inverse\nsquare of distance, and on the elastic properties of the ground, and the large\nsignals we observe are in part due to the relatively soft playa sediment and\nthe shallow installation of the instrument. Ground tilt may be a particularly\nsensitive means of detecting dust devils. The simple point-load model fails for\nlarge dust devils at short ranges, but more elaborate models incorporating the\nwork of Sorrells (1971) may explain some of the more complex features in such\ncases, taking the vortex winds and ground velocity into account. We discuss\nsome implications for the InSight mission to Mars.", "category": "astro-ph_EP" }, { "text": "Asteroid 4 Vesta: dynamical and collisional evolution during the Late\n Heavy Bombardment: Vesta is the only currently identified asteroid for which we possess samples,\nwhich revealed us that the asteroid is differentiated and possesses a\nrelatively thin basaltic crust that survived to the evolution of the asteroid\nbelt and the Solar System. However, little is know about the effects of past\nevents like the Late Heavy Bombardment on this crust. We address this gap in\nour knowledge by simulating the LHB in the different dynamical scenarios\nproposed for the migration of the giant planets in the broad framework of the\nNice Model. The results of simulations generate information about produced\ncrater population, surface saturation, mass loss and mass gain of Vesta and\nnumber of energetic or catastrophic impacts during LHB. Our results reveal that\nplanet-planet scattering is a dynamically favourable migration mechanism for\nthe survival of Vesta and its crust. The number of impacts on Vesta estimated\nas due to the LHB is $31\\pm5$, i.e. about 5 times larger than the number of\nimpacts that would have occurred in an unperturbed main belt in the same time\ninterval. The contribution of a possible extended belt, instead, is quite\nlimited and can be quantified in $2\\pm1$ impacts. The chance of energetic and\ncatastrophic impacts is less than 10\\% and is compatible with the absence of\ngiant craters dated back to 4 Ga ago and with the survival of the asteroid\nduring the LHB. The mass loss translates in the erosion of $3-5$ meters of the\ncrust, consistently with the global survival of the basaltic crust of Vesta\nconfirmed by the Dawn mission. Our analysis revealed that the contribution of\nthe LHB to the cratering of Vesta' surface is not significant and is actually\nerased by the crater population produced by the following 4 Ga of collisional\nevolution of the asteroid, in agreement with the data provided by the Dawn\nmission.", "category": "astro-ph_EP" }, { "text": "Resonance locking in giant planets indicated by the rapid orbital\n expansion of Titan: Tidal effects in planetary systems are the main driver in the orbital\nmigration of natural satellites. They result from physical processes occurring\ndeep inside celestial bodies, whose effects are rarely observable from surface\nimaging. For giant planet systems, the tidal migration rate is determined by\npoorly understood dissipative processes in the planet, and standard theories\nsuggest an orbital expansion rate inversely proportional to the power 11/2 in\ndistance, implying little migration for outer moons such as Saturn's largest\nmoon, Titan. Here, we use two independent measurements obtained with the\nCassini spacecraft to measure Titan's orbital expansion rate. We find Titan\nmigrates away from Saturn at 11.3 $\\pm$ 2.0 cm/year, corresponding to a tidal\nquality factor of Saturn of Q $\\simeq$ 100, and a migration timescale of\nroughly 10 Gyr. This rapid orbital expansion suggests Titan formed\nsignificantly closer to Saturn and has migrated outward to its current\nposition. Our results for Titan and five other moons agree with the predictions\nof a resonance locking tidal theory, sustained by excitation of inertial waves\ninside the planet. The associated tidal expansion is only weakly sensitive to\norbital distance, motivating a revision of the evolutionary history of Saturn's\nmoon system. The resonance locking mechanism could operate in other systems\nsuch as stellar binaries and exoplanet systems, and it may allow for tidal\ndissipation to occur at larger orbital separations than previously believed.", "category": "astro-ph_EP" }, { "text": "Four Small Planets Buried in K2 Systems: What Can We Learn for TESS?: The Kepler, K2, and Transiting Exoplanet Survey Satellite (TESS) missions\nhave provided a wealth of confirmed exoplanets, benefiting from a huge effort\nfrom the planet-hunting and follow-up community. With careful systematics\nmitigation, these missions provide precise photometric time series, which\nenable detection of transiting exoplanet signals. However, exoplanet hunting\ncan be confounded by several factors, including instrumental noise, search\nbiases, and host star variability. In this Letter, we discuss strategies to\novercome these challenges using newly emerging techniques and tools. We\ndemonstrate the power of new, fast open-source community tools (e.g.,\nlightkurve, starry, celerite, exoplanet), and discuss four high signal-to-noise\nratio (S/N) exoplanets that showcase specific challenges present in planet\ndetection: K2-43c, K2-168c, K2-198c, and K2-198d. These planets have been\nundetected in several large K2 planet searches, despite having transit signals\nwith S/N > 10. Two of the planets discussed here are new discoveries. In this\nwork we confirm all four as true planets. Alongside these planet systems, we\ndiscuss three key challenges in finding small transiting exoplanets. The aim of\nthis Letter is to help new researchers understand where planet detection\nefficiency gains can be made, and to encourage the continued use of K2 archive\ndata. The considerations presented in this Letter are equally applicable to\nKepler, K2, and TESS, and the tools discussed here are available for the\ncommunity to apply to improve exoplanet discovery and fitting.", "category": "astro-ph_EP" }, { "text": "NGTS-13b: A hot 4.8 Jupiter-mass planet transiting a subgiant star: We report the discovery of the massive hot Jupiter NGTS-13b by the Next\nGeneration Transit Survey (NGTS). The V = 12.7 host star is likely in the\nsubgiant evolutionary phase with log g$_{*}$ = 4.04 $\\pm$ 0.05, T$_{eff}$ =\n5819 $\\pm$ 73 K, M$_{*}$ = 1.30$^{+0.11}_{-0.18}$ M$_{\\odot}$, and R$_{*}$ =\n1.79 $\\pm$ 0.06 R$_{\\odot}$. NGTS detected a transiting planet with a period of\nP = 4.12 days around the star, which was later validated with the Transiting\nExoplanet Survey Satellite (TESS; TIC 454069765). We confirm the planet using\nradial velocities from the CORALIE spectrograph. Using NGTS and TESS full-frame\nimage photometry combined with CORALIE radial velocities we determine NGTS-13b\nto have a radius of R$_{P}$ = 1.142 $\\pm$ 0.046 R$_{Jup}$, mass of M$_{P}$ =\n4.84 $\\pm$ 0.44 M$_{Jup}$ and eccentricity e = 0.086 $\\pm$ 0.034. Some previous\nstudies suggest that $\\sim$4 M$_{Jup}$ may be a border between two separate\nformation scenarios (e.g., core accretion and disk instability) and that\nmassive giant planets share similar formation mechanisms as lower-mass brown\ndwarfs. NGTS-13b is just above 4 M$_{Jup}$ making it an important addition to\nthe statistical sample needed to understand the differences between various\nclasses of substellar companions. The high metallicity, [Fe/H] = 0.25 $\\pm$\n0.17, of NGTS-13 does not support previous suggestions that massive giants are\nfound preferentially around lower metallicity host stars, but NGTS-13b does\nsupport findings that more massive and evolved hosts may have a higher\noccurrence of close-in massive planets than lower-mass unevolved stars.", "category": "astro-ph_EP" }, { "text": "The Complex History of Trojan Asteroids: The Trojan asteroids provide a unique perspective on the history of Solar\nSystem. As a large population of small bodies, they record important\ngravitational interactions and dynamical evolution of the Solar System. In the\npast decade, significant advances have been made in understanding physical\nproperties, and there has been a revolution in thinking about the origin of\nTrojans. The ice and organics generally presumed to be a significant part of\nTrojan compositions have yet to be detected directly, though low density of the\nbinary system Patroclus (and possibly low density of the binary/moonlet system\nHektor) is consistent with an interior ice component. By contrast, fine-grained\nsilicates that appear to be similar to cometary silicates in composition have\nbeen detected, and a color bimodality may indicate distinct compositional\ngroups among the Trojans. Whereas Trojans had traditionally been thought to\nhave formed near 5 AU, a new paradigm has developed in which the Trojans formed\nin the proto-Kuiper Belt, and they were scattered inward and captured in the\nTrojan swarms as a result of resonant interactions of the giant planets.\nWhereas the orbital and population distributions of current Trojans are\nconsistent with this origin scenario, there are significant differences between\ncurrent physical properties of Trojans and those of Kuiper Belt objects. These\ndifferences may be indicative of surface modification due to the inward\nmigration of objects that became the Trojans, but understanding of appropriate\nmodification mechanisms is poor and would benefit from additional laboratory\nstudies. Many open questions remain, and the future promises significant\nstrides in our understanding of Trojans. The time is ripe for a spacecraft\nmission to the Trojans, to turn these objects into geologic worlds that can be\nstudied in detail to unravel their complex history.", "category": "astro-ph_EP" }, { "text": "Radiation hydrodynamical models of the inner rim in protoplanetary disks: Many stars host planets orbiting within a few astronomical units (AU). The\noccurrence rate and distributions of masses and orbits vary greatly with the\nhost stars mass. These close planets origins are a mystery that motivates\ninvestigating protoplanetary disks central regions. A key factor governing the\nconditions near the star is the silicate sublimation front, which largely\ndetermines where the starlight is absorbed, and which is often called the inner\nrim. We present the first radiation hydrodynamical modeling of the sublimation\nfront in the disks around the young intermediate-mass stars called Herbig Ae\nstars. The models are axisymmetric, and include starlight heating, silicate\ngrains sublimating and condensing to equilibrium at the local, time-dependent\ntemperature and density, and accretion stresses parametrizing the results of\nMHD magneto-rotational turbulence models. The results compare well with\nradiation hydrostatic solutions, and prove to be dynamically stable. Passing\nthe model disks into Monte Carlo radiative transfer calculations, we show that\nthe models satisfy observational constraints on the inner rims location. A\nsmall optically-thin halo of hot dust naturally arises between the inner rim\nand the star. The inner rim has a substantial radial extent, corresponding to\nseveral disk scale heights. While the fronts overall position varies with the\nstellar luminosity, its radial extent depends on the mass accretion rate. A\npressure maximum develops near the location of thermal ionization at\ntemperatures about 1000 K. The pressure maximum is capable of halting solid\npebbles radial drift and concentrating them in a zone where temperatures are\nsufficiently high for annealing to form crystalline silicates.", "category": "astro-ph_EP" }, { "text": "The GAPS Programme at TNG XXXVIII. Five molecules in the atmosphere of\n the warm giant planet WASP-69b detected at high spectral resolution: The field of exo-atmospheric characterisation is progressing at an\nextraordinary pace. Atmospheric observations are now available for tens of\nexoplanets, mainly hot and warm inflated gas giants, and new molecular species\ncontinue to be detected revealing a richer atmospheric composition than\npreviously expected. Thanks to its warm equilibrium temperature (963$\\pm$18~K)\nand low-density (0.219$\\pm$0.031~g cm$^{-3}$), the close-in gas giant WASP-69b\nrepresents a golden target for atmospheric characterization. With the aim of\nsearching for molecules in the atmosphere of WASP-69b and investigating its\nproperties, we performed high-resolution transmission spectroscopy with the\nGIANO-B near-infrared spectrograph at the Telescopio Nazionale Galileo. We\nobserved three transit events of WASP-69b. During a transit, the planetary\nlines are Doppler-shifted due to the large change in the planet's radial\nvelocity, allowing us to separate the planetary signal from the\nquasi-stationary telluric and stellar spectrum. Considering the three nights\ntogether, we report the detection of CH$_4$, NH$_3$, CO, C$_2$H$_2$, and\nH$_2$O, at more than $3.3\\sigma$ level. We did not identify the presence of HCN\nand CO$_2$ with confidence level higher than 3$\\sigma$. This is the first time\nthat five molecules are simultaneously detected in the atmosphere of a warm\ngiant planet. These results suggest that the atmosphere of WASP-69b is possibly\ncarbon-rich and characterised by the presence of disequilibrium chemistry.", "category": "astro-ph_EP" }, { "text": "Preparing an unsupervised massive analysis of SPHERE high contrast data\n with the PACO algorithm: We aim at searching for exoplanets on the whole ESO/VLT-SPHERE archive with\nimproved and unsupervised data analysis algorithm that could allow to detect\nmassive giant planets at 5 au. To prepare, test and optimize our approach, we\ngathered a sample of twenty four solar-type stars observed with SPHERE using\nangular and spectral differential imaging modes. We use PACO, a new generation\nalgorithm recently developed, that has been shown to outperform classical\nmethods. We also improve the SPHERE pre-reduction pipeline, and optimize the\noutputs of PACO to enhance the detection performance. We develop custom built\nspectral prior libraries to optimize the detection capability of the ASDI mode\nfor both IRDIS and IFS. Compared to previous works conducted with more\nclassical algorithms than PACO, the contrast limits we derived are more\nreliable and significantly better, especially at short angular separations\nwhere a gain by a factor ten is obtained between 0.2 and 0.5 arcsec. Under good\nobserving conditions, planets down to 5 MJup, orbiting at 5 au could be\ndetected around stars within 60 parsec. We identified two exoplanet candidates\nthat require follow-up to test for common proper motion. In this work, we\ndemonstrated on a small sample the benefits of PACO in terms of achievable\ncontrast and of control of the confidence levels. Besides, we have developed\ncustom tools to take full benefits of this algorithm and to quantity the total\nerror budget on the estimated astrometry and photometry. This work paves the\nway towards an end-to-end, homogeneous, and unsupervised massive re-reduction\nof archival direct imaging surveys in the quest of new exoJupiters.", "category": "astro-ph_EP" }, { "text": "Super-Eccentric Migrating Jupiters: An important class of formation theories for hot Jupiters involves the\nexcitation of extreme orbital eccentricity (e=0.99 or even larger) followed by\ntidal dissipation at periastron passage that eventually circularizes the\nplanetary orbit at a period less than 10 days. In a steady state, this\nmechanism requires the existence of a significant population of super-eccentric\n(e>0.9) migrating Jupiters with long orbital periods and periastron distances\nof only a few stellar radii. For these super-eccentric planets, the periastron\nis fixed due to conservation of orbital angular momentum and the energy\ndissipated per orbit is constant, implying that the rate of change in\nsemi-major axis a is \\dot a \\propto a^0.5 and consequently the number\ndistribution satisfies dN/dlog a\\propto a^0.5. If this formation process\nproduces most hot Jupiters, Kepler should detect several super-eccentric\nmigrating progenitors of hot Jupiters, allowing for a test of high-eccentricity\nmigration scenarios.", "category": "astro-ph_EP" }, { "text": "Stellar wind effects on the atmospheres of close-in giants: a possible\n reduction in escape instead of increased erosion: The atmospheres of highly irradiated exoplanets are observed to undergo\nhydrodynamic escape. However, due to strong pressures, stellar winds can\nconfine planetary atmospheres, reducing their escape. Here, we investigate\nunder which conditions atmospheric escape of close-in giants could be confined\nby the large pressure of their host star's winds. For that, we simulate escape\nin planets at a range of orbital distances ([0.04, 0.14] au), planetary\ngravities ([36%, 87%] of Jupiter's gravity), and ages ([1, 6.9] Gyr). For each\nof these simulations, we calculate the ram pressure of these escaping\natmospheres and compare them to the expected stellar wind external pressure to\ndetermine whether a given atmosphere is confined or not. We show that, although\nyounger close-in giants should experience higher levels of atmospheric escape,\ndue to higher stellar irradiation, stellar winds are also stronger at young\nages, potentially reducing escape of young exoplanets. Regardless of the age,\nwe also find that there is always a region in our parameter space where\natmospheric escape is confined, preferably occurring at higher planetary\ngravities and orbital distances. We investigate confinement of some known\nexoplanets and find that the atmosphere of several of them, including pi Men c,\nshould be confined by the winds of their host stars, thus potentially\npreventing escape in highly irradiated planets. Thus, the lack of hydrogen\nescape recently reported for pi Men c could be caused by the stellar wind.", "category": "astro-ph_EP" }, { "text": "Meta-modelling the climate of dry tide locked rocky planets: Rocky planets hosted by close-in extrasolar systems are likely to be tidally\nlocked in 1:1 spin-orbit resonance, a configuration where they exhibit\npermanent dayside and nightside. Because of the resulting day-night temperature\ngradient, the climate and large-scale circulation of these planets are strongly\ndetermined by their atmospheric stability against collapse, which designates\nthe runaway condensation of greenhouse gases. To better constrain the surface\nconditions of rocky planets located in the habitable zone of their host star,\nit is therefore crucial to elucidate the mechanisms that govern the day-night\nheat redistribution. As a first attempt to bridge the gap between multiple\nmodelling approaches ranging from idealised models to 3-D General Circulation\nModels (GCM), we developed a General Circulation Meta-Model (GCMM) able to\nreproduce both the closed-form solutions provided by analytical models and the\nnumerical solutions obtained from GCM simulations. We used this approach to\ncharacterise the atmospheric stability of Earth-sized rocky planets with dry\natmospheres containing CO2, and we benchmarked it against 3-D GCM simulations\nusing THOR GCM. We observe that the collapse pressure below which collapse\noccurs can vary by ~40% around the value predicted by analytical scaling laws\ndepending on the mechanisms taken into account among radiative transfer,\natmospheric dynamics, and turbulent diffusion. Particularly, we find (i) that\nthe turbulent diffusion taking place in the dayside planetary boundary layer\n(PBL) globally tends to warm up the nightside surface hemisphere except in the\ntransition zone between optically thin and optically thick regimes, (ii) that\nthe PBL also significantly affects the day-night advection timescale, and (iii)\nthat the slow rotator approximation holds from the moment that the normalised\nequatorial Rossby deformation radius is greater than 2.", "category": "astro-ph_EP" }, { "text": "Polarized microwave emission from space particles in the upper\n atmosphere of the Earth: Tons of space particles enter the Earth atmosphere every year, being detected\nwhen they produce fireballs, meteor showers, or when they impact the Earth\nsurface. Particle detection in the showers could also be attempted from space\nusing satellites in low Earth orbit. Measuring the polarization would provide\nextra crucial information on the dominant alignment mechanisms and the\nproperties of the meteor families. In this article, we evaluate the expected\nsignal to aid in the design of space probes for this purpose. We have used the\nRADMC-3D code to simulate the polarized microwave emission of aligned dust\nparticles with different compositions: silicates, carbonates and irons. We have\nassumed a constant spatial particle density distribution of 0.22 cm$^{-3}$,\nbased on particle density measurements carried during meteor showers. Four\ndifferent grain size distributions with power indices ranging from $-3.5$ to\n$-2.0$ and dust particles with radius ranging from 0.01 $\\mathrm{\\mu}$m to 1 cm\nhave been considered for the simulations. Silicates and carbonates align their\nminor axis with the direction of the solar radiation field; during the flight\ntime into the Earth atmosphere, iron grains get oriented with the Earth's\nmagnetic field depending on their size. Alignment direction is reflected in the\n$Q$-Stokes parameter and in the polarization variation along the orbit.\nPolarization depends on the composition and on the size distribution of the\nparticles. The simulations show that some specific particle populations might\nbe detectable even with a small probe equipped with high sensitivity,\nphoton-counting microwave detectors operating in low Earth orbit.", "category": "astro-ph_EP" }, { "text": "Complete Tidal Evolution of Pluto-Charon: Both Pluto and its satellite Charon have rotation rates synchronous with\ntheir orbital mean motion. This is the theoretical end point of tidal evolution\nwhere transfer of angular momentum has ceased. Here we follow Pluto's tidal\nevolution from an initial state having the current total angular momentum of\nthe system but with Charon in an eccentric orbit with semimajor axis $a \\approx\n4R_P$ (where $R_P$ is the radius of Pluto), consistent with its impact origin.\nTwo tidal models are used, where the tidal dissipation function $Q \\propto$\n1/frequency and $Q=$ constant, where details of the evolution are strongly\nmodel dependent. The inclusion of the gravitational harmonic coefficient\n$C_{22}$ of both bodies in the analysis allows smooth, self consistent\nevolution to the dual synchronous state, whereas its omission frustrates\nsuccessful evolution in some cases. The zonal harmonic $J_2$ can also be\nincluded, but does not cause a significant effect on the overall evolution. The\nratio of dissipation in Charon to that in Pluto controls the behavior of the\norbital eccentricity, where a judicious choice leads to a nearly constant\neccentricity until the final approach to dual synchronous rotation. The tidal\nmodels are complete in the sense that every nuance of tidal evolution is\nrealized while conserving total angular momentum - including temporary capture\ninto spin-orbit resonances as Charon's spin decreases and damped librations\nabout the same.", "category": "astro-ph_EP" }, { "text": "Statistical-likelihood Exo-Planetary Habitability Index (SEPHI): A new Statistical-likelihood Exo-Planetary Habitability Index (SEPHI) is\npresented. It has been developed to cover the current and future features\nrequired for a classification scheme disentangling whether any discovered\nexoplanet is potentially habitable compared with life on Earth. The SEPHI uses\nlikelihood functions to estimate the habitability potential. It is defined as\nthe geometric mean of four sub-indexes related with four comparison criteria:\nIs the planet telluric?; Does it have an atmosphere dense enough and a gravity\ncompatible with life?; Does it have liquid water on its surface?; Does it have\na magnetic field shielding its surface from harmful radiation and stellar\nwinds?. Only with seven physical characteristics, can the SEPHI be estimated:\nPlanetary mass, radius, and orbital period; stellar mass, radius, and effective\ntemperature; planetary system age. We have applied the SEPHI to all the planets\nin the Exoplanet Encyclopaedia using a Monte Carlo Method. Kepler-1229 b,\nKepler-186 f, and Kepler-442 b have the largest SEPHI values assuming certain\nphysical descriptions. Kepler-1229 b is the most unexpected planet in this\nprivileged position since no previous study pointed to this planet as a\npotentially interesting and habitable one. In addition, most of the tidally\nlocked Earth-like planets present a weak magnetic field, incompatible with\nhabitability potential. We must stress that our results are linked to the\nphysics used in this study. Any change in the physics used only implies an\nupdating of the likelihood functions. We have developed a web application\nallowing the on-line estimation of the SEPHI: http://sephi.azurewebsites.net/", "category": "astro-ph_EP" }, { "text": "XX. CoRoT-20b: A very high density, high eccentricity transiting giant\n planet: We report the discovery by the CoRoT space mission of a new giant planet,\nCoRoT-20b. The planet has a mass of 4.24 +/- 0.23 MJ and a radius of 0.84 +/-\n0.04 RJ. With a mean density of 8.87 +/- 1.10 g/cm^3, it is among the most\ncompact planets known so far. Evolution models for the planet suggest a mass of\nheavy elements of the order of 800 ME if embedded in a central core, requiring\na revision either of the planet formation models or of planet evolution and\nstructure models. We note however that smaller amounts of heavy elements are\nexpected from more realistic models in which they are mixed throughout the\nenvelope. The planet orbits a G-type star with an orbital period of 9.24 days\nand an eccentricity of 0.56. The star's projected rotational velocity is vsini\n= 4.5 +/- 1.0 km/s, corresponding to a spin period of 11.5 +/- 3.1 days if its\naxis of rotation is perpendicular to the orbital plane. In the framework of\nDarwinian theories and neglecting stellar magnetic breaking, we calculate the\ntidal evolution of the system and show that CoRoT-20b is presently one of the\nvery few Darwin-stable planets that is evolving towards a triple synchronous\nstate with equality of the orbital, planetary and stellar spin periods.", "category": "astro-ph_EP" }, { "text": "Impact Erosion Model for Gravity-Dominated Planetesimals: Disruptive collisions have been regarded as an important process for planet\nformation, while non-disruptive, small-scale collisions (hereafter called\nerosive collisions) have been underestimated or neglected by many studies.\nHowever, recent studies have suggested that erosive collisions are also\nimportant to the growth of planets, because they are much more frequent than\ndisruptive collisions. Although the thresholds of the specific impact energy\nfor disruptive collisions (Q_RD^*) have been investigated well, there is no\nreliable model for erosive collisions. In this study, we systematically carried\nout impact simulations of gravity-dominated planetesimals for a wide range of\nspecific impact energy (Q_R) from disruptive collisions (Q_R ~ Q_RD^*) to\nerosive ones (Q_R << Q_RD^*) using the smoothed particle hydrodynamics method.\nWe found that the ejected mass normalized by the total mass (M_ej/M_tot)\ndepends on the numerical resolution, the target radius (R_tar) and the impact\nvelocity (v_imp), as well as on Q_R, but that it can be nicely scaled by Q_RD^*\nfor the parameter ranges investigated (R_tar = 30-300 km, v_imp = 2-5 km/s).\nThis means that M_ej/M_tot depends only on Q_R/Q_RD^* in these parameter\nranges. We confirmed that the collision outcomes for much less erosive\ncollisions (Q_R < 0.01 Q_RD^*) converge to the results of an impact onto a\nplanar target for various impact angles and that M_ej/M_tot = C * QR/QRD*\nholds. For disruptive collisions (Q_R ~ Q_RD^*), the curvature of the target\nhas a significant effect on Mej/Mtot. We also examined the angle-averaged value\nof M_ej/M_tot and found that the numerically obtained relation between\nangle-averaged M_ej/M_tot and Q_R/Q_RD^* is very similar to the cases for\n45-degree impacts. We proposed a new erosion model based on our numerical\nsimulations for future research on planet formation with collisional erosion.", "category": "astro-ph_EP" }, { "text": "Listening to the gravitational wave sound of circumbinary exoplanets: To date more than 3500 exoplanets have been discovered orbiting a large\nvariety of stars. Due to the sensitivity limits of the currently used detection\ntechniques, these planets populate zones restricted either to the solar\nneighbourhood or towards the Galactic bulge. This selection problem prevents us\nfrom unveiling the true Galactic planetary population and is not set to change\nfor the next two decades. Here we present a new detection method that overcomes\nthis issue and that will allow us to detect gas giant exoplanets using\ngravitational wave astronomy. We show that the Laser Interferometer Space\nAntenna (LISA) mission can characterise hundreds of new circumbinary exoplanets\norbiting white dwarf binaries everywhere in our Galaxy - a population of\nexoplanets so far completely unprobed - as well as detecting extragalactic\nbound exoplanets in the Magellanic Clouds. Such a method is not limited by\nstellar activity and, in extremely favourable cases, will allow LISA to detect\nsuper-Earths down to 10 Earth masses.", "category": "astro-ph_EP" }, { "text": "Modeling Indications of Technology in Planetary Transit Light Curves --\n Dark-side illumination: We analyze potential effects of an extraterrestrial civilization's use of\norbiting mirrors to illuminate the dark side of a synchronously rotating planet\non planetary transit light curves. Previous efforts to detect civilizations\nbased on side effects of planetary-scale engineering have focused on structures\naffecting the host star output (e.g. Dyson spheres). However, younger\ncivilizations are likely to be less advanced in their engineering efforts, yet\nstill capable of sending small spacecraft into orbit. Since M dwarfs are the\nmost common type of star in the solar neighborhood, it seems plausible that\nmany of the nearest habitable planets orbit dim, low-mass M stars, and will be\nin synchronous rotation. Logically, a civilization evolving on such a planet\nmay be inspired to illuminate their planet's dark side by placing a single\nlarge mirror at the L2 Lagrangian point, or launching a fleet of small thin\nmirrors into planetary orbit. We briefly examine the requirements and\nengineering challenges of such a collection of orbiting mirrors, then explore\ntheir impact on transit light curves. We incorporate stellar limb darkening and\nmodel a simplistic mirror fleet's effects for transits of Earth-like (R = 0.5\nto 2 R_Earth) planets which would be synchronously rotating for orbits within\nthe habitable zone of their host star. Although such an installation is\nundetectable in Kepler data, JWST will provide the sensitivity necessary to\ndetect a fleet of mirrors orbiting Earth-like habitable planets around nearby\nstars.", "category": "astro-ph_EP" }, { "text": "Constraining High Speed Winds in Exoplanet Atmospheres Through\n Observations of Anomalous Doppler Shifts During Transit: Three-dimensional (3-D) dynamical models of hot Jupiter atmospheres predict\nvery strong wind speeds. For tidally locked hot Jupiters, winds at high\naltitude in the planet's atmosphere advect heat from the day side to the cooler\nnight side of the planet. Net wind speeds on the order of 1-10 km/s directed\ntowards the night side of the planet are predicted at mbar pressures, which is\nthe approximate pressure level probed by transmission spectroscopy. These winds\nshould result in an observed blue shift of spectral lines in transmission on\nthe order of the wind speed. Indeed, Snellen et al. (2010) recently observed a\n2 +/- 1 km/s blue shift of CO transmission features for HD 209458b, which has\nbeen interpreted as a detection of the day-to-night winds that have been\npredicted by 3-D atmospheric dynamics modeling. Here we present the results of\na coupled 3-D atmospheric dynamics and transmission spectrum model, which\npredicts the Doppler-shifted spectrum of a hot Jupiter during transit resulting\nfrom winds in the planet's atmosphere. We explore four different models for the\nhot Jupiter atmosphere using different prescriptions for atmospheric drag via\ninteraction with planetary magnetic fields. We find that models with no\nmagnetic drag produce net Doppler blue shifts in the transmission spectrum of\n~2 km/s and that lower Doppler shifts of ~1 km/s are found for the higher drag\ncases, results consistent with -- but not yet strongly constrained by -- the\nSnellen et al. (2010) measurement. We additionally explore the possibility of\nrecovering the average terminator wind speed as a function of altitude by\nmeasuring Doppler shifts of individual spectral lines and spatially resolving\nwind speeds across the leading and trailing terminators during ingress and\negress.", "category": "astro-ph_EP" }, { "text": "An enhanced slope in the transmission spectrum of the hot Jupiter\n WASP-104b: We present the optical transmission spectrum of the hot Jupiter WASP-104b\nbased on one transit observed by the blue and red channels of the DBSP\nspectrograph at the Palomar 200-inch telescope and 14 transits observed by the\nMuSCAT2 four-channel imager at the 1.52 m Telescopio Carlos Sanchez. We also\nanalyse 45 additional K2 transits, after correcting for the flux contamination\nfrom a companion star. Together with the transit light curves acquired by DBSP\nand MuSCAT2, we are able to revise the system parameters and orbital ephemeris,\nconfirming that no transit timing variations exist. Our DBSP and MuSCAT2\ncombined transmission spectrum reveals an enhanced slope at wavelengths shorter\nthan 630 nm and suggests the presence of a cloud deck at longer wavelengths.\nWhile the Bayesian spectral retrieval analyses favour a hazy atmosphere,\nstellar spot contamination cannot be completely ruled out. Further evidence,\nfrom transmission spectroscopy and detailed characterisation of the host star's\nactivity, is required to distinguish the physical origin of the enhanced slope.", "category": "astro-ph_EP" }, { "text": "Where does Titan Sand Come From: Insight from Mechanical Properties of\n Titan Sand Candidates: Extensive equatorial linear dunes exist on Titan, but the origin of the sand,\nwhich appears to be organic, is unknown. We used nanoindentation to study the\nmechanical properties of a few Titan sand candidates, several natural sands on\nEarth, and common materials used in the Titan Wind Tunnel, to understand the\nmobility of Titan sand. We measured the elastic modulus (E), hardness (H), and\nfracture toughness (Kc) of these materials. Tholin's elastic modulus\n(10.4+/-0.5 GPa) and hardness (0.53+/-0.03 GPa) are both an order of magnitude\nsmaller than silicate sand, and is also smaller than the mechanically weak\nwhite gypsum sand. With a magnitude smaller fracture toughness\n(Kc=0.036+/-0.007 MPa-m^(1/2)), tholin is also much more brittle than silicate\nsand. This indicates that Titan sand should be derived close to the equatorial\nregions where the current dunes are located, because tholin is too soft and\nbrittle to be transported for long distances.", "category": "astro-ph_EP" }, { "text": "Computing Apparent Planetary Magnitudes for The Astronomical Almanac: Improved equations for computing planetary magnitudes are reported. These\nformulas model V-band observations acquired from the time of the earliest\nfilter photometry in the 1950s up to the present era. The new equations\nincorporate several terms that have not previously been used for generating\nphysical ephemerides. These include the rotation and revolution angles of Mars,\nthe sub-solar and sub-Earth latitudes of Uranus, and the secular time\ndependence of Neptune. Formulas for use in The Astronomical Almanac cover the\nplanetary phase angles visible from Earth. Supplementary equations cover those\nphase angles beyond the geocentric limits. Geocentric magnitudes were computed\nover a span of at least 50 years and the results were statistically analyzed.\nThe mean, variation and extreme magnitudes for each planet are reported. Other\nbands besides V on the Johnson-Cousins and Sloan photometric systems are\nbriefly discussed. The planetary magnitude data products available from the\nU.S. Naval Observatory are also listed. An appendix describes source code and\ntest data sets that are available on-line for computing planetary magnitudes\naccording to the equations and circumstances given in this paper. The files are\nposted as supplementary material for this paper. They are also available at\nSourceForge under project\nhttps://sourceforge.net/projects/planetary-magnitudes/ under the 'Files' tab in\nthe folder 'Ap_Mag_Current_Version'.", "category": "astro-ph_EP" }, { "text": "Q-type asteroids: Possibility of non-fresh weathered surfaces: Itokawa particles, which are the recovered samples from the S-complex\nasteroid 25143 Itokawa by the Hayabusa spacecraft, demonstrate that S-complex\nasteroids are parent bodies of ordinary chondrite meteorites. Furthermore, they\nclarify that the space weathering age of the Itokawa surface is of the order of\nseveral thousand years. Traditionally, Q-type asteroids have been considered\nfresh-surfaced. However, as the space weathering timescale is approximately\nthree orders of magnitude lesser than the conventionally considered age, the\npreviously proposed formation mechanisms of Q-type asteroids cannot\nsufficiently explain the surface refreshening. In this study, we propose a new\nhypothesis on the surface state of Q-type asteroids: Q-type asteroids have a\nnon-fresh weathered surface with a paucity of fine particles. For verifying\nthis hypothesis, laboratory experiments on the space weathering of ordinary\nchondrites are performed. Based on the results of these experiments, we found\nthat large (more than 100 {\\mu}m) ordinary chondritic particles with space\nweathering exhibit spectra consistent with Q-type asteroids.", "category": "astro-ph_EP" }, { "text": "An N-body Integrator for Gravitating Planetary Rings, and the Outer Edge\n of Saturn's B Ring: A new symplectic N-body integrator is introduced, one designed to calculate\nthe global 360 degree evolution of a self-gravitating planetary ring that is in\norbit about an oblate planet. This freely-available code is called epi_int, and\nit is distinct from other such codes in its use of streamlines to calculate the\neffects of ring self-gravity. The great advantage of this approach is that the\nperturbing forces arise from smooth wires of ring matter rather than discreet\nparticles, so there is very little gravitational scattering and so only a\nmodest number of particles are needed to simulate, say, the scalloped edge of a\nresonantly confined ring or the propagation of spiral density waves.\n The code is applied to the outer edge of Saturn's B ring, and a comparison of\nCassini measurements of the ring's forced response to simulations of Mimas'\nresonant perturbations reveals that the B ring's surface density at its outer\nedge is 195+-60 gm/cm^2 which, if the same everywhere across the ring would\nmean that the B ring's mass is about 90% of Mimas' mass.\n Cassini observations show that the B ring-edge has several free normal modes,\nwhich are long-lived disturbances of the ring-edge that are not driven by any\nknown satellite resonances. Although the mechanism that excites or sustains\nthese normal modes is unknown, we can plant such a disturbance at a simulated\nring's edge, and find that these modes persist without any damping for more\nthan ~10^5 orbits or ~100 yrs despite the simulated ring's viscosity of 100\ncm^2/sec. These simulations also indicate that impulsive disturbances at a ring\ncan excite long-lived normal modes, which suggests that an impact in the recent\npast by perhaps a cloud of cometary debris might have excited these\ndisturbances which are quite common to many of Saturn's sharp-edged rings.", "category": "astro-ph_EP" }, { "text": "Gap carving by a migrating planet embedded in a massive debris disc: When considering gaps in debris discs, a typical approach is to invoke\nclearing by an unseen planet within the gap, and derive the planet mass using\nWisdom overlap or Hill radius arguments. However, this approach can be invalid\nif the disc is massive, because this clearing would also cause planet\nmigration. This could result in a calculated planet mass that is incompatible\nwith the inferred disc mass, because the predicted planet would in reality be\ntoo small to carve the gap without significant migration. We investigate the\ngap that a single embedded planet would carve in a massive debris disc. We show\nthat a degeneracy is introduced, whereby an observed gap could be carved by two\ndifferent planets: either a high-mass, barely-migrating planet, or a smaller\nplanet that clears debris as it migrates. We find that, depending on disc mass,\nthere is a minimum possible gap width that an embedded planet could carve\n(because smaller planets, rather than carving a smaller gap, would actually\nmigrate through the disc and clear a wider region). We provide simple formulae\nfor the planet-to-debris disc mass ratio at which planet migration becomes\nimportant, the gap width that an embedded planet would carve in a massive\ndebris disc, and the interaction timescale. We also apply our results to\nvarious systems, and in particular show that the disc of HD 107146 can be\nreasonably well-reproduced with a migrating, embedded planet. Finally, we\ndiscuss the importance of planet-debris disc interactions as a tool for\nconstraining debris disc masses.", "category": "astro-ph_EP" }, { "text": "Investigating the Temperature Distribution of Diatomic Carbon in Comets\n using the Swan Bands: We present high spectral-resolution observations of comets 122P/de Vico and\n153P/Ikeya-Zhang obtained with the Tull Coud\\'{e} spectrograph on the 2.7m\nHarlan J. Smith telescope of McDonald Observatory. We used these data to study\nthe distribution of the lines of the $\\mathrm{d} ^3\\Pi_g - \\mathrm{a} ^3\\Pi_u$\nC$_2$ (Swan) bands. We show that the data are best represented with two\nrotational temperatures, with the lowest energy lines being at a relatively\ncool temperature and the higher energy lines being at a higher temperature. We\ndiscuss the implications of this two temperature distribution and suggest\nfuture work.", "category": "astro-ph_EP" }, { "text": "Capture of interstellar objects II: by the Solar system: Capture of interstellar objects (ISOs) into the Solar system is dominated by\nISOs with asymptotic incoming speeds $v_\\infty<4\\,$km\\,s$^{-1}$. The capture\nrate is proportional to the ISO phase-space density in the Solar vicinity and\ndoes not vary along the Sun's Galactic orbit, i.e.\\ is not enhanced during a\npassage through a cloud of ISOs (in contrast to previous suggestions). Most\nbound orbits crossing those of Jupiter and Saturn are fully mixed with unbound\nphase space, implying that they hold the same ISO phase-space density. Assuming\nan interstellar number density $n_{iso}\\sim0.1\\,$au$^{-3}$, we estimate that in\n1000 years the planets capture $\\sim2$ ISOs (while $\\sim17$ fall into the Sun),\nresulting in a population of $\\sim8$ captured ISOs within 5\\,au of the Sun at\nany time, less than the number of visiting ISOs passing through the same volume\non hyperbolic orbits. In terms of phase-space volume, capture onto and ejection\nfrom the Solar system are equal, such that on average ISOs will not remain\ncaptive at $a\\lesssim2000\\,$au for extensive periods.", "category": "astro-ph_EP" }, { "text": "Behaviour of electron content in the ionospheric D-region during solar\n X-ray flares: One of the most important parameters in ionospheric plasma research also\nhaving a wide practical application in wireless satellite telecommunications is\nthe total electron content (TEC) representing the columnal electron number\ndensity. The F region with high electron density provides the biggest\ncontribution to TEC while the relatively weakly ionized plasma of the D region\n(60 km - 90 km above Earths surface) is often considered as a negligible cause\nof satellite signal disturbances. However, sudden intensive ionization\nprocesses like those induced by solar X ray flares can cause relative increases\nof electron density that are significantly larger in the D-region than in\nregions at higher altitudes. Therefore, one cannot exclude a priori the D\nregion from investigations of ionospheric influences on propagation of\nelectromagnetic signals emitted by satellites. We discuss here this problem\nwhich has not been sufficiently treated in literature so far. The obtained\nresults are based on data collected from the D region monitoring by very low\nfrequency radio waves and on vertical TEC calculations from the Global\nNavigation Satellite System (GNSS) signal analyses, and they show noticeable\nvariations in the D region electron content (TECD) during activity of a solar X\nray flare (it rises by a factor of 136 in the considered case) when TECD\ncontribution to TEC can reach several percent and which cannot be neglected in\npractical applications like global positioning procedures by satellites.", "category": "astro-ph_EP" }, { "text": "Layer formation in a stably-stratified fluid cooled from above. Towards\n an analog for Jupiter and other gas giants: In 1D evolution models of gas giant planets, an outer convection zone\nadvances into the interior as the surface cools, and multiple convective layers\nform beneath that convective front. To study layer formation below an outer\nconvection zone in a similar scenario, we investigate the evolution of a\nstably-stratified fluid with a linear composition gradient that is constantly\nbeing cooled from above. We use the Boussinesq approximation in a series of 2D\nsimulations at low and high Prandtl numbers ($\\mathrm{Pr} = 0.5$ and 7),\ninitialized with constant temperature everywhere, and cooled at different\nrates. We find that multiple convective layers form at $\\mathrm{Pr} = 7$, {as\nthe result of an instability in the} diffusive thermal boundary layer below the\nouter convection zone. At low Pr, layers do not form because the temperature\ngradient within the boundary layer is much smaller than at large Pr and,\nconsequently, is not large enough to overcome the stabilizing effect of the\ncomposition gradient. For the stratification used in this study, on the\nlong-term the composition gradient is an ineffective barrier against the\npropagation of the outer convection zone and the entire fluid becomes\nfully-mixed, whether layers form or not. Our results challenge 1D evolutionary\nmodels of gas giant planets, which predict that layers are long-lived and that\nthe outer convective envelope stops advancing inwards. We discuss what is\nneeded for future work to build more realistic models.", "category": "astro-ph_EP" }, { "text": "The Runaway Greenhouse Effect on Hycean Worlds: Hycean worlds are a proposed subset of sub-Neptune exoplanets with\nsubstantial water inventories, liquid surface oceans and extended\nhydrogen-dominated atmospheres that could be favourable for habitability. In\nthis work, we aim to quantitatively define the inner edge of the Hycean\nhabitable zone using a 1D radiative-convective model. As a limiting case, we\nmodel a dry hydrogen-helium envelope above a surface ocean. We find that 10 to\n20 bars of atmosphere produces enough greenhouse effect to drive a liquid\nsurface ocean supercritical when forced with current Earth-like instellation.\nIntroducing water vapour into the atmosphere, we show the runaway greenhouse\ninstellation limit is greatly reduced due to the presence of superadiabatic\nlayers where convection is inhibited. This moves the inner edge of the\nhabitable zone from $\\approx$ 1 AU for a G-star to 1.6 AU (3.85 AU) for a\nHycean world with a H$_2$-He inventory of 1 bar (10 bar). For an M-star, the\ninner edge is equivalently moved from 0.17 AU to 0.28 AU (0.54 AU). Our results\nsuggest that most of the current Hycean world observational targets are not\nlikely to sustain a liquid water ocean. We present an analytical framework for\ninterpreting our results, finding that the maximum possible OLR scales\napproximately inversely with the dry mass inventory of the atmosphere. We\ndiscuss the possible limitations of our 1D modelling and recommend the use of\n3D convection-resolving models to explore the robustness of superadiabatic\nlayers.", "category": "astro-ph_EP" }, { "text": "Effects of an eccentric inner Jupiter on the dynamical evolution of icy\n body reservoirs in a planetary scattering scenario: We analyze the process of planetary scattering around M0-type stars. To do\nthis, we carry out N-body simulations with three Jupiter-mass planets close to\ntheir instability limit together with an outer planetesimal disk. This paper\nfocuses on the analysis of systems in which a single Jupiter-mass planet\nsurvives after the dynamical instability event. The small body reservoirs show\ndifferent dynamical behaviors. In fact, our simulations produce particles on\nprograde and retrograde orbits, as well as particles whose orbital plane flips\nfrom prograde to retrograde and back again along their evolution. Such\nparticles are called \"Type-F particles\". We find strong correlations between\nthe inclination $i$ and the ascending node longitude $\\Omega$ of such\nparticles. First, $\\Omega$ librates around 90$^{\\circ}$ or/and 270$^{\\circ}$.\nThis property is very important since it represents a necessary and sufficient\ncondition for the flipping of an orbit. Moreover, the libration periods of $i$\nand $\\Omega$ are equal and they are out to phase by a quarter period. We also\nremark that the larger the libration amplitude of $i$, the larger the libration\namplitude of $\\Omega$. Finally, we analyze the initial conditions of Type-F\nparticles of all our simulations immediately after the dynamical instability\nevent, when a single Jupiter-mass planet survives in the system. We carry out\nthis study with the goal to determine the parameter space that lead to the\nflipping of an orbit. Our results suggest that the orbit of a test particle can\nflip for any value of its initial eccentricity, although we found only two\nType-F particles with initial inclinations $i <$ 17$^{\\circ}$. Moreover, our\nstudy indicates that the minimum value of the inclination of the Type-F\nparticles in a given system decreases with an increase in the eccentricity of\nthe giant planet.", "category": "astro-ph_EP" }, { "text": "The abundance and thermal history of water ice in the disk surrounding\n HD142527 from the DIGIT Herschel Key Program: The presence or absence of ice in protoplanetary disks is of great importance\nfor the formation of planets. By enhancing the solid surface density and\nincreasing the sticking efficiency, ice catalyzes the rapid formation of\nplanetesimals and decreases the time scale for giant planet core accretion.\nAims: In this paper we analyse the composition of the outer disk around the\nHerbig star HD~142527. We focus on the composition of the water ice, but also\nanalyse the abundances of previously proposed minerals. Methods: We present new\nHerschel far infrared spectra and a re-reduction of archival data from the\nInfrared Space Observatory (ISO). We model the disk using full 3D radiative\ntransfer to obtain the disk structure. Also, we use an optically thin analysis\nof the outer disk spectrum to obtain firm constraints on the composition of the\ndust component. Results: The water ice in the disk around HD~142527 contains a\nlarge reservoir of crystalline water ice. We determine the local abundance of\nwater ice in the outer disk (i.e. beyond 130\\,AU). The re-reduced ISO spectrum\ndiffers significantly from that previously published, but matches the new\nHerschel spectrum at their common wavelength range. In particular, we do not\ndetect any significant contribution from carbonates or hydrous silicates, in\ncontrast to earlier claims. Conclusions: The amount of water ice detected in\nthe outer disk requires $\\sim80\\,$\\% of the oxygen atoms. This is comparable to\nthe water ice abundance in the outer solar system, in comets and in dense\ninterstellar clouds. The water ice is highly crystalline while the temperatures\nwhere we detect it are too low to crystallize the water on relevant time\nscales. We discuss the implications of this finding.", "category": "astro-ph_EP" }, { "text": "Migrating super-Earths in low-viscosity discs: unveiling the roles of\n feedback, vortices, and laminar accretion flows: We present the highest resolution study to date of super-Earths migrating in\ninviscid and low-viscosity discs, motivated by the connection to laminar,\nwind-driven models of protoplanetary discs. Our models unveil the critical role\nof vortices in determining the migration behaviour for partial gap-opening\nplanets. Vortices form in pressure maxima at gap edges, and prevent the\ndisc-feedback stopping of migration for intermediate planets in low-viscosity\nand inviscid discs, contrary to the concept of the `inertial limit' or `disc\nfeedback' halting predicted from analytical models. Vortices may also form in\nthe corotation region, and can dramatically modify migration behaviour through\ndirect gravitational interaction with the planet. These features become\napparent at high resolution, and for all but the highest viscosities there\nexist significant difficulties in obtaining numerically converged results. The\nmigration of partial gap-opening planets, however, clearly becomes chaotic for\nsufficiently low viscosities. At moderate viscosity, a smooth disc-feedback\nregime is found in which migration can slow substantially, and the migration\ntime-scale observed corresponds to migration being driven by diffusive\nrelaxation of the gap edges. At high viscosity classical Type I migration is\nrecovered. For Jupiter-analogue planets in inviscid discs, a wide, deep gap is\nformed. Transient Type II migration occurs over radial length-scales\ncorresponding to the gap width, beyond which migration can stall. Finally, we\nexamine the particle trapping driven by structures left in inviscid discs by a\nmigrating planet, and find that particle traps in the form of multiple rings\nand vortices can persist long after the planet has passed. In this case, the\nobservation of particle traps by submillimetre interferometers such as ALMA\ncannot be used to infer the current presence of an adjacent planet.", "category": "astro-ph_EP" }, { "text": "A photochemical model for the carbon-rich planet WASP-12b: The hot Jupiter WASP-12b is a heavily irradiated exoplanet in a short period\norbit around a G0-star with twice the metallicity of the Sun. A recent\nthermochemical equilibrium analysis based on Spitzer and ground-based infrared\nobservations suggests that the presence of $\\ch4$ in its atmosphere and the\nlack of $\\h2o$ features can only be explained if the carbon-to-oxygen ratio in\nthe planet's atmosphere is much greater than the solar ratio ($\\ctoo = 0.54$).\nHere, we use a 1-D photochemical model to study the effect of disequilibrium\nchemistry on the observed abundances of $\\h2o, \\com, \\co2$ and $\\ch4$ in the\nWASP-12b atmosphere. We consider two cases: one with solar $\\ctoo$ and another\nwith $\\ctoo = 1.08$. The solar case predicts that $\\h2o$ and $\\com$ are more\nabundant than $\\co2$ and $\\ch4$, as expected, whereas the high $\\ctoo$ model\nshows that $\\com$, C$_{2}$H$_{2}$ and HCN are more abundant. This indicates\nthat the extra carbon from the high $\\ctoo$ model is in hydrocarbon species.\n$\\h2o$ photolysis is the dominant disequilibrium mechanism that alters the\nchemistry at higher altitudes in the solar $\\ctoo$ case, whereas\nphotodissociation of C$_{2}$H$_{2}$ and HCN is significant in the super-solar\ncase. Furthermore, our analysis indicates that $\\c2h2$ is the major absorber in\nthe atmosphere of WASP-12b and the absorption features detected near 1.6 and 8\nmicron may be arising from C$_{2}$H$_{2}$ rather than $\\ch4$. The Hubble Space\nTelescope's WFC3 can resolve this discrepancy, as $\\c2h2$ has absorption\nbetween $1.51 - 1.54$ microns, while $\\ch4$ does not.", "category": "astro-ph_EP" }, { "text": "Volatile transport on inhomogeneous surfaces: II. Numerical calculations\n (VT3D): Several distant icy worlds have atmospheres that are in vapor-pressure\nequilibrium with their surface volatiles, including Pluto, Triton, and,\nprobably, several large KBOs near perihelion. Studies of the volatile and\nthermal evolution of these have been limited by computational speed, especially\nfor models that treat surfaces that vary with both latitude and longitude. In\norder to expedite such work, I present a new numerical model for the seasonal\nbehavior of Pluto and Triton which (i) uses initial conditions that improve\nconvergence, (ii) uses an expedient method for handling the transition between\nglobal and non-global atmospheres, (iii) includes local conservation of energy\nand global conservation of mass to partition energy between heating,\nconduction, and sublimation or condensation, (iv) uses time-stepping algorithms\nthat ensure stability while allowing larger timesteps, and (v) can include\nlongitudinal variability. This model, called VT3D, has been used in Young\n(2012), Young (2013), Olkin et al. (2015), Young and McKinnon (2013), and\nFrench et al. (2015).", "category": "astro-ph_EP" }, { "text": "Transmission Spectroscopy of the Hot-Jupiter WASP-12b from 0.7 to 5\n microns: Since the first report of a potentially non-solar carbon-to-oxygen ratio\n(C/O) in its dayside atmosphere, the highly irradiated exoplanet WASP-12b has\nbeen under intense scrutiny and the subject of many follow-up observations.\nAdditionally, the recent discovery of stellar binary companions ~1\" from\nWASP-12 has obfuscated interpretation of the observational data. Here we\npresent new ground-based multi-object transmission-spectroscopy observations of\nWASP-12b that we acquired over two consecutive nights in the red optical with\nGemini-N/GMOS. After correcting for the influence of WASP-12's stellar\ncompanions, we find that these data rule out a cloud-free, H2 atmosphere with\nno additional opacity sources. We detect features in the transmission spectrum\nthat may be attributed to metal oxides (such as TiO and VO) for an O-rich\natmosphere or to metal hydrides (such as TiH) for a C-rich atmosphere. We also\nreanalyzed NIR transit-spectroscopy observations of WASP-12b from HST/WFC3 and\nbroadband transit photometry from Warm Spitzer. We attribute the broad spectral\nfeatures in the WFC3 data to either H2O or CH4 and HCN for an O-rich or C-rich\natmosphere, respectively. The Spitzer data suggest shallower transit depths\nthan the models predict at infrared wavelengths, albeit at low statistical\nsignificance. A multi-instrument, broad-wavelength analysis of WASP-12b\nsuggests that the transmission spectrum is well approximated by a simple\nRayleigh scattering model with a planet terminator temperature of 1870 +/- 130\nK. We conclude that additional high-precision data and isolated spectroscopic\nmeasurements of the companion stars are required to place definitive\nconstraints on the composition of WASP-12b's atmosphere.", "category": "astro-ph_EP" }, { "text": "A Framework for Prioritizing the TESS Planetary Candidates Most Amenable\n to Atmospheric Characterization: A key legacy of the recently launched TESS mission will be to provide the\nastronomical community with many of the best transiting exoplanet targets for\natmospheric characterization. However, time is of the essence to take full\nadvantage of this opportunity. JWST, although delayed, will still complete its\nnominal five year mission on a timeline that motivates rapid identification,\nconfirmation, and mass measurement of the top atmospheric characterization\ntargets from TESS. Beyond JWST, future dedicated missions for atmospheric\nstudies such as ARIEL require the discovery and confirmation of several hundred\nadditional sub-Jovian size planets (R_p < 10 R_Earth) orbiting bright stars,\nbeyond those known today, to ensure a successful statistical census of\nexoplanet atmospheres. Ground-based ELTs will also contribute to surveying the\natmospheres of the transiting planets discovered by TESS. Here we present a set\nof two straightforward analytic metrics, quantifying the expected\nsignal-to-noise in transmission and thermal emission spectroscopy for a given\nplanet, that will allow the top atmospheric characterization targets to be\nreadily identified among the TESS planet candidates. Targets that meet our\nproposed threshold values for these metrics would be encouraged for rapid\nfollow-up and confirmation via radial velocity mass measurements. Based on the\ncatalog of simulated TESS detections by Sullivan et al. (2015), we determine\nappropriate cutoff values of the metrics, such that the TESS mission will\nultimately yield a sample of $\\sim300$ high-quality atmospheric\ncharacterization targets across a range of planet size bins, extending down to\nEarth-size, potentially habitable worlds.", "category": "astro-ph_EP" }, { "text": "Combining astrometry and JUICE -- Europa Clipper radio science to\n improve the ephemerides of the Galilean moons: The upcoming JUICE and Europa Clipper missions to Jupiter's Galilean\nsatellites will provide radio science tracking measurements of both spacecraft.\nSuch data are expected to significantly help estimating the moons' ephemerides\nand related dynamical parameters. However, the two missions will yield an\nimbalanced dataset, with no flybys planned at Io, condensed over less than six\nyears. Current ephemerides' solutions for the Galilean moons, on the other\nhand, rely on ground-based astrometry collected over more than a century which,\nwhile being less accurate, bring very valuable constraints on the long-term\ndynamics of the system. An improved solution for the Galilean satellites'\ncomplex dynamics could however be achieved by exploiting the existing synergies\nbetween these different observation sets. To quantify this, we merged simulated\nJUICE and Clipper radio science data with existing ground-based astrometric and\nradar observations, and performed the inversion. Our study specifically\nfocusses on the resulting formal uncertainties in the moons' states, as well as\nIo's and Jupiter's tidal dissipation parameters. Adding astrometry stabilises\nthe moons' state solution, especially beyond the missions' timelines. It\nfurthermore reduces the uncertainties in $1/Q$ (inverse of the tidal quality\nfactor) by a factor two to four for Jupiter, and about 30-35\\% for Io. Among\nall data types, classical astrometry data prior to 1960 proved particularly\nbeneficial. We also show that ground observations of Io add the most to the\nsolution, confirming that ground observations can fill the lack of radio\nscience data for this specific moon. We obtained a noticeable solution\nimprovement when exploiting the complementarity between all different\nobservation sets. These promising simulation results thus motivate future\nefforts to achieve a global solution from actual JUICE and Clipper radio\nscience data.", "category": "astro-ph_EP" }, { "text": "Formation of dust-rich planetesimals from sublimated pebbles inside of\n the snow line: Content: For up to a few millions of years, pebbles must provide a\nquasi-steady inflow of solids from the outer parts of protoplanetary disks to\ntheir inner regions. Aims: We wish to understand how a significant fraction of\nthe pebbles grows into planetesimals instead of being lost to the host star.\nMethods:We examined analytically how the inward flow of pebbles is affected by\nthe snow line and under which conditions dust-rich (rocky) planetesimals form.\nWhen calculating the inward drift of solids that is due to gas drag, we\nincluded the back-reaction of the gas to the motion of the solids. Results: We\nshow that in low-viscosity protoplanetary disks (with a monotonous surface\ndensity similar to that of the minimum-mass solar nebula), the flow of pebbles\ndoes not usually reach the required surface density to form planetesimals by\nstreaming instability. We show, however, that if the pebble-to-gas-mass flux\nexceeds a critical value, no steady solution can be found for the solid-to-gas\nratio. This is particularly important for low-viscosity disks (alpha < 10^(-3))\nwhere we show that inside of the snow line, silicate-dust grains ejected from\nsublimating pebbles can accumulate, eventually leading to the formation of\ndust-rich planetesimals directly by gravitational instability. Conclusions:\nThis formation of dust-rich planetesimals may occur for extended periods of\ntime, while the snow line sweeps from several au to inside of 1 au. The\nrock-to-ice ratio may thus be globally significantly higher in planetesimals\nand planets than in the central star.", "category": "astro-ph_EP" }, { "text": "Large eccentricity, low mutual inclination: the three-dimensional\n architecture of a hierarchical system of giant planets: We establish the three-dimensional architecture of the Kepler-419 (previously\nKOI-1474) system to be eccentric yet with a low mutual inclination. Kepler-419b\nis a warm Jupiter at semi-major axis a = 0.370 +0.007/-0.006 AU with a large\neccentricity e=0.85 +0.08/-0.07 measured via the \"photoeccentric effect.\" It\nexhibits transit timing variations induced by the non-transiting Kepler-419c,\nwhich we uniquely constrain to be a moderately eccentric (e=0.184 +/- 0.002),\nhierarchically-separated (a=1.68 +/- 0.03 AU) giant planet (7.3 +/- 0.4 MJup).\nWe combine sixteen quarters of Kepler photometry, radial-velocity (RV)\nmeasurements from the HIgh Resolution Echelle Spectrometer (HIRES) on Keck, and\nimproved stellar parameters that we derive from spectroscopy and\nasteroseismology. From the RVs, we measure the mass of inner planet to be\n2.5+/-0.3MJup and confirm its photometrically-measured eccentricity, refining\nthe value to e=0.83+/-0.01. The RV acceleration is consistent with the\nproperties of the outer planet derived from TTVs. We find that, despite their\nsizable eccentricities, the planets are coplanar to within 9 +8/-6 degrees, and\ntherefore the inner planet's large eccentricity and close-in orbit are unlikely\nto be the result of Kozai migration. Moreover, even over many secular cycles,\nthe inner planet's periapse is most likely never small enough for tidal\ncircularization. Finally, we present and measure a transit time and impact\nparameter from four simultaneous ground-based light curves from 1m-class\ntelescopes, demonstrating the feasibility of ground-based follow-up of Kepler\ngiant planets exhibiting large TTVs.", "category": "astro-ph_EP" }, { "text": "Asteroid Photometry: Asteroid photometry has three major applications: providing clues about\nasteroid surface physical properties and compositions, facilitating photometric\ncorrections, and helping design and plan ground-based and spacecraft\nobservations. The most significant advances in asteroid photometry in the past\ndecade were driven by spacecraft observations that collected spatially resolved\nimaging and spectroscopy data. In the mean time, laboratory measurements and\ntheoretical developments are revealing controversies regarding the physical\ninterpretations of models and model parameter values. We will review the new\ndevelopments in asteroid photometry that have occurred over the past decade in\nthe three complementary areas of observations, laboratory work, and theory.\nFinally we will summarize and discuss the implications of recent findings.", "category": "astro-ph_EP" }, { "text": "Electrostatic lofting of dust grains from the surfaces of Thebe and\n Amalthea: Energetic electrons from the inner radiation belt provide significant\nelectric charging of the surfaces of Jupiter's moons Thebe and Amalthea whose\norbits are located within this radiation belt. We estimate theoretically the\nelectric fields in the vicinity of the polar regions of Thebe and Amalthea and\nargue that these fields are sufficient for lofting of micron and\nsubmicron-sized dust grains from the surfaces of the moons. Thus, the lofting\nof charged dust grains in the electric fields can be considered as an\nadditional source supplying dust to the gossamer rings in addition to dust\nejection by micrometeoroid impacts onto the moons' surfaces. The suggested\nmechanism can explain qualitatively some peculiarities of the dust grain\ndistributions within the gossamer rings.", "category": "astro-ph_EP" }, { "text": "Constraining the origin of the planetary debris surrounding ZTF\n J0139+5245 through rotational fission of a triaxial asteroid: White dwarfs containing orbiting planetesimals or their debris represent\ncrucial benchmarks by which theoretical investigations of post-main-sequence\nplanetary systems may be calibrated. The photometric transit signatures of\nlikely planetary debris in the ZTF J0139+5245 white dwarf system has an orbital\nperiod of about 110 days. An asteroid which breaks up to produce this debris\nmay spin itself to destruction through repeated close encounters with the star\nwithout entering its Roche radius and without influence from the white dwarf's\nluminosity. Here, we place coupled constraints on the orbital pericentre ($q$)\nand the ratio ($\\beta$) of the middle to longest semiaxes of a triaxial\nasteroid which disrupts outside of this white dwarf's Roche radius ($r_{\\rm\nRoche}$) soon after attaining its 110-day orbit. We find that disruption within\ntens of years is likely when $\\beta \\lesssim 0.6$ and $q\\approx 1.0-2.0r_{\\rm\nRoche}$, and when $\\beta \\lesssim 0.2$ out to $q\\approx 2.5r_{\\rm Roche}$.\nAnalysing the longer-timescale disruption of triaxial asteroids around ZTF\nJ0139+5245 is desirable but may require either an analytical approach relying\non ergodic theory or novel numerical techniques.", "category": "astro-ph_EP" }, { "text": "HAT-P-28b and HAT-P-29b: Two Sub-Jupiter Mass Transiting Planets: We present the discovery of two transiting exoplanets. HAT-P-28b orbits a\nV=13.03 G3 dwarf star with a period P = 3.2572 d and has a mass of 0.63 +- 0.04\nMJ and a radius of 1.21 + 0.11 -0.08 RJ yielding a mean density of 0.44 +- 0.09\ng cm-3. HAT-P-29b orbits a V=11.90 F8 dwarf star with a period P = 5.7232 d and\nhas a mass of 0.78 +0.08 -0.04 MJ and a radius of 1.11 +0.14 -0.08 RJ yielding\na mean density of 0.71 +- 0.18 g cm-3. We discuss the properties of these\nplanets in the context of other known transiting planets.", "category": "astro-ph_EP" }, { "text": "Constraining spatial pattern of early activity of comet 67P/C-G with 3D\n modeling of the MIRO observations: Our aim is to investigate early activity (July 2014) of 67P/CG with 3D coma\nand radiative transfer modeling of MIRO measurements, accounting for nucleus\nshape, illumination, and orientation of the comet. We investigate MIRO line\nshape information for spatial distribution of water activity on the nucleus\nduring the onset of activity. During this period we show that MIRO line shape\nhave enough information to clearly isolate contribution from Hapi and Inhotep\nindependently, and compare it to the nominal case of activity from the entire\nilluminated surface. We also demonstrate that spectral line shapes differ from\nthe 1D model for different viewing geometries and coma conditions relevant to\nthis study. Specifically, line shapes are somewhat sensitive to the location of\nthe terminator in the coma. At last, fitting the MIRO observations we show that\nthe Imhotep region (possible extended source of H$_{2}$O due to CO$_{2}$\nactivity) contributes only a small fraction of the total number of water\nmolecules into MIRO beam in the early activity. On the other hand, a strong\nenhancement of water activity from the Hapi region seems required to fit the\nMIRO line shapes. This is consistent with earlier Rosetta results.\nNevertheless, within the assumption of our coma and surface boundary\nconditions, we cannot get a reasonable fit to all MIRO mapping observations in\nJuly 2014, which may illustrate that a more sophisticated coma model or more\naccurate temperature/velocity distribution is needed.", "category": "astro-ph_EP" }, { "text": "Detection of an atmosphere around the super-Earth 55 Cancri e: We report the analysis of two new spectroscopic observations of the\nsuper-Earth 55 Cancri e, in the near infrared, obtained with the WFC3 camera\nonboard the HST. 55 Cancri e orbits so close to its parent star, that\ntemperatures much higher than 2000 K are expected on its surface. Given the\nbrightness of 55 Cancri, the observations were obtained in scanning mode,\nadopting a very long scanning length and a very high scanning speed. We use our\nspecialized pipeline to take into account systematics introduced by these\nobservational parameters when coupled with the geometrical distortions of the\ninstrument. We measure the transit depth per wavelength channel with an average\nrelative uncertainty of 22 ppm per visit and find modulations that depart from\na straight line model with a 6$\\sigma$ confidence level. These results suggest\nthat 55 Cancri e is surrounded by an atmosphere, which is probably\nhydrogen-rich. Our fully Bayesian spectral retrieval code, T-REx, has\nidentified HCN to be the most likely molecular candidate able to explain the\nfeatures at 1.42 and 1.54 $\\mu$m. While additional spectroscopic observations\nin a broader wavelength range in the infrared will be needed to confirm the HCN\ndetection, we discuss here the implications of such result. Our chemical model,\ndeveloped with combustion specialists, indicates that relatively high mixing\nratios of HCN may be caused by a high C/O ratio. This result suggests this\nsuper-Earth is a carbon-rich environment even more exotic than previously\nthought.", "category": "astro-ph_EP" }, { "text": "Hypotheses for near-surface exchange of methane on Mars: The Curiosity rover recently detected a background of 0.7 ppb and spikes of 7\nppb of methane on Mars. This in situ measurement reorients our understanding of\nthe Martian environment and its potential for life, as the current theories do\nnot entail any geological source or sink of methane that varies sub-annually.\nIn particular, the 10-fold elevation during the southern winter indicates\nepisodic sources of methane that are yet to be discovered. Here we suggest a\nnear-surface reservoir could explain this variability. Using the temperature\nand humidity measurements from the rover, we find that perchlorate salts in the\nregolith deliquesce to form liquid solutions, and deliquescence progresses to\ndeeper subsurface in the season of the methane spikes. We therefore formulate\nthe following three testable hypotheses. The first scenario is that the\nregolith in Gale Crater adsorbs methane when dry and releases this methane to\nthe atmosphere upon deliquescence. The adsorption energy needs to be 36 kJ/mol\nto explain the magnitude of the methane spikes, higher than existing laboratory\nmeasurements. The second scenario is that microorganisms convert organic matter\nin the soil to methane when they are in liquid solutions. This scenario does\nnot require regolith adsorption, but entails extant life on Mars. The third\nscenario is that deep subsurface aquifers produce the bursts of methane.\nContinued in situ measurements of methane and water, as well as laboratory\nstudies of adsorption and deliquescence, will test these hypotheses and inform\nthe existence of the near-surface reservoir and its exchange with the\natmosphere.", "category": "astro-ph_EP" }, { "text": "Insights into planet formation from debris disks: II. Giant impacts in\n extrasolar planetary systems: Giant impacts refer to collisions between two objects each of which is\nmassive enough to be considered at least a planetary embryo. The putative\ncollision suffered by the proto-Earth that created the Moon is a prime example,\nthough most Solar System bodies bear signatures of such collisions. Current\nplanet formation models predict that an epoch of giant impacts may be\ninevitable, and observations of debris around other stars are providing\nmounting evidence that giant impacts feature in the evolution of many planetary\nsystems. This chapter reviews giant impacts, focussing on what we can learn\nabout planet formation by studying debris around other stars. Giant impact\ndebris evolves through mutual collisions and dynamical interactions with\nplanets. General aspects of this evolution are outlined, noting the importance\nof the collision-point geometry. The detectability of the debris is discussed\nusing the example of the Moon-forming impact. Such debris could be detectable\naround another star up to 10Myr post-impact, but model uncertainties could\nreduce detectability to a few 100yr window. Nevertheless the 3% of young stars\nwith debris at levels expected during terrestrial planet formation provide\nvaluable constraints on formation models; implications for super-Earth\nformation are also discussed. Variability recently observed in some bright\ndisks promises to illuminate the evolution during the earliest phases when\nvapour condensates may be optically thick and acutely affected by the\ncollision-point geometry. The outer reaches of planetary systems may also\nexhibit signatures of giant impacts, such as the clumpy debris structures seen\naround some stars.", "category": "astro-ph_EP" }, { "text": "Outburst activity in comets: II. A multi-band photometric monitoring of\n comet 29p/Schwassmann-Wachmann 1: We have carried out a continuous multi-band photometric monitoring of the\nnuclear activity of comet 29P/Schwassmann-Wachmann 1 from 2008 to 2010. Our\nmain aim has been to study the outburst mechanism on the basis of a follow-up\nof the photometric variations associated with the release of dust. We used a\nstandardized method to obtain the 10 arc-sec nucleus photometry in the V, R,\nand I filters of the Johnson-Kron-Cousins system, being accurately calibrated\nwith standard Landolt stars. Production of dust in the R and I bands during the\n2010 Feb. 3 outburst has been also computed. We conclude that the massive\nejection of large (optically-thin) particles from the surface at the time of\nthe outburst is the triggering mechanism to produce the outburst. Ulterior\nsublimation of these ice-rich dust particles during the following days induces\nfragmentation, generating micrometer-sized grains that increase the dust\nspatial density to produce the outburst in the optical range due to scattering\nof sun light. The material leaving the nucleus adopts a fan-like dust feature,\nformed by micrometer-sized particles that are decaying in brightness as it\nevolved outwards. By analyzing the photometric signal measured in a\nstandardized 10-arcsec aperture using the Phase Dispersion Minimization\ntechnique we have found a clear periodicity of 50 days. Remarkably, this value\nis also consistent with an outburst frequency of 7.4 outbursts/year deduced\nfrom the number of outbursts noticed during the effective observing time.", "category": "astro-ph_EP" }, { "text": "The Radial Distribution of Dust Particles in the HL Tau Disk from ALMA\n and VLA Observations: Understanding planet formation requires to discern how dust grows in\nprotoplanetary disks. An important parameter to measure in disks is the maximum\ndust grain size present. This is usually estimated through measurements of the\ndust opacity at different millimeter wavelengths assuming optically thin\nemission and dust opacity dominated by absorption. However, ALMA observations\nhave shown that these assumptions might not be correct in the case of\nprotoplanetary disks, leading to overestimation of particle sizes and to\nunderestimation of the disk's mass. Here, we present an analysis of high\nquality ALMA and VLA images of the HL Tau protoplanetary disk, covering a wide\nrange of wavelengths, from 0.8 mm to 1 cm, and with a physical resolution of\n$\\sim$7.35 au. We describe a procedure to analyze a set of millimeter images\nwithout any assumption about the optical depth of the emission, and including\nthe effects of absorption and scattering in the dust opacity. This procedure\nallows us to obtain the dust temperature, the dust surface density and the\nmaximum particle size at each radius. In the HL Tau disk, we found that\nparticles have already grown up to a few millimeters in size. We detect\ndifferences in the dust properties between dark and bright rings, with dark\nrings containing low dust density and small dust particles. Different features\nin the HL Tau disk seem to have different origins. Planet-disk interactions can\nexplain substructure at the external half of the disk, but the internal rings\nseem to be associated to the presence of snow lines of several molecules.", "category": "astro-ph_EP" }, { "text": "Instantaneous Three-dimensional Thermal Structure of the South Polar\n Vortex of Venus: The Venus thermal radiation spectrum exhibits the signature of $CO_2$\nabsorption bands. By means of inversion techniques, those bands enable the\nretrieval of atmospheric temperature profiles. We have analyzed VIRTIS-M-IR\nnight-side data obtaining high-resolution thermal maps of Venus south polar\nregion between 55 and 85 km altitudes for three dynamical configurations of the\nvortex. The cold collar is clearly distinguishable at $\\sim 62$ km altitude\nlevel, and it is more than 15 K colder than the pole on average. The South\nPolar Vortex appears as a vertically extended hot region close to the pole and\nsqueezed by the cold collar between altitudes 55 and 67 km but spreading\nequatorward at about 74 km. Both the instantaneous temperature maps and their\nzonal averages show that the top altitude limit of the thermal signature of the\nvortex is at $\\sim 80$ km altitude, at least on the night-side of the planet.\nThe upper part of the atmosphere (67 - 85 km) is more homogeneous and has\nlong-scale horizontal temperature differences of about 25 K over horizontal\ndistances of $\\sim 2,000$ km. The lower part (55 - 67 km) shows more fine-scale\nstructure, creating the vortex' morphology, with thermal differences of up to\nabout 50 K over $\\sim 500$ km horizontal distances. We also study the vertical\nstability of different atmospheric layers within the 55 - 85 km altitude range\nfor the three vortex configurations. It is always positive, but the cold collar\nis the most vertically stable structure at polar latitudes, while the vortex\nand sub-polar latitudes show lower stability values. Furthermore, the hot\nfilaments present within the vortex exhibit lower stability values than their\nsurroundings. The layer between 62 and 67 km resulted to be the most stable.\nThese results are in good agreement with conclusions from previous radio\noccultation analyses.", "category": "astro-ph_EP" }, { "text": "Gravito-turbulence in irradiated protoplanetary discs: Using radiation hydrodynamics simulations in a local stratified shearing box\nwith realistic equations of state and opacities, we explored the outcome of\nself-gravity at 50 AU in a protoplanetary disc irradiated by the central star.\nWe found that gravito-turbulence is sustained for a finite range of the surface\ndensity, from $\\sim 80$ to $\\sim$ 250 gcm$^{-2}$. The disk is laminar below the\nrange while fragments above it. In the range of gravito-turbulence, the Toomre\nparameter decreases monotonically from $\\sim 1$ to $\\sim 0.7$ as the surface\ndensity increases while an effective cooling time is almost constant at $\\sim\n4$ in terms of the inverse of the orbital frequency. The turbulent motions are\nsupersonic at all heights, which dissipates through both shock waves and\ncompressional heating. The compressional motions, occurring near the midplane,\ncreate upward flows, which not only contribute to supporting the disc but also\nto transporting the dissipated energy to the disc surfaces. The irradiation\ndoes not affect much the gravito-turbulence near the midplane unless the\ngrazing angle is larger than 0.32. We also show that a simple cooling function\nwith a constant cooling time does not approximate the realistic cooling.", "category": "astro-ph_EP" }, { "text": "The Architecture of the V892 Tau System: the Binary and its Circumbinary\n Disk: We present high resolution millimeter continuum and CO line observations for\nthe circumbinary disk around V892 Tau to constrain the stellar and disk\nproperties. The total mass of the two near-equal-mass A stars is estimated to\nbe $6.0\\pm0.2\\,M_{\\odot}$ based on our models of the Keplerian-dominated gas\ndisk rotation. The detection of strong ionized gas emission associated with the\ntwo stars at 8 mm, when combined with previous astrometric measurements in the\nnear-infrared, provides an updated view of the binary orbit with $a=7.1\\pm0.1$\nau, $e=0.27\\pm0.1$, and $P=7.7\\pm0.2$ yr, which is about half of a previously\nreported orbital period. The binary orbital plane is proposed to be near\ncoplanar to the circumbinary disk plane (with a mutual inclination of only\n$\\Delta=8\\pm4.2$ deg; another solution with $\\Delta=113$ deg is less likely\ngiven the short re-alignment timescale). An asymmetric dust disk ring peaking\nat a radius of 0.''2 is detected at 1.3 mm and its fainter counterparts are\nalso detected at the longer 8 and 9.8 mm. The CO gas disk, though dominated by\nKeplerian rotation, presents a mild inner and outer disk misalignment, such\nthat the inner disk to the SW and outer disk to the NE appear brighter than\ntheir counterparts at the opposite disk sides. The radial extension of the\ndisk, its asymmetric dust ring, and the presence of a disk warp could all be\nexplained by the interaction between the eccentric binary and the circumbinary\ndisk, which we assume were formed with non-zero mutual inclination. Some\ntentatively detected gas spirals in the outer disk are likely produced by\ninteractions with the low mass tertiary component located 4'' to the northeast.\nOur analyses demonstrate the promising usage of V892 Tau as an excellent\nbenchmark system to study the details of binary--disk interactions.", "category": "astro-ph_EP" }, { "text": "XO-2b: a Prograde Planet with a Negligible Eccentricity, and an\n Additional Radial Velocity Variation: We present precise radial velocities of XO-2 taken with the Subaru HDS,\ncovering two transits of XO-2b with an interval of nearly two years. The data\nsuggest that the orbital eccentricity of XO-2b is consistent with zero within\n2$\\sigma$ ($e=0.045\\pm0.024$) and the orbit of XO-2b is prograde (the\nsky-projected spin-orbit alignment angle $\\lambda=10^{\\circ}\\pm72^{\\circ}$).\nThe poor constraint of $\\lambda$ is due to a small impact parameter (the\norbital inclination of XO-2b is almost 90$^{\\circ}$). The data also provide an\nimproved estimate of the mass of XO-2b as $0.62\\pm0.02$ $M_{\\rm Jup}$. We also\nfind a long-term radial velocity variation in this system. Further radial\nvelocity measurements are necessary to specify the cause of this additional\nvariation.", "category": "astro-ph_EP" }, { "text": "Particle transport in evolving protoplanetary disks: Implications for\n results from Stardust: Samples returned from comet 81P/Wild 2 by Stardust confirm that substantial\nquantities of crystalline silicates were incorporated into the comet at\nformation. We investigate the constraints that this observation places upon\nprotoplanetary disk physics, assuming that outward transport of particles\nprocessed at high temperatures occurs via advection and turbulent diffusion in\nan evolving disk. We also look for constraints on particle formation locations.\nOur results are based upon 1D disk models that evolve with time under the\naction of viscosity and photoevaporation, and track solid transport using an\nensemble of individual particle trajectories. We find that two classes of disk\nmodel are consistent with the Stardust findings. One class features a high\nparticle diffusivity (a Schmidt number Sc < 1), which suffices to diffuse\nparticles up to 20 microns in size outward against the mean gas flow. For Sc >\n1, such models are unlikely to be viable, and significant outward transport\nrequires that the particles of interest settle into a midplane layer that\nexperiences an outward gas flow. In either class of models, the mass of inner\ndisk material that reaches the outer disk is a strong function of the disk's\ninitial compactness. Hence, models of grain transport within steady-state disks\nunderestimate the efficiency of outward transport. Neither model results in\nsustained outward transport of very large particles exceeding a mm in size. We\nshow that the transport efficiency generally falls off rapidly with time.\nHence, high-temperature material must be rapidly incorporated into icy bodies\nto avoid fallback, and significant radial transport may only occur during the\ninitial phase of rapid disk evolution. It may also vary substantially between\ndisks depending upon their initial mass distributions. We discuss implications\nfor Spitzer observations of crystalline silicates in T Tauri disks.", "category": "astro-ph_EP" }, { "text": "Ground-based detections of thermal emission from CoRoT-1b and WASP-12b: We report a new detection of the H-band thermal emission of CoRoT-1b and two\nconfirmation detections of the Ks-band thermal emission of WASP-12b at\nsecondary eclipses. The H-band measurement of CoRoT-1b shows an eclipse depth\nof 0.145%\\pm0.049% with a 3-{\\sigma} percentile between 0.033% - 0.235%. This\ndepth is consistent with the previous conclusions that the planet has an\nisother- mal region with inefficient heat transport from dayside to nightside,\nand has a dayside thermal inversion layer at high altitude. The two Ks band\ndetections of WASP-12b show a joint eclipse depth of 0.299%\\pm0.065%. This\nresult agrees with the measurement of Croll & collaborators, providing\nindependent confirmation of their measurement. The repeatability of the\nWASP-12b measurements also validates our data analysis method. Our\nmeasurements, in addition to a number of previous results made with other\ntelescopes, demonstrate that ground-based observations are becoming widely\navailable for characterization of atmospheres of hot Jupiters.", "category": "astro-ph_EP" }, { "text": "Shedding Light on the Eccentricity Valley: Gap Heating and Eccentricity\n Excitation of Giant Planets in Protoplanetary Disks: We show that the first order (non co-orbital) corotation torques are\nsignificantly modified by entropy gradients in a non-barotropic protoplanetary\ndisk. Such non-barotropic torques can dramatically alter the balance that, for\nbarotropic cases, results in the net eccentricity damping for giant\ngap-clearing planets embedded in the disk. We demonstrate that stellar\nillumination can heat the gap enough for the planet's orbital eccentricity to\ninstead be excited. We also discuss the \"Eccentricity Valley\" noted in the\nknown exoplanet population, where low-metallicity stars have a deficit of\neccentric planets between $\\sim 0.1$ and $\\sim 1$ AU compared to metal-rich\nsystems (Dawson & Murray-Clay 2013). We show that this feature in the planet\ndistribution may be due to the self-shadowing of the disk by a rim located at\nthe dust sublimation radius $\\sim 0.1$ AU, which is known to exist for several\nT Tauri systems. In the shadowed region between $\\sim 0.1$ and $\\sim 1$ AU lack\nof gap insolation allows disk interactions to damp eccentricity. Outside such\nshadowed regions stellar illumination can heat the planetary gaps and drive\neccentricity growth for giant planets. We suggest that the self-shadowing does\nnot arise at higher metallicity due to the increased optical depth of the gas\ninterior to the dust sublimation radius.", "category": "astro-ph_EP" }, { "text": "Origin Scenarios for the Kepler 36 Planetary System: We explore scenarios for the origin of two different density planets in the\nKepler 36 system in adjacent orbits near the 7:6 mean motion resonance. We find\nthat fine tuning is required in the stochastic forcing amplitude, the migration\nrate and planet eccentricities to allow two convergently migrating planets to\nbypass mean motion resonances such as the 4:3, 5:4 and 6:5, and yet allow\ncapture into the 7:6 resonance. Stochastic forcing can eject the system from\nresonance causing a collision between the planets, unless the disk inducing\nmigration and stochastic forcing is depleted soon after resonance capture.\n We explore a scenario with approximately Mars mass embryos originating\nexterior to the two planets and migrating inwards toward two planets. We find\nthat gravitational interactions with embryos can nudge the system out of\nresonances. Numerical integrations with about a half dozen embryos can leave\nthe two planets in the 7:6 resonance. Collisions between planets and embryos\nhave a wide distribution of impact angles and velocities ranging from\naccretionary to disruptive. We find that impacts can occur at sufficiently high\nimpact angle and velocity that the envelope of a planet could have been\nstripped, leaving behind a dense core. Some of our integrations show the two\nplanets exchanging locations, allowing the outer planet that had experienced\nmultiple collisions with embryos to become the innermost planet. A scenario\ninvolving gravitational interactions and collisions with embryos may account\nfor both the proximity of the Kepler 36 planets and their large density\ncontrast.", "category": "astro-ph_EP" }, { "text": "Friends of Hot Jupiters II: No Correspondence Between Hot-Jupiter\n Spin-Orbit Misalignment and the Incidence of Directly Imaged Stellar\n Companions: Multi-star systems are common, yet little is known about a stellar\ncompanion's influence on the formation and evolution of planetary systems. For\ninstance, stellar companions may have facilitated the inward migration of hot\nJupiters towards to their present day positions. Many observed short period gas\ngiant planets also have orbits that are misaligned with respect to their star's\nspin axis, which has also been attributed to the presence of a massive outer\ncompanion on a non-coplanar orbit. We present the results of a multi-band\ndirect imaging survey using Keck NIRC2 to measure the fraction of short period\ngas giant planets found in multi-star systems. Over three years, we completed a\nsurvey of 50 targets (\"Friends of Hot Jupiters\") with 27 targets showing some\nsignature of multi-body interaction (misaligned or eccentric orbits) and 23\ntargets in a control sample (well-aligned and circular orbits). We report the\nmasses, projected separations, and confirmed common proper motion for the 19\nstellar companions found around 17 stars. Correcting for survey incompleteness,\nwe report companion fractions of $48\\%\\pm9\\%$, $47\\%\\pm12\\%$, and $51\\%\\pm13\\%$\nin our total, misaligned/eccentric, and control samples, respectively. This\ntotal stellar companion fraction is $2.8\\,\\sigma$ larger than the fraction of\nfield stars with companions approximately $50-2000\\,$AU. We observe no\ncorrelation between misaligned/eccentric hot Jupiter systems and the incidence\nof stellar companions. Combining this result with our previous radial velocity\nsurvey, we determine that $72\\% \\pm 16\\%$ of hot Jupiters are part of\nmulti-planet and/or multi-star systems.", "category": "astro-ph_EP" }, { "text": "Identification of a new spectral signature at 3 $\u03bc$m over Martian\n northern high latitudes: implications for surface composition: Mars northern polar latitudes are known to harbor an enhanced 3 ${\\mu}$m\nspectral signature when observed from orbit. This may indicate a greater amount\nof surface adsorbed or bound water, although it has not yet been possible to\neasily reconcile orbital observations with ground measurements by Phoenix. Here\nwe re-analyzed OMEGA/Mars Express observations acquired during the Northern\nsummer to further characterize this 3 ${\\mu}$m absorption band increase. We\nidentify the presence of a new specific spectral signature composed of an\nadditional narrow absorption feature centered at 3.03 ${\\mu}$m coupled with an\nabsorption at ${\\lambda}$ ${\\geq}$ 3.8 ${\\mu}$m. This signature is\nhomogeneously distributed over a high-albedo open ring surrounding the\ncircumpolar low-albedo terrains between ~ 68{\\deg}N and 76{\\deg}N and ~\n0{\\deg}E and 270{\\deg}E. This location includes the Phoenix landing site. This\nfeature shows no time variability and can be confidently attributed to a\nseasonally stable surface component. All together, the stability, spectral\nshape and absence of significant correlation with other signatures in the 1 $-$\n2.5 ${\\mu}$m range discard interpretations relying on water ice or easily\nexchangeable adsorbed water. Sulfates, notably anhydrite, provide interesting\ncomparisons to several sections of the spectrum. Analogies with Earth samples\nalso show that the spectral signature could result from a latitudinal\nmodification of the hydration state and/or grains size of salts contaminants.\nWhile the exact full spectral shape cannot be easily reproduced, plausible\nexplanations to this observation seem to involve geologically recent water\nalteration at high northern latitudes.", "category": "astro-ph_EP" }, { "text": "Direct Imaging of Extra-solar Planets - Homogeneous Comparison of\n Detected Planets and Candidates: Searching the literature, we found 25 stars with directly imaged planets and\ncandidates. We gathered photometric and spectral information for all these\nobjects to derive their luminosities in a homogeneous way, taking a bolometric\ncorrection into account. Using theoretical evolutionary models, one can then\nestimate the mass from luminosity, temperature, and age. According to our mass\nestimates, all of them can have a mass below 25 Jup masses, so that they are\nconsidered as planets.", "category": "astro-ph_EP" }, { "text": "On the co-orbital asteroids in the solar system: medium-term timescale\n analysis of the quasi-coplanar objects: The focus of this work is the current distribution of asteroids in co-orbital\nmotion with Venus, Earth and Jupiter, under a quasi-coplanar configuration and\nfor a medium-term timescale of the order of 900 years. A co-orbital trajectory\nis a heliocentric orbit trapped in a 1:1 mean-motion resonance with a given\nplanet. As such, to model it this work considers the Restricted Three-Body\nProblem in the circular-planar case with the help of averaging techniques. The\ndomain of each co-orbital regime, that is, the quasi-satellite motion, the\nhorseshoe motion and the tadpole motion, can be neatly defined by means of an\nintegrable model and a simple bi-dimensional map, that is invariant with\nrespect to the mass parameter of the planet, and turns out to be a remarkable\ntool to investigate the distribution of the co-orbitals objects of interest.\nThe study is based on the data corresponding to the ephemerides computed by the\nJPL Horizons system for asteroids with a sufficient low orbital inclination\nwith respect to the Sun-planet orbital plane. These objects are cataloged\naccording to their current dynamics, together with the transitions that occur\nin the given time frame from a given type of co-orbital motion to another. The\nresults provide a general catalog of co-orbital asteroids in the solar system,\nthe first one to our knowledge, and an efficient mean to study transitions.", "category": "astro-ph_EP" }, { "text": "Giant Impact onto a Vesta-Like Asteroid and Formation of Mesosiderites\n through Mixing of Metallic Core and Surface Crust: Mesosiderites are a type of stony-iron meteorites composed of a mixture of\nsilicates and Fe-Ni metals. The mesosiderite silicates and metals are\nconsidered to have originated from the crust and metal core, respectively, of a\ndifferentiated asteroid. In contrast, mesosiderites rarely contain the olivine\nthat is mainly included in a mantle. Although a giant impact onto a\ndifferentiated asteroid is considered to be a probable mechanism to mix crust\nand metal materials to form mesosiderites, it is not obvious how such a giant\nimpact can form mesosiderite-like materials without including mantle materials.\nWe conducted numerical simulations of giant impacts onto differentiated\nasteroids, using the smoothed particle hydrodynamics method, to investigate the\ndetailed distribution of mixed materials on the resultant bodies. For the\ninternal structure of a target body, we used a thin-crust model derived from\nthe magma ocean crystallization model of the asteroid Vesta and a thick-crust\nand a large-core model suggested from the proximity observation of Vesta by the\nDawn probe. In the simulations with the former model, excavation of the metal\ncore requires nearly catastrophic impacts and mantle is exposed over large\nsurface areas. Thus, stony-iron materials produced on its surface are likely to\ninclude mantle materials and it is difficult to produce mesosiderite-like\nmaterials. Conversely, in the simulations with the latter model, mantle\nmaterials are exposed only at impact sites, even when the impacts excavate the\nmetal core, and the formation of a surface with little mantle material and the\nformation of mesosiderite-like materials are possible. Therefore, our\nsimulations suggest that an internal structure with a thick crust and a large\ncore is more likely as a mesosiderite parent body rather than the thin-crust\ninternal structure inferred from the conventional magma ocean model.", "category": "astro-ph_EP" }, { "text": "The giant nature of WD 1856 b implies that transiting rocky planets are\n rare around white dwarfs: White dwarfs (WDs) have roughly Earth-sized radii - a fact long recognized to\nfacilitate the potential discovery of sub-Earth sized planets via transits, as\nwell atmospheric characterization including biosignatures. Despite this, the\nfirst (and still only) transiting planet discovered in 2020 was a roughly\nJupiter-sized world, found using TESS photometry. Given the relative paucity of\ngiant planets compared to terrestrials indicated by both exoplanet demographics\nand theoretical simulations (a \"bottom-heavy\" radius distribution), this is\nperhaps somewhat surprising. Here, we quantify the surprisingness of this fact\naccounting for geometric bias and detection bias assuming 1) a bottom-heavy\nKepler derived radius distribution, and 2) a top-heavy radial velocity inspired\nradius distribution. Both are concerning, with the latter implying rocky\nplanets are highly unusual and the former implying WD 1856 b would have to be\nhighly surprising event at the <0.5% level. Using an HBM, we infer the implied\npower-law radius distribution conditioned upon WD 1856 b and arrive at a\ntop-heavy distribution, such that 0.1-2 REarth planets are an\norder-of-magnitude less common than 2-20 REarth planets in the period range of\n0.1-10 days. The implied hypothesis is that transiting WD rocky planets are\nrare. We discuss ways to reconcile this with other evidence for minor bodies\naround WDs, and ultimately argue that it should be easily testable.", "category": "astro-ph_EP" }, { "text": "Cometary glycolaldehyde as a source of pre-RNA molecules: Over 200 molecules have been detected in multiple extraterrestrial\nenvironments, including glycolaldehyde (C2(H2O)2, GLA), a two-carbon sugar\nprecursor that has been detected in regions of the interstellar medium. Its\nrecent in situ detection on the nucleus of comet 67P/Churyumov-Gerasimenko and\nvia remote observations in the comae of others, provides tantalizing evidence\nthat it is common on most (if not all) comets. Impact experiments conducted at\nthe Experimental Impact Laboratory at NASA's Johnson Space Center have shown\nthat samples of GLA and GLA mixed with montmorillonite clays can survive impact\ndelivery in the pressure range of 4.5 GPa to 25 GPa. Extrapolated to amounts of\nGLA observed on individual comets and assuming a monotonic impact rate in the\nfirst billion years of solar system history, these experimental results show\nthat up to 10^23 kg of cometary GLA could have survived impact delivery, with\nsubstantial amounts of threose, erythrose, glycolic acid, and ethylene glycol\nalso produced or delivered. Importantly, independent of the profile of the\nimpact flux in the early solar system, comet delivery of GLA would have\nprovided (and may continue to provide) a reservoir of starting material for the\nformose reaction (to form ribose) and the Strecker reaction (to form amino\nacids). Thus, comets may have been important delivery vehicles for starting\nmolecules necessary for life as we know it.", "category": "astro-ph_EP" }, { "text": "Asteroseismology of iota Draconis and Discovery of an Additional\n Long-Period Companion: Giant stars as known exoplanet hosts are relatively rare due to the potential\nchallenges in acquiring precision radial velocities and the small predicted\ntransit depths. However, these giant host stars are also some of the brightest\nin the sky and so enable high signal-to-noise follow-up measurements. Here we\nreport on new observations of the bright (V ~ 3.3) giant star $\\iota$ Draconis\n($\\iota$ Dra), known to host a planet in a highly eccentric ~511 day period\norbit. TESS observations of the star over 137 days reveal asteroseismic\nsignatures, allowing us to constrain the stellar radius, mass, and age to ~2%,\n~6%, and ~28%, respectively. We present the results of continued radial\nvelocity monitoring of the star using the Automated Planet Finder over several\norbits of the planet. We provide more precise planet parameters of the known\nplanet and, through the combination of our radial velocity measurements with\nHipparcos and Gaia astrometry, we discover an additional long-period companion\nwith an orbital period of ~$68^{+60}_{-36}$ years. Mass predictions from our\nanalysis place this sub-stellar companion on the border of the planet and brown\ndwarf regimes. The bright nature of the star combined with the revised orbital\narchitecture of the system provides an opportunity to study planetary orbital\ndynamics that evolve as the star moves into the giant phase of its evolution.", "category": "astro-ph_EP" }, { "text": "Dynamic Limits on Planar Libration-Orbit Coupling Around an Oblate\n Primary: This paper explores the dynamic properties of the planar system of an\nellipsoidal satellite in an equatorial orbit about an oblate primary. In\nparticular, we investigate the conditions for which the satellite is bound in\nlibrational motion or when the satellite will circulate with respect to the\nprimary. We find the existence of stable equilibrium points about which the\nsatellite can librate, and explore both the linearized and non-linear dynamics\naround these points. Absolute bounds are placed on the phase space of the\nlibration-orbit coupling through the use of zero-velocity curves that exist in\nthe system. These zero-velocity curves are used to derive a sufficient\ncondition for when the satellite's libration is bound to less than 90 degrees.\nWhen this condition is not satisfied so that circulation of the satellite is\npossible, the initial conditions at zero libration angle are determined which\nlead to circulation of the satellite. Exact analytical conditions for\ncirculation and the maximum libration angle are derived for the case of a small\nsatellite in orbits of any eccentricity.", "category": "astro-ph_EP" }, { "text": "Accessible Carbon on the Moon: Carbon is one of the most essential elements to support a sustained human\npresence in space, and more immediately, several large-scale methalox-based\ntransport systems will begin operating in the near future. This raises the\nquestion of whether indigenous carbon on the Moon is abundant and concentrated\nto the extent where it could be used as a viable resource including as\npropellant. Here, I assess potential sources of lunar carbon based on previous\nwork focused on polar water ice. A simplified model is used to estimate the\ntemperature-dependent Carbon Content of Ices at the lunar poles, and this is\ncombined with remote sensing data to estimate the total amount of carbon and\ngenerate a Carbon Favorability Index that highlights promising deposits for\nfuture ground-based prospecting. Hotspots in the index maps are identified, and\nnearby staging areas are analyzed using quantitative models of trafficability\nand solar irradiance. Overall, the Moon is extremely poor in carbon sources\ncompared to more abundant and readily accessible options at Mars. However, a\nhandful of polar regions may contain appreciable amounts of subsurface\ncarbon-bearing ices that could serve as a rich source in the near term, but\nwould be easily exhausted on longer timescales. Four of those regions were\nfound to have safe nearby staging areas with equatorial-like illumination at a\nmodest height above the surface. Any one of these sites could yield enough C, H\nand O to produce propellant for hundreds of refuelings of a large spacecraft.\nOther potential lunar carbon sources including bulk regolith and pyroclastic\nglasses are less viable due to their low carbon concentrations.", "category": "astro-ph_EP" }, { "text": "The Absence of Cold Dust around Warm Debris Disk Star HD 15407A: We report Herschel and AKARI photometric observations at far-infrared (FIR)\nwavelengths of the debris disk around the F3V star HD 15407A, in which the\npresence of an extremely large amount of warm dust (~500-600 K) has been\nsuggested by mid-infrared (MIR) photometry and spectroscopy. The observed flux\ndensities of the debris disk at 60-160 micron are clearly above the\nphotospheric level of the star, suggesting excess emission at FIR as well as at\nMIR wavelengths previously reported. The observed FIR excess emission is\nconsistent with the continuum level extrapolated from the MIR excess,\nsuggesting that it originates in the inner warm debris dust and cold dust\n(~50-130 K) is absent in the outer region of the disk. The absence of cold dust\ndoes not support a late heavy bombardment-like event as an origin of the large\namount of warm debris dust around HD 15047A.", "category": "astro-ph_EP" }, { "text": "Information Content Analysis for Selection of Optimal JWST Observing\n Modes for Transiting Exoplanet Atmospheres: The James Webb Space Telescope (JWST) is nearing its launch date of 2018, and\nwill undoubtedly revolutionize our knowledge of exoplanet atmospheres. While\nseveral studies have explored what the limits of the telescope will be in terms\nof exoplanet characterization, less has been done to specifically identify\nwhich observing modes will be most useful for characterizing a diverse range of\nexoplanetary atmospheres. We use an information content based approach commonly\nused in the studies of Solar System atmospheres. We develop a system based upon\nthese information content methods to trace the instrumental and atmospheric\nmodel phase space in order to identify which observing modes are best suited\nfor particular classes of planets, focusing on transmission spectra.\nSpecifically, the atmospheric parameter space we cover is T=600-1800 K,\nC/O=0.55-1, [M/H]=1-100$\\times$Solar for a R=1.39 R$_J$, M=0.59 M$_J$ planet\norbiting WASP-62-like star. We find that obtaining broader wavelength coverage\nover multiple modes is preferred over higher precision in a single mode given\nthe same amount of observing time. Regardless of the planet temperature and\ncomposition, the best modes for constraining terminator temperatures, C/O\nratios, and metalicity are NIRISS SOSS+NIRSpec G395. If the target's host star\nis dim enough such that the NIRSpec prism can be used, then it cam be used\ninstead of NIRISS SOSS+NIRSpec G395. Lastly, observations that use more than\ntwo modes, should be carefully analyzed because sometimes the addition of a\nthird mode results in no gain of information. In these cases, higher precision\nin the original two modes is favorable.", "category": "astro-ph_EP" }, { "text": "Collisional Grooming Models of the Kuiper Belt Dust Cloud: We modeled the 3-D structure of the Kuiper Belt dust cloud at four different\ndust production rates, incorporating both planet-dust interactions and\ngrain-grain collisions using the collisional grooming algorithm. Simulated\nimages of a model with a face-on optical depth of ~10^-4 primarily show an\nazimuthally-symmetric ring at 40-47 AU in submillimeter and infrared\nwavelengths; this ring is associated with the cold classical Kuiper Belt. For\nmodels with lower optical depths (10^-6 and 10^-7), synthetic infrared images\nshow that the ring widens and a gap opens in the ring at the location of of\nNeptune; this feature is caused by trapping of dust grains in Neptune's mean\nmotion resonances. At low optical depths, a secondary ring also appears\nassociated with the hole cleared in the center of the disk by Saturn. Our\nsimulations, which incorporate 25 different grain sizes, illustrate that\ngrain-grain collisions are important in sculpting today's Kuiper Belt dust, and\nprobably other aspects of the Solar System dust complex; collisions erase all\nsigns of azimuthal asymmetry from the submillimeter image of the disk at every\ndust level we considered. The model images switch from being dominated by\nresonantly-trapped small grains (\"transport dominated\") to being dominated by\nthe birth ring (\"collision dominated\") when the optical depth reaches a\ncritical value of tau ~ v/c, where v is the local Keplerian speed.", "category": "astro-ph_EP" }, { "text": "The EChO science case: The discovery of almost 2000 exoplanets has revealed an unexpectedly diverse\nplanet population. Observations to date have shown that our Solar System is\ncertainly not representative of the general population of planets in our Milky\nWay. The key science questions that urgently need addressing are therefore:\nWhat are exoplanets made of? Why are planets as they are? What causes the\nexceptional diversity observed as compared to the Solar System?\n EChO (Exoplanet Characterisation Observatory) has been designed as a\ndedicated survey mission for transit and eclipse spectroscopy capable of\nobserving a large and diverse planet sample within its four-year mission\nlifetime. EChO can target the atmospheres of super-Earths, Neptune-like, and\nJupiter-like planets, in the very hot to temperate zones (planet temperatures\nof 300K-3000K) of F to M-type host stars. Over the next ten years, several new\nground- and space-based transit surveys will come on-line (e.g. NGTS, CHEOPS,\nTESS, PLATO), which will specifically focus on finding bright, nearby systems.\nThe current rapid rate of discovery would allow the target list to be further\noptimised in the years prior to EChO's launch and enable the atmospheric\ncharacterisation of hundreds of planets. Placing the satellite at L2 provides a\ncold and stable thermal environment, as well as a large field of regard to\nallow efficient time-critical observation of targets randomly distributed over\nthe sky. A 1m class telescope is sufficiently large to achieve the necessary\nspectro-photometric precision. The spectral coverage (0.5-11 micron, goal 16\nmicron) and SNR to be achieved by EChO, thanks to its high stability and\ndedicated design, would enable a very accurate measurement of the atmospheric\ncomposition and structure of hundreds of exoplanets.", "category": "astro-ph_EP" }, { "text": "The Rate of Planet-star Coalescences Due to Tides and Stellar Evolution: Orbits of close-in planets can shrink significantly due to dissipation of\ntidal energy in a host star. This process can result in star-planet coalescence\nwithin the Galactic lifetime. In some cases, such events can be accompanied by\nan optical or/and UV/X-ray transient. Potentially, these outbursts can be\nobserved in near future with new facilities such as LSST from distances about\nfew Mpc. We use a population synthesis model to study this process and derive\nthe rate of star-planet mergers of different types. Mostly, planets are\nabsorbed by red giants. However, these events, happening with the rate about 3\nper year, mostly do not produce detectable transients. The rate of mergers with\nmain sequence stars depends on the effectiveness of tidal dissipation; for\nreasonable values of stellar tidal quality factor, such events happen in a\nMilky Way-like galaxy approximately once in 70 yrs or more rarely. This rate is\ndominated by planets with low masses. Such events do not produce bright\ntransients having maximum luminosities $\\lesssim 10^{36.5}$erg s$^{-1}$.\nBrighter events, related to massive planets, with maximum luminosity $\\sim\n10^{37.5}$--$10^{38}$erg s$^{-1}$, have the rate nearly five times smaller.", "category": "astro-ph_EP" }, { "text": "Global Calculations of Density Waves and Gap Formation in Protoplanetary\n Disks using a Moving Mesh: We calculate the global quasi-steady state of a thin disk perturbed by a\nlow-mass protoplanet orbiting at a fixed radius using extremely high-resolution\nnumerical integrations of Euler's equations in two dimensions. The calculations\nare carried out using a moving computational domain, which greatly reduces\nadvection errors and allows for much longer time-steps than a fixed grid. We\ncalculate the angular momentum flux and the torque density as a function of\nradius and compare them with analytical predictions. We discuss the\nquasi-steady state after 100 orbits and the prospects for gap formation by low\nmass planets.", "category": "astro-ph_EP" }, { "text": "Millimetre spectral indices of transition disks and their relation to\n the cavity radius: Transition disks are protoplanetary disks with inner depleted dust cavities\nand excellent candidates to investigate the dust evolution under the existence\nof a pressure bump. A pressure bump at the outer edge of the cavity allows dust\ngrains from the outer regions to stop their rapid inward migration towards the\nstar and efficiently grow to millimetre sizes. Dynamical interactions with\nplanet(s) have been one of the most exciting theories to explain the clearing\nof the inner disk. We look for evidence of the presence of millimetre dust\nparticles in transition disks by measuring their spectral index with new and\navailable photometric data. We investigate the influence of the size of the\ndust depleted cavity on the disk integrated millimetre spectral index. We\npresent the 3mm photometric observations carried out with PdBI of four\ntransition disks: LkHa330, UXTauA, LRLL31, and LRLL67. We use available values\nof their fluxes at 345GHz to calculate their spectral index, as well as the\nspectral index for a sample of twenty transition disks. We compare the\nobservations with two kind of models. In the first set of models, we consider\ncoagulation and fragmentation of dust in a disk in which a cavity is formed by\na massive planet located at different positions. The second set of models\nassumes disks with truncated inner parts at different radius and with power-law\ndust size distributions, where the maximum size of grains is calculated\nconsidering turbulence as the source of destructive collisions. We show that\nthe integrated spectral index is higher for transition disks than for regular\nprotoplanetary disks. For transition disks, the probability that the measured\nspectral index is positively correlated with the cavity radius is 95%. High\nangular resolution imaging of transition disks is needed to distinguish between\nthe dust trapping scenario and the truncated disk case.", "category": "astro-ph_EP" }, { "text": "Debiasing the Minimum-Mass Extrasolar Nebula: On the Diversity of Solid\n Disk Profiles: A foundational idea in the theory of in situ planet formation is the \"minimum\nmass extrasolar nebula\" (MMEN), a surface density profile ($\\Sigma$) of disk\nsolids that is necessary to form the planets in their present locations. While\nmost previous studies have fit a single power-law to all exoplanets in an\nobserved ensemble, it is unclear whether most exoplanetary systems form from a\nuniversal disk template. We use an advanced statistical model for the\nunderlying architectures of multi-planet systems to reconstruct the MMEN. The\nsimulated physical and Kepler-observed catalogs allows us to directly assess\nthe role of detection biases, and in particular the effect of non-transiting or\notherwise undetected planets, in altering the inferred MMEN. We find that\nfitting a power-law of the form $\\Sigma = \\Sigma_0^* (a/a_0)^\\beta$ to each\nmulti-planet system results in a broad distribution of disk profiles;\n$\\Sigma_0^* = 336_{-291}^{+727}$ g/cm$^2$ and $\\beta = -1.98_{-1.52}^{+1.55}$\nencompass the 16th-84th percentiles of the marginal distributions in an\nunderlying population, where $\\Sigma_0^*$ is the normalization at $a_0 = 0.3$\nAU. Around half of inner planet-forming disks have minimum solid masses of\n$\\gtrsim 40 M_\\oplus$ within 1 AU. While transit observations do not tend to\nbias the median $\\beta$, they can lead to both significantly over- and\nunder-estimated $\\Sigma_0^*$ and thus broaden the inferred distribution of disk\nmasses. Nevertheless, detection biases cannot account for the full variance in\nthe observed disk profiles; there is no universal MMEN if all planets formed in\nsitu. The great diversity of solid disk profiles suggests that a substantial\nfraction ($\\gtrsim 23\\%$) of planetary systems experienced a history of\nmigration.", "category": "astro-ph_EP" }, { "text": "The Far-Ultraviolet \"Continuum\" in Protoplanetary Disk Systems I:\n Electron-Impact H2 and Accretion Shocks: We present deep spectroscopic observations of the classical T Tauri stars DF\nTau and V4046 Sgr in order to better characterize two important sources of\nfar-ultraviolet continuum emission in protoplanetary disks. These new Hubble\nSpace Telescope-Cosmic Origins Spectrograph observations reveal a combination\nof line and continuum emission from collisionally excited H2 and emission from\naccretion shocks. H2 is the dominant emission in the 1400-1650 A band spectrum\nof V4046 Sgr, while an accretion continuum contributes strongly across the\nfar-ultraviolet spectrum of DF Tau. We compare the spectrum of V4046 Sgr to\nmodels of electron-impact induced H2 emission to constrain the physical\nproperties of the emitting region, after making corrections for attenuation\nwithin the disk. We find reasonable agreement with the broad spectral\ncharacteristics of the H2 model, implying N(H2) ~ 10^{18} cm^{-2}, T(H2) =\n3000^{+1000}_{-500} K, and a characteristic electron energy in the range of ~\n50 - 100 eV. We propose that self-absorption and hydrocarbons provide the\ndominant attenuation for H2 line photons originating within the disk. For both\nDF Tau and V4046 Sgr, we find that a linear fit to the far-UV data can\nreproduce near-UV/optical accretion spectra. We discuss outstanding issues\nconcerning how these processes operate in protostellar/protoplanetary disks,\nincluding the effective temperature and absolute strength of the radiation\nfield in low-mass protoplanetary environments. We find that the 912-2000A\ncontinuum in low-mass systems has an effective temperature of ~10^{4} K with\nfluxes 10^{5-7} times the interstellar level at 1 AU.", "category": "astro-ph_EP" }, { "text": "Water delivery to the TRAPPIST-1 planets: Three of the seven rocky planets (e, f, and g) in TRAPPIST-1 system orbit in\nthe habitable zone of the host star. Therefore, water can be in liquid state at\ntheir surface being essential for life. Recent studies suggest that these\nplanets formed beyond the snow line in a water-rich region. The initial water\nreservoir can be lost during the planet formation due to the stellar activity\nof the infant low-mass star. However, a potential subsequent water delivery\nevent, like the late heavy bombardment (LHB) in the Solar System, can replenish\nplanetary water reservoirs. To study this water delivery process, we set up a\nsimple model in which an additional 5 M_Earth--50 M_Earth planet is embedded in\na water-rich asteroid belt beyond the snow line of TRAPPIST-1. Asteroids\nperturbed out from the chaotic zone of the putative planet can enter into the\ninner system and accreted by the known planets. Our main finding is that the\nlarger is the orbital distance of planet, the higher is the amount of water\ndelivered to the planet by an LHB-like event.", "category": "astro-ph_EP" }, { "text": "Nebular history of an ultrarefractory phase bearing CAI from a reduced\n type CV chondrite: Ultrarefractory (UR) phases in CAIs could have formed at higher T compared to\ncommon CAI minerals and thus they potentially provide constraints on very\nhigh-T processes in the solar nebula. We report a detailed characterization of\nan UR phase davisite bearing CAI from a reduced type CV chondrite. Absence of\nsecondary iron- and/or alkali-rich phases and occurrence of LIME olivine\nindicate that primitive chemical and isotopic compositions are preserved in the\nCAI. Davisite occur only in one lithological unit that consists of three\nchemically and isotopically distinct parts: i) $^{16}$O-poor regions with\nreversely-zoned melilite and davisite; ii) $^{16}$O-rich regions consisting of\nunzoned, gehlenitic melilite, diopside and spinel; and iii) spinel framboids\ncomposed of $^{16}$O-rich spinel and $^{16}$O-poor melilite. Random\ndistribution of chemical and isotopic heterogeneities with sharp boundaries in\nthe CAI indicates its formation by an aggregation of mineral assemblages formed\nand processed separately at different time and/or space. Although isotope\nexchange prior to the final agglomeration of the CAI cannot be ruled out, we\nsuggest that modification of chemical and isotopic composition of porous CAI\nprecursors or aggregation of isotopically distinct mineral assemblages are\nalternative scenarios for the origin of O-isotopic heterogeneity in CAIs. In\neither case, coexistence of spatially and/or temporally distinct $^{16}$O-rich\nand -poor gaseous reservoirs at the earliest stage of the solar system\nformation is required. The grain-scale oxygen isotopic disequilibrium in the\nCAI indicate that post-formation heating of the CAI was short, which can be\nachieved by rapid outward transport of the CAI. High\nTi$^{3+}$/Ti$^{\\mathrm{tot}}$ ratios of pyroxene and presence of LIME olivine\ndocument that the entire CAI formation process took place under highly reducing\nconditions.", "category": "astro-ph_EP" }, { "text": "LHS6343C: A Transiting Field Brown Dwarf Discovered by the Kepler\n Mission: We report the discovery of a brown dwarf that transits one member of the M+M\nbinary system LHS6343AB every 12.71 days. The transits were discovered using\nphotometric data from the Kelper public data release. The LHS6343 stellar\nsystem was previously identified as a single high-proper-motion M dwarf. We use\nhigh-contrast imaging to resolve the system into two low-mass stars with masses\n0.45 Msun and 0.36 Msun, respectively, and a projected separation of 55 arcsec.\nHigh-resolution spectroscopy shows that the more massive component undergoes\nDoppler variations consistent with Keplerian motion, with a period equal to the\ntransit period and an amplitude consistent with a companion mass of M_C = 62.8\n+/- 2.3 Mjup. Based on an analysis of the Kepler light curve we estimate the\nradius of the companion to be R_C = 0.832 +/- 0.021 Rjup, which is consistent\nwith theoretical predictions of the radius of a > 1 Gyr brown dwarf.", "category": "astro-ph_EP" }, { "text": "Radiative transfer models of mid-infrared H2O lines in the\n Planet-forming Region of Circumstellar Disks: The study of warm molecular gas in the inner regions of protoplanetary disks\nis of key importance for the study of planet formation and especially for the\ntransport of H2O and organic molecules to the surfaces of rocky\nplanets/satellites. Recent Spitzer observations have shown that the\nmid-infrared spectra of protoplanetary disks are covered in emission lines due\nto water and other molecules. Here, we present a non-LTE 2D radiative transfer\nmodel of water lines in the 10-36 mum range that can be used to constrain the\nabundance structure of water vapor, given an observed spectrum, and show that\nan assumption of local thermodynamic equilibrium (LTE) does not accurately\nestimate the physical conditions of the water vapor emission zones. By applying\nthe model to published Spitzer spectra we find that: 1) most water lines are\nsubthermally excited, 2) the gas-to-dust ratio must be one to two orders of\nmagnitude higher than the canonical interstellar medium ratio of 100-200, and\n3) the gas temperature must be higher than the dust temperature, and 4) the\nwater vapor abundance in the disk surface must be truncated beyond ~ 1 AU. A\nlow efficiency of water formation below ~ 300 K may naturally result in a lower\nwater abundance beyond a certain radius. However, we find that chemistry, may\nnot be sufficient to produce an abundance drop of many orders of magnitude and\nspeculate that the depletion may also be caused by vertical turbulent diffusion\nof water vapor from the superheated surface to regions below the snow line,\nwhere the water can freeze out and be transported to the midplane as part of\nthe general dust settling. Such a vertical cold finger effect is likely to be\nefficient due to the lack of a replenishment mechanism of large, water-ice\ncoated dust grains to the disk surface.", "category": "astro-ph_EP" }, { "text": "Improvements on analytic modelling of stellar spots: In this work we present the solution of the stellar spot problem using the\nKelvin-Stokes theorem. Our result is applicable for any given location and\ndimension of the spots on the stellar surface. We present explicitely the\nresult up to the second degree in the limb darkening law. This technique can be\nused to calculate very efficiently mutual photometric effects produced by\neclipsing bodies occulting stellar spots and to construct complex spot shapes.", "category": "astro-ph_EP" }, { "text": "Reconstructing the photometric light curves of Earth as a planet along\n its history: By utilizing satellite-based estimations of the distribution of clouds, we\nhave studied the Earth's large-scale cloudiness behavior according to latitude\nand surface types (ice, water, vegetation and desert). These empirical\nrelationships are used here to reconstruct the possible cloud distribution of\nhistorical epochs of the Earth's history such as the Late Cretaceous (90 Ma\nago), the Late Triassic (230 Ma ago), the Mississippian (340 Ma ago), and the\nLate Cambrian (500 Ma ago), when the landmass distributions were different from\ntoday's. With this information, we have been able to simulate the\nglobally-integrated photometric variability of the planet at these epochs. We\nfind that our simple model reproduces well the observed cloud distribution and\nalbedo variability of the modern Earth. Moreover, the model suggests that the\nphotometric variability of the Earth was probably much larger in past epochs.\nThis enhanced photometric variability could improve the chances for the\ndifficult determination of the rotational period and the identification of\ncontinental landmasses for a distant planets.", "category": "astro-ph_EP" }, { "text": "Following the TraCS of exoplanets with Pan-Planets: Wendelstein-1b and\n Wendelstein-2b: Hot Jupiters seem to get rarer with decreasing stellar mass. The goal of the\nPan-Planets transit survey was the detection of such planets and a statistical\ncharacterization of their frequency. Here, we announce the discovery and\nvalidation of two planets found in that survey, Wendelstein-1b and\nWendelstein-2b, which are two short-period hot Jupiters that orbit late K host\nstars. We validated them both by the traditional method of radial velocity\nmeasurements with the HIgh Resolution Echelle Spectrometer (HIRES) and the\nHabitable-zone Planet Finder (HPF) instruments and then by their Transit Color\nSignature (TraCS). We observed the targets in the wavelength range of $4000 -\n24000$ Angstr\\\"om and performed a simultaneous multiband transit fit and\nadditionally determined their thermal emission via secondary eclipse\nobservations. Wendelstein-1b is a hot Jupiter with a radius of\n$1.0314_{-0.0061}^{+0.0061}$ $R_J$ and mass of $0.592_{-0.129}^{+0.165}$ $M_J$,\norbiting a K7V dwarf star at a period of $2.66$ d, and has an estimated surface\ntemperature of about $1727_{-90}^{+78}$ K. Wendelstein-2b is a hot Jupiter with\na radius of $1.1592_{-0.0210}^{+0.0204}$ $R_J$ and a mass of\n$0.731_{-0.311}^{+0.541}$ $M_J$, orbiting a K6V dwarf star at a period of\n$1.75$ d, and has an estimated surface temperature of about\n$1852_{-140}^{+120}$ K. With this, we demonstrate that multiband photometry is\nan effective way of validating transiting exoplanets, in particular for fainter\ntargets since radial velocity (RV) follow-up becomes more and more costly for\nthose targets.", "category": "astro-ph_EP" }, { "text": "How initial and boundary conditions affect protoplanetary migration in a\n turbulent sub-Keplerian accretion disc: 2D non viscous SPH simulations: Current theories on planetary formation establish that giant planet formation\nshould be contextual to their quick migration towards the central star due to\nthe protoplanets-disc interactions on a timescale of the order of $10^5$ years,\nfor objects of nearly 10 terrestrial masses. Such a timescale should be smaller\nby an order of magnitude than that of gas accretion onto the protoplanet during\nthe hierarchical growing-up of protoplanets by collisions with other minor\nobjects. These arguments have recently been analysed using N-body and/or\nfluid-dynamics codes or a mixing of them. In this work, inviscid 2D simulations\nare performed, using the SPH method, to study the migration of one protoplanet,\nto evaluate the effectiveness of the accretion disc in the protoplanet dragging\ntowards the central star, as a function of the mass of the planet itself, of\ndisc tangential kinematics. To this purpose, the SPH scheme is considered\nsuitable to study the roles of turbulence, kinematic and boundary conditions,\ndue to its intrinsic advective turbulence, especially in 2D and in 3D codes.\nSimulations are performed both in disc sub-Keplerian and in Keplerian kinematic\nconditions as a parameter study of protoplanetary migration if moderate and\nconsistent deviations from Keplerian Kinematics occur. Our results show\nmigration times of a few orbital periods for Earth-like planets in\nsub-Keplerian conditions, while for Jupiter-like planets estimates give that\nabout $10^4$ orbital periods are needed to half the orbital size. Timescales of\nplanet migration are strongly dependent on the relative position of the planet\nwith respect to the shock region near the centrifugal barrier of the disc flow.", "category": "astro-ph_EP" }, { "text": "Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the\n Context of Its Environment: Here we review how environmental context can be used to interpret whether O2\nis a biosignature in extrasolar planetary observations. This paper builds on\nthe overview of current biosignature research discussed in Schwieterman et al.\n(2017), and provides an in-depth, interdisciplinary example of biosignature\nidentification and observation that serves as a basis for the development of\nthe general framework for biosignature assessment described in Catling et al.,\n(2017). O2 is a potentially strong biosignature that was originally thought to\nbe an unambiguous indicator for life at high-abundance. We describe the\ncoevolution of life with the early Earth's environment, and how the interplay\nof sources and sinks in the planetary environment may have resulted in\nsuppression of O2 release into the atmosphere for several billion years, a\nfalse negative for biologically generated O2. False positives may also be\npossible, with recent research showing potential mechanisms in exoplanet\nenvironments that may generate relatively high abundances of atmospheric O2\nwithout a biosphere being present. These studies suggest that planetary\ncharacteristics that may enhance false negatives should be considered when\nselecting targets for biosignature searches. Similarly our ability to interpret\nO2 observed in an exoplanetary atmosphere is also crucially dependent on\nenvironmental context to rule out false positive mechanisms. We describe future\nphotometric, spectroscopic and time-dependent observations of O2 and the\nplanetary environment that could increase our confidence that any observed O2\nis a biosignature, and help discriminate it from potential false positives. By\nobserving and understanding O2 in its planetary context we can increase our\nconfidence in the remote detection of life, and provide a model for\nbiosignature development for other proposed biosignatures.", "category": "astro-ph_EP" }, { "text": "The Hill Stability of Triple Minor Planets in the Solar System: The triple asteroids and triple Kuiper belt objects (collectively called the\ntriple minor planets) in the Solar system are of particular interest to the\nscientific community since the discovery of the first triple asteroid system in\n2004. In this paper, the Hill stability of the nine known triple minor planets\nin the Solar system is investigated. Seven of the systems are of large size\nratio, i.e. they consist of a larger primary and two moonlets, while the other\ntwo systems have components of comparable size. Each case is treated\nseparately. For the triple minor planets that have large size ratio, the\nsufficient condition for Hill stability is expressed in closed form. This is\nnot possible for the systems with comparable size components, for which the\nHill stability is assessed by a combination of analytical and numerical means.\nIt is found that all the known triple minor planets are Hill stable, except\n3749 Balam, for which the incomplete orbital parameters make the Hill stability\nof the system uncertain. This suggests that there might be more such stable\ntriple minor planets in the Solar system yet to be observed. It is also shown\nthat the Hill stability regions increase as the mutual inclination between the\ninner orbit and outer orbit decreases, the semimajor axis ratio of the inner\norbit with respect to the outer orbit decreases, and the mass ratio of the\nouter satellite with respect to the inner satellite increases. This study\ntherefore provides useful information about dynamical properties of the triple\nminor planets in the Solar system.", "category": "astro-ph_EP" }, { "text": "Spatially Resolved Observations of Meteor Radio Afterglows with the\n OVRO-LWA: We conducted an all-sky imaging transient search with the Owens Valley Radio\nObservatory Long Wavelength Array (OVRO-LWA) data collected during the Perseid\nmeteor shower in 2018. The data collection during the meteor shower was\nmotivated to conduct a search for intrinsic radio emission from meteors below\n60 MHz known as the meteor radio afterglows (MRAs). The data collected were\ncalibrated and imaged using the core array to obtain lower angular resolution\nimages of the sky. These images were input to a pre-existing LWA transient\nsearch pipeline to search for MRAs as well as cosmic radio transients. This\nsearch detected 5 MRAs and did not find any cosmic transients. We further\nconducted peeling of bright sources, near-field correction, visibility\ndifferencing and higher angular resolution imaging using the full array for\nthese 5 MRAs. These higher angular resolution images were used to study their\nplasma emission structures and monitor their evolution as a function of\nfrequency and time. With higher angular resolution imaging, we resolved the\nradio emission size scales to less than 1 km physical size at 100 km heights.\nThe spectral index mapping of one of the long duration event showed signs of\ndiffusion of plasma within the meteor trails. The unpolarized emission from the\nresolved radio components suggest resonant transition radiation as the possible\nradiation mechanism of MRAs.", "category": "astro-ph_EP" }, { "text": "How long-lived grains dominate the shape of the Zodiacal Cloud: Grain-grain collisions shape the 3-dimensional size and velocity distribution\nof the inner Zodiacal Cloud and the impact rates of dust on inner planets, yet\nthey remain the least understood sink of zodiacal dust grains. For the first\ntime, we combine the collisional grooming method combined with a dynamical\nmeteoroid model of Jupiter-family comets (JFCs) that covers four orders of\nmagnitude in particle diameter to investigate the consequences of grain-grain\ncollisions in the inner Zodiacal Cloud. We compare this model to a suite of\nobservational constraints from meteor radars, the Infrared Astronomical\nSatellite (IRAS), mass fluxes at Earth, and inner solar probes, and use it to\nderive the population and collisional strength parameters for the JFC dust\ncloud. We derive a critical specific energy of $Q^*_D=5\\times10^5 \\pm\n4\\times10^5 R_\\mathrm{met}^{-0.24}$ J kg$^{-1}$ for particles from\nJupiter-family comet particles, making them 2-3 orders of magnitude more\nresistant to collisions than previously assumed. We find that the differential\npower law size index $-4.2\\pm0.1$ for particles generated by JFCs provides a\ngood match to observed data. Our model provides a good match to the mass\nproduction rates derived from the Parker Solar Probe observations and their\nscaling with the heliocentric distance. The higher resistance to collisions of\ndust particles might have strong implications to models of collisions in solar\nand exo-solar dust clouds. The migration via Poynting-Roberson drag might be\nmore important for denser clouds, the mass production rates of astrophysical\ndebris disks might be overestimated, and the mass of the source populations\nmight be underestimated. Our models and code are freely available online.", "category": "astro-ph_EP" }, { "text": "Tilting Uranus: Collisions versus Spin--Orbit Resonance: In this paper, we investigate whether Uranus's 98$^{\\circ}$ obliquity was a\nby-product of a secular spin-orbit resonance assuming that the planet\noriginated closer to the Sun. In this position, Uranus's spin precession\nfrequency is fast enough to resonate with another planet located beyond Saturn.\nUsing numerical integration, we show that resonance capture is possible in a\nvariety of past solar system configurations, but that the timescale required to\ntilt the planet to 90$^{\\circ}$ is of the order $\\sim\\!10^{8}$ yr -- a timespan\nthat is uncomfortably long. A resonance kick could tilt the planet to a\nsignificant 40$^{\\circ}$ in $\\sim\\!10^{7}$ yr only if conditions were ideal. We\nalso revisit the collisional hypothesis for the origin of Uranus's large\nobliquity. We consider multiple impacts with a new collisional code that builds\nup a planet by summing the angular momentum imparted from impactors. Because\ngas accretion imparts an unknown but likely large part of the planet's spin\nangular momentum, we compare different collisional models for tilted, untilted,\nspinning, and nonspinning planets. We find that a 1 $M_{\\oplus}$ strike is\nsufficient to explain the planet's current spin state, but that two\n$0.5\\,M_{\\oplus}$ collisions produce better likelihoods. Finally, we\ninvestigate hybrid models and show that resonances must produce a tilt of at\nleast $\\sim\\!40^{\\circ}$ for any noticeable improvements to the collision\nmodel. Because it is difficult for spin-orbit resonances to drive Uranus's\nobliquity to 98$^{\\circ}$ even under these ideal conditions, giant impacts seem\ninescapable.", "category": "astro-ph_EP" }, { "text": "Simulating the Formation of Carbon-rich Molecules on an idealised\n Graphitic Surface: There is accumulating evidence for the presence of complex molecules,\nincluding carbon-bearing and organic molecules, in the interstellar medium.\nMuch of this evidence comes to us from studies of chemical composition, photo-\nand mass-spectroscopy in cometary, meteoritic and asteroid samples, indicating\na need to better understand the surface chemistry of astrophysical objects.\nThere is also considerable interest in the origins of life-forming and\nlife-sustaining molecules on Earth. Here, we perform reactive molecular\ndynamics simulations to probe the formation of carbon-rich molecules and\nclusters on carbonaceous surfaces resembling dust grains and meteoroids. Our\nresults show that large chains form on graphitic surfaces at low temperatures\n(100K - 500K) and smaller fullerene-like molecules form at higher temperatures\n(2000K - 3000K). The formation is faster on the surface than in the gas at low\ntemperatures but slower at high temperatures as surface interactions prevent\nsmall clusters from coagulation. We find that for efficient formation of\nmolecular complexity, mobility about the surface is important and helps to\nbuild larger carbon chains on the surface than in the gas phase at low\ntemperatures. Finally, we show that the temperature of the surface strongly\ndetermines what kind of structures forms and that low turbulent environments\nare needed for efficient formation.", "category": "astro-ph_EP" }, { "text": "Asteroid models from generalised projections: Essential facts for\n asteroid modellers and geometric inverse problem solvers: We present a review of the problem of asteroid shape and spin reconstruction\nfrom generalised projections; i.e., from lightcurves, disk-resolved images,\noccultation silhouettes, radar range-Doppler data, and interferometry. The aim\nof this text is to summarize all important mathematical facts and proofs\nrelated to this inverse problem, to describe their implications to observers\nand modellers, and to provide the reader with all relevant references.", "category": "astro-ph_EP" }, { "text": "Comparison of planetary H\u03b1-emission models: A new correlation with\n accretion luminosity: Accreting planets have been detected through their hydrogen-line emission,\nspecifically H$\\alpha$. To interpret this, stellar-regime empirical\ncorrelations between the H$\\alpha$ luminosity $L_\\mathrm{H\\alpha}$ and the\naccretion luminosity $L_\\mathrm{acc}$ or accretion rate $\\dot{M}$ have been\nextrapolated to planetary masses, however without validation. We present a\ntheoretical $L_\\mathrm{acc}$--$L_\\mathrm{H\\alpha}$ relationship applicable to a\nshock at the surface of a planet. We consider wide ranges of accretion rates\nand masses and use detailed spectrally-resolved, non-equilibrium models of the\npostshock cooling. The new relationship gives a markedly higher\n$L_\\mathrm{acc}$ for a given $L_\\mathrm{H\\alpha}$ than fits to young stellar\nobjects, because Ly-$\\alpha$, which is not observable, carries a large fraction\nof $L_\\mathrm{acc}$. Specifically, an $L_\\mathrm{H\\alpha}$ measurement needs\nten to 100 times higher $L_\\mathrm{acc}$ and $\\dot{M}$ than previously\npredicted, which may explain the rarity of planetary H$\\alpha$ detections. We\nalso compare the $\\dot{M}$--$L_\\mathrm{H\\alpha}$ relationships coming from the\nplanet-surface shock or implied by accretion-funnel emission. Both can\ncontribute simultaneously to an observed H$\\alpha$ signal but at low (high)\n$\\dot{M}$ the planetary-surface shock (heated funnel) dominates. Only the shock\nproduces Gaussian line wings. Finally, we discuss accretion contexts in which\ndifferent emission scenarios may apply, putting recent literature models in\nperspective, and also present $L_\\mathrm{acc}$--$L_\\mathrm{line}$ relationships\nfor several other hydrogen lines.", "category": "astro-ph_EP" }, { "text": "A Harsh Test of Far-Field Scrambling with the Habitable Zone Planet\n Finder and the Hobby Eberly Telescope: The Habitable zone Planet Finder (HPF) is a fiber fed precise radial velocity\nspectrograph at the 10 m Hobby Eberly Telescope (HET). Due to its fixed\naltitude design, the HET pupil changes appreciably across a track, leading to\nsignificant changes of the fiber far-field illumination. HPF's fiber scrambler\nis designed to suppress the impact of these illumination changes on the radial\nvelocities -- but the residual impact on the radial velocity measurements has\nyet to be probed on sky. We use GJ 411, a bright early type (M2) M dwarf to\nprobe the effects of far-field input trends due to these pupil variations on\nHPF radial velocities (RVs). These large changes ($\\sim$ 2x) in pupil area and\ncentroid present a harsh test of HPF's far-field scrambling. Our results show\nthat the RVs are effectively decoupled from these extreme far-field input\nchanges due to pupil centroid offsets, attesting to the effectiveness of the\nscrambler design. This experiment allows us to test the impact of these changes\nwith large pupil variation on-sky, something we would not easily be able to do\nat a conventional optical telescope. While the pupil and illumination changes\nexpected at these other telescopes are small, scaling from our results enables\nus to estimate and bound these effects, and show that they are controllable\neven for the new and next generation of RV instruments in their quest to beat\ndown instrumental noise sources towards the goal of a few cm/s.", "category": "astro-ph_EP" }, { "text": "Localized precipitation and runoff on Mars: We use the Mars Regional Atmospheric Modeling System (MRAMS) to simulate lake\nstorms on Mars, finding that intense localized precipitation will occur for\nlake size >=10^3 km^2. Mars has a low-density atmosphere, so deep convection\ncan be triggered by small amounts of latent heat release. In our reference\nsimulation, the buoyant plume lifts vapor above condensation level, forming a\n20km-high optically-thick cloud. Ice grains grow to 200 microns radius and fall\nnear (or in) the lake at mean rates up to 1.5 mm/hr water equivalent (maximum\nrates up to 6 mm/hr water equivalent). Because atmospheric temperatures outside\nthe surface layer are always well below 273K, supersaturation and condensation\nbegin at low altitudes above lakes on Mars. In contrast to Earth lake-effect\nstorms, lake storms on Mars involve continuous precipitation, and their\nvertical velocities and plume heights exceed those of tropical thunderstorms on\nEarth. Convection does not reach above the planetary boundary layer for lakes\n<<10^3 km^2 or for atmospheric pressure >O(10^2) mbar. Instead, vapor is\nadvected downwind with little cloud formation. Precipitation occurs as snow,\nand the daytime radiative forcing at the land surface due to plume vapor and\nstorm clouds is too small to melt snow directly (<+10 W/m^2). However, if\norbital conditions are favorable, then the snow may be seasonally unstable to\nmelting and produce runoff to form channels. We calculate the probability of\nmelting by running thermal models over all possible orbital conditions and\nweighting their outcomes by probabilities given by Laskar et al., 2004. We\ndetermine that for an equatorial vapor source, sunlight 15% fainter than at\npresent, and snowpack with albedo 0.28 (0.35), melting may occur with 4%(0.1%)\nprobability. This rises to 56%(12%) if the ancient greenhouse effect was\nmodestly (6K) greater than today.", "category": "astro-ph_EP" }, { "text": "An integrable model for first-order three-planet mean motion resonances: Recent works on three-planet mean motion resonances (MMRs) have highlighted\ntheir importance for understanding the details of the dynamics of planet\nformation and evolution. While the dynamics of two-planet MMRs are well\nunderstood and approximately described by a one degree of freedom Hamiltonian,\nlittle is known of the exact dynamics of three-bodies resonances besides the\ncases of zeroth-order MMRs or when one of the body is a test particle. In this\nwork, I propose the first general integrable model for first-order three-planet\nmean motion resonances. I show that one can generalize the strategy proposed in\nthe two-planet case to obtain a one degree of freedom Hamiltonian. The dynamics\nof these resonances are governed by the second fundamental model of resonance.\nThe model is valid for any mass ratio between the planets and for every\nfirst-order resonance. I show the agreement of the analytical model with\nnumerical simulations. As examples of application I show how this model could\nimprove our understanding of the capture into MMRs as well as their role on the\nstability of planetary systems.", "category": "astro-ph_EP" }, { "text": "A Pluto--Charon Sonata: Dynamical Limits on the Masses of the Small\n Satellites: During 2005-2012, images from Hubble Space Telescope (HST) revealed four\nmoons orbiting Pluto-Charon (Weaver et al 2006, Showalter et al 2011, 2012).\nAlthough their orbits and geometric shapes are well-known, the 2$\\sigma$\nuncertainties in the masses of the two largest satellites - Nix and Hydra - are\ncomparable to their HST masses (Brozovic et al 2015, Showalter & Hamilton 2015,\nWeaver et al 2016). Remarkably, gravitational $n$-body computer calculations of\nthe long-term system stability on 0.1-1 Gyr time scales place much tighter\nconstraints on the masses of Nix and Hydra, with upper limits $\\sim$ 10% larger\nthan the HST mass. Constraints on the mass density using size measurements from\nNew Horizons suggest Nix and Hydra formed in icier material than Pluto and\nCharon.", "category": "astro-ph_EP" }, { "text": "Flybys in debris disk systems with Gaia eDR3: We aim to observationally and statistically constrain the influence of flybys\nin the formation and evolution of debris disks. We compiled a sample of 254\ndebris disks with ages between 2 Myr and 8 Gyr that are either part of an\nassociation or isolated, drawing the binary and planetary companions of the\nsystems mainly from the literature. Using the Gaia eDR3 astrometric data and\nradial velocities of our sample, as well as all the sources in a specific\nregion of the sky, we reconstructed the relative linear motions in the last 5\nMyr and made predictions for the next 2 Myr. Relating the Hill radius of each\ndebris disk system and the closest distances reached by the two sources, we\ndefined the flyby events in terms of position and time. We find that in the\nperiod between the last 5 Myrs and the next 2 Myrs, 90% of the analyzed systems\nhave experienced at least a close flyby, while 7% of them have experienced\nflybys at distances greater than 0.5R Hill. In particular, 75% of them have\nexperienced at least one past close encounter and 36% multiple past close\nencounters. From the sub-sample of resolved debris disk (41 out of 94), 80% of\nthe analyzed systems experience at least an encounter within 0.8 pc. From the\nsubsample of 10 debris disks with planets, half of these systems do show\nmisalignments between disk and planet, stirring, or asymmetries. Systems with a\nmisalignment between the planetary orbit and the disk do indeed experience at\nleast one flyby event. In particular, when the planet orbits have a difference\nwith the disk inclination higher than about 20 degree, as in the case of HD\n38529, we find that multiple close encounters have taken place in the last 5\nMyr, as theoretically predicted. The high incidence of encounters, particularly\nclose encounters, experienced by the systems in the last 5 Myr suggests the\nfundamental impact of flybys on the evolution of debris disks.", "category": "astro-ph_EP" }, { "text": "Interpretation and diversity of exoplanetary material orbiting white\n dwarfs: Nine metal-polluted white dwarfs are observed with medium-resolution optical\nspectroscopy,where photospheric abundances are determined and interpreted\nthrough comparison against solar system objects. An improved method of making\nsuch comparisons is presented that overcomes potential weaknesses of prior\nanalyses, with the numerous sources of error considered to highlight the\nlimitations on interpretation. The stars are inferred to be accreting rocky,\nvolatile-poor asteroidal materials with origins in differentiated bodies, in\nline with the consensus model. The most heavily polluted star in the sample has\n14 metals detected, and appears to be accreting material from a rocky\nplanetesimal, whose composition is mantle-like with a small Fe-Ni core\ncomponent. Some unusual abundances are present: one star is strongly depleted\nin Ca, while two others show Na abundances elevated above bulk Earth,\nspeculated either to reflect diversity in the formation conditions of the\nsource material, or to be traces of past accretion events. Another star shows\nclear signs that accretion ceased around 5 Myr ago,causing Mg to dominate the\nphotospheric abundances, as it has the longest diffusion time of the observed\nelements. Observing such post-accretion systems allows constraints to be placed\non models of the accretion process.", "category": "astro-ph_EP" }, { "text": "Early Mars' habitability and global cooling by H2-based methanogens: During the Noachian, Mars' crust may have provided a favorable environment\nfor microbial life. The porous brine-saturated regolith would have created a\nphysical space sheltered from UV and cosmic radiations and provided a solvent,\nwhile the below-ground temperature and diffusion of a dense reduced atmosphere\nmay have supported simple microbial organisms that consume H2 and CO2 as energy\nand carbon sources and produce methane as a waste. On Earth, hydrogenotrophic\nmethanogenesis was among the earliest metabolisms but its viability on early\nMars has never been quantitatively evaluated. Here we present a probabilistic\nassessment of Mars' Noachian habitability to H2-based methanogens, and quantify\ntheir biological feedback on Mars' atmosphere and climate. We find that\nsubsurface habitability was very likely, and limited mainly by the extent of\nsurface ice coverage. Biomass productivity could have been as high as in early\nEarth's ocean. However, the predicted atmospheric composition shift caused by\nmethanogenesis would have triggered a global cooling event, ending potential\nearly warm conditions, compromising surface habitability and forcing the\nbiosphere deep into the Martian crust. Spatial projections of our predictions\npoint to lowland sites at low-to-medium latitudes as good candidates to uncover\ntraces of this early life at or near the surface.", "category": "astro-ph_EP" }, { "text": "Salty ice and the dilemma of ocean exoplanet habitability: Habitability of exoplanet's deepest oceans could be limited by the presence\nof high-pressure ices at their base. New work demonstrates that efficient\nchemical transport within deep planetary ice mantles is possible through\nsignificant salt incorporation within the high-pressure ice.", "category": "astro-ph_EP" }, { "text": "The HARPS search for southern extra-solar planets XL. Searching for\n Neptunes around metal-poor stars: Stellar metallicity -- as a probe of the metallicity of proto-planetary disks\n-- is an important ingredient for giant planet formation, likely through its\neffect on the timescales in which rocky/icy planet cores can form. Giant\nplanets have been found to be more frequent around metal-rich stars, in\nagreement with predictions based on the core-accretion theory. In the\nmetal-poor regime, however, the frequency of planets, especially low-mass\nplanets, and how it depends on metallicity are still largely unknown. As part\nof a planet search programme focused on metal-poor stars, we study the targets\nfrom this survey that were observed with HARPS on more than 75 nights. The main\ngoals are to assess the presence of low-mass planets and provide a first\nestimate of the frequency of Neptunes and super-Earths around metal-poor stars.\nWe perform a systematic search for planetary companions, both by analysing the\nperiodograms of the radial-velocities and by comparing, in a\nstatistically-meaningful way, models with an increasing number of Keplerians. A\nfirst constraint on the frequency of planets in our metal-poor sample is\ncalculated considering the previous detection (in our sample) of a\nNeptune-sized planet around HD175607 and one candidate planet (with an orbital\nperiod of 68.42d and minimum mass $M_p \\sin i = 11.14 \\pm 2.47 M_{\\oplus}$) for\nHD87838, announced in the present study. This frequency is determined to be\nclose to 13% and is compared with results for solar-metallicity stars.", "category": "astro-ph_EP" }, { "text": "On the stability of low-mass planets with supercritical hydrospheres: Short-period and low-mass water-rich planets are subject to strong\nirradiation from their host star, resulting in hydrospheres in supercritical\nstate. In this context, we explore the role of irradiation on small terrestrial\nplanets that are moderately wet in the low-mass regime (0.2--1$M_{\\oplus}$). We\ninvestigate their bulk properties for water contents in the 0.01--5\\% range by\nmaking use of an internal structure model that is coupled to an atmosphere\nmodel. This coupling allows us to take into account both the compression of the\ninterior due to the weight of the hydrosphere and the possibility of\natmospheric instability in the low-mass regime. We show that even for low\nmasses and low water contents, these planets display inflated atmospheres. For\nextremely low planetary masses and high irradiation temperatures, we find that\nsteam atmospheres become gravitationally unstable when the ratio $\\eta$ of\ntheir scale height to planetary radius exceeds a critical value of $\\sim 0.1$.\nThis result is supported by observational data, as all currently detected\nexoplanets exhibit values of $\\eta$ smaller than 0.013. Depending on their\nwater content, our results show that highly irradiated and low-mass planets up\nto $0.9M_{\\oplus}$ with significative hydrospheres are not in stable form and\nshould loose their volatile envelope.", "category": "astro-ph_EP" }, { "text": "Dust Coagulation in the Vicinity of a Gap-Opening Jupiter-Mass Planet: We analyze the coagulation of dust in and around a gap opened by a\nJupiter-mass planet. To this end, we carry out a high-resolution\nmagnetohydrodynamic (MHD) simulation of the gap environment, which is turbulent\ndue to the magnetorotational instability. From the MHD simulation, we obtain\nvalues of the gas velocities, densities and turbulent stresses a) close to the\ngap edge, b) in one of the two gas streams that accrete onto the planet, c)\ninside the low-density gap, and d) outside the gap. The MHD values are then\nsupplied to a Monte Carlo dust coagulation algorithm, which models grain\nsticking and compaction. We consider two dust populations for each region: one\nwhose initial size distribution is monodisperse, with monomer radius equal to 1\n$\\mu$m, and another one whose initial size distribution follows the\nMathis-Rumpl-Nordsieck distribution for interstellar dust grains, with an\ninitial range of monomer radii between 0.5 and 10 $\\mu$m. Our Monte Carlo\ncalculations show initial growth of dust aggregates followed by compaction in\nall cases but one, that of aggregates belonging to the initially monodisperse\npopulation subject to gas conditions outside the gap. In this latter case, the\nmass-weighted (MW) average porosity of the population reaches extremely high\nfinal values of 98\\%. The final MW porosities in all other cases range between\n30\\% and 82\\%. The efficiency of compaction is due to high turbulent relative\nspeeds between dust particles. Future studies will need to explore the effect\nof different planet masses and electric charge on grains.", "category": "astro-ph_EP" }, { "text": "Influence of Stellar Multiplicity On Planet Formation. IV. Adaptive\n Optics Imaging of Kepler Stars With Multiple Transiting Planet Candidates: The Kepler mission provides a wealth of multiple transiting planet systems\n(MTPS). The formation and evolution of multi-planet systems are likely to be\ninfluenced by companion stars given the abundance of multi stellar systems. We\nstudy the influence of stellar companions by measuring the stellar multiplicity\nrate of MTPS. We select 138 bright (KP < 13.5) Kepler MTPS and search for\nstellar companions with AO imaging data and archival radial velocity (RV) data.\nWe obtain new AO images for 73 MTPS. Other MTPS in the sample have archival AO\nimaging data from the Kepler Community Follow-up Observation Program (CFOP).\nFrom these imaging data, we detect 42 stellar companions around 35 host stars.\nFor stellar separation 1 AU < a < 100 AU, the stellar multiplicity rate is 5.2\n$\\pm$ 5.0% for MTPS, which is 2.8{\\sigma} lower than 21.1 $\\pm$ 2.8% for the\ncontrol sample, i.e., the field stars in the solar neighborhood. We identify\ntwo origins for the deficit of stellar companions within 100 AU to MTPS: (1) a\nsuppressive planet formation, and (2) the disruption of orbital coplanarity due\nto stellar companions. To distinguish between the two origins, we compare the\nstellar multiplicity rates of MTPS and single transiting planet systems (STPS).\nHowever, current data are not sufficient for this purpose. For 100 AU < a <\n2000 AU, the stellar multiplicity rates are comparable for MTPS (8.0 $\\pm$\n4.0%), STPS (6.4 $\\pm$ 5.8%), and the control sample (12.5 $\\pm$ 2.8%).", "category": "astro-ph_EP" }, { "text": "Ejecta Cloud from a Kinetic Impact on the Secondary of a Binary\n Asteroid: I. Mechanical Environment and Dynamic Model: An understanding of the post-impact dynamics of ejecta clouds are crucial to\nthe planning of a kinetic impact mission to an asteroid, and also has great\nimplications for the history of planetary formation. The purpose of this\narticle to track the evolution of ejecta produced by AIDA mission, which\ntargets for kinetic impact the secondary of near-Earth binary asteroid 65803\nDidymos on 2022, and to feedback essential informations to AIDA's ongoing\nphase-A study. We present a detailed dynamic model for the simulation of an\nejecta cloud from a binary asteroid that synthesizes all relevant forces based\non a previous analysis of the mechanical environment. We apply our method to\ngain insight into the expected response of Didymos to the AIDA impact,\nincluding the subsequent evolution of debris and dust. The crater scaling\nrelations from laboratory experiments are employed to approximate the\ndistributions of ejecta mass and launching speed. The size composition of\nfragments is modeled with a power law fitted from observations of real asteroid\nsurface. A full-scale demonstration is simulated using parameters specified by\nthe mission. We report the results of the simulation, which include the\ncomputed spread of the ejecta cloud and the recorded history of ejecta\naccretion and escape. The violent period of the ejecta evolution is found to be\nshort, and is followed by a stage where the remaining ejecta is gradually\ncleared. Solar radiation pressure proves to be efficient in cleaning dust-size\nejecta, and the simulation results after two weeks shows that large debris on\npolar orbits (perpendicular to the binary orbital plane) has a survival\nadvantage over smaller ejecta and ejecta that keep to low latitudes.", "category": "astro-ph_EP" }, { "text": "Nonlinear behaviour of warped discs around a central object with a\n quadrupole moment: The nonlinear behaviour of low-viscosity warped discs is poorly understood.\nWe verified a nonlinear bending-wave theory, in which fluid columns undergo\naffine transformations, with direct 3D hydrodynamical simulations. We employed\na second-order Godunov-type scheme, Meshless Finite Mass (MFM), and also the\nSmoothed Particle Hydrodynamics (SPH) method, with up to 128M particles. For\nmoderate nonlinearity, MFM maintains well the steady nonlinear warp predicted\nby the affine model for a tilted inviscid disc around a central object with a\nquadrupole moment. However, numerical dissipation in SPH is so severe that even\na low-amplitude nonlinear warp degrades at a resolution where MFM performs\nwell. A low-amplitude arbitrary warp tends to evolve towards a nonlinear steady\nstate. However, no such state exists in our thin disc with an angular\nsemi-thickness H/R = 0.02 when the outer tilt angle is beyond about 14 degrees.\nThe warp breaks tenuously and reconnects in adiabatic simulations, or breaks\ninto distinct annuli in isothermal simulations. The breaking radius lies close\nto the location with the most extreme nonlinear deformation. Parametric\ninstability is captured only in our highest-resolution simulation, leading to\nring structures that may serve as incubators for planets around binaries.", "category": "astro-ph_EP" }, { "text": "Surveying the Inner Solar System with an Infrared Space Telescope: We present an analysis of surveying the inner Solar System for objects that\nmay pose some threat to the Earth. Most of the analysis is based on\nunderstanding the capability provided by Sentinel, a concept for an infrared\nspace-based telescope placed in a heliocentric orbit near the distance of\nVenus. From this analysis, we show 1) the size range being targeted can affect\nthe survey design, 2) the orbit distribution of the target sample can affect\nthe survey design, 3) minimum observational arc length during the survey is an\nimportant metric of survey performance, and 4) surveys must consider objects as\nsmall as D=15-30 m to meet the goal of identifying objects that have the\npotential to cause damage on Earth in the next 100 years. Sentinel will be able\nto find 50% of all impactors larger than 40 meters in a 6.5 year survey. The\nSentinel mission concept is shown to be as effective as any survey in finding\nobjects bigger than D=140 m but is more effective when applied to finding\nsmaller objects on Earth-impacting orbits. Sentinel is also more effective at\nfinding objects of interest for human exploration that benefit from lower\npropulsion requirements. To explore the interaction between space and ground\nsearch programs, we also study a case where Sentinel is combined with the Large\nSynoptic Survey Telescope and show the benefit of placing a space-based\nobservatory in an orbit that reduces the overlap in search regions with a\nground-based telescope. In this case, Sentinel+LSST can find more than 70% of\nthe impactors larger than 40 meters assuming a 6.5 year lifetime for Sentinel\nand 10 years for LSST.", "category": "astro-ph_EP" }, { "text": "Diversity of planetary systems in low-mass disks: Terrestrial-type\n planet formation and water delivery: Several studies, observational and theoretical, suggest that planetary\nsystems with only rocky planets should be the most common in the Universe. We\nstudy the diversity of planetary systems that might form around Sun-like stars\nin low-mass disks without giant planets. We focus on the formation process of\nterrestrial planets in the habitable zone (HZ) and analyze their water contents\nwith the goal to determine systems of astrobiological interest. Besides, we\nstudy the formation of planets on wide orbits because they can be detected with\nthe microlensing technique. N-body simulations of high resolution (embryos +\nplanetesimals) are developed for a wide range of surface density profiles. The\nsurface density profile combines a power law to the inside of the disk of the\nform r^{-gamma}, with an exponential decay to the outside. We adopt a disk of\n0.03M_sun and values of gamma = 0.5, 1 and 1.5. All our simulations form\nplanets in the HZ with different masses and final water contents depending on\nthe 3 profiles. For gamma = 0.5, we produce 3 planets in the HZ with masses\nbetween 0.03 M_e to 0.1 M_e and water contents between 0.2 and 16 Earth oceans.\nFor gamma = 1, 3 planets form in the HZ with masses between 0.18 M_e and 0.52\nM_e and water contents from 34 to 167 Earth oceans. For gamma = 1.5, we find 4\nplanets in the HZ with masses from 0.66 M_e to 2.21 M_e and water contents\nbetween 192 and 2326 Earth oceans. This profile shows distinctive results\nbecause it is the only one of those studied here that leads to the formation of\nwater worlds. Since planetary systems with gamma = 1 and 1.5 present planets in\nthe HZ with suitable masses to retain a long-live atmosphere and to maintain\nplate tectonics, they seem to be the most outstanding candidates to be\npotentially habitable. Particularly, these systems form Earths and Super-Earths\nnear the snow line which can be discovered by microlensing.", "category": "astro-ph_EP" }, { "text": "Effect of Dust Size on the Near-Infrared Spectra (1.0-5.0 $\u03bc$m) of\n Brown Dwarf Atmospheres: In this study, we demonstrate the dependence of atmospheric dust size on the\nnear-infrared spectra of ten L dwarfs, and constrain the sizes of dust grains\nin each L dwarf atmosphere. In previous studies, by comparing observed and\nmodeled spectra, it was suggested that the deviations of their spectral shapes\nfrom theoretical prediction are general characteristics. Here, we focus on the\ndust size in brown dwarf atmospheres to understand the observed spectra. We\nconfirm that changing the dust size changes the temperature-pressure structure\nof the atmosphere, with the shape of the spectrum changing accordingly. At the\nwavelength at which dust is the main absorber of radiation (the dust-dominated\nregime), a large dust opacity combined with a medium grain size, e.g., 0.1\n$\\mu$m, results in a low photospheric temperature, and thus a small flux.\nConversely, for the wavelength at which gas absorption is dominant (the\ngas-dominated regime), a large dust opacity modifies the temperature-pressure\nstructure, resulting in a high photospheric temperature, which corresponds to\nlarge flux emissions. Taking into account the size effect, we compare the model\nspectral fluxes in the wavelength range 1-5 $\\mu$m with the observational ones\nto constrain the main dust size in the atmosphere of each of the ten L dwarfs\nobserved with AKARI and SpeX or CGS4. Ultimately, we reveal that the observed\ndata are reproduced with higher fidelity by models based on a medium dust size\nof 0.1-3.0 $\\mu$m for six of these L dwarfs; therefore, we suggest that such\natmospheric dust sizes apply to the majority of L dwarfs.", "category": "astro-ph_EP" }, { "text": "EPIC Simulations of Neptune's Dark Spots Using an Active Cloud\n Microphysical Model: The Great Dark Spot (GDS-89) observed by Voyager 2 was the first of several\nlarge-scale vortices observed on Neptune, the most recent of which was observed\nin 2018 in the northern hemisphere (NDS-2018). Ongoing observations of these\nfeatures are constraining cloud formation, drift, shape oscillations, and other\ndynamic properties. In order to effectively model these characteristics, an\nexplicit calculation of methane cloud microphysics is needed. Using an updated\nversion of the Explicit Planetary Isentropic Coordinate General Circulation\nModel (EPIC GCM) and its active cloud microphysics module to account for the\ncondensation of methane, we investigate the evolution of large scale vortices\non Neptune. We model the effect of methane deep abundance and cloud formation\non vortex stability and dynamics. In our simulations, the vortex shows a sharp\ncontrast in methane vapor density inside compared to outside the vortex.\nMethane vapor column density is analogous to optical depth and provides a more\nconsistent tracer to track the vortex, so we use that variable over potential\nvorticity. We match the meridional drift rate of the GDS and gain an initial\ninsight into the evolution of vortices in the northern hemisphere, such as the\nNDS-2018.", "category": "astro-ph_EP" }, { "text": "Tidal Evolution of Close Binary Asteroid Systems: We provide a generalized discussion of tidal evolution to arbitrary order in\nthe expansion of the gravitational potential between two spherical bodies of\nany mass ratio. To accurately reproduce the tidal evolution of a system at\nseparations less than five times the radius of the larger primary component,\nthe tidal potential due to the presence of a smaller secondary component is\nexpanded in terms of Legendre polynomials to arbitrary order rather than\ntruncated at leading order as is typically done in studies of well-separated\nsystem like the Earth and Moon. The equations of tidal evolution including\ntidal torques, the changes in spin rates of the components, and the change in\nsemimajor axis (orbital separation) are then derived for binary asteroid\nsystems with circular and equatorial mutual orbits. Accounting for higher-order\nterms in the tidal potential serves to speed up the tidal evolution of the\nsystem leading to underestimates in the time rates of change of the spin rates,\nsemimajor axis, and mean motion in the mutual orbit if such corrections are\nignored. Special attention is given to the effect of close orbits on the\ncalculation of material properties of the components, in terms of the rigidity\nand tidal dissipation function, based on the tidal evolution of the system. It\nis found that accurate determinations of the physical parameters of the system,\ne.g., densities, sizes, and current separation, are typically more important\nthan accounting for higher-order terms in the potential when calculating\nmaterial properties. In the scope of the long-term tidal evolution of the\nsemimajor axis and the component spin rates, correcting for close orbits is a\nsmall effect, but for an instantaneous rate of change in spin rate, semimajor\naxis, or mean motion, the close-orbit correction can be on the order of tens of\npercent.", "category": "astro-ph_EP" }, { "text": "A Bayesian Periodogram Finds Evidence for Three Planets in 47 Ursae\n Majoris: A Bayesian analysis of 47 Ursae Majoris (47 UMa) radial velocity data\nconfirms and refines the properties of two previously reported planets with\nperiods of 1079 and 2325 days and finds evidence for an additional long period\nplanet with a period of approximately 10000 days. The three planet model is\nfound to be 10^5 times more probable than the next most probable model which is\na two planet model. The nonlinear model fitting is accomplished with a new\nhybrid Markov chain Monte Carlo (HMCMC) algorithm which incorporates parallel\ntempering, simulated annealing and genetic crossover operations. Each of these\nfeatures facilitate the detection of a global minimum in chi-squared. By\ncombining all three, the HMCMC greatly increases the probability of realizing\nthis goal. When applied to the Kepler problem it acts as a powerful\nmulti-planet Kepler periodogram. The measured periods are 1078 \\pm 2,\n2391{+100}{-87}, and 14002{+4018}{-5095}d, and the corresponding eccentricities\nare 0.032 \\pm 0.014, 0.098{+.047}{-.096}, and 0.16{+.09}{-.16}. The results\nfavor low eccentricity orbits for all three. Assuming the three signals (each\none consistent with a Keplerian orbit) are caused by planets, the corresponding\nlimits on planetary mass (M sin i) and semi-major axis are (2.53{+.07}{-.06}MJ,\n2.10\\pm0.02au), (0.54\\pm0.07MJ, 3.6\\pm0.1au), and (1.6{+0.3}{-0.5}MJ,\n11.6{+2.1}{-2.9}au), respectively. We have also characterized a noise induced\neccentricity bias and designed a correction filter that can be used as an\nalternate prior for eccentricity, to enhance the detection of planetary orbits\nof low or moderate eccentricity.", "category": "astro-ph_EP" }, { "text": "On the nature of the transition disk around LkCa 15: We present CARMA 1.3 mm continuum observations of the T Tauri star LkCa\n15,which resolve the circumstellar dust continuum emission on angular scales\nbetween 0.2-3 arcsec, corresponding to 28-420 AU at the distance of the star.\nThe observations resolve the inner gap in the dust emission and reveal an\nasymmetric dust distribution in the outer disk. (Abridge) We calculate that 90%\nof the dust emission arises from an azimuthally symmetric ring that contains\nabout 5x10^{-4} M_sun of dust. A low surface-brightness tail that extends to\nthe northwest out to a radius of about 300 AU contains the remaining 10% of the\nobserved continuum emission. The ring is modeled with a rather flat surface\ndensity profile between 40 and 120 AU, while the inner cavity is consistent\nwith either a sharp drop of the 1.3 mm dust optical depth at about 42 AU or a\nsmooth inward decrease between 3 and 85 AU. (Abridge). Within 40 AU, the\nobservations constrain the amount of dust between 10^{-6} and 7 Earth masses,\nwhere the minimum and maximum limits are set by the near-IR SED modeling and by\nthe mm-wave observations of the dust emission respectively. In addition, we\nconfirm the discrepancy in the outer disk radius inferred from the dust and\ngas, which corresponds to 150 AU and 900 AU respectively. We cannot reconcile\nthis difference by adopting an exponentially tapered surface density profile as\nsuggested for other systems, but we instead suggest that the gas surface\ndensity in the outer disk decreases less steeply than that predicted by model\nfits to the dust continuum emission. The lack of continuum emission at radii\nlager than 120 AU suggests a drop of at least a factor of 5 in the dust-to-gas\nratio, or in the dust opacity. We show that a sharp dust opacity drop of this\nmagnitude is consistent with a radial variation of the grain size distribution\nas predicted by existing grain growth models.", "category": "astro-ph_EP" }, { "text": "Model for Nitric oxide and its dayglow emission in the Martian upper\n atmosphere using NGIMS/MAVEN measured neutral and ion densities: A comprehensive study of Nitric oxide (NO) chemistry in the Martian upper\natmosphere is restricted due to the lack of requisite measurements. NO is an\nabundant form of odd nitrogen species in the Martian lower atmosphere and its\ndensity depends on several photochemical processes. We have developed a\nphotochemical model to study the NO density in the dayside of Martian upper\natmosphere by accounting for various production and loss mechanisms. By\nutilizing the Neutral Gas and Ion Mass Spectrometer (NGIMS) on-board Mars\nAtmosphere and Volatile Evolution (MAVEN) mission measured neutral and ion\ndensities during deep dip 8 and 9 campaigns, we modelled NO number density in\nthe Martian sunlit upper atmosphere for the altitudes between 120 and 200 km.\nThe modelled NO densities are employed to calculate NO (1,0) gamma band\nemission intensity profiles in the dayside upper atmosphere of Mars. The\ncalculated NO density and its gamma band intensity profiles are found to be\nconsistent with Imaging Ultraviolet Spectrograph (IUVS) onboard MAVEN\nobservations and also with other modelling studies. We found that the local CO2\nand N2 density variations can lead to a change in NO density and consequently\nits dayglow intensity by a factor of 2 to 5. Since NO is a trace constituent\nand also its dayglow emissions are strongly obscured by CO Cameron band\nemissions, we suggest that the derivation of NO number density based on our\napproach can constrain its abundance in the dayside upper atmosphere of Mars.\nMore observations of (1-0) gamma band emission along with modelling will help\nto study the global distribution of NO in the Martian atmosphere.", "category": "astro-ph_EP" }, { "text": "The M3 project: 2 -- Global distributions of mafic mineral abundances on\n Mars: A radiative transfer model was used to reproduce several millions of OMEGA\n(Observatoire pour la Min\\'eralogie, l'Eau, les Glaces et l'Activit\\'e) spectra\nrepresentative of igneous terrains of Mars. This task provided the modal\ncomposition and grain sizes at a planetary scale. The lithology can be\nsummarized in five mineral maps at km-scale. We found that the low albedo\nequatorial regions of the Martian surface (from 60{\\deg}S to 30{\\deg}N) are\nglobally dominated by plagioclase with average abundance ~50 vol% and pyroxenes\nwith total averaged abundance close to 40 vol%. An evolution of the\nLCP/(LCP+HCP) ratio is observed with time at the global scale, suggesting an\nevolution of the degree of partial melting throughout the Martian eras. Olivine\nand Martian dust are minor components of the modelled terrains. The olivine\ndistribution is quite different from the other minerals because it is found on\nlocalized areas with abundance reaching 20 vol%. A statistical approach, to\nclassify the pixels of the abundances maps, using k-means clustering,\nhighlighted seven distinct mineral assemblages on the surface. This\nclassification illustrates that diverse mineralogical units are found in the\nNoachian and Hesperian terrains, which suggests the presence of various and\ncomplex magmatic processes at a global scale during the two oldest eras. The\nchemical composition was derived from the modal composition maps. The\nOMEGA-derived chemical composition is quite consistent with several distinctive\ngeochemical characteristics previously considered as fingerprints of the\nMartian surface. A major discrepancy is in regards to the Fe content that is\nsignificantly smaller than soil and rock analyses from GRS and in situ\nmeasurements. The discrepancy could be partly explained by the assumptions used\nfor the spectral modelling or could also indicate surface alteration rinds.", "category": "astro-ph_EP" }, { "text": "Model for Cameron band emission in comets: A case for EPOXI mission\n target comet 103P/Hartley 2: The CO2 production rate has been derived in comets using the Cameron band\n(a3Pi - X1Sigma) emission of CO molecule assuming that photodissociative\nexcitation of CO2 is the main production mechanism of CO in a3Pi metastable\nstate. We have devoloped a model for the production and loss of CO(a3Pi) which\nhas been applied to comet 103P/Hartley 2: the target of EPOXI mission. Our\nmodel calculations show that photoelectron impact excitation of CO and\ndissociative excitation of CO2 can together contribute about 60-90% to the\nCameron band emission. The modeled brightness of (0-0) Cameron band emission on\ncomet Hartley 2 is consistent with Hubble Space Telescope observations for 3-5%\nCO2 (depending on model input solar flux) and 0.5% CO relative to water, where\nphotoelectron impact contribution is about 50-75%. We suggest that estimation\nof CO2 abundances on comets using Cameron band emission may be reconsidered. We\npredict the height integrated column brightness of Cameron band of ~1300 R\nduring EPOXI mission encounter period.", "category": "astro-ph_EP" }, { "text": "Chemical Constraints on the Oxygen Abundances in Jupiter and Saturn: We perform a comparative analysis of the chemical kinetics of CO and $\\rm\nPH_3$ in Jupiter and Saturn to assess the full set of constraints available on\nthe troposphere water abundance in the two giant planets. For carbon monoxide\nwe employ both a widely used CO kinetic scheme from Yung et al, and a newly\nidentified CO chemical scheme from Visscher and Moses. For $\\rm PH_3$ chemical\nscheme, we use the same chemical scheme as in Visscher and Fegley. Yung's\nchemical scheme for CO yields a water enrichment of 0.95 - 23.0 times solar\nabundance on Jupiter, and an upper limit of 14.0 for Saturn. Visscher's\nchemical scheme in contrast produces a water enrichment of 0.24 - 2.6 times\nsolar abundance in Jupiter, and for Saturn an upper limit for water enrichment\nof 8.0. From this scheme, which takes advantage of the most up-to-date\nkinetics, we preclude high water enrichments on Jupiter and Saturn, and show\nthat the kinetics approach yields Jovian bulk abundance in which values of C/O\nelevated relative to solar are admissible. Our result is consistent with recent\nreinterpretation of Galileo Probe data in which Jupiter formed in a\nwater-depleted portion of the protoplanetary disk (Mousis et al).", "category": "astro-ph_EP" }, { "text": "Alternative Sample Mass Measurement Technique for OSIRIS-REX Sample\n Collection Phase: The Origins, Spectral Interpretation, Resource Identification, and\nSecurity-Regolith Explorer (OSIRIS-REx) spacecraft is the third NASA New\nFrontiers Program mission and arrived at the near-Earth asteroid (101955) Bennu\nin December 2018. Following completion of sample collection in October 2020,\notherwise known as Touch-And-Go (TAG), the OSIRIS-REx spacecraft was set to\nverify its collected sample mass requirement (> 60g of material). The\nthoroughly tested Sample Mass Measurement (SMM) method was to be used for this\nverification. Imaging of the Touch-And-Go Sample Acquisition Mechanism (TAGSAM)\nwas received shortly following the TAG event, intended to ensure mechanism\nhealth prior to moving forward with the SMM activity. These images displayed\nsample leakage, prompting discussion for alternative paths forward. Risk of\ncontinued sample loss and a desire to retain as much material as possible lead\nthe team to pursue an accelerated sample stow schedule and forgo the planned\nSMM activity. Once the sample was safely stowed in the return capsule an\nalternative SMM method was proposed. The alternative SMM technique utilized\nreaction wheel momentum data from identical TAGSAM movements prior to and\nfollowing the TAG event to estimate changes in spacecraft moment of inertia.\nConservation of momentum was used to isolate the sample mass from this inertia\nchange. Using this new method, the spacecraft team was able to successfully\nestimate collected sample mass to be 250.37 +/- 101 g.", "category": "astro-ph_EP" }, { "text": "The evolution of dust-disk sizes from a homogeneous analysis of 1-10\n Myr-old stars: We utilize ALMA archival data to estimate the dust disk size of 152\nprotoplanetary disks in Lupus (1-3 Myr), Chamaeleon I (2-3 Myr), and Upper-Sco\n(5-11 Myr). We combine our sample with 47 disks from Tau/Aur and Oph whose dust\ndisk radii were estimated, as here, through fitting radial profile models to\nvisibility data. We use these 199 homogeneously derived disk sizes to identify\nempirical disk-disk and disk-host property relations as well as to search for\nevolutionary trends. In agreement with previous studies, we find that dust disk\nsizes and millimeter luminosities are correlated, but show for the first time\nthat the relationship is not universal between regions. We find that disks in\nthe 2-3 Myr-old Cha I are not smaller than disks in other regions of similar\nage, and confirm the Barenfeld et al. (2017) finding that the 5-10 Myr USco\ndisks are smaller than disks belonging to younger regions. Finally, we find\nthat the outer edge of the Solar System, as defined by the Kuiper Belt, is\nconsistent with a population of dust disk sizes which have not experienced\nsignificant truncation.", "category": "astro-ph_EP" }, { "text": "Growing the seeds of pebble accretion through planetesimal accretion: We explore the growth of planetary embryos by planetesimal accretion up to\nand beyond the point where pebble accretion becomes efficient at the so-called\nHill-transition mass. Both the transition mass and the characteristic mass of\nplanetesimals formed by the streaming instability increase with increasing\ndistance from the star. We developed a model for the growth of a large\nplanetesimal (embryo) embedded in a population of smaller planetesimals formed\nin a filament by the streaming instability. The model includes in a\nself-consistent way the collisional mass growth of the embryo, the\nfragmentation of the planetesimals, the velocity evolution of all involved\nbodies, as well as the viscous spreading of the filament. We find that the\nembryo accretes all available material in the filament during the lifetime of\nthe protoplanetary disc only in the inner regions of the disc. In contrast, we\nfind little or no growth in the outer parts of the disc beyond 5--10 AU.\nOverall, our results demonstrate very long timescales for collisional growth of\nplanetesimals in the regions of the protoplanetary disc where giant planets\nform. As such, in order to form giant planets in cold orbits, pebble accretion\nmust act directly on the largest bodies present in the initial mass-function of\nplanetesimals with little or no help from mutual collisions.", "category": "astro-ph_EP" }, { "text": "The missing cavities in the SEEDS polarized scattered light images of\n transitional protoplanetary disks: a generic disk model: Transitional circumstellar disks around young stellar objects have a\ndistinctive infrared deficit around 10 microns in their Spectral Energy\nDistributions (SED), recently measured by the Spitzer Infrared Spectrograph\n(IRS), suggesting dust depletion in the inner regions. These disks have been\nconfirmed to have giant central cavities by imaging of the submillimeter\n(sub-mm) continuum emission using the Submillimeter Array (SMA). However, the\npolarized near-infrared scattered light images for most objects in a systematic\nIRS/SMA cross sample, obtained by HiCIAO on the Subaru telescope, show no\nevidence for the cavity, in clear contrast with SMA and Spitzer observations.\nRadiative transfer modeling indicates that many of these scattered light images\nare consistent with a smooth spatial distribution for micron-sized grains, with\nlittle discontinuity in the surface density of the micron-sized grains at the\ncavity edge. Here we present a generic disk model that can simultaneously\naccount for the general features in IRS, SMA, and Subaru observations.\nParticularly, the scattered light images for this model are computed, which\nagree with the general trend seen in Subaru data. Decoupling between the\nspatial distributions of the micron-sized dust and mm-sized dust inside the\ncavity is suggested by the model, which, if confirmed, necessitates a\nmechanism, such as dust filtration, for differentiating the small and big dust\nin the cavity clearing process. Our model also suggests an inwardly increasing\ngas-to-dust-ratio in the inner disk, and different spatial distributions for\nthe small dust inside and outside the cavity, echoing the predictions in grain\ncoagulation and growth models.", "category": "astro-ph_EP" }, { "text": "The Apparently Decaying Orbit of WASP-12: We present new transit and occultation times for the hot Jupiter WASP-12b.\nThe data are compatible with a constant period derivative: $\\dot{P}=-29 \\pm 3$\nms yr$^{-1}$ and $P/\\dot{P}= 3.2$ Myr. However, it is difficult to tell whether\nwe have observed orbital decay, or a portion of a 14-year apsidal precession\ncycle. If interpreted as decay, the star's tidal quality parameter $Q_\\star$ is\nabout $2\\times 10^5$. If interpreted as precession, the planet's Love number is\n$0.44\\pm 0.10$. Orbital decay appears to be the more parsimonious model: it is\nfavored by $\\Delta\\chi^2=5.5$ despite having two fewer free parameters than the\nprecession model. The decay model implies that WASP-12 was discovered within\nthe final $\\sim$0.2% of its existence, which is an unlikely coincidence but\nharmonizes with independent evidence that the planet is nearing disruption.\nPrecession does not invoke any temporal coincidence, but does require some\nmechanism to maintain an eccentricity of $\\approx$0.002 in the face of rapid\ntidal circularization. To distinguish unequivocally between decay and\nprecession will probably require a few more years of monitoring. Particularly\nhelpful will be occultation timing in 2019 and thereafter.", "category": "astro-ph_EP" }, { "text": "The physics of wind-blown sand and dust: The transport of sand and dust by wind is a potent erosional force, creates\nsand dunes and ripples, and loads the atmosphere with suspended dust aerosols.\nThis article presents an extensive review of the physics of wind-blown sand and\ndust on Earth and Mars. Specifically, we review the physics of aeolian\nsaltation, the formation and development of sand dunes and ripples, the physics\nof dust aerosol emission, the weather phenomena that trigger dust storms, and\nthe lifting of dust by dust devils and other small-scale vortices. We also\ndiscuss the physics of wind-blown sand and dune formation on Venus and Titan.", "category": "astro-ph_EP" }, { "text": "HD45364, a pair of planets in a 3:2 mean motion resonance: Precise radial-velocity measurements with the HARPS spectrograph reveal the\npresence of two planets orbiting the solar-type star HD45364. The companion\nmasses are 0.187 Mjup and 0.658 Mjup, with semi-major axes of 0.681 AU and\n0.897 AU, and eccentricities of 0.168 and 0.097, respectively. A dynamical\nanalysis of the system further shows a 3:2 mean motion resonance between the\ntwo planets, which prevents close encounters and ensures the stability of the\nsystem over 5 Gyr. This is the first time that such a resonant configuration\nhas been observed for extra-solar planets, although there is an analogue in our\nSolar System formed by Neptune and Pluto. This singular planetary system may\nprovide important constraints on planetary formation and migration scenarios.", "category": "astro-ph_EP" }, { "text": "Discovery of a Two-Armed Spiral Structure in the Gapped Disk in HD\n 100453: We present VLT/SPHERE adaptive optics imaging in Y$-$, J$-$, H$-$, and\nK-bands of the HD 100453 system and the discovery of a two-armed spiral\nstructure in a disk extending to 0.37\" ($\\sim$42 AU) from the star, with highly\nsymmetric arms to the Northeast and Southwest. Inside of the spiral arms, we\nresolve a ring of emission from 0.18\"-0.25\" ($\\sim$21-29 AU). By assuming that\nthe ring is intrinsically circular we estimate an inclination of $\\sim$34$^{o}$\nfrom face-on. We detect dark crescents on opposite sides (NW and SE) which\nbegin at 0.18\" and continue to radii smaller than our inner working angle of\n0.15\", which we interpret as the signature of a gap at $\\lesssim$21 AU that has\nlikely been cleared by forming planets. We also detect the $\\sim$120 AU\ncompanion HD 100453 B, and by comparing our data to 2003 HST/ACS and VLT/NACO\nimages we estimate an orbital period of $\\sim$850 yr. We discuss what\nimplications the discovery of the spiral arms and finer structures of the disk\nmay have on our understanding of the possible planetary system in HD 100453,\nand how the morphology of this disk compares to other related objects.", "category": "astro-ph_EP" }, { "text": "Supermassive Hot Jupiters Provide More Favourable Conditions for the\n Generation of Radio Emission via the Cyclotron Maser Instability - A Case\n Study Based on Tau Bootis b: We investigate under which conditions supermassive hot Jupiters can sustain\nsource regions for radio emission, and whether this emission could propagate to\nan observer outside the system. We study Tau Bootis b-like planets (a\nsupermassive hot Jupiter with 5.84 Jupiter masses and 1.06 Jupiter radii), but\nlocated at different orbital distances (between its actual orbit of 0.046 AU\nand 0.2 AU). Due to the strong gravity of such planets and efficient radiative\ncooling, the upper atmosphere is (almost) hydrostatic and the exobase remains\nvery close to the planet, which makes it a good candidate for radio\nobservations. We expect similar conditions as for Jupiter, i.e. a region\nbetween the exobase and the magnetopause that is filled with a depleted plasma\ndensity compared with cases where the whole magnetosphere cavity is filled with\nhydrodynamically outward flowing ionospheric plasma. Thus, unlike classical hot\nJupiters like the previously studied planets HD 209458b and HD 189733b,\nsupermassive hot Jupiters should be in general better targets for radio\nobservations.", "category": "astro-ph_EP" }, { "text": "A Past Episode of Rapid Tidal Evolution of Enceladus?: Saturn possesses a dynamically rich system containing numerous moons and\nimpressive rings. Whether the rings of Saturn are much younger than the planet\nitself has been a long-open question; more recently a young age has been\nproposed for some moons. Recent detection of the fast orbital evolution of Rhea\nand Titan strongly suggest a highly frequency-dependent tidal response of\nSaturn, possibly through excitation of inertial waves within the planet's\nconvective envelope. Here we show that the resonance locking to inertial waves\ncannot explain the dynamical structure of the Saturnian system or the current\ntidal heating of Enceladus. On the other hand, both the observation and our\nmodelling results indicate that the system is not consistent with evolution\nunder equilibrium tides. We propose that the system's architecture can best be\nexplained by relatively high \"background\" tidal response coupled with discrete\nresonant modes. In this view, only Titan may be in a true long-term resonance\nlock with a tidal mode of Saturn. Rhea is most likely currently experiencing a\ntransient period of fast tidal evolution as it passes through a mode, rather\nthan being locked to it. Assuming that Enceladus went through a temporary\nperiod of fast tidal evolution, we can reproduce its present resonance with\nDione and satisfy other dynamical constraints. Additionally, we conclude that\nthe long-term tidal response of Saturn to Tethys must be weaker than expected\nfrom frequency-independent tides, as already found by observations.", "category": "astro-ph_EP" }, { "text": "Secondary eclipses of WASP-18b -- Near Infrared observations with the\n Anglo Australian Telescope, the Magellan Clay Telescope and the LCOGT network: We present new eclipse observations for one of the hottest \"hot Jupiters\"\nWASP-18b, for which previously published data from HST WFC3 and Spitzer have\nled to radically conflicting conclusions about the composition of this planet's\natmosphere. We measure eclipse depths of $0.15\\pm0.02\\%$ at $Ks$ and\n$0.07\\pm0.01\\%$ at $z'$ bands. Using the VSTAR line-by-line radiative transfer\ncode and both these new observations with previously published data, we derive\na new model of the planetary atmosphere. We have varied both the metallicity\nand C/O ratio in our modelling, and find no need for the extreme metallicity\nsuggested by Sheppard et al.(2017). Our best fitting models slightly\nunderestimate the emission at $z'$ band and overestimate the observed flux at\n$Ks$-band. To explain these discrepancies, we examine the impact on the\nplanetary emission spectrum of the presence of several types of hazes which\ncould form on the night-side of the planet. Our $Ks$ band eclipse flux\nmeasurement is lower than expected from clear atmosphere models and this could\nbe explained by a haze particles larger than 0.2 $\\mu$m with the optical\nproperties of Al$_{2}$O$_{3}$, CaTiO$_{3}$ or MgSiO$_{3}$. We find that $z'$\nband measurements are important for understanding the contribution of\nphotochemical hazes with particles smaller than 0.1 $\\mu$m at the top of the\natmosphere.", "category": "astro-ph_EP" }, { "text": "Finding Signs of Life in Transit: High-resolution Transmission Spectra\n of Earth-like Planets around FGKM Host Stars: Thousands of transiting exoplanets have already been detected orbiting a wide\nrange of host stars, including the first planets that could potentially be\nsimilar to Earth. The upcoming Extremely Large Telescopes and the James Webb\nSpace Telescope will enable the first searches for signatures of life in\ntransiting exoplanet atmospheres. Here, we quantify the strength of spectral\nfeatures in transit that could indicate a biosphere similar to the modern Earth\non exoplanets orbiting a wide grid of host stars (F0 to M8) with effective\ntemperatures between 2,500 and 7,000K: transit depths vary between about\n6,000ppm (M8 host) to 30 ppm (F0 host) due to the different sizes of the host\nstars. CO2 possesses the strongest spectral features in transit between 0.4 and\n20microns. The atmospheric biosignature pairs O2+CH4 and O3+CH4 - which\nidentify Earth as a living planet - are most prominent for Sun-like and cooler\nhost stars in transit spectra of modern Earth analogs. Assessing biosignatures\nand water on such planets orbiting hotter stars than the Sun will be extremely\nchallenging even for high-resolution observations. All high-resolution transit\nspectra and model profiles are available online: they provide a tool for\nobservers to prioritize exoplanets for transmission spectroscopy, test\natmospheric retrieval algorithms, and optimize observing strategies to find\nlife in the cosmos. In the search for life in the cosmos, transiting planets\nprovide the first opportunity to discover whether or not we are alone, with\nthis database as one of the keys to optimize the search strategies.", "category": "astro-ph_EP" }, { "text": "Stability of Planetary Motion in Binary Star Systems: We considered the problem of stability for planets of finite mass in binary\nstar systems. We selected a huge set of initial conditions for planetary orbits\nof the S-type, to perform high precision and very extended in time\nintegrations.\n For our numerical integrations, we resorted to the use of a 15th order\nintegration scheme (IAS15, available within the REBOUND framework), that\nprovides an optimal solution for long-term time integrations. We estimated the\nprobability of different types of instability: planet collisions with the\nprimary or secondary star or planet ejected away from the binary star system.\nWe confirm and generalize to massive planets the dependence of the critical\nsemi-major axis on eccentricity and mass ratio of the binary already found by\nHolman and Wiegert (1999). We were also able to pick a significant number of\norbits that are only `marginally' stable, according to the classification\nintroduced by Musielak et al. (2005).\n A, natural, extension of this work has been the study of the effect of\nperturbations induced to circumbinary planet motion by a passing-by star, like\nit often happens in a star cluster. One of the targets of this analysis is the\ninvestigation of the possibility that a planet, formerly on a stable S-type\norbit around one of the two stars, could transit to a stable P-type orbit (or\nviceversa). We performed a series of more than 4500 scattering experiments with\ndifferent initial conditions typical of encounters in small star clusters. We\nfound some interesting behaviors of the systems after perturbation and showed\nhow a transition from an inner (S-type) stable orbit to a circumbinary (P-type)\n(and vice-versa) has a very low (but non null) probability.", "category": "astro-ph_EP" }, { "text": "Nano dust impacts on spacecraft and boom antenna charging: High rate sampling detectors measuring the potential difference between the\nmain body and boom antennas of interplanetary spacecraft have been shown to be\nefficient means to measure the voltage pulses induced by nano dust impacts on\nthe spacecraft body itself (see Meyer-Vernet et al, Solar Phys. 256, 463\n(2009)). However, rough estimates of the free charge liberated in post impact\nexpanding plasma cloud indicate that the cloud's own internal electrostatic\nfield is too weak to account for measured pulses as the ones from the TDS\ninstrument on the STEREO spacecraft frequently exceeding 0.1 V/m. In this paper\nwe argue that the detected pulses are not a direct measure of the potential\nstructure of the plasma cloud, but are rather the consequence of a transitional\ninterruption of the photoelectron return current towards the portion of the\nantenna located within the expanding cloud.", "category": "astro-ph_EP" }, { "text": "Binary planet formation by gas-assisted encounters of planetary embryos: We present radiation hydrodynamic simulations in which binary planets form by\nclose encounters in a system of several super-Earth embryos. The embryos are\nembedded in a protoplanetary disk consisting of gas and pebbles and evolve in a\nregion where the disk structure supports convergent migration due to Type I\ntorques. As the embryos accrete pebbles, they become heated and thus affected\nby the thermal torque (Ben\\'{i}tez-Llambay et al. 2015) and the hot-trail\neffect (Chrenko et al. 2017) which excites orbital eccentricities. Motivated by\nfindings of Eklund & Masset (2017), we assume the hot-trail effect operates\nalso vertically and reduces the efficiency of inclination damping. Non-zero\ninclinations allow the embryos to become closely packed and also vertically\nstirred within the convergence zone. Subsequently, close encounters of two\nembryos assisted by the disk gravity can form transient binary planets which\nquickly dissolve. Binary planets with a longer lifetime $\\sim$$10^{4}$ yr form\nin 3-body interactions of a transient pair with one of the remaining embryos.\nThe separation of binary components generally decreases in subsequent\nencounters and due to pebble accretion until the binary merges, forming a giant\nplanet core. We provide an order-of-magnitude estimate of the expected\noccurrence rate of binary planets, yielding one binary planet per\n$\\simeq$$2$--$5\\times10^{4}$ planetary systems. Therefore, although rare, the\nbinary planets may exist in exoplanetary systems and they should be\nsystematically searched for.", "category": "astro-ph_EP" }, { "text": "Searching sub-stellar objects in DR1-TGAS, effectiveness and efficiency\n of Gaias' astrometry: We used 1,477,047 data from DR1-TGAS, in order to analyse the minimum\nrequire- ments of accuracy, necessary to detect sub-stellar objects in the\nastrometric mea- surements of Gaia. We found that the first set of data (DR1)\ndoes not have enough accuracy, so sub-stellar objects can not be easily\ndetected. Barely, it would be possible to detect jovian and higher mass\nobjects, with orbital periods over 5 years. We made the calculations of the\nminimum values of the astrometric angle produced by an or- biting sub-stellar\nobject using a range of different masses. We estimate the efficiency and\neffectiveness of the DR1-TGAS data in order to detect sub-stellar objects and\nthe minimum accuracy that Gaia would be required to detect these objects using\nthe datasets that the mission will release in the near future.", "category": "astro-ph_EP" }, { "text": "Modelling the optical energy profile of the 2021 October Jupiter impact\n flash: We have conducted numerical simulations to reproduce the observed optical\nenergy profile of the 15 October 2021 (UT) impact flash on Jupiter, which was\nthe largest and the most well-observed flash event detected by ground-based\nmovie observations. The observed long-duration ($\\sim 5.5~{\\rm s}$) optical\nemission can be reproduced by an impact of an object with an exceptionally\nsmall angle of entry relative to the horizontal. The apparent lack of the\nimpact debris feature despite the large impact object was possibly due to the\nshallower angle of entry ($\\le 12^\\circ$), which resulted in the lower ablation\nper unit volume at altitudes higher than $50 \\, {\\rm km}$, and the volume\ndensities of the ablated materials were too low to allow the debris\nparticulates to coagulate. The absence of temporal methane absorption change in\nthe observed flash spectrum is consistent with the best-fit results. The model\nbetter fits the observed optical energy profile for weaker material (cometary\nand stony) cases than for metallic ones. Based on the simulation results,\nprospects for future observations of impact flashes are discussed.", "category": "astro-ph_EP" }, { "text": "Laboratory light scattering from regolith surface and simulation of data\n by Hapke model: The small atmosphereless objects of our solar system, such as asteroids, the\nmoon are covered by layer of dust particles known as regolith, formed by\nmeteoritic impact. The light scattering studies of such dust layer by\nlaboratory experiment and numerical simulation are two important tools to\ninvestigate their physical properties. In the present work, the light scattered\nfrom a layer of dust particles, containing 0.3{\\mu}m Al2O3 at wavelength 632.8\nnm is analysed. This work has been performed by using a light scattering\ninstrument 'ellipsometer', at the Department of Physics, Assam Universiy,\nSilchar, India. Through this experiment, we generated in laboratory the\nphotometric and polarimetric phase curves of light scattered from such a layer.\nIn order to numerically simulate this data, we used Hapke's model combined with\nMie's single particle scattering properties. The perpendicular and parallel\ncomponents of single particle albedo and the phase function were derived from\nMie theory. By using the Hapke's model combined with Mie theory, the physical\nproperties of the dust grain such as grain size, optical constant (n,k) and\nwavelength can be studied through this scheme. In literature, till today no\ntheoretical model to represent polarisation caused due to scattering from rough\nsurface is available, which can successfully explain the scattering process. So\nthe main objective of this work is to develop a model which can theoretically\nestimate polarisation as caused due to scattering from rough surface and also\nto validate our model with the laboratory data generated in the present work.", "category": "astro-ph_EP" }, { "text": "$V$-band photometry of asteroids from ASAS-SN: Finding asteroids with\n slow spin: We present $V$-band photometry of the 20,000 brightest asteroids using data\nfrom the All-Sky Automated Survey for Supernovae (ASAS-SN) between 2012 and\n2018. We were able to apply the convex inversion method to more than 5,000\nasteroids with more than 60 good measurements in order to derive their sidereal\nrotation periods, spin axis orientations, and shape models. We derive unique\nspin state and shape solutions for 760 asteroids, including 163 new\ndeterminations. This corresponds to a success rate of about 15%, which is\nsignificantly higher than the success rate previously achieved using photometry\nfrom surveys. We derive the first sidereal rotation periods for additional 69\nasteroids. We find good agreement in spin periods and pole orientations for\nobjects with prior solutions. We obtain a statistical sample of asteroid\nphysical properties that is sufficient for the detection of several previously\nknown trends, such as the underrepresentation of slow rotators in current\ndatabases, and the anisotropic distribution of spin orientations driven by the\nnongravitational forces. We also investigate the dependence of spin\norientations on the rotation period. Since 2018, ASAS-SN has been observing the\nsky with higher cadence and deeper limiting magnitude, which will lead to many\nmore new solutions in just a few years.", "category": "astro-ph_EP" }, { "text": "Ejection of iron-bearing giant-impact fragments and the dynamical and\n geochemical influence of the fragment re-accretion: The Earth was born in violence. Many giant collisions of protoplanets are\nthought to have occurred during the terrestrial planet formation. Here we\ninvestigated the giant impact stage by using a hybrid code that consistently\ndeals with the orbital evolution of protoplanets around the Sun and the details\nof processes during giant impacts between two protoplanets. A significant\namount of materials (up to several tens of percent of the total mass of the\nprotoplanets) is ejected by giant impacts. We call these ejected fragments the\ngiant-impact fragments (GIFs). In some of the erosive hit-and-run and\nhigh-velocity collisions, metallic iron is also ejected, which comes from the\ncolliding protoplanets' cores. From ten numerical simulations for the giant\nimpact stage, we found that the mass fraction of metallic iron in GIFs ranges\nfrom ~ 1wt% to ~ 25wt%. We also discussed the effects of the GIFs on the\ndynamical and geochemical characteristics of formed terrestrial planets. We\nfound that the GIFs have the potential to solve the following dynamical and\ngeochemical conflicts: (1) The Earth, currently in a near circular orbit, is\nlikely to have had a highly eccentric orbit during the giant impact stage. The\nGIFs are large enough in total mass to lower the eccentricity of the Earth to\nits current value via their dynamical friction. (2) The concentrations of\nhighly siderophile elements (HSEs) in the Earth's mantle are greater than what\nwas predicted experimentally. Re-accretion of the iron-bearing GIFs onto the\nEarth can contribute to the excess of HSEs. In addition, the estimated amount\nof iron-bearing GIFs provides significant reducing agent that could transform\nprimitive CO2-H2O atmosphere and ocean into more reducing H2-bearing\natmosphere. Thus, GIFs are important for the origin of Earth's life and its\nearly evolution.", "category": "astro-ph_EP" }, { "text": "Mineral cloud and hydrocarbon haze particles in the atmosphere of the\n hot Jupiter JWST target WASP-43b: Having a short orbital period and being tidally locked makes WASP-43b an\nideal candidate for JWST observations. Phase curve observations of an entire\norbit will enable the mapping of the atmospheric structure across the planet,\nwith different wavelengths of observation allowing different atmospheric depths\nto be seen. We provide insight into the details of the clouds that may form on\nWASP-43b in order to prepare the forthcoming interpretation of the JWST and\nfollow-up data. We utilize 3D GCM results as input for a kinetic,\nnon-equilibrium model for mineral cloud particles, and for a kinetic model to\nstudy a photochemicaly-driven hydrocarbon haze component. Mineral condensation\nseeds form throughout the atmosphere of WASP-43b. This is in stark contrast to\nthe ultra-hot Jupiters, like WASP-18b and HAT-P-7b. The dayside is loaded with\nfew but large mineral cloud particles in addition to hydrocarbon haze particles\nof comparable abundance. Photochemically driven hydrocarbon haze appears on the\ndayside, but does not contribute to the cloud formation on the nightside. The\ngeometrical cloud extension differs across the globe due to the changing\nthermodynamic conditions. Day and night differ by 6000km in pressure scale\nheight. As reported for other planets, the C/O is not constant throughout the\natmosphere. The mean molecular weight is approximately constant in a\nH2-dominated WASP-43b. WASP-43b is expected to be fully covered in clouds which\nare not homogeneously distributed throughout the atmosphere. The dayside and\nthe terminator clouds will be a combination of mineral particles of locally\nvarying size and composition, and of hydrocarbon hazes. The optical depth of\nhydrocarbon hazes is considerably lower than that of mineral cloud particles\nsuch that a wavelength-dependent radius measurement of WASP-43b would be\ndetermined by the mineral cloud particles but not by hazes.", "category": "astro-ph_EP" }, { "text": "Protoplanetary Disk Heating and Evolution Driven by the Spiral Density\n Waves: High-resolution imaging of some protoplanetary disks in scattered light\nreveals presence of the global spiral arms of significant amplitude, likely\nexcited by massive planets or stellar companions. Assuming that these arms are\ndensity waves, evolving into spiral shocks, we assess their effect on the\nthermodynamics, accretion, and global evolution of the disk. We derive\nanalytical expressions for the direct (irreversible) heating, angular momentum\ntransport, and mass accretion rate induced by the disk shocks of arbitrary\nstrength. We find these processes to be very sensitive to the shock amplitude.\nFocusing on the waves of moderate strength (density jump at the shock\n$\\Delta\\Sigma/\\Sigma\\sim 1$) we show the associated disk heating to be\nnegligible (contributing at $\\sim 1\\%$ level to the energy budget) in passive,\nirradiated protoplanetary disks on $\\sim 100$ AU scales, but becoming important\nwithin several AU from the star. At the same time, shock heating can be a\nsignificant (or even dominant) energy source in disks of cataclysmic variables,\nstellar X-ray binaries, and supermassive black hole binaries, heated mainly by\nviscous dissipation. Mass accretion induced by the global spiral shocks is\ncomparable to (or exceeds) the mass inflow due to viscous stresses.\nProtoplanetary disks featuring prominent global spirals must be evolving\nrapidly, in $\\lesssim 0.5$ Myr at $\\sim 100$ AU. A direct upper limit on the\ndisk evolution timescale can be established via the measurement of the\ngravitational torque due to the spiral arms from the imaging data. Our findings\nsuggest that, regardless of their origin, global spiral waves must be important\nagents of the protoplanetary disk evolution. They may serve as an effective\nmechanism of disk dispersal and could be related to the transitional disk\nphenomenon.", "category": "astro-ph_EP" }, { "text": "Revisiting Lambert's Problem: The orbital boundary value problem, also known as Lambert Problem, is\nrevisited. Building upon Lancaster and Blanchard approach, new relations are\nrevealed and a new variable representing all problem classes, under\nL-similarity, is used to express the time of flight equation. In the new\nvariable, the time of flight curves have two oblique asymptotes and they mostly\nappear to be conveniently approximated by piecewise continuous lines. We use\nand invert such a simple approximation to provide an efficient initial guess to\nan Householder iterative method that is then able to converge, for the single\nrevoltuion case, in only two iterations. The resulting algorithm is compared to\nGooding's procedure revealing to be numerically as accurate, while having a\nsmaller computational complexity.", "category": "astro-ph_EP" }, { "text": "Close Stellar Encounters in Young, Substructured, Dissolving Star\n Clusters: Statistics and Effects on Planetary Systems: Both simulations and observations indicate that stars form in filamentary,\nhierarchically clustered associations, most of which disperse into their\ngalactic field once feedback destroys their parent clouds. However, during\ntheir early evolution in these substructured environments, stars can undergo\nclose encounters with one another that might have significant impacts on their\nprotoplanetary disks or young planetary systems. We perform N-body simulations\nof the early evolution of dissolving, substructured clusters with a wide range\nof properties, with the aim of quantifying the expected number and orbital\nelement distributions of encounters as a function of cluster properties. We\nshow that the presence of substructure both boosts the encounter rate and\nmodifies the distribution of encounter velocities compared to what would be\nexpected for a dynamically relaxed cluster. However, the boost only lasts for a\ndynamical time, and as a result the overall number of encounters expected\nremains low enough that gravitational stripping is unlikely to be a significant\neffect for the vast majority of star-forming environments in the Galaxy. We\nbriefly discuss the implications of this result for models of the origin of the\nSolar System, and of free-floating planets. We also provide tabulated encounter\nrates and orbital element distributions suitable for inclusion in population\nsynthesis models of planet formation in a clustered environment.", "category": "astro-ph_EP" }, { "text": "The impact of ultraviolet heating and cooling on the dynamics and\n observability of lava planet atmospheres: Lava planets have non-global, condensible atmospheres similar to icy bodies\nwithin the solar system. Because they depend on interior dynamics, studying the\natmospheres of lava planets can lead to understanding unique geological\nprocesses driven by their extreme environment. Models of lava planet\natmospheres have thus far focused on either radiative transfer or\nhydrodynamics. In this study, we couple the two processes by introducing\nultraviolet and infrared radiation to a turbulent boundary layer model. We also\ntest the effect of different vertical temperature profiles on atmospheric\ndynamics. Results from the model show that UV radiation affects the atmosphere\nmuch more than IR. UV heating and cooling work together to produce a\nhorizontally isothermal atmosphere away from the sub-stellar point regardless\nof the vertical temperature profile. We also find that stronger temperature\ninversions induce stronger winds and hence cool the atmosphere. Our simulated\ntransmission spectra of the bound atmosphere show a strong SiO feature in the\nUV that would be challenging to observe in the planet's transit spectrum due to\nthe precision required. Our simulated emission spectra are more promising, with\nsignificant SiO spectral features at 4.5 and 9 $\\mu$m that can be observed with\nthe James Webb Space Telescope. Different vertical temperature profiles produce\ndiscernible dayside emission spectra, but not in the way one would expect.", "category": "astro-ph_EP" }, { "text": "A Deep Search for Additional Satellites around the Dwarf Planet Haumea: Haumea is a dwarf planet with two known satellites, an unusually high spin\nrate, and a large collisional family, making it one of the most interesting\nobjects in the outer solar system. A fully self-consistent formation scenario\nresponsible for the satellite and family formation is still elusive, but some\nprocesses predict the initial formation of many small moons, similar to the\nsmall moons recently discovered around Pluto. Deep searches for regular\nsatellites around KBOs are difficult due to observational limitations, but\nHaumea is one of the few for which sufficient data exist. We analyze Hubble\nSpace Telescope (HST) observations, focusing on a ten-consecutive-orbit\nsequence obtained in July 2010, to search for new very small satellites. To\nmaximize the search depth, we implement and validate a non-linear\nshift-and-stack method. No additional satellites of Haumea are found, but by\nimplanting and recovering artificial sources, we characterize our sensitivity.\nAt distances between $\\sim$10,000 km and $\\sim$350,000 km from Haumea,\nsatellites with radii as small as $\\sim$10 km are ruled out, assuming an albedo\n($p \\simeq 0.7$) similar to Haumea. We also rule out satellites larger than\n$\\gtrsim$40 km in most of the Hill sphere using other HST data. This search\nmethod rules out objects similar in size to the small moons of Pluto. By\ndeveloping clear criteria for determining the number of non-linear rates to\nuse, we find that far fewer shift rates are required ($\\sim$35) than might be\nexpected. The non-linear shift-and-stack method to discover satellites (and\nother moving transients) is tractable, particularly in the regime where\nnon-linear motion begins to manifest itself.", "category": "astro-ph_EP" }, { "text": "The infrared colors of 51 Eridani b: micrometereoid dust or chemical\n disequilibrium?: We reanalyze near-infrared spectra of the young extrasolar giant planet 51\nEridani b which was originally presented in (Macintosh et al. 2015) and (Rajan\net al. 2017) using modern atmospheric models which include a self-consistent\ntreatment of disequilibrium chemistry due to turbulent vertical mixing. In\naddition, we investigate the possibility that significant opacity from\nmicrometeors or other impactors in the planet's atmosphere may be responsible\nfor shaping the observed spectral energy distribution (SED). We find that\ndisequilibrium chemistry is useful for describing the mid-infrared colors of\nthe planet's spectra, especially in regards to photometric data at M band\naround 4.5 $\\mu$m which is the result of super-equilibrium abundances of carbon\nmonoxide, while the micrometeors are unlikely to play a pivotal role in shaping\nthe SED. The best-fitting, micrometeroid-dust-free, disequilibrium chemistry,\npatchy cloud model has the following parameters: effective temperature\n$T_\\textrm{eff} = 681$ K with clouds (or without clouds, i.e. the grid\ntemperature $T_\\textrm{grid}$ = 900 K), surface gravity $g$ = 1000 m/s$^2$,\nsedimentation efficiency $f_\\textrm{sed}$ = 10, vertical eddy diffusion\ncoefficient $K_\\textrm{zz}$ = 10$^3$ cm$^2$/s, cloud hole fraction\n$f_\\textrm{hole}$ = 0.2, and planet radius $R_\\textrm{planet}$ = 1.0\nR$_\\textrm{Jup}$.", "category": "astro-ph_EP" }, { "text": "Five New Post-Main-Sequence Debris Disks with Gaseous Emission: Observations of debris disks, the products of the collisional evolution of\nrocky planetesimals, can be used to trace planetary activity across a wide\nrange of stellar types. The most common end points of stellar evolution are no\nexception as debris disks have been observed around several dozen white dwarf\nstars. But instead of planetary formation, post-main-sequence debris disks are\na signpost of planetary destruction, resulting in compact debris disks from the\ntidal disruption of remnant planetesimals. In this work, we present the\ndiscovery of five new debris disks around white dwarf stars with gaseous debris\nin emission. All five systems exhibit excess infrared radiation from dusty\ndebris, emission lines from gaseous debris, and atmospheric absorption features\nindicating on-going accretion of metal-rich debris. In four of the systems, we\ndetect multiple metal species in emission, some of which occur at strengths and\ntransitions previously unseen in debris disks around white dwarf stars. Our\nfirst year of spectroscopic follow-up hints at strong variability in the\nemission lines that can be studied in the future, expanding the range of\nphenomena these post-main-sequence debris disks exhibit.", "category": "astro-ph_EP" }, { "text": "Reflected light from giant planets in habitable zones: Tapping into the\n power of the Cross-Correlation Function: The direct detection of reflected light from exoplanets is an excellent probe\nfor the characterization of their atmospheres. The greatest challenge for this\ntask is the low planet-to-star flux ratio, which even in the most favourable\ncase is of the order of $10^{-4}$ in the optical. This ratio decreases even\nmore for planets in their host habitable zone, typically lower than $10^{-7}$.\nTo reach the signal-to-noise level required for such detections, we propose to\nunleash the power of the Cross Correlation Function in combination with the\ncollecting power of next generation observing facilities. The technique we\npropose has already yielded positive results by detecting the reflected\nspectral signature of 51 Pegasi b (see Martins et al. 2015). In this work, we\nattempted to infer the number of hours required for the detection of several\nplanets in their host habitable zone using the aforementioned technique from\ntheoretical EELT observations. Our results show that for 5 of the selected\nplanets it should be possible to directly recover their reflected spectral\nsignature.", "category": "astro-ph_EP" }, { "text": "A self-consistent cloud model for brown dwarfs and young giant\n exoplanets: comparison with photometric and spectroscopic observations: We developed a simple, physical and self-consistent cloud model for brown\ndwarfs and young giant exoplanets. We compared different parametrisations for\nthe cloud particle size, by either fixing particle radii, or fixing the mixing\nefficiency (parameter fsed) or estimating particle radii from simple\nmicrophysics. The cloud scheme with simple microphysics appears as the best\nparametrisation by successfully reproducing the observed photometry and spectra\nof brown dwarfs and young giant exoplanets. In particular, it reproduces the\nL-T transition, due to the condensation of silicate and iron clouds below the\nvisible/near-IR photosphere. It also reproduces the reddening observed for\nlow-gravity objects, due to an increase of cloud optical depth for low gravity.\nIn addition, we found that the cloud greenhouse effect shifts chemical\nequilibriums, increasing the abundances of species stable at high temperature.\nThis effect should significantly contribute to the strong variation of methane\nabundance at the L-T transition and to the methane depletion observed on young\nexoplanets. Finally, we predict the existence of a continuum of brown dwarfs\nand exoplanets for absolute J magnitude=15-18 and J-K color=0-3, due to the\nevolution of the L-T transition with gravity. This self-consistent model\ntherefore provides a general framework to understand the effects of clouds and\nappears well-suited for atmospheric retrievals.", "category": "astro-ph_EP" }, { "text": "Exoplanetary Interiors: The first mass-estimate of an exoplanet around a Sun-like star, 51 Peg b and\nthe first radius measurement of an exoplanet, HD209458b pointed to the\nchallenges of understanding the atmosphere, interior, and evolution of\nexoplanets including the possibility of mass loss of planets on close-orbits\nthat are exposed to strong irradiation. These discoveries raised the question\nof heating and inflation mechanisms, and of the nature of these objects in\nterms of composition compared to the known planets in the Solar system. The\nfield of exoplanet interior modeling was born. Here, we outline and discuss\ncurrent big science questions: (i) What is the amount of heavy elements in a\nplanet and do all planets possess an iron-rock core? We suggest that a\npromising and novel approach for exoplanets can be measuring their tidal\nresponse in form of the Love numbers h2 and k2. (ii) How much and through what\nmechanisms are the interiors of planets heated or delayed from cooling? Many\nstrongly irradiated gaseous planets require an additional heat source to\nexplain their large radii. (iii) What is the origin of the observed populations\nin the radius-period diagram? Objects in and along the radius valley are\nexcellent targets to study planetary formation and evaporation. (iv) What does\nthe composition of rocky planets tell us about their formation? Planets more\niron-rich than Mercury are found, as well as planets that if rocky, are\ndepleted in iron with respect to Earth. We do not have yet a reliable formation\ntheory that would explain their existence.", "category": "astro-ph_EP" }, { "text": "Using the Sun to estimate Earth-like planets detection capabilities.I.\n Impact of cold spots: Stellar spots may in some cases produce radial velocity (RV) signatures\nsimilar to those of exoplanets. To further investigate the impact of spots, we\naim at studying the detectability of Earth mass planets in the habitable zone\n(HZ) of solar type stars, if covered by spots similar to the sunspots. We have\nused the Sunspots properties recorded over one solar cycle between 1993 and\n2003 to build the RV curve that a solar type star seen edge-on would show, if\ncovered by such spots with Tsun -Tspot = 550K. We also simulate the RV of such\na spotted star surrounded by an Earth mass planet located in the HZ. Under\npresent assumptions, the detection of a 1 M Earth planet located between 0.8\nand 1.2 AU requires an intensive monitoring (weekly or better), during several\nyears of low activity phasis. The temporal sampling is more crucial than the\nprecision of the data (assuming precisions in the range [1-10] cm/s). Cooler\nspots may become a problem for such detections. Also, we anticipate that\nplages, not considered in this paper, could further complicate or even\ncompromise the detections.", "category": "astro-ph_EP" }, { "text": "Cool Gaseous Exoplanets: surveying the new frontier with Twinkle: Cool gaseous exoplanets ($1.75\\ R_\\oplus < R_\\text{p} < 3\\ R_\\text{J}$, $200$\nK $ $5\\sigma$\nsignificance. We find that an injected mass-metallicity trend is\nwell-recovered, demonstrating Twinkle's ability to elucidate this fundamental\nrelationship into cool regime. We also find Twinkle will be able to detect\ncloud layers at 3$\\sigma$ or greater in all cool gaseous planets for clouds at\n$\\leq$ 10 Pa pressure level, but will be insensitive to clouds deeper than\n$10^4$ Pa in all cases. With these results we demonstrate the capability of the\nTwinkle mission to greatly expand the current knowledge of cool gaseous\nplanets, enabling key insights and constraints to be obtained for this\npoorly-charted region of exoplanet parameter space.", "category": "astro-ph_EP" }, { "text": "On the Detection of Exomoons Transiting Isolated Planetary-Mass Objects: All-sky imaging surveys have identified several dozen isolated planetary-mass\nobjects (IPMOs), far away from any star. Here, we examine the prospects for\ndetecting transiting moons around these objects. We expect transiting moons to\nbe common, occurring around 10-15% of IPMOs, given that close-orbiting moons\nhave a high geometric transit probability and are expected to be a common\noutcome of giant planet formation. IPMOs offer an advantage over other directly\nimaged planets in that high-contrast imaging is not necessary to detect the\nphotometric transit signal. For at least 30 (>50%) of the currently known\nIPMOs, observations of a single transit with the James Webb Space Telescope\nwould have low enough forecasted noise levels to allow for the detection of an\nIo-like or Titan-like moon. Intrinsic variability of the IPMOs will be an\nobstacle. Using archival time-series photometry of IPMOs with the Spitzer Space\nTelescope as a proof-of-concept, we found evidence for a fading event of 2MASS\nJ1119-1137 AB that might have been caused by intrinsic variability, but is also\nconsistent with a single transit of a habitable-zone 1.7$R_\\oplus$ exomoon.\nAlthough the interpretation of this particular event is inconclusive, the\ncharacteristics of the data and the candidate signal suggest that Earth-sized\nhabitable-zone exomoons around IPMOs are detectable with existing\ninstrumentation.", "category": "astro-ph_EP" }, { "text": "Ethyl cyanide on Titan: Spectroscopic detection and mapping using ALMA: We report the first spectroscopic detection of ethyl cyanide (C$_2$H$_5$CN)\nin Titan's atmosphere, obtained using spectrally and spatially resolved\nobservations of multiple emission lines with the Atacama Large\nMillimeter/submillimeter array (ALMA). The presence of C$_2$H$_5$CN in Titan's\nionosphere was previously inferred from Cassini ion mass spectrometry\nmeasurements of C$_2$H$_5$CNH$^+$. Here we report the detection of 27\nrotational lines from C$_2$H$_5$CN (in 19 separate emission features detected\nat $>3\\sigma$ confidence), in the frequency range 222-241 GHz. Simultaneous\ndetections of multiple emission lines from HC$_3$N, CH$_3$CN and CH$_3$CCH were\nalso obtained. In contrast to HC$_3$N, CH$_3$CN and CH$_3$CCH, which peak in\nTitan's northern (spring) hemisphere, the emission from C$_2$H$_5$CN is found\nto be concentrated in the southern (autumn) hemisphere, suggesting a distinctly\ndifferent chemistry for this species, consistent with a relatively short\nchemical lifetime for C$_2$H$_5$CN. Radiative transfer models show that most of\nthe C$_2$H$_5$CN is concentrated at altitudes 300-600 km, suggesting production\npredominantly in the mesosphere and above. Vertical column densities are found\nto be in the range (2-5)$\\times10^{14}$ cm$^{-2}$.", "category": "astro-ph_EP" }, { "text": "Spherical Harmonics for the 1D Radiative Transfer Equation II: Thermal\n Emission: Approximate methods to estimate solutions to the radiative transfer equation\nare essential for the understanding of atmospheres of exoplanets and brown\ndwarfs. The simplest and most popular choice is the \"two-stream method\" which\nis often used to produce simple yet effective models for radiative transfer in\nscattering and absorbing media. Toon et al. (1989) (Toon89) outlined a\ntwo-stream method for computing reflected light and thermal spectra and was\nlater implemented in the open-source radiative transfer model PICASO. In Part~I\nof this series, we developed an analytical spherical harmonics method for\nsolving the radiative transfer equation for reflected solar radiation (Rooney\net al. 2023), which was implemented in PICASO to increase the accuracy of the\ncode by offering a higher-order approximation. This work is an extension of\nthis spherical harmonics derivation to study thermal emission spectroscopy. We\nhighlight the model differences in the approach for thermal emission and\nbenchmark the 4-term method (SH4) against Toon89 and a high-stream\ndiscrete-ordinates method, CDISORT. By comparing the spectra produced by each\nmodel we demonstrate that the SH4 method provides a significant increase in\naccuracy, compared to Toon89, which can be attributed to the increased order of\napproximation and to the choice of phase function. We also explore the\ntrade-off between computational time and model accuracy. We find that our\n4-term method is twice as slow as our 2-term method, but is up to five times\nmore accurate, when compared with CDISORT. Therefore, SH4 provides excellent\nimprovement in model accuracy with minimal sacrifice in numerical expense.", "category": "astro-ph_EP" }, { "text": "Seasonal Water \"Pump\" in the Atmosphere of Mars: Vertical Transport to\n the Thermosphere: We present results of simulations with the Max Planck Institute general\ncirculation model (MPI-MGCM) implementing a hydrological cycle scheme. The\nsimulations reveal a seasonal water \"pump\" mechanism responsible for the upward\ntransport of water vapor. This mechanism occurs in high latitudes above\n60$^\\circ$ of the southern hemisphere at perihelion, when the upward branch of\nthe meridional circulation is particularly strong. A combination of the mean\nvertical flux with variations induced by solar tides facilitates penetration of\nwater across the \"bottleneck\" at approximately 60 km. The meridional\ncirculation then transports water across the globe to the northern hemisphere.\nSince the intensity of the meridional cell is tightly controlled by airborne\ndust, the water abundance in the thermosphere strongly increases during dust\nstorms.", "category": "astro-ph_EP" }, { "text": "Boundary Layer Circumplanetary Accretion: How Fast Could an Unmagnetized\n Planet Spin Up Through Its Disk?: Gas giant planets are expected to accrete most of their mass via a\ncircumplanetary disk. If the planet is unmagnetized and initially slowly\nrotating, it will accrete gas via a radially narrow boundary layer and rapidly\nspin up. Radial broadening of the boundary layer as the planet spins up reduces\nthe specific angular momentum of accreted gas, allowing the planet to find a\nterminal rotation rate short of the breakup rate. Here, we use axisymmetric\nviscous hydrodynamic simulations to quantify the terminal rotation rate of\nplanets accreting from their circumplanetary disks. For an isothermal\nplanet-disk system with a disk scale height $h/r =0.1$ near the planetary\nsurface, spin up switches to spin down at between 70\\% and 80\\% of the planet's\nbreakup angular velocity. In a qualitative difference from vertically-averaged\nmodels -- where spin down can co-exist with mass accretion -- we observe\n\\emph{decretion} accompanying solutions where angular momentum is being lost.\nThe critical spin rate depends upon the disk thickness near the planet. For an\nisothermal system with a disk scale height of $h/r = 0.15$ near the planet, the\ncritical spin rate drops to between 60\\% and 70\\% of the planet's breakup\nangular velocity. In the disk outside the boundary layer, we identify\nmeridional circulation flows, which are unsteady and instantaneously asymmetric\nacross the mid-plane. The simulated flows are strong enough to vertically\nredistribute solid material in early-stage satellite formation. We discuss how\nextrasolar planetary rotation measurements, when combined with spectroscopic\nand variability studies of protoplanets with circumplanetary disks, could\ndetermine the role of magnetic and non-magnetic processes in setting giant\nplanet spins.", "category": "astro-ph_EP" }, { "text": "Seeking echoes of circumstellar disks in Kepler light curves: Light echoes of flares on active stars offer the opportunity for direct\ndetection of circumstellar dust. We revisit the problem of identifying faint\nechoes in post-flare light curves, focusing on debris disks from on-going\nplanet formation. Starting with simulations, we develop an algorithm for\nestimating the radial extent and total mass from disk echo profiles. We apply\nthis algorithm to light curves from over 2,100 stars observed by NASA's Kepler\nmission, selected for multiple, short-lived flares in either the long-cadence\nor short-cadence data sets. While flux uncertainties in light curves from\nindividual stars preclude useful mass limits on circumstellar disks,\ncatalog-averaged light curves yield constraints on disk mass that are\ncomparable to estimates from known debris disks. The average mass in micron- to\nmillimeter-sized dust around the Kepler stars cannot exceed 10% of an Earth\nmass in exo-Kuiper belts or 10% of a Lunar mass in the terrestrial zone. We\ngroup stars according to IR excess, based on WISE W1-W3 color, as an indicator\nfor the presence of circumstellar dust. The mass limits are greater for stars\nwith strong IR excess, a hint that echoes are lurking not far beneath the noise\nin post-flare light curves. With increased sensitivity, echo detection will let\ntime-domain astronomy complement spectroscopic and direct-imaging studies in\nmapping how, when, and where planets form.", "category": "astro-ph_EP" }, { "text": "A Fast Approximate Approach to Microlensing Survey Analysis: Microlensing can be used to discover exoplanets of a wide range of masses\nwith orbits beyond ~ 1 AU, and even free-floating planets. The WFIRST mission\nwill use microlensing to discover approximately 1600 planets by monitoring ~100\nmillion stars to find ~50000 microlensing events. Modelling each microlensing\nevent, especially the ones involving two or more lenses, is typically\ncomplicated and time-consuming, and analyzing thousands of WFIRST microlensing\nevents is possibly infeasible using current methods. Here, we present an\nalgorithm that is able to rapidly evaluate thousands of simulated WFIRST\nbinary-lens microlensing light curves, returning an estimate for the physical\nparameters of the lens systems. We find that this algorithm can recover\nprojected separations between the planet and the star very well for\nlow-mass-ratio events, and can also estimate mass ratios within an order of\nmagnitude for events with wide and close caustic topologies.", "category": "astro-ph_EP" }, { "text": "The composition of hot Jupiter atmospheres assembled within chemically\n evolved protoplanetary discs: The radial-dependent positions of snowlines of abundant oxygen- and\ncarbon-bearing molecules in protoplanetary discs will result in systematic\nradial variations in the C/O ratios in the gas and ice. This variation is\nproposed as a tracer of the formation location of gas-giant planets. However,\ndisc chemistry can affect the C/O ratios in the gas and ice, thus potentially\nerasing the chemical fingerprint of snowlines in gas-giant atmospheres. We\ncalculate the molecular composition of hot Jupiter atmospheres using elemental\nabundances extracted from a chemical kinetics model of a disc midplane where we\nhave varied the initial abundances and ionization rates. The models predict a\nwider diversity of possible atmospheres than those predicted using elemental\nratios from snowlines only. As found in previous work, as the C/O ratio exceeds\nthe solar value, the mixing ratio of CH$_{4}$ increases in the lower\natmosphere, and those of C$_{2}$H$_{2}$ and HCN increase mainly in the upper\natmosphere. The mixing ratio of H$_{2}$O correspondingly decreases. We find\nthat hot Jupiters with C/O$>1$ can only form between the CO$_{2}$ and CH$_{4}$\nsnowlines. Moreover, they can only form in a disc which has fully inherited\ninterstellar abundances, and where negligible chemistry has occurred. Hence,\ncarbon-rich planets are likely rare, unless efficient transport of\nhydrocarbon-rich ices via pebble drift to within the CH$_{4}$ snowline is a\ncommon phenomenon. We predict combinations of C/O ratios and elemental\nabundances that can constrain gas-giant planet formation locations relative to\nsnowline positions, and that can provide insight into the disc chemical\nhistory.", "category": "astro-ph_EP" }, { "text": "Cooling Requirements for the Vertical Shear Instability in\n Protoplanetary Disks: The vertical shear instability (VSI) offers a potential hydrodynamic\nmechanism for angular momentum transport in protoplanetary disks (PPDs). The\nVSI is driven by a weak vertical gradient in the disk's orbital motion, but\nmust overcome vertical buoyancy, a strongly stabilizing influence in cold\ndisks, where heating is dominated by external irradiation. Rapid radiative\ncooling reduces the effective buoyancy and allows the VSI to operate. We\nquantify the cooling timescale $t_c$ needed for efficient VSI growth, through a\nlinear analysis of the VSI with cooling in vertically global, radially local\ndisk models. We find the VSI is most vigorous for rapid cooling with\n$t_c<\\Omega_\\mathrm{K}^{-1}h|q|/(\\gamma -1)$ in terms of the Keplerian orbital\nfrequency, $\\Omega_\\mathrm{K}$; the disk's aspect-ratio, $h\\ll1$; the radial\npower-law temperature gradient, $q$; and the adiabatic index, $\\gamma$. For\nlonger $t_c$, the VSI is much less effective because growth slows and shifts to\nsmaller length scales, which are more prone to viscous or turbulent decay. We\napply our results to PPD models where $t_c$ is determined by the opacity of\ndust grains. We find that the VSI is most effective at intermediate radii, from\n$\\sim5$AU to $\\sim50$AU with a characteristic growth time of $\\sim30$ local\norbital periods. Growth is suppressed by long cooling times both in the opaque\ninner disk and the optically thin outer disk. Reducing the dust opacity by a\nfactor of 10 increases cooling times enough to quench the VSI at all disk\nradii. Thus the formation of solid protoplanets, a sink for dust grains, can\nimpede the VSI.", "category": "astro-ph_EP" }, { "text": "The case of HD 106906 debris disc: A binary's revenge: Debris disc architecture presents [exo-]planetary scientists with precious\nclues for processes of planet formation and evolution, including constraints on\nplanetary mass perturbers. This is particularly true of the disc in HD 106906,\nwhich in early HST, then follow up polarimetric observations, presented\nasymmetries and needle-like features that have been attributed to perturbations\nby a massive, and unusually distant external planetary companion. Here, we\nrevisit the long-term secular dynamical evolution of the HD 106906 disc\nallowing for the combined gravitational action of the planetary companion and\nthe inner stellar binary which holds the system together. We argue that the\nbinary is strong enough to impose a dynamical break at the disc's location,\nresulting in distinctive observational signatures which we render via simulated\nsurface density maps and vertical structure profiles. Within uncertainties on\nthe planet's orbit, we show that the disc can go from being fully dominated by\nthe inner binary to significantly so, and is hardly ever outside its reach. The\nextent of binary dominance impacts the disc's mean eccentricity, a metric which\nwe map as a function of the planet's semi-major axis and orbital eccentricity,\nwith and without radiation pressure. We can thus constrain the planet's orbit\nto ease the tension between evident axisymmetry in the millimeter, and apparent\nasymmetry in scattered light. We discuss phase space structure, then\ninclination distribution, arguing for the relevance of our results to a variety\nof hierarchical systems, as we set the stage for generalizations that allow for\ndisc self-gravity and collisional evolution.", "category": "astro-ph_EP" }, { "text": "A pair of TESS planets spanning the radius valley around the nearby\n mid-M dwarf LTT 3780: We present the confirmation of two new planets transiting the nearby mid-M\ndwarf LTT 3780 (TIC 36724087, TOI-732, $V=13.07$, $K_s=8.204$, $R_s$=0.374\nR$_{\\odot}$, $M_s$=0.401 M$_{\\odot}$, d=22 pc). The two planet candidates are\nidentified in a single TESS sector and are validated with reconnaissance\nspectroscopy, ground-based photometric follow-up, and high-resolution imaging.\nWith measured orbital periods of $P_b=0.77$ days, $P_c=12.25$ days and sizes\n$r_{p,b}=1.33\\pm 0.07$ R$_{\\oplus}$, $r_{p,c}=2.30\\pm 0.16$ R$_{\\oplus}$, the\ntwo planets span the radius valley in period-radius space around low mass stars\nthus making the system a laboratory to test competing theories of the emergence\nof the radius valley in that stellar mass regime. By combining 63 precise\nradial-velocity measurements from HARPS and HARPS-N, we measure planet masses\nof $m_{p,b}=2.62^{+0.48}_{-0.46}$ M$_{\\oplus}$ and $m_{p,c}=8.6^{+1.6}_{-1.3}$\nM$_{\\oplus}$, which indicates that LTT 3780b has a bulk composition consistent\nwith being Earth-like, while LTT 3780c likely hosts an extended H/He envelope.\nWe show that the recovered planetary masses are consistent with predictions\nfrom both photoevaporation and from core-powered mass loss models. The\nbrightness and small size of LTT 3780, along with the measured planetary\nparameters, render LTT 3780b and c as accessible targets for atmospheric\ncharacterization of planets within the same planetary system and spanning the\nradius valley.", "category": "astro-ph_EP" }, { "text": "The inner solar system cratering record and the evolution of impactor\n populations: We review previously published and newly obtained crater size-frequency\ndistributions in the inner solar system. These data indicate that the Moon and\nthe terrestrial planets have been bombarded by two populations of objects.\nPopulation 1, dominating at early times, had nearly the same size distribution\nas the present-day asteroid belt, and produced the heavily cratered surfaces\nwith a complex, multi-sloped crater size-frequency distribution. Population 2,\ndominating since about 3.8-3.7 Ga, has the same size distribution as near-Earth\nobjects (NEOs), had a much lower impact flux, and produced a crater size\ndistribution characterized by a differential -3 single-slope power law in the\ncrater diameter range 0.02 km to 100 km. Taken together with the results from a\nlarge body of work on age-dating of lunar and meteorite samples and theoretical\nwork in solar system dynamics, a plausible interpretation of these data is as\nfollows. The NEO population is the source of Population 2 and it has been in\nnear-steady state over the past ~3.7-3.8 gigayears; these objects are derived\nfrom the main asteroid belt by size-dependent non-gravitational effects that\nfavor the ejection of smaller asteroids. However, Population 1 were main belt\nasteroids ejected from their source region in a size-independent manner,\npossibly by means of gravitational resonance sweeping during giant planet orbit\nmigration; this caused the so-called Late Heavy Bombardment (LHB). The LHB\nbegan some time before ~3.9 Ga, peaked and declined rapidly over the next ~100\nto 300 megayears, and possibly more slowly from about 3.8-3.7 Ga to ~2 Ga. A\nthird crater population (Population S) consists of secondary impact craters\nthat can dominate the cratering record at small diameters.", "category": "astro-ph_EP" }, { "text": "Signatures of an eccentric disc cavity: Dust and gas in IRS 48: We test the hypothesis that the disc cavity in the `transition disc' Oph IRS\n48 is carved by an unseen binary companion. We use 3D dust-gas\nsmoothed-particle hydrodynamics simulations to demonstrate that marginally\ncoupled dust grains concentrate in the gas over-density that forms in in the\ncavity around a low binary mass ratio binary. This produces high contrast ratio\ndust asymmetries at the cavity edge similar to those observed in the disc\naround IRS 48 and other transition discs. This structure was previously assumed\nto be a vortex. However, we show that the observed velocity map of IRS 48\ndisplays a peculiar asymmetry that is not predicted by the vortex hypothesis.\nWe show the unusual kinematics are naturally explained by the non-Keplerian\nflow of gas in an eccentric circumbinary cavity. We further show that\nperturbations observed in the isovelocity curves of IRS 48 may be explained as\nthe product of the dynamical interaction between the companion and the disc.\nThe presence of a $\\sim$0.4 M$_{\\odot}$ companion at a $\\sim$10 au separation\ncan qualitatively explain these observations. High spatial resolution line and\ncontinuum imaging should be able to confirm this hypothesis.", "category": "astro-ph_EP" }, { "text": "Insight from laboratory measurements on dust in debris discs: Extreme adaptive optics instruments have revealed exquisite details on debris\ndiscs, allowing to extract the optical properties of the dust particles such as\nthe phase function, the degree of polarisation and the spectral reflectance.\nThese are three powerful diagnostic tools to understand the physical properties\nof the dust : the size, shape and composition of the dust particles. This can\ninform us on the population of parent bodies, also called planetesimals, which\ngenerate those particles through collisions. It is however very rare to be able\nto combine all those three observables for the same system, as this requires\ndifferent high-contrast imaging techniques to suppress the starlight and reveal\nthe faint scattered light emission from the dust. Due to its brightness, the\nring detected around the A-type star HR 4796 is a notable exception, with both\nunpolarised and polarised images covering near-infrared wavelengths. Here, we\nshow how measurements of dust particles in the laboratory can reproduce the\nobserved near-infrared photo-polarimetric properties of the HR 4796 disc.\nExperimental characterisation of dust allows to bypass the current limitations\nof dust models to reproduce simultaneously the phase function, the degree of\npolarisation and the spectral reflectance.", "category": "astro-ph_EP" }, { "text": "Oort cloud Ecology II: Extra-solar Oort clouds and the origin of\n asteroidal interlopers: We simulate the formation and evolution of Oort clouds around the 200 nearest\nstars (within 16pc according to the Gaia DR2) database. This study is performed\nby numerically integrating the planets and minor bodies in orbit around the\nparent star and in the Galactic potential. The calculations start 1\\,Gyr ago\nand continue for 100Myr into the future. In this time frame, we simulate how\nasteroids (and planets) are ejected from the star's vicinity and settle in an\nOort cloud and how they escape the local stellar gravity to form tidal steams.\nA fraction of 0.0098 to 0.026 of the asteroids remain bound to their parent\nstar. The orbits of these asteroids isotropizes and circularizes due to the\ninfluence of the Galactic tidal field to eventually form an Oort cloud between\n10^4 and 2 10^5au. We estimate that 6% of the nearby stars may have a planet in\nits Oort cloud. The majority of asteroids (and some of the planets) become\nunbound from the parent star to become free floating in the Galactic potential.\nThese soli lapides remain in a similar orbit around the Galactic center as\ntheir host star, forming dense streams of rogue interstellar asteroids and\nplanets.\n The Solar system occasionally passes through such tidal streams, potentially\ngiving rise to occasional close encounters with object in this stream. The two\nrecently discovered objects, 1I/(2017 Q3) 'Oumuamua and 2I/(2019 Q4) Borisov,\nmay be such objects. Although the direction from which an individual solus\nlapis originated cannot easily be traced back to the original host, multiple\nsuch objects coming from the same source might help to identify their origin.\nAt the moment the Solar system is in the bow or wake of the tidal stream of 10\nof the nearby stars which might contribute considerably to the interaction\nrate. (abridged)", "category": "astro-ph_EP" }, { "text": "Traditional formation scenarios fail to explain 4:3 mean motion\n resonances: At least two multi-planetary systems in a 4:3 mean motion resonance have been\nfound by radial velocity surveys. These planets are gas giants and the systems\nare only stable when protected by a resonance. Additionally the Kepler mission\nhas detected at least 4 strong candidate planetary systems with a period ratio\nclose to 4:3.\n This paper investigates traditional dynamical scenarios for the formation of\nthese systems. We systematically study migration scenarios with both N-body and\nhydro-dynamic simulations. We investigate scenarios involving the in-situ\nformation of two planets in resonance. We look at the results from finely tuned\nplanet-planet scattering simulations with gas disk damping. Finally, we\ninvestigate a formation scenario involving isolation-mass embryos.\n Although the combined planet-planet scattering and damping scenario seems\npromising, none of the above scenarios is successful in forming enough systems\nin 4:3 resonance with planetary masses similar to the observed ones. This is a\nnegative result but it has important implications for planet formation.\nPrevious studies were successful in forming 2:1 and 3:2 resonances. This is\ngenerally believed to be evidence of planet migration. We highlight the main\ndifferences between those studies and our failure in forming a 4:3 resonance.\nWe also speculate on more exotic and complicated ideas. These results will\nguide future investigators toward exploring the above scenarios and alternative\nmechanisms in a more general framework.", "category": "astro-ph_EP" }, { "text": "Using Star Spots to Measure the Spin-orbit Alignment of Transiting\n Planets: Spectroscopic follow-up of dozens of transiting planets has revealed the\ndegree of alignment between the equators of stars and the orbits of the planets\nthey host. Here we determine a method, applicable to spotted stars, that can\nreveal the same information from the photometric discovery data, with no need\nfor follow-up. A spot model fit to the global light curve, parametrized by the\nspin orientation of the star, predicts when the planet will transit the spots.\nObserving several spot crossings during different transits then leads to\nconstraints on the spin-orbit alignment. In cases where stellar spots are\nsmall, the stellar inclination, and hence the true alignment, rather than just\nthe sky projection, can be obtained. This method has become possible with the\nadvent of space telescopes such as CoRoT and Kepler, which photometrically\nmonitor transiting planets over a nearly continuous, long time baseline. We\napply our method to CoRoT-2, and find the projected spin-orbit alignment angle,\nlambda= 4.7 deg +/- 12.3 deg, in excellent agreement with a previous\ndetermination that employed the Rossiter-McLaughlin effect. The large spots of\nthe parent star, CoRoT-2, limit our precision on the stellar inclination: i_s =\n84 deg +/- 36 deg, where i_s < 90 deg (> 90 deg) indicates the rotation axis is\ntilted towards (away from) the line of sight.", "category": "astro-ph_EP" }, { "text": "Searching for the HR 8799 Debris Disk with HST/STIS: We present a new algorithm for space telescope high contrast imaging of\nclose-to-face-on planetary disks called Optimized Spatially Filtered (OSFi)\nnormalization. This algorithm is used on HR 8799 Hubble Space Telescope (HST)\ncoronagraphic archival data, showing an over-luminosity after reference star\npoint spread function (PSF) subtraction that may be from the inner disk and/or\nplanetesimal belt components of this system. The PSF-subtracted radial profiles\nin two separate epochs from 2011 and 2012 are consistent with one another, and\nself-subtraction shows no residual in both epochs. We explore a number of\npossible false-positive scenarios that could explain this residual flux,\nincluding telescope breathing, spectral differences between HR 8799 and the\nreference star, imaging of the known warm inner disk component, OSFi algorithm\nthroughput and consistency with the standard spider normalization HST PSF\nsubtraction technique, and coronagraph misalignment from pointing accuracy. In\ncomparison to another similar STIS dataset, we find that the over-luminosity is\nlikely a result of telescope breathing and spectral difference between HR 8799\nand the reference star. Thus, assuming a non-detection, we derive upper limits\non the HR 8799 dust belt mass in small grains. In this scenario, we find that\nthe flux of these micron-sized dust grains leaving the system due to radiation\npressure is small enough to be consistent with measurements of other debris\ndisk halos.", "category": "astro-ph_EP" }, { "text": "Organic hazes as a source of life's building blocks to warm little ponds\n on the Hadean Earth: Over 4 billion years ago, Earth is thought to have been a hazy world akin to\nSaturn's moon Titan. The organic hazes in the atmosphere at this time could\ncontain a vast inventory of life's building blocks, and thus may have seeded\nwarm little ponds for life. In this work, we produce organic hazes in the lab\nin atmospheres with high (5%) and low (0.5%) CH4 abundances and analyze the\nsolid particles for nucleobases, amino acids, and a few other organics using\nGC/MS/MS to obtain their concentrations. We also analyze heated (200\n$^{\\circ}$C) samples from the high methane organic haze experiment to simulate\nthese particles sitting on an uninhabitable surface. Finally, we use our\nexperimental results and estimates of atmospheric haze production as inputs for\na comprehensive numerical pond model to calculate the concentrations of\nnucleobases from organic hazes in these environments. We find that organic\nhazes typically provide up to 0.2-6.5 $\\mu$M concentrations of nucleobases to\nwarm little ponds for potentially habitable Hadean conditions. However, without\nseepage, uracil and thymine can reach ~100 $\\mu$M concentrations, which is the\npresent lower experimental limit to react these species to form nucleotides.\nHeating samples leads to partial or complete decay of biomolecules, suggesting\nthat biomolecule stockpiling on the hot surface is unlikely. The ideal\nconditions for the delivery of life's building blocks from organic hazes would\nbe when the Hadean atmosphere is rich in methane, but not so rich as to create\nan uninhabitable surface.", "category": "astro-ph_EP" }, { "text": "Realistic collisional water transport during terrestrial planet\n formation: Self-consistent modeling by an N-body--SPH hybrid code: According to current evidence the water inventory of Earth (and perhaps\nsimilar exoplanets) was transported inwards via (giant) collisions during the\nchaotic final phase of planet formation. In dynamical simulations water\ndelivery is still studied almost exclusively by assuming oversimplified perfect\nmerging (PM), even though it is particularly prone to collisional transfer and\nloss. To close this gap we have developed a framework to model collisional\nwater transport by direct combination of long-term N-body computations with\ndedicated 3D SPH simulations for each collision. Post-collision water\ninventories are self-consistently traced further, in accretionary or erosive as\nwell as hit-and-run encounters. The latter are frequent outcomes among\nprotoplanets, where besides collisional losses, water transfer between the\nencountering bodies has to be considered. This hybrid approach enables us for\nthe first time to trace the full dynamical and collisional evolution of ~200\nbodies throughout the whole late-stage accretion phase (several 100 Myrs). As a\nfirst application we choose a Solar System-like architecture, with already\nformed giant planets on either circular or eccentric orbits and a debris disk\nspanning from 0.5 - 4 au. Realistic collision treatment leads to considerably\ndifferent results than PM, with lower mass planets and water inventories\nreduced by a factor of two or more. Due to a combination of collisional losses\nand considerably lengthened accretion, final water contents especially with\ngiant planets on circular orbits are strongly reduced to more Earth-like\nvalues. Water delivery to potentially habitable planets is dominated by few\ndecisive collisions, mostly with embryo-sized or larger bodies. The high\nfrequency of hit-and-run, with generally low water (and mass) transfer\nefficiencies, are a crucial part of this process, and of system-wide evolution\nin general.", "category": "astro-ph_EP" }, { "text": "Detection and Characterization of Extrasolar Planets through Doppler\n Spectroscopy: Over 300 extrasolar planets have been found since 1992, showing that\nplanetary systems are common and exhibit an outstanding variety of\ncharacteristics. As the number of detections grows and as models of planet\nformation progress to account for the existence of these new worlds,\nstatistical studies and confrontations of observation with theory allow to\nprogressively unravel the key processes underlying planet formation. In this\nchapter we review the dominant contribution of Doppler spectroscopy to the\npresent discoveries and to our general understanding of planetary systems. We\nalso emphasize the synergy of Doppler spectroscopy and transit photometry in\ncharacterizing the physical properties of transiting extrasolar planets. As we\nwill see, Doppler spectroscopy has not reached its limits yet and it will\nundoubtly play a leading role in the detection and characterization of the\nfirst Earth-mass planets.", "category": "astro-ph_EP" }, { "text": "On the dynamics of Extrasolar Planetary Systems under dissipation.\n Migration of planets: We study the dynamics of planetary systems with two planets moving in the\nsame plane, when frictional forces act on the two planets, in addition to the\ngravitational forces. The model of the general three-body problem is used.\nDifferent laws of friction are considered. The topology of the phase space is\nessential in understanding the evolution of the system. The topology is\ndetermined by the families of stable and unstable periodic orbits, both\nsymmetric and non symmetric. It is along the stable families, or close to them,\nthat the planets migrate when dissipative forces act. At the critical points\nwhere the stability along the family changes, there is a bifurcation of a new\nfamily of stable periodic orbits and the migration process changes route and\nfollows the new stable family up to large eccentricities or to a chaotic\nregion. We consider both resonant and non resonant planetary systems. The 2/1,\n3/1 and 3/2 resonances are studied. The migration to larger or smaller\neccentricities depends on the particular law of friction. Also, in some cases\nthe semimajor axes increase and in other cases they are stabilized. For\nparticular laws of friction and for special values of the parameters of the\nfrictional forces, it is possible to have partially stationary solutions, where\nthe eccentricities and the semimajor axes are fixed.", "category": "astro-ph_EP" }, { "text": "TOI-1842b: A Transiting Warm Saturn Undergoing Re-Inflation around an\n Evolving Subgiant: The imminent launch of space telescopes designed to probe the atmospheres of\nexoplanets has prompted new efforts to prioritise the thousands of transiting\nplanet candidates for follow-up characterisation. We report the detection and\nconfirmation of TOI-1842b, a warm Saturn identified by TESS and confirmed with\nground-based observations from Minerva-Australis, NRES, and the Las Cumbres\nObservatory Global Telescope. This planet has a radius of\n$1.04^{+0.06}_{-0.05}\\,R_{Jup}$, a mass of $0.214^{+0.040}_{-0.038}\\,M_{Jup}$,\nan orbital period of $9.5739^{+0.0002}_{-0.0001}$ days, and an extremely low\ndensity ($\\rho$=0.252$\\pm$0.091 g cm$^{-3}$). TOI-1842b has among the best\nknown combinations of large atmospheric scale height (893 km) and host-star\nbrightness ($J=8.747$ mag), making it an attractive target for atmospheric\ncharacterisation. As the host star is beginning to evolve off the main\nsequence, TOI-1842b presents an excellent opportunity to test models of gas\ngiant re-inflation. The primary transit duration of only 4.3 hours also makes\nTOI-1842b an easily-schedulable target for further ground-based atmospheric\ncharacterisation.", "category": "astro-ph_EP" }, { "text": "Frequencies and resonances around $L_4$ in the elliptic restricted\n three-body problem: The stability of the Lagrangian point $L_4$ is investigated in the elliptic\nrestricted three-body problem by using Floquet's theory. Stable and unstable\ndomains are determined in the parameter plane of the mass parameter and the\neccentricity by computing the characteristic exponents. Frequencies of motion\naround $L_4$ have been determined both in the stable and unstable domains and\nfitting functions for the frequencies are derived depending on the mass\nparameter and the eccentricity. Resonances between the frequencies are studied\nin the whole parameter plane. It is shown that the 1:1 resonances are not\nrestricted only to single curves but extend to the whole unstable domain. In\nthe unstable domains longer escape times of the test particle from the\nneighbourhood of $L_4$ are related to certain resonances, but changing the\nparameters the same resonances may lead to faster escape.", "category": "astro-ph_EP" }, { "text": "The obliquity of Enceladus: The extraordinary activity at Enceladus' warm south pole indicates the\npresence of an internal global or local reservoir of liquid water beneath the\nsurface. While Tyler (2009, 2011) has suggested that the geological activity\nand the large heat flow of Enceladus could result from tidal heating triggered\nby a large obliquity of at least 0.05{\\deg}-0.1{\\deg}, theoretical models of\nthe Cassini state predict the obliquity to be two to three orders of magnitude\nsmaller for an entirely solid and rigid Enceladus. We investigate the influence\nof an internal subsurface ocean and of tidal deformations of the solid layers\non the obliquity of Enceladus. Our Cassini state model takes into account the\nexternal torque exerted by Saturn on each layer of the satellite and the\ninternal gravitational and pressure torques induced by the presence of the\nliquid layer. As a new feature, our model also includes additional torques that\narise because of the periodic tides experienced by the satellite. We find that\nthe upper limit for the obliquity of a solid Enceladus is 0.00045 degrees and\nis negligibly affected by elastic deformations. The presence of an internal\nocean decreases this upper limit by 13.1%, elasticity attenuating this decrease\nby only 0.5%. Since the obliquity of Enceladus cannot reach Tyler's\nrequirement, obliquity tides are unlikely to be the source of the large heat\nflow of Enceladus. More likely, the geological activity at Enceladus' south\npole results from eccentricity tides. Even in the most favorable case, the\nupper limit for the obliquity of Enceladus corresponds to about two meters at\nmost at the surface of Enceladus. This is well below the resolution of Cassini\nimages. Control point calculations cannot be used to detect the obliquity of\nEnceladus, let alone to constrain its interior from an obliquity measurement.", "category": "astro-ph_EP" }, { "text": "Distribution of solids in the rings of the HD 163296 disk: a\n multiwavelength study: In this paper we analyze new observations from ALMA and VLA, at a high\nangular resolution corresponding to 5 - 8 au, of the protoplanetary disk around\nHD 163296 to determine the dust spatial distribution and grain properties. We\nfit the spectral energy distribution as a function of the radius at five\nwavelengths from 0.9 to 9\\,mm, using a simple power law and a physical model\nbased on an analytic description of radiative transfer that includes isothermal\nscattering. We considered eight dust populations and compared the models'\nperformance using Bayesian evidence. Our analysis shows that the moderately\nhigh optical depth ($\\tau$>1) at $\\lambda \\leq$ 1.3 mm in the dust rings\nartificially lower the millimeter spectral index, which should therefore not be\nconsidered as a reliable direct proxy of the dust properties and especially the\ngrain size. We find that the outer disk is composed of small grains on the\norder of 200 $\\mu$m with no significant difference between rings at 66 and 100\nau and the adjacent gaps, while in the innermost 30 au, larger grains\n($\\geq$mm) could be present. We show that the assumptions on the dust\ncomposition have a strong impact on the derived surface densities and grain\nsize. In particular, increasing the porosity of the grains to 80\\% results in a\ntotal dust mass about five times higher with respect to grains with 25\\%\nporosity. Finally, we find that the derived opacities as a function of\nfrequency deviate from a simple power law and that grains with a lower porosity\nseem to better reproduce the observations of HD163296. While we do not find\nevidence of differential trapping in the rings of HD163296, our overall results\nare consistent with the postulated presence of giant planets affecting the dust\ntemperature structure and surface density, and possibly originating a\nsecond-generation dust population of small grains.", "category": "astro-ph_EP" }, { "text": "First detection of orbital motion for HD 106906 b: A wide-separation\n exoplanet on a Planet Nine-like orbit: HD 106906 is a 15 Myr old short-period (49 days) spectroscopic binary that\nhosts a wide-separation (737 au) planetary-mass ($\\sim11\\,M_{\\rm Jup}$) common\nproper motion companion, HD 106906 b. Additionally, a circumbinary debris disk\nis resolved at optical and near-infrared wavelengths that exhibits a\nsignificant asymmetry at wide separations that may be driven by gravitational\nperturbations from the planet. In this study we present the first detection of\norbital motion of HD 106906 b using Hubble Space Telescope images spanning a 14\nyr period. We achieve high astrometric precision by cross-registering the\nlocations of background stars with the Gaia astrometric catalog, providing the\nsubpixel location of HD 106906 that is either saturated or obscured by\ncoronagraphic optical elements. We measure a statistically significant\n$31.8\\pm7.0$ mas eastward motion of the planet between the two most\nconstraining measurements taken in 2004 and 2017. This motion enables a\nmeasurement of the inclination between the orbit of the planet and the inner\ndebris disk of either $36_{-14}^{+27}$ deg or $44_{-14}^{+27}$ deg, depending\non the true orientation of the orbit of the planet. There is a strong negative\ncorrelation between periastron and mutual inclination; orbits with smaller\nperiastra are more misaligned with the disk plane. With a periastron of\n$510_{-320}^{+480}$ au, HD 106906 b is likely detached from the planetary\nregion within 100 au radius, showing that a Planet Nine-like architecture can\nbe established very early in the evolution of a planetary system.", "category": "astro-ph_EP" }, { "text": "Jetting during oblique impacts of spherical impactors: During the early stages of an impact a small amount material may be jetted\nand ejected at speeds exceeding the impact velocity. Jetting is an important\nprocess for producing melt during relatively low velocity impacts. How impact\nangle affects the jetting process has yet to be fully understood. Here, we\nsimulate jetting during oblique impacts using the iSALE shock physics code.\nAssuming both the target and impactor have the same composition (dunite), we\nexamine the jetted material which exceeds the impact velocity. Our results show\nthat oblique impacts always produce more jetted ejecta than vertical impacts,\nexcept for grazing impacts with impact angles $< 15^{\\circ}$. A 45$^{\\circ}$\nimpact with an impact velocity of 3 km/s produces jetted material equal to\n$\\sim$ 7 \\% of the impactor mass. This is 6 times the jetted mass produced by a\nvertical impact with similar impact conditions. We also find that the origin of\njetted ejecta depends on impact angle; for impact angles less than\n45$^{\\circ}$, most of the jet is composed of impactor material, while at higher\nimpact angles the jet is dominated by target material. Our findings are\nconsistent with previous experimental work. In all cases, jetted materials are\npreferentially distributed downrange of the impactor.", "category": "astro-ph_EP" }, { "text": "Dynamics of Planetary Systems Within Star Clusters: Aspects of the Solar\n System's Early Evolution: Most planetary systems -- including our own -- are born within stellar\nclusters, where interactions with neighboring stars can help shape the system\narchitecture. This paper develops an orbit-averaged formalism to characterize\nthe cluster's mean-field effects as well as the physics of long-period stellar\nencounters. Our secular approach allows for an analytic description of the\ndynamical consequences of the cluster environment on its constituent planetary\nsystems. We analyze special cases of the resulting Hamiltonian, corresponding\nto eccentricity evolution driven by planar encounters, as well as hyperbolic\nperturbations upon dissipative disks. We subsequently apply our results to the\nearly evolution of our solar system, where the cluster's collective potential\nperturbs the solar system's plane, and stellar encounters act to increase the\nvelocity dispersion of the Kuiper belt. Our results are two-fold: first, we\nfind that cluster effects can alter the mean plane of the solar system by\n$\\lesssim1\\deg$, and are thus insufficient to explain the $\\psi\\approx6\\deg$\nobliquity of the sun. Second, we delineate the extent to which stellar flybys\nexcite the orbital dispersion of the cold classical Kuiper belt, and show that\nwhile stellar flybys may grow the cold belt's inclination by the observed\namount, the resulting distribution is incompatible with the data.\nCorrespondingly, our calculations place an upper limit on the product of the\nstellar number density and residence time of the sun in its birth cluster,\n$\\eta\\,\\tau\\lesssim2\\times10^4\\,$Myr/pc$^3$.", "category": "astro-ph_EP" }, { "text": "Chondrule size and related physical properties: a compilation and\n evaluation of current data across all meteorite groups: The examination of the physical properties of chondrules has generally\nreceived less emphasis than other properties of meteorites such as their\nmineralogy, petrology, and chemical and isotopic compositions. Among the\nvarious physical properties of chondrules, chondrule size is especially\nimportant for the classification of chondrites into chemical groups, since each\nchemical group possesses a distinct size-frequency distribution of chondrules.\nKnowledge of the physical properties of chondrules is also vital for the\ndevelopment of astrophysical models for chondrule formation, and for\nunderstanding how to utilize asteroidal resources in space exploration. To\nexamine our current knowledge of chondrule sizes, we have compiled and provide\ncommentary on available chondrule dimension literature data. We include all\nchondrite chemical groups as well as the acapulcoite primitive achondrites,\nsome of which contain relict chondrules. We also compile and review current\nliterature data for other astrophysically-relevant physical properties\n(chondrule mass and density). Finally, we briefly examine some additional\nphysical aspects of chondrules such as the frequencies of compound and\n'cratered' chondrules. A purpose of this compilation is to provide a useful\nresource for meteoriticists and astrophysicists alike.", "category": "astro-ph_EP" }, { "text": "Mars Express measurements of surface albedo changes over 2004 - 2010: The pervasive Mars dust is continually transported between the surface and\nthe atmosphere. When on the surface, dust increases the albedo of darker\nunderlying rocks and regolith, which modifies climate energy balance and must\nbe quantified. Remote observation of surface albedo absolute value and albedo\nchange is however complicated by dust itself when lifted in the atmosphere.\nHere we present a method to calculate and map the bolometric solar\nhemispherical albedo of the Martian surface using the 2004 - 2010 OMEGA imaging\nspectrometer dataset. This method takes into account aerosols radiative\ntransfer, surface photometry, and instrumental issues such as registration\ndifferences between visible and near-IR detectors. Resulting albedos are on\naverage 17% higher than previous estimates for bright surfaces while similar\nfor dark surfaces. We observed that surface albedo changes occur mostly during\nthe storm season due to isolated events. The main variations are observed\nduring the 2007 global dust storm and during the following year. A wide variety\nof change timings are detected such as dust deposited and then cleaned over a\nMartian year, areas modified only during successive global dust storms, and\nperennial changes over decades. Both similarities and differences with previous\nglobal dust storms are observed. While an optically thin layer of bright dust\nis involved in most changes, this coating turns out to be sufficient to mask\nunderlying mineralogical near-IR spectral signatures. Overall, changes result\nfrom apparently erratic events; however, a cyclic evolution emerges for some\n(but not all) areas over long timescales.", "category": "astro-ph_EP" }, { "text": "Dust Ejection from Planetary Bodies by Temperature Gradients: Laboratory\n Experiments: Laboratory experiments show that dusty bodies in a gaseous environment eject\ndust particles if they are illuminated. We find that even more intense dust\neruptions occur when the light source is turned off. We attribute this to a\ncompression of gas by thermal creep in response to the changing temperature\ngradients in the top dust layers. The effect is studied at a light flux of 13\nkW/(m*m) and 1 mbar ambient pressure. The effect is applicable to\nprotoplanetary disks and Mars. In the inner part of protoplanetary disks,\nplanetesimals can be eroded especially at the terminator of a rotating body.\nThis leads to the production of dust which can then be transported towards the\ndisk edges or the outer disk regions. The generated dust might constitute a\nsignificant fraction of the warm dust observed in extrasolar protoplanetary\ndisks. We estimate erosion rates of about 1 kg/s for 100 m parent bodies. The\ndust might also contribute to subsequent planetary growth in different\nlocations or on existing protoplanets which are large enough not to be\nsusceptible to particle loss by light induced ejection. Due to the ejections,\nplanetesimals and smaller bodies will be accelerated or decelerated and drift\noutward or inward, respectively. The effect might also explain the entrainment\nof dust in dust devils on Mars, especially at high altitudes where gas drag\nalone might not be sufficient.", "category": "astro-ph_EP" }, { "text": "Compact Ultra Dense Matter Impactors: We study interactions of meteorlike compact ultradense objects (CUDO), having\nnuclear or greater density, with Earth and other rocky bodies in the Solar\nSystem as a possible source of information about novel forms of matter. We\nstudy the energy loss in CUDO puncture of the body and discuss differences\nbetween regular matter and CUDO impacts.", "category": "astro-ph_EP" }, { "text": "Multiple Explanations for the Single Transit of KIC 5951458 based on\n Radial Velocity Measurements Extracted with a Novel Matched-template\n Technique: Planetary systems that show single-transit events are a critical pathway to\nincreasing the yield of long-period exoplanets from transit surveys. From the\nprimary Kepler mission, KIC 5951458b (Kepler-456b) was thought to be a\nsingle-transit giant planet with an orbital period of 1310 days. However,\nradial velocity (RV) observations of KIC 5951458 from the HIRES instrument on\nthe Keck telescope suggest that the system is far more complicated. To extract\nprecise RVs for this $V\\approx13$ star, we develop a novel matched-template\ntechnique that takes advantage of a broad library of template spectra acquired\nwith HIRES. We validate this technique and measure its noise floor to be 4 - 8\nm s$^{-1}$ (in addition to internal RV error) for most stars that would be\ntargeted for precision RVs. For KIC 5951458, we detect a long-term RV trend\nthat suggests the existence of a stellar companion with an orbital period\ngreater than a few thousand days. We also detect an additional signal in the\nRVs that is possibly caused by a planetary or brown dwarf companion with mass\nin the range of 0.6 - 82 $M_{\\rm J}$ and orbital period below a few thousand\ndays. Curiously, from just the data on hand, it is not possible to determine\nwhich object caused the single \"transit\" event. We demonstrate how a modest set\nof RVs allows us to update the properties of this unusual system and predict\nthe optimal timing for future observations.", "category": "astro-ph_EP" }, { "text": "Topographic Constraints on the Origin of the Equatorial Ridge on Iapetus: Saturn's moon Iapetus has an equatorial ridge system, which may be as high as\n20 km, that may have formed by endogenic forces, such as tectonic and\nconvective forces, or exogenic processes such as debris infall. We use\nhigh-resolution topographic data to conduct a topographic analysis of the\nridge, which suggests a predominantly triangular morphology, with some ridge\nface slopes reaching 40 degrees, allowing for an exogenic formation mechanism.", "category": "astro-ph_EP" }, { "text": "Mapping the Skies of Ultracool Worlds: Detecting Storms and Spots with\n Extremely Large Telescopes: Extremely large telescopes (ELTs) present an unparalleled opportunity to\nstudy the magnetism, atmospheric dynamics, and chemistry of very low mass stars\n(VLMs), brown dwarfs, and exoplanets. Instruments such as the Giant Magellan\nTelescope - Consortium Large Earth Finder (GMT/GCLEF), the Thirty Meter\nTelescope's Multi-Objective Diffraction-limited High-Resolution Infrared\nSpectrograph (TMT/MODHIS), and the European Southern Observatory's Mid-Infrared\nELT Imager and Spectrograph (ELT/METIS) provide the spectral resolution and\nsignal-to-noise (S/N) necessary to Doppler image ultracool targets' surfaces\nbased on temporal spectral variations due to surface inhomogeneities. Using our\npublicly-available code, $Imber$, developed and validated in Plummer & Wang\n(2022), we evaluate these instruments' abilities to discern magnetic star spots\nand cloud systems on a VLM star (TRAPPIST-1); two L/T transition ultracool\ndwarfs (VHS J1256$-$1257 b and SIMP J0136+0933); and three exoplanets (Beta Pic\nb and HR 8799 d and e). We find that TMT/MODHIS and ELT/METIS are suitable for\nDoppler imaging the ultracool dwarfs and Beta Pic b over a single rotation.\nUncertainties for longitude and radius are typically $\\lesssim 10^{\\circ}$, and\nlatitude uncertainties range from $\\sim 10^{\\circ} \\ \\rm{to} \\ 30^{\\circ}$.\nTRAPPIST-1's edge-on inclination and low $\\upsilon \\sin i$ provide a challenge\nfor all three instruments while GMT/GCLEF and the HR 8799 planets may require\nobservations over multiple rotations. We compare the spectroscopic technique,\nphotometry-only inference, and the combination of the two. We find combining\nspectroscopic and photometric observations can lead to improved Bayesian\ninference of surface inhomogeneities and offers insight into whether ultracool\natmospheres are dominated by spotted or banded features.", "category": "astro-ph_EP" }, { "text": "Modeling a Transient Secondary Paleo-Lunar Atmosphere: 3-D Simulations\n and Analysis: The lunar history of water deposition, loss, and transport post-accretion has\nbecome an important consideration in relation to the possibility of a human\noutpost on the Moon. Very recent work has shown that a secondary primordial\natmosphere of up to 10 mb could have been emplaced ~3.5 billion years ago due\nto volcanic outgassing from the maria. Using a zero dimensional chemistry model\nwe demonstrate the temperature dependence of the resulting major atmospheric\ncomponents (CO or CO$_2$). We use a three dimensional general circulation model\nto test the viability of such an atmosphere and derive its climatological\ncharacteristics. Based on these results we then conjecture on its capability to\ntransport volatiles outgassed from the maria to the permanently shadowed\nregions at the poles. Our preliminary results demonstrate that atmospheres as\nlow as 1 mb are viable and that permanent cold trapping of volatiles is only\npossible at the poles.", "category": "astro-ph_EP" }, { "text": "Tracking Advanced Planetary Systems (TAPAS) with HARPS-N VII. Elder suns\n with low-mass companions: We present the current status of and new results from our search for\nexoplanets in a sample of solar-mass, evolved stars observed with the HARPS-N\nand the 3.6-m Telescopio Nazionale Galileo (TNG), and the High Resolution\nSpectrograph (HRS) and the 9.2-m Hobby Eberly Telescope (HET).\n The aim of this project is to detect and characterise planetary-mass\ncompanions to solar-mass stars in a sample of 122 targets at various stages of\nevolution from the main sequence (MS) to the red giant branch (RGB), mostly\nsub-gaints and giants, selected from the Pennsylvania-Toru\\'n Planet Search\n(PTPS) sample, and use this sample to study relations between stellar\nproperties, such as metallicity, luminosity, and the planet occurrence rate.\n This work is based on precise radial velocity (RV) measurements. We have\nobserved the program stars for up to 11 years with the HET/HRS and the\nTNG/HARPS-N.\n We present the analysis of RV measurements with the HET/HRS and the\nTNG/HARPS-N of four solar-mass stars, HD 4760, HD 96992 , BD+02 3313, and TYC\n0434-04538-1. We found that: HD 4760 hosts a companion with a minimum mass of\n13.9 MJ (a=1.14 au, e=0.23); HD 96992 is a host to a msin i=1.14 MJ companion\non a a=1.24 au and e=0.41 orbit, and TYC 0434-04538-1 hosts an msin i=6.1MJ\ncompanion on a a=0.66 au and e=0.08$ orbit. In the case of BD+02 3313 we found\na correlation between the measured RVs and one of the stellar activity\nindicators, suggesting that the observed RV variations may originate in either\nstellar activity or be caused by the presence of an unresolved companion. We\nalso discuss the current status of the project and a statistical analysis of\nthe RV variations in our sample of target stars.", "category": "astro-ph_EP" }, { "text": "OSSOS XVIII: Constraining migration models with the 2:1 resonance using\n the Outer Solar System Origins Survey: Resonant dynamics plays a significant role in the past evolution and current\nstate of our outer Solar System. The population ratios and spatial distribution\nof Neptune's resonant populations are direct clues to understanding the history\nof our planetary system. The orbital structure of the objects in Neptune's 2:1\nmean-motion resonance (\\emph{twotinos}) has the potential to be a tracer of\nplanetary migration processes. Different migration processes produce distinct\narchitectures, recognizable by well-characterized surveys. However, previous\ncharacterized surveys only discovered a few twotinos, making it impossible to\nmodel the intrinsic twotino population. With a well-designed cadence and nearly\n100\\% tracking success, the Outer Solar System Origins Survey (OSSOS)\ndiscovered 838 trans-Neptunian objects, of which 34 are securely twotinos with\nwell-constrained libration angles and amplitudes. We use the OSSOS twotinos and\nthe survey characterization parameters via the OSSOS Survey Simulator to\ninspect the intrinsic population and orbital distributions of twotino. The\nestimated twotino population, 4400$^{+1500}_{-1100}$ with $H_r<8.66$\n(diameter$\\sim$100km) at 95\\% confidence, is consistent with the previous\nlow-precision estimate. We also constrain the width of the inclination\ndistribution to a relatively narrow value of $\\sigma_i$=6$^\\circ$$^{+1}_{-1}$,\nand find the eccentricity distribution is consistent with a Gaussian centered\non $e_\\mathrm{c}=0.275$ with a width $e_\\mathrm{w}=0.06$. We find a\nsingle-slope exponential luminosity function with $\\alpha=0.6$ for the\ntwotinos. Finally, we for the first time meaningfully constrain the fraction of\nsymmetric twotinos, and the ratio of the leading asymmetric islands; both\nfractions are in a range of 0.2--0.6. These measurements rule out certain\ntheoretical models of Neptune's migration history.", "category": "astro-ph_EP" }, { "text": "Signals embedded in the radial velocity noise. Periodic variations in\n the tau Ceti velocities: The abilities of radial velocity exoplanet surveys to detect the lowest-mass\nextra-solar planets are currently limited by a combination of instrument\nprecision, lack of data, and \"jitter\". Jitter is a general term for any unknown\nfeatures in the noise, and reflects a lack of detailed knowledge of stellar\nphysics (asteroseismology, starspots, magnetic cycles, granulation, and other\nstellar surface phenomena), as well as the possible underestimation of\ninstrument noise. We study an extensive set of radial velocities for the star\nHD 10700 ($\\tau$ Ceti) to determine the properties of the jitter arising from\nstellar surface inhomogeneities, activity, and telescope-instrument systems,\nand perform a comprehensive search for planetary signals in the radial\nvelocities. We perform Bayesian comparisons of statistical models describing\nthe radial velocity data to quantify the number of significant signals and the\nmagnitude and properties of the excess noise in the data. We reach our goal by\nadding artificial signals to the \"flat\" radial velocity data of HD 10700 and by\nseeing which one of our statistical noise models receives the greatest\nposterior probabilities while still being able to extract the artificial\nsignals correctly from the data. We utilise various noise components to assess\nproperties of the noise in the data and analyse the HARPS, AAPS, and HIRES data\nfor HD 10700 to quantify these properties and search for previously unknown\nlow-amplitude Keplerian signals. ...", "category": "astro-ph_EP" }, { "text": "Analysis of the arm-like structure in the outer disk of PDS 70. Spiral\n density wave or vortex?: Observing dynamical interactions between planets and disks is key to\nunderstanding their formation and evolution. Two protoplanets have recently\nbeen discovered within PDS 70's protoplanetary disk, along with an arm-like\nstructure towards the north-west of the star. Our aim is to constrain the\nmorphology and origin of this arm-like structure, and to assess whether it\ncould trace a spiral density wave caused by the dynamical interaction between\nthe planet PDS 70c and the disk. We analyze polarized and angular differential\nimaging (PDI and ADI) data taken with VLT/SPHERE, spanning six years of\nobservations. PDI data sets are reduced using the IRDAP polarimetric data\nreduction pipeline, while ADI data sets are processed using MUSTARD, a novel\ninverse problem algorithm to tackle the geometrical biases spoiling the images\npreviously used for the analysis of this disk. We confirm the presence of the\narm-like structure in all PDI and ADI datasets. We do not observe a south-east\nsymmetric arm with respect to the disk minor axis, which seems to disfavor the\nprevious hypothesis that the arm is the footprint of a double-ring structure.\nIf the structure traces a spiral density wave following the motion of PDS 70c,\nwe would expect\n$11\\overset{\\circ}{.}28^{+2\\overset{\\circ}{.}20}_{-0\\overset{\\circ}{.}86}$\nrotation for the spiral in six years. However, we do not measure any\nsignificant movement of the structure. If the arm-like structure is a\nplanet-driven spiral arm, the observed lack of rotation would suggest that the\nassumption of rigid-body rotation may be inappropriate for spirals induced by\nplanets. We suggest that the arm-like structure may rather trace a vortex\nappearing as a one-armed spiral in scattered light due to projection effects.\nThe vortex hypothesis accounts for both the lack of observed rotation and the\npresence of a nearby sub-mm continuum asymmetry detected with ALMA.", "category": "astro-ph_EP" }, { "text": "Is the Solar System Stable ?: Since the formulation of the problem by Newton, and during three centuries,\nastronomers and mathematicians have sought to demonstrate the stability of the\nSolar System. Thanks to the numerical experiments of the last two decades, we\nknow now that the motion of the planets in the Solar System is chaotic, which\nprohibits any accurate prediction of their trajectories beyond a few tens of\nmillions of years. The recent simulations even show that planetary collisions\nor ejections are possible on a period of less than 5 billion years, before the\nend of the life of the Sun.", "category": "astro-ph_EP" }, { "text": "Computing optical meteor flux using Global Meteor Network data: Meteor showers and their outbursts are the dominant source of meteoroid\nimpact risk to spacecraft on short time scales. Meteor shower prediction models\ndepend on historical observations to produce accurate forecasts. However, the\ncurrent lack of quality and persistent world-wide monitoring at optical\nmeteoroid sizes has left some recent major outbursts poorly observed. A novel\nmethod of computing meteor shower flux is developed and applied to Global\nMeteor Network data. The method is verified against previously published\nobservations of the Perseids and the Geminids. The complete mathematical and\nalgorithmic details of computing meteor shower fluxes from video observations\nare described. As an example application of our approach, the flux measurements\nof the 2021 Perseid outburst, the 2020-2022 Quadrantids, and 2020-2021 Geminids\nare presented. The flux of the 2021 Perseids reached similar levels to the\n1991-1994 and 2016 outbursts (ZHR $\\sim$ 280). The flux of the Quadrantids\nshows high year-to-year variability in the core of the stream while the longer\nlasting background activity is less variable, consistent with an age difference\nbetween the two components. The Geminids show a double peak in flux near the\ntime of peak.", "category": "astro-ph_EP" }, { "text": "The peculiar shapes of Saturn's small inner moons as evidence of mergers\n of similar-sized moonlets: The Cassini spacecraft revealed the spectacular, highly irregular shapes of\nthe small inner moons of Saturn, ranging from the unique \"ravioli-like\" forms\nof Pan and Atlas to the highly elongated structure of Prometheus. Closest to\nSaturn, these bodies provide important clues regarding the formation process of\nsmall moons in close orbits around their host planet, but their range of\nirregular shapes has not been explained yet. Here we show that the spectrum of\nshapes among Saturn's small moons is a natural outcome of merging collisions\namong similar-sized moonlets possessing physical properties and orbits that are\nconsistent with those of the current moons. A significant fraction of such\nmerging collisions take place either at the first encounter or after 1-2\nhit-and-run events, with impact velocities in the range of 1-5 times the mutual\nescape velocity. Close to head-on mergers result in flattened objects with\nlarge equatorial ridges, as observed on Atlas and Pan. With slightly more\noblique impact angles, collisions lead to elongated, Prometheus-like shapes.\nThese results suggest that the current forms of the small moons provide direct\nevidence of the processes at the final stages of their formation, involving\npairwise encounters of moonlets of comparable size. Finally, we show that this\nmechanism may also explain the formation of Iapetus' equatorial ridge, as well\nas its oblate shape.", "category": "astro-ph_EP" }, { "text": "Induced Turbulence and the Density Structure of the Dust Layer in a\n Protoplanetary Disk: We study the turbulence induced in the dust layer of a protoplanetary disk\nbased on the energetics of dust accretion due to gas drag. We estimate\nturbulence strength from the energy supplied by dust accretion, using the\nradial drift velocity of the dust particles in a laminar disk. Our estimate of\nthe turbulence strength agrees with previous analytical and numerical research\non the turbulence induced by Kelvin-Helmholtz and/or streaming instabilities\nfor particles whose stopping time is less than the Keplerian time. For such\nsmall particles, the strongest turbulence is expected to occur when the\ndust-to-gas ratio of the disk is ~C_eff^(1/2) (h_g / r) ~ 10^(-2), where C_eff\n~ 0.2 represents the energy supply efficiency to turbulence and h_g / r ~ 5 x\n10^(-2) is the aspect ratio of the gas disk. The maximum viscosity parameter is\nalpha_max ~ C_eff T_s (h_g / r)^2 ~ 10^(-4) T_s, where T_s (<1) is the\nnon-dimensional stopping time of the dust particles. Modification in the\ndust-to-gas ratio from the standard value, 10^(-2), by any process, results in\nweaker turbulence and a thinner dust layer, and consequently may accelerate the\ngrowth process of the dust particles.", "category": "astro-ph_EP" }, { "text": "Albedos of Small Hilda Group Asteroids as Revealed by Spitzer: We present thermal 24 $\\mu$m observations from the \\textit{Spitzer Space\nTelescope} of 62 Hilda asteroid group members with diameters ranging from 3 to\n12 kilometers. Measurements of the thermal emission when combined with reported\nabsolute magnitudes allow us to constrain the albedo and diameter of each\nobject. From our \\textit{Spitzer} sample, we find the mean geometric albedo,\n$p_{V} =$ 0.07 $\\pm$ 0.05 for small (D $<$ 10 km) Hilda group asteroids. This\nvalue of $p_{V}$ is greater than and spans a larger range in albedo space than\nthe mean albedo of large (D $\\gtrsim$ 10 km) Hilda group asteroids which is\n$p_{V} =$ 0.04 $\\pm$ 0.01. Though this difference may be attributed to space\nweathering, the small Hilda group population reportedly displays greater\ntaxonomic range from C-, D- and X-type whose albedo distributions are\ncommensurate with the range of determined albedos. We discuss the derived Hilda\nsize-frequency distribution, color-color space, and geometric albedo for our\nsurvey sample in the context of the expected migration induced \"seeding\" of the\nHilda asteroid group with outer solar system proto-planetesimals as outlined in\nthe \"Nice\" formalism.", "category": "astro-ph_EP" }, { "text": "Uncertainty for calculating transport on Titan: a probabilistic\n description of bimolecular diffusion parameters: Bimolecular diffusion coefficients are important parameters used by\natmospheric models to calculate altitude profiles of minor constituents in an\natmosphere. Unfortunately, laboratory measurements of these coefficients were\nnever conducted at temperature conditions relevant to the atmosphere of Titan.\nHere we conduct a detailed uncertainty analysis of the bimolecular diffusion\ncoefficient parameters as applied to Titan's upper atmosphere to provide a\nbetter understanding of the impact of uncertainty for this parameter on models.\nBecause temperature and pressure conditions are much lower than the laboratory\nconditions in which bimolecular diffusion parameters were measured, we apply a\nBayesian framework, a problem-agnostic framework, to determine parameter\nestimates and associated uncertainties. We solve the Bayesian calibration\nproblem using the open-source QUESO library which also performs a propagation\nof uncertainties in the calibrated parameters to temperature and pressure\nconditions observed in Titan's upper atmosphere. Our results show that, after\npropagating uncertainty through the Massman model, the uncertainty in molecular\ndiffusion is highly correlated to temperature and we observe no noticeable\ncorrelation with pressure. We propagate the calibrated molecular diffusion\nestimate and associated uncertainty to obtain an estimate with uncertainty due\nto bimolecular diffusion for the methane molar fraction as a function of\naltitude. Results show that the uncertainty in methane abundance due to\nmolecular diffusion is in general small compared to eddy diffusion and the\nchemical kinetics description. However, methane abundance is most sensitive to\nuncertainty in molecular diffusion above 1200 km where the errors are\nnontrivial and could have important implications for scientific research based\non diffusion models in this altitude range.", "category": "astro-ph_EP" }, { "text": "A Search for Wide Companions to the Extrasolar Planetary System HR 8799: The extrasolar planetary system around HR 8799 is the first multiplanet\nsystem ever imaged. It is also, by a wide margin, the highest mass system with\n>27 Jupiters of planetary mass past 25 AU. This is a remarkable system with no\nanalogue with any other known planetary system. In the first part of this paper\nwe investigate the nature of two faint objects imaged near the system. These\nobjects are considerably fainter (H=20.4, and 21.6 mag) and more distant\n(projected separations of 612, and 534 AU) than the three known planetary\ncompanions b, c, and d (68-24 AU). It is possible that these two objects could\nbe lower mass planets (of mass ~5 and ~3 Jupiters) that have been scattered to\nwider orbits. We make the first direct comparison of newly reduced archival\nGemini adaptive optics images to archival HST/NICMOS images. With nearly a\ndecade between these epochs we can accurately assess the proper motion nature\nof each candidate companion. We find that both objects are unbound to HR 8799\nand are background. We estimate that HR 8799 has no companions of H<22 from\n~5-15 arcsec. Any scattered giant planets in the HR 8799 system are >600 AU or\nless than 3 Jupiters in mass. In the second part of this paper we carry out a\nsearch for wider common proper motion objects. While we identify no bound\ncompanions to HR 8799, our search yields 16 objects within 1 degree in the\nNOMAD catalog and POSS DSS images with similar (+/-20 mas/yr) proper motions to\nHR 8799, three of which warrant follow-up observations.", "category": "astro-ph_EP" }, { "text": "On the Effects of Planetary Oblateness on Exoplanet Studies: When studying transiting exoplanets it is common to assume a spherical planet\nshape. However short rotational periods can cause a planet to bulge at its\nequator, as is the case with Saturn whose equatorial radius is almost 10%\nlarger than its polar radius. As a new generation of instruments comes online,\nit is important to continually assess the underlying assumptions of models to\nensure robust and accurate inferences. We analyze bulk samples of known\ntransiting planets and calculate their expected signal strength if they were to\nbe oblate. We find that for noise levels below 100ppm, as many as 100 planets\ncould have detectable oblateness. We also investigate the effects of fitting\nspherical planet models to synthetic oblate lightcurves. We find that this\nbiases the retrieved parameters by several standard deviations for oblateness\nvalues > 0.1-0.2. When attempting to fit an oblateness model to both spherical\nand oblate lightcurves, we find that the sensitivity of such fits is correlated\nwith both the SNR as well as the time sampling of the data, which can mask the\noblateness signal. For typical values of these quantities for Kepler\nobservations, it is difficult to rule out oblateness values less than ~0.25.\nThis results in an accuracy wall of 10-15% for the density of planets which may\nbe oblate. Finally, we find that a precessing oblate planet has the ability to\nmimic the signature of a long-period companion via transit timing variations,\ninducing offsets at the level of 10s of seconds.", "category": "astro-ph_EP" }, { "text": "Dynamics of the TrES-2 system: The TrES-2 system harbors one planet which was discovered with the transit\ntechnique. In this work we investigate the dynamical behavior of possible\nadditional, lower-mass planets. We identify the regions where such planets can\nmove on stable orbits and show how they depend on the initial eccentricity and\ninclination. We find, that there are stable regions inside and outside the\norbit of TrES-2b where additional, smaller planets can move. We also show that\nthose planets can have a large orbital inclination which makes a detection with\nthe transit technique very difficult.", "category": "astro-ph_EP" }, { "text": "Changes in the physical environment of the inner coma of\n 67P/Churyumov-Gerasimenko with decreasing heliocentric distance: The Wide Angle Camera of the OSIRIS instrument on board the Rosetta\nspacecraft is equipped with several narrowband filters that are centered on the\nemission lines and bands of various fragment species. These are used to\ndetermine the evolution of the production and spatial distribution of the gas\nin the inner coma of comet 67P with time and heliocentric distance, here\nbetween 2.6 - 1.3 AU pre-perihelion. Our observations indicate that the\nemission observed in the OH, OI, CN, NH, and NH2 filters is mostly produced by\ndissociative electron impact excitation of different parent species. We\nconclude that CO2 rather than H2O is a significant source of the [OI] 630 nm\nemission. A strong plume-like feature observed in the in CN and [OI] filters is\npresent throughout our observations. This plume is not present in OH emission\nand indicates a local enhancement of the CO2/H2O ratio by as much as a factor\nof 3. We observed a sudden decrease in intensity levels after March 2015, which\nwe attribute to decreased electron temperatures in the first kilometers above\nthe nucleus surface.", "category": "astro-ph_EP" }, { "text": "Laboratory Studies of Methane and Its Relationship to Prebiotic\n Chemistry: In order to examine how the terrestrial life emerged, a number of laboratory\nexperiments have been conducted since the 1950s. Methane has been one of the\nkey molecules in these studies. In earlier studies, strongly reducing gas\nmixtures containing methane and ammonia were mainly used to simulate possible\nreactions in primitive Earth atmosphere, and amino acids and other organic\ncompounds were detected. Since the primitive Earth atmosphere was estimated to\nbe less reducing, contribution of extraterrestrial organics to the origin of\nlife is considered quite important. Extraterrestrial organic chemistry has been\nexperimentally and theoretically studied intensively, including laboratory\nexperiments simulating interstellar molecular reactions. Endogenous and\nexogenous organics should have been supplied to the primitive ocean. Now\nsubmarine hydrothermal systems are considered one of the plausible sites of\ngeneration of life. Experiments simulating submarine hydrothermal systems where\nmethane played an important role are now intensively being conducted. We have\nrecognized the importance of such studies on possible reactions in other solar\nsystem bodies to understand the origins of life. Titan and other icy bodies,\nwhere methane plays significant roles, are especially good targets to be\nstudied. In the case of Titan, not only methane-containing atmospheres but also\nliquidospheres composed of methane and other hydrocarbons have been used in\nsimulation experiments. This paper summarizes experiments simulating various\nterrestrial and extraterrestrial environments, and possible roles of methane in\nchemical evolution are discussed.", "category": "astro-ph_EP" }, { "text": "On the Vertical Shear Instability in Magnetized Protoplanetary Disks: The vertical shear instability (VSI) is a robust phenomenon in irradiated\nprotoplanetary disks (PPDs). While there is extensive literature on the VSI in\nthe hydrodynamic limit, PPDs are expected to be magnetized and their extremely\nlow ionization fractions imply that non-ideal magneto-hydrodynamic (MHD)\neffects should be properly considered. To this end, we present linear analyses\nof the VSI in magnetized disks with Ohmic resistivity. We primarily consider\ntoroidal magnetic fields, which are likely to dominate the field geometry in\nPPDs. We perform vertically global and radially local analyses to capture\ncharacteristic VSI modes with extended vertical structures. To focus on the\neffect of magnetism, we use a locally isothermal equation of state. We find\nthat magnetism provides a stabilizing effect to dampen the VSI, with surface\nmodes, rather than body modes, being the first to vanish with increasing\nmagnetization. Subdued VSI modes can be revived by Ohmic resistivity, where\nsufficient magnetic diffusion overcome magnetic stabilization, and hydrodynamic\nresults are recovered. We also briefly consider poloidal fields to account for\nthe magnetorotational instability (MRI), which may develop towards surface\nlayers in the outer parts of PPDs. The MRI grows efficiently at small radial\nwavenumbers, in contrast to the VSI. When resistivity is considered, we find\nthe VSI dominates over the MRI for Ohmic Els\\\"{a}sser numbers $\\lesssim 0.09$\nat plasma beta parameter $\\beta_Z \\sim 10^4$.", "category": "astro-ph_EP" }, { "text": "Post-Impact Thermal Evolution of Porous Planetesimals: Impacts between planetesimals have largely been ruled out as a heat source in\nthe early Solar System, by calculations that show them to be an inefficient\nheat source and unlikely to cause global heating. However, the long-term,\nlocalized thermal effects of impacts on planetesimals have never been fully\nquantified. Here, we simulate a range of impact scenarios between planetesimals\nto determine the post-impact thermal histories of the parent bodies, and hence\nthe importance of impact heating in the thermal evolution of planetesimals. We\nfind on a local scale that heating material to petrologic type 6 is achievable\nfor a range of impact velocities and initial porosities, and impact melting is\npossible in porous material at a velocity of > 4 km/s. Burial of heated\nimpactor material beneath the impact crater is common, insulating that material\nand allowing the parent body to retain the heat for extended periods (~\nmillions of years). Cooling rates at 773 K are typically 1 - 1000 K/Ma,\nmatching a wide range of measurements of metallographic cooling rates from\nchondritic materials. While the heating presented here is localized to the\nimpact site, multiple impacts over the lifetime of a parent body are likely to\nhave occurred. Moreover, as most meteorite samples are on the centimeter to\nmeter scale, the localized effects of impact heating cannot be ignored.", "category": "astro-ph_EP" }, { "text": "Evolution of the Dust Trail of Comet 17P/Holmes: The massive outburst of the comet 17P/Holmes in October 2007 is the largest\nknown outburst by a comet thus far. We present a new comprehensive model\ndescribing the evolution of the dust trail produced in this phenomenon. The\nmodel comprises of multiparticle Monte Carlo approach including the solar\nradiation pressure effects, gravitational disturbance caused by Venus, Earth\nand Moon, Mars, Jupiter and Saturn, and gravitational interaction of the dust\nparticles with the parent comet itself. Good accuracy of computations is\nachieved by its implementation in Orekit, which executes Dormad-Prince\nnumerical integration methods with higher precision. We demonstrate performance\nof the model by simulating particle populations with sizes from 0.001 mm to 1\nmm with corresponding spherically symmetric ejection speed distribution, and\ntowards the Sun outburst modelling. The model is supplemented with and\nvalidated against the observations of the dust trail in common nodes for 0.5\nand 1 revolutions. In all cases, the predicted trail position showed a good\nmatch to the observations. Additionally, the hourglass pattern of the trail was\nobserved for the first time within this work. By using variations of the\noutburst model in our simulations, we determine that the assumption of the\nspherical symmetry of the ejected particles leads to the scenario compatible\nwith the observed hourglass pattern. Using these data, we make predictions for\nthe two-revolution dust trail behavior near the outburst point that should be\ndetectable by using ground-based telescopes in 2022.", "category": "astro-ph_EP" }, { "text": "Kepler-93b: A Terrestrial World Measured to within 120 km, and a Test\n Case for a New Spitzer Observing Mode: We present the characterization of the Kepler-93 exoplanetary system, based\non three years of photometry gathered by the Kepler spacecraft. The duration\nand cadence of the Kepler observations, in tandem with the brightness of the\nstar, enable unusually precise constraints on both the planet and its host. We\nconduct an asteroseismic analysis of the Kepler photometry and conclude that\nthe star has an average density of 1.652+/-0.006 g/cm^3. Its mass of\n0.911+/-0.033 M_Sun renders it one of the lowest-mass subjects of asteroseismic\nstudy. An analysis of the transit signature produced by the planet Kepler-93b,\nwhich appears with a period of 4.72673978+/-9.7x10^-7 days, returns a\nconsistent but less precise measurement of the stellar density, 1.72+0.02-0.28\ng/cm^3. The agreement of these two values lends credence to the planetary\ninterpretation of the transit signal. The achromatic transit depth, as compared\nbetween Kepler and the Spitzer Space Telescope, supports the same conclusion.\nWe observed seven transits of Kepler-93b with Spitzer, three of which we\nconducted in a new observing mode. The pointing strategy we employed to gather\nthis subset of observations halved our uncertainty on the transit radius ratio\nR_p/R_star. We find, after folding together the stellar radius measurement of\n0.919+/-0.011 R_Sun with the transit depth, a best-fit value for the planetary\nradius of 1.481+/-0.019 R_Earth. The uncertainty of 120 km on our measurement\nof the planet's size currently renders it one of the most precisely measured\nplanetary radii outside of the Solar System. Together with the radius, the\nplanetary mass of 3.8+/-1.5 M_Earth corresponds to a rocky density of 6.3+/-2.6\ng/cm^3. After applying a prior on the plausible maximum densities of\nsimilarly-sized worlds between 1--1.5 R_Earth, we find that Kepler-93b\npossesses an average density within this group.", "category": "astro-ph_EP" }, { "text": "Innocent Bystanders: Orbital Dynamics of Exomoons during Planet-Planet\n Scattering: Planet-planet scattering is the leading mechanism to explain the broad\neccentricity distribution of observed giant exoplanets. Here we study the\norbital stability of primordial giant planet moons in this scenario. We use\nN-body simulations including realistic oblateness and evolving spin evolution\nfor the giant planets. We find that the vast majority (80-90% across all our\nsimulations) of orbital parameter space for moons is destabilized. There is a\nstrong radial dependence, as moons past 0.1 Hill radii are systematically\nremoved. Closer-in moons on Galilean-moon-like orbits (< 0.04 Hill radii) have\na good ( 20-40%) chance of survival. Destabilized moons may undergo a collision\nwith the star or a planet, be ejected from the system, be captured by another\nplanet, be ejected but still orbiting its free-floating host planet, or survive\non heliocentric orbits as \"planets.\" The survival rate of moons increases with\nthe host planet mass but is independent of the planet's final (post-scattering)\norbits. Based on our simulations we predict the existence of an abundant\ngalactic population of free- floating (former) moons.", "category": "astro-ph_EP" }, { "text": "Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS: Evidence\n for Strong Stellar Contamination in the Transmission Spectra: TRAPPIST-1 is a nearby system of seven Earth-sized, temperate, rocky\nexoplanets transiting a Jupiter-sized M8.5V star, ideally suited for in-depth\natmospheric studies. Each TRAPPIST-1 planet has been observed in transmission\nboth from space and from the ground, confidently rejecting cloud-free,\nhydrogen-rich atmospheres. Secondary eclipse observations of TRAPPIST-1 b with\nJWST/MIRI are consistent with little to no atmosphere given the lack of heat\nredistribution. Here we present the first transmission spectra of TRAPPIST-1 b\nobtained with JWST/NIRISS over two visits. The two transmission spectra show\nmoderate to strong evidence of contamination from unocculted stellar\nheterogeneities, which dominates the signal in both visits. The transmission\nspectrum of the first visit is consistent with unocculted starspots and the\nsecond visit exhibits signatures of unocculted faculae. Fitting the stellar\ncontamination and planetary atmosphere either sequentially or simultaneously,\nwe confirm the absence of cloud-free hydrogen-rich atmospheres, but cannot\nassess the presence of secondary atmospheres. We find that the uncertainties\nassociated with the lack of stellar model fidelity are one order of magnitude\nabove the observation precision of 89 ppm (combining the two visits). Without\naffecting the conclusion regarding the atmosphere of TRAPPIST-1 b, this\nhighlights an important caveat for future explorations, which calls for\nadditional observations to characterize stellar heterogeneities empirically\nand/or theoretical works to improve model fidelity for such cool stars. This\nneed is all the more justified as stellar contamination can affect the search\nfor atmospheres around the outer, cooler TRAPPIST-1 planets for which\ntransmission spectroscopy is currently the most efficient technique.", "category": "astro-ph_EP" }, { "text": "A sub-Mercury-sized exoplanet: Since the discovery of the first exoplanet we have known that other planetary\nsystems can look quite unlike our own. However, until recently we have only\nbeen able to probe the upper range of the planet size distribution. The high\nprecision of the Kepler space telescope has allowed us to detect planets that\nare the size of Earth and somewhat smaller, but no previous planets have been\nfound that are smaller than those we see in our own Solar System. Here we\nreport the discovery of a planet significantly smaller than Mercury. This tiny\nplanet is the innermost of three planets that orbit the Sun-like host star,\nwhich we have designated Kepler-37. Owing to its extremely small size, similar\nto that of Earth's Moon, and highly irradiated surface, Kepler-37b is probably\na rocky planet with no atmosphere or water, similar to Mercury.", "category": "astro-ph_EP" }, { "text": "Measurement of the vertical atmospheric density profile from the X-ray\n Earth occultation of the Crab Nebula with Insight-HXMT: In this paper, the X-ray Earth occultation (XEO) of the Crab Nebula is\ninvestigated by using the Hard X-ray Modulation Telescope (Insight-HXMT). The\npointing observation data on the 30th September, 2018 recorded by the Low\nEnergy X-ray telescope (LE) of Insight-HXMT are selected and analyzed. The\nextinction lightcurves and spectra during the X-ray Earth occultation process\nare extracted. A forward model for the XEO lightcurve is established and the\ntheoretical observational signal for lightcurve is predicted. The atmospheric\ndensity model is built with a scale factor to the commonly used MSIS density\nprofile within a certain altitude range. A Bayesian data analysis method is\ndeveloped for the XEO lightcurve modeling and the atmospheric density\nretrieval. The posterior probability distribution of the model parameters is\nderived through the Markov Chain Monte Carlo (MCMC) algorithm with the\nNRLMSISE-00 model and the NRLMSIS 2.0 model as basis functions and the best-fit\ndensity profiles are retrieved respectively. It is found that in the altitude\nrange of 105--200 km, the retrieved density profile is 88.8% of the density of\nNRLMSISE-00 and 109.7% of the density of NRLMSIS 2.0 by fitting the lightcurve\nin the energy range of 1.0--2.5 keV based on XEOS method. In the altitude range\nof 95--125 km, the retrieved density profile is 81.0% of the density of\nNRLMSISE-00 and 92.3% of the density of NRLMSIS 2.0 by fitting the lightcurve\nin the energy range of 2.5--6.0 keV based on XEOS method. In the altitude range\nof 85--110 km, the retrieved density profile is 87.7% of the density of\nNRLMSISE-00 and 101.4% of the density of NRLMSIS 2.0 by fitting the lightcurve\nin the energy range of 6.0--10.0 keV based on XEOS method. This study\ndemonstrates that the XEOS from the X-ray astronomical satellite Insight-HXMT\ncan provide an approach for the study of the upper atmosphere.", "category": "astro-ph_EP" }, { "text": "Moist Convection and the 2010-2011 Revival of Jupiter's South Equatorial\n Belt: The transformation of Jupiter's South Equatorial Belt (SEB) from its faded,\nwhitened state in 2009-2010 to its normal brown appearance is documented via\ncomparisons of thermal-infrared (5-20 $\\mu$m) and visible-light imaging between\nNovember 2010 and November 2011. The SEB revival consisted of convective\neruptions triggered over $\\sim100$ days, potentially powered by the latent heat\nreleased by the condensation of water. The plumes rise from the water cloud\nbase and ultimately diverge and cool in the stably-stratified upper\ntroposphere. Thermal-IR images were acquired 2 days after the SEB disturbance\nwas first detected by amateur observers on November 9th 2010. Subsequent images\nrevealed the cold, putatively anticyclonic and cloudy plume tops surrounded by\nwarm, cloud-free conditions at their peripheries. The majority of the plumes\nerupted from a single source near $140-160^\\circ$W, coincident with the remnant\ncyclonic circulation of a brown barge that had formed during the fade.\nAdditional plumes erupted from the leading edge of the central disturbance\nimmediately east of the source. The tropospheric plumes excited stratospheric\nthermal waves over the SEB, showing a direct connection between moist\nconvection and stratospheric wave activity. The subsidence of dry, unsaturated\nair warmed the troposphere and removed the white aerosols. The aerosol-free air\nwas redistributed throughout the SEB by the zonal flow, following a\nwestward-moving southern branch and an eastward-moving northern branch that\nrevived the brown colouration over $\\sim200$ days. The last stage of the\nrevival was the re-establishment of normal convective activity northwest of the\nGRS in September 2011. Moist convection may therefore play an important role in\ncontrolling the timescale and atmospheric variability during the SEB life\ncycle. [Abridged]", "category": "astro-ph_EP" }, { "text": "Bifurcation of planetary building blocks during Solar System formation: Geochemical and astronomical evidence demonstrate that planet formation\noccurred in two spatially and temporally separated reservoirs. The origin of\nthis dichotomy is unknown. We use numerical models to investigate how the\nevolution of the solar protoplanetary disk influenced the timing of protoplanet\nformation and their internal evolution. Migration of the water snow line can\ngenerate two distinct bursts of planetesimal formation that sample different\nsource regions. These reservoirs evolve in divergent geophysical modes and\ndevelop distinct volatile contents, consistent with constraints from accretion\nchronology, thermo-chemistry, and the mass divergence of inner and outer Solar\nSystem. Our simulations suggest that the compositional fractionation and\nisotopic dichotomy of the Solar System was initiated by the interplay between\ndisk dynamics, heterogeneous accretion, and internal evolution of forming\nprotoplanets.", "category": "astro-ph_EP" }, { "text": "Homogeneous model for the TRAPPIST-1e planet with an icy layer: In this work we investigate whether a multilayered planet can be approximated\nas a homogeneous planet, and in particular how well the dissipation rate of a\nmultilayered planet can be reproduced with a homogeneous rheology. We study the\ncase of a stratified body with an icy crust that, according to recent studies,\ndisplays a double peak feature in the tidal response that cannot be reproduced\nwith a homogeneous planet with an Andrade rheology. We revisit the problem with\na slightly more complex rheology for the homogeneous body, the Sundberg-Cooper\nrheology, which naturally has a double peak feature, and apply the model to the\nTRAPPIST-1e planet. Our results compare very well with the results obtained\nwhen employing a multilayered model, showing that it is possible to approximate\nthe behavior of a multilayer icy planet with a homogeneous planet using the\nSundberg-Cooper rheology. This highlights the fact that we do not need the\ncomplexity of the multilayer planet model in order to estimate the tidal\ndissipation of an icy planet.", "category": "astro-ph_EP" }, { "text": "Thermophysical modeling of NEOWISE observations of DESTINY+ targets\n Phaethon and 2005 UD: Thermophysical models allow for improved constraints on the physical and\nthermal surface properties of asteroids beyond what can be inferred from more\nsimple thermal modeling, provided a sufficient number of observations is\navailable. We present thermophysical modeling results of observations from the\nNEOWISE mission for two near-Earth asteroids which are the targets of the\nDESTINY+ flyby mission: (3200) Phaethon and (155140) 2005 UD. Our model assumes\na rotating, cratered, spherical surface, and employs a Monte Carlo Markov Chain\nto explore the multi-dimensional parameter space of the fit. We find an\neffective spherical diameter for Phaethon of $4.6^{+0.2}_{-0.3}~$km, a\ngeometric albedo of $p_V=0.16\\pm0.02$, and a thermal inertia $\\Gamma=880$\n$^{+580}_{-330}$, using five epochs of NEOWISE observations. The best model fit\nfor (155140) 2005 UD was less well constrained due to only having two NEOWISE\nobservation epochs, giving a diameter of $1.2\\pm0.4~$km and a geometric albedo\nof $p_V=0.14\\pm0.09$.", "category": "astro-ph_EP" }, { "text": "Detection of a Satellite of the Trojan Asteroid (3548) Eurybates -- A\n Lucy Mission Target: We describe the discovery of a satellite of the Trojan asteroid (3548)\nEurybates in images obtained with the Hubble Space Telescope. The satellite was\ndetected on three separate epochs, two in September 2018 and one in January\n2020. The satellite has a brightness in all three epochs consistent with an\neffective diameter of d2 =1.2+/-0.4 km. The projected separation from Eurybates\nwas s~1700-2300 km and varied in position, consistent with a large range of\npossible orbits. Eurybates is a target of the Lucy Discovery mission and the\nearly detection of a satellite provides an opportunity for a significant\nexpansion of the scientific return from this encounter.", "category": "astro-ph_EP" }, { "text": "The flipped orbit of KELT-19Ab inferred from the symmetric TESS transit\n light curves: Dozens of planets are now discovered with large orbital obliquity, and have\nbecome the proof for the dynamical evolution of planetary orbits. In the\ncurrent samples, there is an apparent clustering of planets around $90^\\circ$,\nand also an absence of planets around $180^\\circ$ although the latter is\nexpected by some theories. Statistical extrapolation using Hierarchical\nBayesian Analysis have recently refuted the significant clustering around\n$90^\\circ$ and suggested that the distribution may actually be broader. In this\nwork, the symmetric TESS transit light curve of KELT-19Ab is analyzed using\ngravity darkening to measure its true obliquity. Its large sky projected\nobliquity $\\lambda = -179.7^{\\circ+3.7^\\circ}_{\\,\\,-3.8^\\circ}$ makes KELT-19Ab\nthe only currently known planet with obliquity potentially close to\n$180^\\circ$. We apply spectroscopic constraints on $v\\mathrm{sin}i$ and\n$\\lambda$ as well as theoretical constraints on the limb-darkening coefficients\nto find that the KELT-19Ab's obliquity is $\\psi =\n155^{\\circ+17^\\circ}_{\\,\\,-21^\\circ}$, in favor of a flipped orbit. The result\nis consistent with the statistically inferred uniformity of obliquity\ndistribution, and also highlights the applicability of the gravity darkening\ntechnique to symmetric light curves.", "category": "astro-ph_EP" }, { "text": "The evolution of photo-evaporating viscous discs in binaries: A large fraction of stars are in binary systems, yet the evolution of\nproto-planetary discs in binaries has been little explored from the theoretical\nside. In this paper we investigate the evolution of the discs surrounding the\nprimary and secondary components of binary systems on the assumption that this\nis driven by photoevaporation induced by X-rays from the respective star. We\nshow how for close enough separations (20-30 AU for average X-ray luminosities)\nthe tidal torque of the companion changes the qualitative behaviour of disc\ndispersal from inside out to outside in. Fewer transition discs created by\nphotoevaporation are thus expected in binaries. We also demonstrate that in\nclose binaries the reduction in viscous time leads to accelerated disc clearing\naround both components, consistent with $\\textit{unresolved}$ observations.\nWhen looking at the $\\textit{differential}$ disc evolution around the two\ncomponents, in close binaries discs around the secondary clear first due to the\nshorter viscous timescale associated with the smaller outer radius. In wide\nbinaries instead the difference in photo-evaporation rate makes the secondaries\nlonger lived, though this is somewhat dependent on the assumed scaling of\nviscosity with stellar mass. We find that our models are broadly compatible\nwith the growing sample of $\\textit{resolved}$ observations of discs in\nbinaries. We also predict that binaries have higher accretion rates than single\nstars for the same disc mass. Thus binaries probably contribute to the observed\nscatter in the relationship between disc mass and accretion rate in young\nstars.", "category": "astro-ph_EP" }, { "text": "Polar stellar-spots and grazing planetary transits: possible explanation\n for the low number of discovered grazing planets: We assess a physically feasible explanation for the low number of discovered\n(near-)grazing planetary transits through all ground and space based transit\nsurveys. We performed simulations to generate the synthetic distribution of\ndetectable planets based on their impact parameter, and found that a larger\nnumber of (near-)grazing planets should have been detected than have been\ndetected. Our explanation for the insufficient number of (near-)grazing planets\nis based on a simple assumption that a large number of (near-)grazing planets\ntransit host stars which harbor dark giant polar spot, and thus the transit\nlight-curve vanishes due to the occultation of grazing planet and the polar\nspot. We conclude by evaluating the properties required of polar spots in order\nto make disappear the grazing transit light-curve, and we conclude that their\nproperties are compatible with the expected properties from observations.", "category": "astro-ph_EP" }, { "text": "Spectroscopic Coronagraphy for Planetary Radial Velocimetry of\n Exoplanets: We propose the application of coronagraphic techniques to the spectroscopic\ndirect detection of exoplanets via the Doppler shift of planetary molecular\nlines. Even for an unresolved close-in planetary system, we show that the\ncombination of a visible nuller and an extreme adaptive optics system can\nreduce the photon noise of a main star and increase the total signal-to-noise\nratio (S/N) of the molecular absorption of the exoplanetary atmosphere: it\nworks as a spectroscopic coronagraph. Assuming a 30 m telescope, we demonstrate\nthe benefit of these high-contrast instruments for nearby close-in planets that\nmimic 55 Cnc b ($0.6 \\lambda/D$ of the angular separation in the K band). We\nfind that the tip-tilt error is the most crucial factor; however, low-order\nspeckles also contribute to the noise. Assuming relatively conservative\nestimates for future wavefront control techniques, the spectroscopic\ncoronagraph can increase the contrast to $ \\sim 50-130 $ times and enable us to\nobtain $\\sim 3-6 $ times larger S/N for warm Jupiters and Neptunes at 10 pc\nthose without it. If the tip-tilt error can be reduced to $\\lesssim 0.3$ mas\n(rms), it gains $\\sim 10-30$ times larger S/N and enables us to detect warm\nsuper-Earths with an extremely large telescope. This paper demonstrates the\nconcept of spectroscopic coronagraphy for future spectroscopic direct\ndetection. Further studies of the selection of coronagraphs and tip-tilt\nsensors will extend the range of application of the spectroscopic direct\ndetection beyond the photon collecting area limit.", "category": "astro-ph_EP" }, { "text": "A Consistent Reduced Network for HCN Chemistry in Early Earth and Titan\n Atmospheres: Quantum Calculations of Reaction Rate Coefficients: HCN is a key ingredient for synthesizing biomolecules such as nucleobases and\namino acids. We calculate 42 reaction rate coefficients directly involved with\nor in competition with the production of HCN in the early Earth or Titan\natmospheres. These reactions are driven by methane and nitrogen radicals\nproduced via UV photodissociation or lightning. For every reaction in this\nnetwork, we calculate rate coefficients at 298 K using canonical variational\ntransition state theory (CVT) paired with computational quantum chemistry\nsimulations at the BHandHLYP/augcc-pVDZ level of theory. We also calculate the\ntemperature dependence of the rate coefficients for the reactions that have\nbarriers from 50 to 400 K. We present 15 new reaction rate coefficients with no\npreviously known value; 93% of our calculated coefficients are within an order\nof magnitude of the nearest experimental or recommended values. Above 320 K,\nthe rate coefficient for the new reaction H2CN -> HCN + H dominates. Contrary\nto experiments, we find the HCN reaction pathway, N + CH3 -> HCN + H2, to be\ninefficient and suggest that the experimental rate coefficient actually\ncorresponds to an indirect pathway, through the H2CN intermediate. We present\nCVT using energies computed with density functional theory as a feasible and\naccurate method for calculating a large network of rate coefficients of\nsmall-molecule reactions.", "category": "astro-ph_EP" }, { "text": "Layered semi-convection and tides in giant planet interiors - I.\n Propagation of internal waves: Layered semi-convection is a possible candidate to explain Saturn's\nluminosity excess and the abnormally large radius of some hot Jupiters. In\ngiant planet interiors, it could lead to the creation of density staircases,\nwhich are convective layers separated by thin stably stratified interfaces. We\nstudy the propagation of internal waves in a region of layered semi-convection,\nwith the aim to predict energy transport by internal waves incident upon a\ndensity staircase. The goal is then to understand the resulting tidal\ndissipation when these waves are excited by other bodies such as moons in giant\nplanets systems. We use a local Cartesian analytical model, taking into account\nthe complete Coriolis acceleration at any latitude, thus generalizing previous\nworks. We find transmission of incident internal waves to be strongly affected\nby the presence of a density staircase, even if these waves are initially pure\ninertial waves (which are restored by the Coriolis acceleration). In\nparticular, low-frequency waves of all wavelengths are perfectly transmitted\nnear the critical latitude. Otherwise, short-wavelength waves are only\nefficiently transmitted if they are resonant with a free mode (interfacial\ngravity wave or short-wavelength inertial mode) of the staircase. In all other\ncases, waves are primarily reflected unless their wavelengths are longer than\nthe vertical extent of the entire staircase (not just a single step). We expect\nincident internal waves to be strongly affected by the presence of a density\nstaircase in a frequency-, latitude- and wavelength-dependent manner. First,\nthis could lead to new criteria to probe the interior of giant planets by\nseismology; and second, this may have important consequences for tidal\ndissipation and our understanding of the evolution of giant planet systems.", "category": "astro-ph_EP" }, { "text": "Evidence that the Directly-Imaged Planet HD 131399 Ab is a Background\n Star: We present evidence that the recently discovered, directly-imaged planet HD\n131399 Ab is a background star with non-zero proper motion. From new JHK1L'\nphotometry and spectroscopy obtained with the Gemini Planet Imager, VLT/SPHERE,\nand Keck/NIRC2, and a reanalysis of the discovery data obtained with\nVLT/SPHERE, we derive colors, spectra, and astrometry for HD 131399 Ab. The\nbroader wavelength coverage and higher data quality allow us to re-investigate\nits status. Its near-infrared spectral energy distribution excludes spectral\ntypes later than L0 and is consistent with a K or M dwarf, which are the most\nlikely candidates for a background object in this direction at the apparent\nmagnitude observed. If it were a physically associated object, the projected\nvelocity of HD 131399 Ab would exceed escape velocity given the mass and\ndistance to HD 131399 A. We show that HD 131399 Ab is also not following the\nexpected track for a stationary background star at infinite distance. Solving\nfor the proper motion and parallax required to explain the relative motion of\nHD 131399 Ab, we find a proper motion of 12.3 mas/yr. When compared to\npredicted background objects drawn from a galactic model, we find this proper\nmotion to be high, but consistent with the top 4% fastest-moving background\nstars. From our analysis we conclude that HD 131399 Ab is a background K or M\ndwarf.", "category": "astro-ph_EP" }, { "text": "Observations of Mass Loss from the Transiting Exoplanet HD 209458b: Using the new Cosmic Origins Spectrograph (COS) on the {\\it Hubble Space\nTelescope (HST)}, we obtained moderate-resolution, high signal/noise\nultraviolet spectra of HD 209458 and its exoplanet HD 209458b during transit,\nboth orbital quadratures, and secondary eclipse. We compare transit spectra\nwith spectra obtained at non-transit phases to identify spectral features due\nto the exoplanet's expanding atmosphere. We find that the mean flux decreased\nby $7.8\\pm 1.3$% for the C II 1334.5323\\AA\\ and 1335.6854\\AA\\ lines and by\n$8.2\\pm 1.4$% for the Si III 1206.500\\AA\\ line during transit compared to\nnon-transit times in the velocity interval --50 to +50 km s$^{-1}$. Comparison\nof the C II and Si III line depths and transit/non-transit line ratios shows\ndeeper absorption features near --10 and +15 km s$^{-1}$ and less certain\nfeatures near --40 and +30--70 km s$^{-1}$, but future observations are needed\nto verify this first detection of velocity structure in the expanding\natmosphere of an exoplanet. Our results for the C II lines and the\nnon-detection of Si IV 1394.76\\AA\\ absorption are in agreement with\n\\citet{Vidal-Madjar2004}, but we find absorption during transit in the Si III\nline contrary to the earlier result. The $8\\pm 1$% obscuration of the star\nduring transit is far larger than the 1.5% obscuration by the exoplanet's disk.\nAbsorption during transit at velocities between --50 and +50 km s$^{-1}$ in the\nC II and Si III lines requires high-velocity ion absorbers, but models that\nassume that the absorbers are high-temperature thermal ions are inconsistent\nwith the COS spectra. Assuming hydrodynamic model values for the gas\ntemperature and outflow velocity at the limb of the outflow as seen in the C II\nlines, we find mass-loss rates in the range (8--40)$\\times 10^{10}$ g s$^{-1}$.", "category": "astro-ph_EP" }, { "text": "Dissipative Divergence of Resonant Orbits: A considerable fraction of multi-planet systems discovered by the\nobservational surveys of extrasolar planets reside in mild proximity to\nfirst-order mean motion resonances. However, the relative remoteness of such\nsystems from nominal resonant period ratios (e.g. 2:1, 3:2, 4:3) has been\ninterpreted as evidence for lack of resonant interactions. Here we show that a\nslow divergence away from exact commensurability is a natural outcome of\ndissipative evolution and demonstrate that libration of critical angles can be\nmaintained tens of percent away from nominal resonance. We construct an\nanalytical theory for the long-term dynamical evolution of dissipated resonant\nplanetary pairs and confirm our calculations numerically. Collectively, our\nresults suggest that a significant fraction of the near-commensurate extrasolar\nplanets are in fact resonant and have undergone significant dissipative\nevolution.", "category": "astro-ph_EP" }, { "text": "Modelling the Spectra of Planets, Brown Dwarfs and Stars using VSTAR: We describe a new software package capable of predicting the spectra of\nsolar-system planets, exoplanets, brown dwarfs and cool stars. The Versatile\nSoftware for Transfer of Atmospheric Radiation (VSTAR) code combines a\nline-by-line approach to molecular and atomic absorption with a full multiple\nscattering treatment of radiative transfer. VSTAR is a modular system\nincorporating an ionization and chemical equilibrium model, a comprehensive\ntreatment of spectral line absorption using a database of more than 2.9 billion\nspectral lines, a scattering package and a radiative transfer module. We test\nthe methods by comparison with other models and benchmark calculations. We\npresent examples of the use of VSTAR to model the spectra of terrestrial and\ngiant planet in our own solar system, brown dwarfs and cool stars.", "category": "astro-ph_EP" }, { "text": "The Peculiar Photometric Properties of 2010 WG9: A Slowly-Rotating\n Trans-Neptunian Object from the Oort Cloud: We present long-term BVRI observations of 2010 WG9, an ~100-km diameter\ntrans-Neptunian object (TNO) with an extremely high inclination of 70 deg\ndiscovered by the La Silla - QUEST southern sky survey. Most of the\nobservations were obtained with ANDICAM on the SMARTS 1.3m at Cerro Tololo,\nChile from Dec 2010 to Nov 2012. Additional observations were made with EFOSC2\non the 3.5-m NTT telescope of the European Southern Observatory at La Silla,\nChile in Feb 2011. The observations reveal a sinusoidal light curve with\namplitude 0.14 mag and period 5.4955 +/- 0.0025d, which is likely half the true\nrotation period. Such long rotation periods have previously been observed only\nfor tidally-evolved binary TNOs, suggesting that 2010 WG9 may be such a system.\nWe predict a nominal separation of at least 790 km, resolvable with HST and\nground-based systems. We measure B-R = 1.318 +/- 0.029 and V-R = 0.520 +/-\n0.018, consistent with the colors of modestly red Centaurs and Damocloids. At\nI-band wavelengths, we observe an unusually large variation of color with\nrotational phase, with R-I ranging from 0.394 +/- 0.025 to 0.571 +/- 0.044. We\nalso measure an absolute R-band absolute magnitude of 7.93 +/- 0.05 and solar\nphase coefficient 0.049 +/- 0.019 mag/deg.", "category": "astro-ph_EP" }, { "text": "The effect of late giant collisions on the atmospheres of protoplanets\n and the formation of cold sub-Saturns: We investigate the origins of cold sub-Saturns (CSS), an exoplanetary\npopulation inferred from microlensing surveys. If confirmed, these planets\nwould rebut a theorised gap in planets' mass distribution between those of\nNeptune and Jupiter caused by the rapid runaway accretion of super-critical\ncores. In an attempt to resolve this theoretical-observational disparity, we\nexamine the outcomes of giant collisions between sub-critical protoplanets. Due\nto the secular interaction among protoplanets, these events may occur in\nrapidly depleting discs. We show that impactors ~ 5% the mass of near-runaway\nenvelopes around massive cores can efficiently remove these envelopes entirely\nvia a thermally-driven super-Eddington wind emanating from the core itself, in\ncontrast with the stellar Parker winds usually considered. After a brief\ncooling phase, the merged cores resume accretion. But, the evolution timescale\nof transitional discs is too brief for the cores to acquire sufficiently\nmassive envelopes to undergo runaway accretion despite their large combined\nmasses. Consequently, these events lead to the emergence of CSS without their\ntransformation into gas giants. We show that these results are robust for a\nwide range of disc densities, grain opacities and silicate abundance in the\nenvelope. Our fiducial case reproduces CSS with heavy (>= 30 M_Earth) cores and\nless massive (a few M_Earth) sub-critical envelopes. We also investigate the\nother limiting cases, where continuous mergers of comparable-mass cores yield\nCSS with wider ranges of core-to-envelope mass ratios and envelope opacities.\nOur results indicate that it is possible for CSS and Uranus and Neptune to\nemerge within the framework of well studied processes and they may be more\ncommon than previously postulated.", "category": "astro-ph_EP" }, { "text": "Sub-Seasonal Variation in Neptune's Mid-Infrared Emission: We present an analysis of all currently available ground-based imaging of\nNeptune in the mid-infrared. Dating between 2003 and 2020, the images reveal\nchanges in Neptune's mid-infrared ($\\sim 8-25\\mu$m) emission over time in the\nyears surrounding Neptune's 2005 southern summer solstice. Images sensitive to\nstratospheric ethane ($\\sim12\\mu$m), methane ($\\sim8\\mu$m), and CH$_3$D\n($\\sim9\\mu$m) display significant sub-seasonal temporal variation on regional\nand global scales. Comparison with H$_2$ S(1) hydrogen-quadrupole\n($\\sim17.035\\mu$m) spectra suggests these changes are primarily related to\nstratospheric temperature changes. The stratosphere appears to have cooled\nbetween 2003 and 2009 across multiple filtered wavelengths, followed by a\ndramatic warming of the south pole between 2018 and 2020. Conversely,\nupper-tropospheric temperatures -- inferred from $\\sim 17-25$-micron imaging --\nappear invariant during this period, except for the south pole, which appeared\nwarmest between 2003 and 2006. We discuss the observed variability in the\ncontext of seasonal forcing, tropospheric meteorology, and the solar cycle.\nCollectively, these data provide the strongest evidence to date that processes\nproduce sub-seasonal variation on both global and regional scales in Neptune's\nstratosphere.", "category": "astro-ph_EP" }, { "text": "Time and phase resolved optical spectra of potentially hazardous\n asteroid 2014 JO25: The asteroid 2014 JO25, considered to be \"potentially hazardous\" by the Minor\nPlanet Center, was spectroscopically followed during its close-Earth encounter\non 19th and 20th of April 2017. The spectra of the asteroid were taken with the\nlow resolution spectrograph (LISA), mounted on the 1.2-m telescope at the Mount\nAbu Infrared Observatory, India. Coming from a region close to the Hungaria\npopulation of asteroids, this asteroid follows a comet-like orbit with a\nrelatively high inclination and large eccentricity. Hence, we carried out\noptical spectroscopic observations of the asteroid to look for comet-like\nmolecular emissions or outbursts. However, the asteroid showed a featureless\nspectrum, devoid of any comet-like features. The asteroid's light curve was\nanalyzed using V band magnitudes derived from the spectra and the most likely\nsolution for the rotation of the asteroid was obtained. The absolute magnitude\n$H$ and the slope parameter $G$ were determined for the asteroid in V filter\nband using the IAU accepted standard two parameter H-G model. A peculiar,\nrarely found result from these observations is its phase bluing trend. The\nrelative B-V color index seems to decrease with increasing phase angle, which\nindicates a phase bluing trend. Such trends have seldom been reported in\nliterature. However, phase reddening in asteroids is very common. The asymmetry\nparameter $g$ and the single scattering albedo $w$ were estimated for the\nasteroid by fitting the Hapke phase function to the observed data. The asteroid\nshows relatively large value for the single scattering albedo and a highly back\nscattering surface.", "category": "astro-ph_EP" }, { "text": "Breakup of the Synchronous State of Binary Asteroid Systems: This paper continues the authors' previous work and presents a coplanar\naveraged ellipsoid-ellipsoid model of synchronous binary asteroid system (BAS)\nplus thermal and tidal effects. Using this model, we analyze the breakup\nmechanism of the synchronous BAS. Different from the classical spin-orbit\ncoupling model which neglects the rotational motion's influence on the orbital\nmotion, our model considers simultaneously the orbital motion and the\nrotational motions. Our findings are following. (1) Stable region of the\nsecondary's synchronous state is mainly up to the secondary's shape. The\nprimary's shape has little influence on it. (2) The stable region shrinks\ncontinuously with the increasing value of the secondary's shape parameter\n$a_B/b_B$. Beyond the value of $a_B/b_B=\\sqrt{2}$, the planar stable region for\nthe secondary's synchronous rotation is small but not zero. (3) Considering the\nBYORP torque, our model shows agreement with the 1-degree of freedom adiabatic\ninvariance theory in the outwards migration process, but an obvious difference\nin the inwards migration process. In particular, our studies show that the\nso-called 'long-term' stable equilibrium between the BYORP torque and the tidal\ntorque is never a real equilibrium state, although the binary asteroid system\ncan be captured in this state for quite a long time. (4) In case that the\nprimary's angular velocity gradually reduces due to the YORP effect, the\nsecondary's synchronous state may be broken when the primary's rotational\nmotion crosses some major spin-orbit resonances.", "category": "astro-ph_EP" }, { "text": "Cosmogenic nuclide enhancement via deposition from long-period comets as\n a test of the Younger Dryas impact hypothesis: We explore the idea that detectable excursions in 26Al may arise from direct\ndeposition by any bolide, and excursions in 14C and 10Be abundances in the\natmosphere may result from long-period comet impacts. This is very different\nfrom the usual processes of production by cosmic rays within Earths atmosphere.\nLong-period comets experience greatly increased cosmic ray flux beyond the\nprotection of the suns magnetic field. We report the computed amount of 14C,\n10Be, and 26Al present on long-period comets as a function of comet mass. We\nfind that the amount of nuclide mass on large long-period comets entering the\nEarths atmosphere may be sufficient for creating anomalies in the records of\n14C and 10Be from past impacts. In particular, the estimated mass of the\nproposed Younger Dryas comet is consistent with its having deposited sufficient\nisotopes to account for recorded 14C and 10Be increases at that time. The\n26Al/10Be ratio is much larger in extraterrestrial objects than in the\natmosphere, and so, we note that measuring this ratio in ice cores is a\nsuitable definitive test for the Younger Dryas impact hypothesis, even if the\nhypothetical bolide is not a long-period comet and/or did not contribute to the\n14C and 10Be increases.", "category": "astro-ph_EP" }, { "text": "Probing the turbulent mixing strength in protoplanetary disks across the\n stellar mass range: no significant variations: Dust settling and grain growth are the first steps in the planet-formation\nprocess in protoplanetary disks. These disks are observed around stars with\ndifferent spectral types, and there are indications that the disks around lower\nmass stars are significantly flatter, which could indicate that they settle and\nevolve faster, or in a different way.\n We aim to test this assumption by modeling the median spectral energy\ndistributions (SEDs) of three samples of protoplanetary disks: around Herbig\nstars, T Tauri stars and brown dwarfs. We focus on the turbulent mixing\nstrength to avoid a strong observational bias from disk and stellar properties\nthat depend on stellar mass.\n We generated SEDs with the radiative transfer code MCMax, using a hydrostatic\ndisk structure and settling the dust in a self-consistent way with the\nalpha-prescription to probe the turbulent mixing strength.\n We are able to fit all three samples with a disk with the same input\nparameters, scaling the inner edge to the dust evaporation radius and disk mass\nto millimeter photometry. The Herbig stars require a special treatment for the\ninner rim regions, while the T-Tauri stars require viscous heating, and the\nbrown dwarfs lack a good estimate of the disk mass because only few millimeter\ndetections exist.\n We find that the turbulent mixing strength does not vary across the stellar\nmass range for a fixed grain size distribution and gas-to-dust ratio. Regions\nwith the same temperature have a self-similar vertical structure independent of\nstellar mass, but regions at the same distance from the central star appear\nmore settled in disks around lower mass stars. We find a relatively low\nturbulent mixing strength of alpha = 10^(-4) for a standard grain size\ndistribution, but our results are also consistent with alpha = 0.01 for a grain\nsize distribution with fewer small grains or a lower gas-to-dust ratio.", "category": "astro-ph_EP" }, { "text": "Massive Protostellar Disks as a Hot Laboratory of Silicate Grain\n Evolution: Typical accretion disks around massive protostars are hot enough for water\nice to sublimate. We here propose to utilize the massive protostellar disks for\ninvestigating the collisional evolution of silicate grains with no ice mantle,\nwhich is an essential process for the formation of rocky planetesimals in\nprotoplanetary disks around lower-mass stars. We for the first time develop a\nmodel of massive protostellar disks that includes the coagulation,\nfragmentation, and radial drift of dust. We show that the maximum grain size in\nthe disks is limited by collisional fragmentation rather than by radial drift.\nWe derive analytic formulas that produce the radial distribution of the maximum\ngrain size and dust surface density in the steady state. Applying the analytic\nformulas to the massive protostellar disk of GGD27-MM1, where the grain size is\nconstrained from a millimeter polarimetric observation, we infer that the\nsilicate grains in this disk fragment at collision velocities above ~ 10 m/s.\nThe inferred fragmentation threshold velocity is lower than the maximum grain\ncollision velocity in typical protoplanetary disks around low-mass stars,\nimplying that coagulation alone may not lead to the formation of rocky\nplanetesimals in those disks. With future measurements of grain sizes in\nmassive protostellar disks, our model will provide more robust constraints on\nthe sticking property of silicate grains.", "category": "astro-ph_EP" }, { "text": "An accurate, extensive, and practical line list of methane for the\n HITEMP database: A methane line list for the HITEMP spectroscopic database, covering 0-13,400\ncm$^{-1}$ ($>$746 nm), is presented. To create this compilation, ab initio line\nlists of $^{12}$CH$_{4}$ from Rey et al. (2017) ApJ, 847, 105 (provided at\nseparate temperatures in the TheoReTS information system), are now combined\nwith HITRAN2016 methane data to produce a single line list suitable for\nhigh-temperature line-by-line calculations up to 2000 K. An\neffective-temperature interpolation model was created in order to represent\ncontinuum-like features at any temperature of interest. This model is\nadvantageous to previously-used approaches that employ so-called\n``super-lines'', which are suitable only at a given temperature and require\nseparate line lists for different temperatures. The resultant HITEMP line list\ncontains $\\sim$32 million lines and is significantly more flexible than\nalternative line lists of methane, while accuracy required for astrophysical or\ncombustion applications is retained. Comparisons against experimental\nobservations of methane absorption at high temperatures have been used to\ndemonstrate the accuracy of the new work. The line list includes both strong\nlines and quasi-continuum features and is provided in the common user-friendly\nHITRAN/HITEMP format, making it the most practical methane line list for\nradiative transfer modeling at high-temperature conditions.", "category": "astro-ph_EP" }, { "text": "Tidal Downsizing Model. IV. Destructive feedback in planets: I argue that feedback is as important to formation of planets as it is to\nformation of stars and galaxies. Energy released by massive solid cores puffs\nup pre-collapse gas giant planets, making them vulnerable to tidal disruptions\nby their host stars. I find that feedback is the ultimate reason for some of\nthe most robust properties of the observed exoplanet populations: the rarity of\ngas giants at all separations from $\\sim 0.1$ to $\\sim 100$~AU, the abundance\nof $\\sim 10 M_\\oplus$ cores but dearth of planets more massive than $\\sim 20\nM_\\oplus$. Feedback effects can also explain (i) rapid assembly of massive\ncores at large separations as needed for Uranus, Neptune and the suspected HL\nTau planets; (ii) the small core in Jupiter yet large cores in Uranus and\nNeptune; (iii) the existence of rare \"metal monster\" planets such as CoRoT-20b,\na gas giant made of heavy elements by up to $\\sim 50$\\%.", "category": "astro-ph_EP" }, { "text": "How does Background Air Pressure Influence the Inner Edge of the\n Habitable Zone for Tidally Locked Planets in a 3D View?: We examine the effect of varying background N2 surface pressure (labelled as\npN2) on the inner edge of the habitable zone for 1:1 tidally locked planets\naround M dwarfs, using the three-dimensional (3D) atmospheric general\ncirculation model (AGCM) ExoCAM. In our experiments, the rotation period is\nfixed when varying the stellar flux, in order to more clearly isolate the role\nof pN2. We find that the stellar flux threshold for the runaway greenhouse is a\nnon-monotonous function of pN2. This is due to the competing effects of five\nprocesses: pressure broadening, heat capacity, lapse rate, relative humidity,\nand clouds. These competing processes increase the complexity in predicting the\nlocation of the inner edge of the habitable zone. For a slow rotation orbit of\n60 Earth days, the critical stellar flux for the runaway greenhouse onset is\n1700--1750, 1900--1950, and 1750--1800 W m$^{-2}$ under 0.25, 1.0, and 4.0 bar\nof pN2, respectively, suggesting that the magnitude of the effect of pN2 is\nwithin ~13%. For a rapid rotation orbit, the effect of varying pN2 on the inner\nedge is smaller, within a range of ~7%. Moreover, we show that Rayleigh\nscattering effect as varying pN2 is unimportant for the inner edge due to the\nmasking effect of cloud scattering and to the strong shortwave absorption by\nwater vapor under hot climates. Future work using AGCMs having different cloud\nand convection schemes and cloud-resolving models having explicit cloud and\nconvection are required to revise this problem.", "category": "astro-ph_EP" }, { "text": "The heating history of Vesta and the onset of differentiation: In this work we study the link between the evolution of the internal\nstructure of Vesta and thermal heating due to 26Al and 60Fe and long-lived\nradionuclides, taking into account the chemical differentiation of the body and\nthe affinity of 26Al with silicates. Differentiation takes place in all\nscenarios in which Vesta completes its accretion in less than 1.4 Ma after the\ninjection of 26Al into the Solar Nebula. In all those scenarios where Vesta\ncompletes its formation in less than 1 Ma from the injection of 26Al, the\ndegree of silicate melting reaches 100 vol. % throughout the whole asteroid. If\nVesta completed its formation between 1 and 1.4 Ma after 26Al injection, the\ndegree of silicate melting exceeds 50 vol. % over the whole asteroid but\nreaches 100 vol. % only in the hottest, outermost part of the mantle in all\nscenarios where the porosity is lower than 5 vol. %. If the formation of Vesta\noccurred later than 1.5 Ma after the injection of 26Al, the degree of silicate\nmelting is always lower than 50 vol. % and is limited only to a small region of\nthe asteroid. The radiation at the surface dominates the evolution of the crust\nwhich ranges in thickness from 8 to about 30 km after 5 Ma: a layer about 3-20\nkm thick is composed of primitive unmelted chondritic material while a layer of\nabout 5-10 km is eucritic.", "category": "astro-ph_EP" }, { "text": "Testing the Early Mars H2-CO2 Greenhouse Hypothesis with a 1-D\n Photochemical Model: A recent study by Ramirez et al. (2014) demonstrated that an atmosphere with\n1.3-4 bar of CO2 and H2O, in addition to 5-20% H2, could have raised the mean\nannual and global surface temperature of early Mars above the freezing point of\nwater. Such warm temperatures appear necessary to generate the rainfall (or\nsnowfall) amounts required to carve the ancient martian valleys. Here, we use\nour best estimates for early martian outgassing rates, along with a 1-D\nphotochemical model, to assess the conversion efficiency of CO, CH4, and H2S to\nCO2, SO2, and H2. Our outgassing estimates assume that Mars was actively\nrecycling volatiles between its crust and interior, as Earth does today. H2\nproduction from serpentinization and deposition of banded iron-formations is\nalso considered. Under these assumptions, maintaining an H2 concentration of\n~1-2% by volume is achievable, but reaching 5% H2 requires additional H2\nsources or a slowing of the hydrogen escape rate below the diffusion limit. If\nthe early martian atmosphere was indeed H2-rich, we might be able to see\nevidence of this in the rock record. The hypothesis proposed here is consistent\nwith new data from the Curiosity Rover, which show evidence for a long-lived\nlake in Gale Crater near Mt. Sharp. It is also consistent with measured oxygen\nfugacities of martian meteorites, which show evidence for progressive mantle\noxidation over time.", "category": "astro-ph_EP" }, { "text": "The size-frequency distribution of H>13 NEOs and ARM targets detected by\n Pan-STARRS1: We determine the absolute magnitude (H) distribution (or size-frequency\ndistribution, SFD; $N(H) \\propto 10^{\\alpha H}$ where $\\alpha$ is the slope of\nthe distribution) for near-Earth objects (NEO) with $1322$. There is also another change in slope from steep\nto shallow around H=27. The three ARM target candidates detected by Pan-STARRS1\nin one year of surveying have a corrected SFD with slope $\\alpha =\n0.40^{+0.33}_{-0.45}$.\n We also show that the window for follow up observations of small\n(H$\\gtrsim$22) NEOs with the NASA IRTF telescope and Arecibo and Goldstone\nradars are extremely short - on order of days, and procedures for fast response\nmust be implemented in order to measure physical characteristics of small\nEarth-approaching objects. CFHT's MegaCam and Pan-STARRS1 have longer observing\nwindows and are capable of following-up more NEOs due to their deeper limiting\nmagnitudes and wider fields of view.", "category": "astro-ph_EP" }, { "text": "Exoplanet Nodal Precession Induced by Rapidly Rotating Stars: Impacts on\n Transit Probabilities and Biases: For the majority of short period exoplanets transiting massive stars with\nradiative envelopes, the spin angular momentum of the host star is greater than\nthe planetary orbital angular momentum. In this case, the orbits of the planets\nwill undergo nodal precession, which can significantly impact the probability\nthat the planets transit their parent star. In particular, for some\ncombinations of the spin-orbit angle $\\psi$ and the inclination of the stellar\nspin $i_*$, all such planets will eventually transit at some point over the\nduration of their precession period. Thus, as the time over which the sky has\nbeen monitored for transiting planets increases, the frequency of planets with\ndetectable transits will increase, potentially leading to biased estimates of\nexoplanet occurrence rates, especially orbiting more massive stars.\nFurthermore, due to the dependence of the precession period on orbital\nparameters such as spin-orbit misalignment, the observed distributions of such\nparameters may also be biased. We derive the transit probability of a given\nexoplanet in the presence of nodal precession induced by a rapidly spinning\nhost star. We find that the effect of nodal precession has already started to\nbecome relevant for some short-period planets, i.e., Hot Jupiters, orbiting\nmassive stars, by increasing transit probabilities by of order a few percent\nfor such systems within the original $Kepler$ field. We additionally derive\nsimple expressions to describe the time evolution of the impact parameter $b$\nfor applicable systems, which should aid in future investigations of exoplanet\nnodal precession and spin-orbit alignment.", "category": "astro-ph_EP" }, { "text": "Detection of the hydrogen Balmer lines in the ultra-hot Jupiter WASP-33b: Ultra-hot Jupiters (UHJs) are highly irradiated giant exoplanets with\nextremely high day-side temperatures, which lead to thermal dissociation of\nmost of the molecular species. It is expected that the neutral hydrogen atom is\none of the main species in the upper atmospheres of ultra-hot Jupiters. Neutral\nhydrogen has been detected in several UHJs by observing its Balmer line\nabsorption. Here, we report four transit observations of the ultra-hot Jupiter\nWASP-33b, performed with the CARMENES and HARPS-North spectrographs, and the\ndetection of the H${\\alpha}$, H${\\beta}$, and H${\\gamma}$ lines in the\nplanetary transmission spectrum. The combined H$\\alpha$ transmission spectrum\nof the four transits has an absorption depth of 0.99$\\pm$0.05 %, which\ncorresponds to an effective radius of 1.31$\\pm$0.01 Rp . The strong H${\\alpha}$\nabsorption indicates that the line probes the high-altitude thermosphere. We\nfurther fitted the three Balmer lines using the PAWN model, assuming that the\natmosphere is hydrodynamic and in LTE. We retrieved a thermosphere temperature\n$12200^{+1300}_{-1000}$ K and a mass-loss rate ${\\rm\n\\dot{M}}=10^{11.8^{+0.6}_{-0.5}}$ g/s. The retrieved large mass-loss rate is\ncompatible with the \"Balmer-driven\" atmospheric escape scenario, in which the\nstellar Balmer continua radiation in the near-ultraviolet is substantially\nabsorbed by the excited hydrogen atoms in the planetary thermosphere.", "category": "astro-ph_EP" }, { "text": "Properties of the irregular satellite system around Uranus inferred from\n K2, Herschel and Spitzer observations: In this paper we present visible range light curves of the irregular Uranian\nsatellites Sycorax, Caliban, Prospero, Ferdinand and Setebos taken with Kepler\nSpace Telescope in the course of the K2 mission. Thermal emission measurements\nobtained with the Herschel/PACS and Spitzer/MIPS instruments of Sycorax and\nCaliban were also analysed and used to determine size, albedo and surface\ncharacteristics of these bodies. We compare these properties with the\nrotational and surface characteristics of irregular satellites in other giant\nplanet systems and also with those of main belt and Trojan asteroids and\ntrans-Neptunian objects. Our results indicate that the Uranian irregular\nsatellite system likely went through a more intense collisional evolution than\nthe irregular satellites of Jupiter and Saturn. Surface characteristics of\nUranian irregular satellites seems to resemble the Centaurs and trans-Neptunian\nobjects more than irregular satellites around other giant planets, suggesting\nthe existence of a compositional discontinuity in the young Solar system inside\nthe orbit of Uranus.", "category": "astro-ph_EP" }, { "text": "Accurate reference spectra of HD in H$_2$/He bath for planetary\n applications: The hydrogen deuteride (HD) molecule is an important deuterium tracer in\nastrophysical studies. The atmospheres of gas giants are dominated by molecular\nhydrogen, and simultaneous observation of H$_2$ and HD lines provides reliable\ninformation on the D/H ratios on these planets. The reference spectroscopic\nparameters play a crucial role in such studies. Under thermodynamic conditions\nencountered in these atmospheres, the spectroscopic studies of HD require not\nonly the knowledge of line intensities and positions but also accurate\nreference data on pressure-induced line shapes and shifts. Our aim is to\nprovide accurate collision-induced line-shape parameters for HD lines that\ncover any thermodynamic conditions relevant to the atmospheres of giant\nplanets, i.e., any relevant temperature, pressure, and perturbing gas (the\nH$_2$/He mixture) composition. We perform quantum-scattering calculations on a\nnew highly accurate ab initio potential energy surface, and we use scattering\nS-matrices obtained this way to determine the collision-induced line-shape\nparameters. We use the cavity ring-down spectroscopy for validation of our\ntheoretical methodology. We report accurate collision-induced line-shape\nparameters for the pure rotational R(0), R(1), and R(2) lines, the most\nrelevant HD lines for the investigations of atmospheres of the giant planets.\nBesides the basic Voigt-profile collisional parameters (i.e. the broadening and\nshift parameters), we also report their speed dependences and the complex Dicke\nparameter, which can influence the effective width and height of the HD lines\nup to almost a factor of 2 for giant planet conditions. The sub-percent-level\naccuracy, reached in this work, considerably improves the previously available\ndata. All the reported parameters are consistent with the HITRAN database\nformat, hence allowing for the use of HAPI for generating the beyond-Voigt\nspectra of HD.", "category": "astro-ph_EP" }, { "text": "Physical properties of near-Earth asteroid (2102) Tantalus from\n multi-wavelength observations: Between 2010 and 2017 we have collected new optical and radar observations of\nthe potentially hazardous asteroid (2102)~Tantalus from the ESO NTT and Danish\ntelescopes at the La Silla Observatory and from the Arecibo planetary radar.\nThe object appears to be nearly spherical, showing a low amplitude light-curve\nvariation and limited large-scale features in the radar images. The spin-state\nis difficult to constrain with the available data; including a certain\nlight-curve subset significantly changes the spin-state estimates, and the\nuncertainties on period determination are significant. Constraining any change\nin rotation rate was not possible, despite decades of observations. The convex\nlightcurve-inversion model, with rotational pole at\n${\\lambda}=210{\\pm}41${\\deg} and ${\\beta}=-30{\\pm}35${\\deg}, is more flattened\nthan the two models reconstructed by including radar observations: with\nprograde (${\\lambda}=36{\\pm}23${\\deg}, ${\\beta}=30{\\pm}15${\\deg}), and with\nretrograde rotation mode (${\\lambda}=180{\\pm}24${\\deg},\n${\\beta}=-30{\\pm}16${\\deg}). Using data from WISE we were able to determine\nthat the prograde model produces the best agreement in size determination\nbetween radar and thermophysical modelling. Radar measurements indicate\npossible variation in surface properties, suggesting one side might have lower\nradar albedo and be rougher at centimetre-to-decimetre scale than the other.\nHowever, further observations are needed to confirm this. Thermophysical\nanalysis indicates a surface covered in fine-grained regolith, consistent with\nradar albedo and polarisation ratio measurements. Finally, geophysical\ninvestigation of the spin-stability of Tantalus shows that it could be\nexceeding its critical spin-rate via cohesive forces.", "category": "astro-ph_EP" }, { "text": "Effects of the Planetary Temperature on the Circumplanetary Disk and on\n the Gap: Circumplanetary disks regulate the late accretion to the giant planet and\nserve as the birthplace for satellites. Understanding their characteristics via\nsimulations also helps to prepare for their observations. Here we study disks\naround 1, 3, 5, 10 $\\mathrm{M_{Jup}}$ planets with three dimensional, global\nradiative hydrodynamic simulations with sub-planet peak resolution, and various\nplanetary temperatures. We found that as the 1 $\\mathrm{M_{Jup}}$ planet\nradiates away its formation heat, the circumplanetary envelope transitions to a\ndisk between $T_p = 6000$ K and 4000 K. In the case of 3-10 $\\mathrm{M_{Jup}}$\nplanets a disk always forms. The temperature profile of the circumplanetary\ndisks is very steep, the inner 1/6th is over the silicate condensation\ntemperature and the entire disk is above water freezing point, making satellite\nformation impossible in this early stage ($<$1 Myr). Satellites might form much\nlater and first in the outer parts of the disk migrating inwards later on. Our\ndisk masses are $1, 7, 20, 40 \\times 10^{-3}\\mathrm{M_{Jup}}$ for the 1, 3, 5,\n10 $\\mathrm{M_{Jup}}$ gas giants respectively, and we provide an empirical\nformula to estimate the subdisk masses based on the planet- and circumstellar\ndisk mass. Our finding is that the cooler the planet, the lower the temperature\nof the subdisk, the higher the vertical influx velocities, and the planetary\ngap is both deeper and wider. We also show that the gaps in 2D and 3D are\ndifferent. The subdisk eccentricity increases with planetary mass and violently\ninteracts with the circumstellar disk, making satellite-formation less likely,\nif $\\mathrm{M_p} \\gtrsim 5 \\mathrm{M_{Jup}}$.", "category": "astro-ph_EP" }, { "text": "Search for serendipitous TNO occultation in X-rays: To study the population properties of small, remote objects beyond Neptune's\norbit in the outer solar system, of kilometer size or smaller, serendipitous\noccultation search is so far the only way. For hectometer-sized Trans-Neptunian\nObjects (TNOs), optical shadows actually disappear because of diffraction.\nObservations at shorter wave lengths are needed. Here we report the effort of\nTNO occultation search in X-rays using RXTE/PCA data of Sco X-1 taken from June\n2007 to October 2011. No definite TNO occultation events were found in the 334\nks data. We investigate the detection efficiency dependence on the TNO size to\nbetter define the sensible size range of our approach and suggest upper limits\nto the TNO size distribution in the size range from 30 m to 300 m. A list of\nX-ray sources suitable for future larger facilities to observe is proposed.", "category": "astro-ph_EP" }, { "text": "A radiative-convective equilibrium model for young giant exoplanets:\n Application to beta Pictoris b: We present a radiative-convective equilibrium model for young giant\nexoplanets. Model predictions are compared with the existing photometric\nmeasurements of planet beta Pictoris b in the J, H, Ks, L', NB 4.05, M' bands .\nThis model will be used to interpret future photometric and spectroscopic\nobservations of exoplanets with SPHERE, mounted at the VLT with a first light\nexpected mid-2014.", "category": "astro-ph_EP" }, { "text": "An evidence for solar activity influence on the meteorological processes\n in the south polar region of Mars during the great opposition in AD 1924: A time series of the Martian south ice polar cap mean diameter for the period\nJuly-December 1924 is investigated. The data are based on the high quality\npictures, which are obtained by visual observations of 60 cm telescope in\nHamburg Observatory during the great opposition of Mars in AD 1924. After\nremoving of the seasonal trend (caused by the springtime regression of the cap)\nquasi 36 and 80-82 days cycles in residuals has been obtained. The sunspot\nactivity spectra for the corresponding period is almost the same one. The local\nmaximums of polar cap area residuals has been occured of about 10 days after\nthe corresponding minimums of sunspot activity. The so obtained results are\nbriefly discussed.", "category": "astro-ph_EP" }, { "text": "Do we really know the dust? Systematics and uncertainties of the\n mid-infrared spectral analysis methods: The spectral region around 10 micrometer, showing prominent dust emission\nbands, is commonly used to derive the chemical composition of protoplanetary\ndust. Different analysis methods have been proposed for this purpose, but so\nfar, no comparative test has been performed to test their validity. We\ncalculated model spectra of disk models with different geometries and central\nsources, using a 2D radiative transfer code. These spectra were then fitted in\na blind test using four different spectral decomposition methods. We studied\nthe effect of disk structure (flared vs. flat), inclination angle, size of the\ninner disk hole and stellar luminosity on the fitted chemical composition. Our\nresults show that the derived dust compositions by all methods deviate\nsystematically from the real chemical composition. Out of the four tested\nspectral decomposition methods, our new two-layer temperature distribution\nmethod, differs the least from the input dust composition and the results show\nthe weakest systematic effects. The reason for the deviations of the results\ngiven by other methods lies in their simplifying assumptions (e.g. single\naverage grain temperature or one component continuum). We also tested the\ninfluence of different noise levels on the results of the spectral\ndecomposition methods. We find that, for ground-based observations (8-13\nmicrometer) the expected uncertainty in the value of the crystallinity is about\n11% for a signal-to-noise ratio of 100, while for space-based observations\n(7-17 micrometer) the uncertainty is about 5%. On the basis of our results, we\npropose a recipe for the analysis and interpretation of dust spectroscopy data\nin the mid-infrared which should be especially valuable for analysing Spitzer\ndata and ground-based infrared spectroscopy data in the 10 micrometer window.", "category": "astro-ph_EP" }, { "text": "Rapid Mid-Infrared Variability in Protostellar Disks: Spectral energy distribution (SED) in protostellar disks is determined by the\ndisks'internal dissipation and reprocessing of irradiation from their host\nstars. Around T Tauri stars, most mid-infrared (MIR) radiation (in a few to a\nfew ten {\\mu}m wavelength range) emerge from regions around a fraction to a few\nAU's. This region is interesting because it contains both the habitable zone\nand the snow line. Recent observations reveal that SED variations, in the MIR\nwavelength range. These variations are puzzling because they occur on time\nscale (a few days) which is much shorter than the dynamical (months to years)\ntime scale at 1AU to a few AU's. They are probably caused by shadows casted by\ninner onto outer disk regions. Interaction between disks and their misaligned\nmagnetized host stars can lead to warped structure and periodic SED\nmodulations. Rapid aperiodic SED variations may also be induced by observed\nX-ray flares from T Tauri stars. These flares can significantly modulate the\nionization fraction of the gas and the net charge carried by the grains near\nthe surface of the inner disk. The newly charged grains may be accelerated by\nthe stellar or disk magnetic field and adjust their distances from the\nmidplane. Shadows casted by these grains attenuates the flux of stellar photons\nirradiated onto regions at several AU's from the central stars. We use this\nmodel to account for the observed rapid aperiodic SED variabilities. We suggest\nregular monitoring of SED variations will not only provide valuable information\non the distribution of the disk aspect ratio near the habitable zone but also\nprovide a probe on the interaction between the inner regions of the disk with\nthe magnetosphere of their host stars.", "category": "astro-ph_EP" }, { "text": "Ghost in the time series: no planet for Alpha Cen B: We re-analyse the publicly available radial velocity (RV) measurements for\nAlpha Cen B, a star hosting an Earth-mass planet candidate, Alpha Cen Bb, with\n3.24 day orbital period. We demonstrate that the 3.24 d signal observed in the\nAlpha Cen B data almost certainly arises from the window function (time\nsampling) of the original data. We show that when stellar activity signals are\nremoved from the RV variations, other significant peaks in the power spectrum\nof the window function are coincidentally suppressed, leaving behind a spurious\nyet apparently-significant 'ghost' of a signal that was present in the window\nfunction's power spectrum to begin with. Even when fitting synthetic data with\ntime sampling identical to the original data, but devoid of any genuine\nperiodicities close to that of the planet candidate, the original model used to\ninfer the presence of Alpha Cen Bb leads to identical conclusions: viz., the\n3$\\sigma$ detection of a half-a-metre-per-second signal with 3.236 day period.\nOur analysis underscores the difficulty of detecting weak planetary signals in\nRV data, and the importance of understanding in detail how every component of\nan RV data set, including its time sampling, influences final statistical\ninference.", "category": "astro-ph_EP" }, { "text": "Wall emission in circumbinary disks: the case of CoKu Tau/4: A few years ago, the mid-IR spectrum of a Weak Line T Tauri Star, CoKu Tau/4,\nwas explained as emission from the inner wall of a circumstellar disk, with the\ninner disk truncated at ~10 AU. Based on the SED shape and the assumption that\nit was produced by a single star and its disk, CoKu Tau/4 was classified as a\nprototypical transitional disk, with a clean inner hole possibly carved out by\na planet, some other orbiting body, or by photodissociation. However, recently\nit has been discovered that CoKu Tau/4 is a close binary system. This implies\nthat the observed mid-IR SED is probably produced by the circumbinary disk. The\naim of the present paper is to model the SED of CoKu Tau/4 as arising from the\ninner wall of a circumbinary disk, with parameters constrained by what is known\nabout the central stars and by a dynamical model for the interaction between\nthese stars and their surrounding disk. In order to fit the Spitzer IRS SED,\nthe binary orbit should be almost circular, implying a small mid-IR variability\n(10%) related to the variable distances of the stars to the inner wall of the\ncircumbinary disk. Our models suggest that the inner wall of CoKu Tau/4 is\nlocated at 1.7a, where a is the semi-major axis of the binary system (a~8AU). A\nsmall amount of optically thin dust in the hole (<0.01 lunar masses) helps to\nimprove the fit to the 10microns silicate band. Also, we find that water ice\nshould be absent or have a very small abundance (a dust to gas mass ratio\n<5.6X10^{-5}). In general, for a binary system with eccentricity e>0, the model\npredicts mid-IR variability with periods similar to orbital timescales,\nassuming that thermal equilibrium is reached instantaneously.", "category": "astro-ph_EP" }, { "text": "Cleaning our Hazy Lens: Exploring Trends in Transmission Spectra of Warm\n Exoplanets: Relatively little is understood about the atmospheric composition of\ntemperate to warm exoplanets (equilibrium temperature $T_{\\rm eq}<$ 1000 K), as\nmany of them are found to have uncharacteristically flat transmission spectra.\nTheir flattened spectra are likely due to atmospheric opacity sources such as\nplanet-wide photochemical hazes and condensation clouds. We compile the\ntransmission spectra of 25 warm exoplanets previously observed by the Hubble\nSpace Telescope and quantify the haziness of each exoplanet using a normalized\namplitude of the water absorption feature ($A_{\\rm H}$). By examining the\nrelationships between $A_{\\rm H}$ and various planetary and stellar forcing\nparameters, we endeavor to find correlations of haziness associated with\nplanetary properties. We adopt new statistical correlation tests that are more\nsuitable for the small, non-normally distributed warm exoplanet sample. Our\nanalysis shows that none of the parameters hold statistically significant\ncorrelation with $A_{\\rm H}$ ($p \\le 0.01$) with the addition of new exoplanet\ndata, including the previously identified linear trends between $A_{\\rm H}$ and\n$T_{\\rm{eq}}$ or hydrogen-helium envelope mass fraction (f$_{\\rm{HHe}}$). This\nsuggests that haziness in warm exoplanets is not simply controlled by any\nsingle planetary/stellar parameter. Among all the parameters we investigated,\nplanet gravity ($g_{\\rm p}$), atmospheric scale height ($H$), planet density\n($\\rho_{\\rm p}$), orbital eccentricity ($e$), and age of the star ($t_{\\rm\nage}$) hold tentative correlations with $A_{\\rm H}$. Specifically, lower $H$,\nhigher $g_{\\rm p}$, $\\rho_{\\rm p}$, $e$, or $t_{\\rm age}$ may lead to clearer\natmospheres. We still need more observations and laboratory experiments to\nfully understand the complex physics and chemistry involved in creating hazy\nwarm exoplanets.", "category": "astro-ph_EP" }, { "text": "Earths are not Super-Earths, Saturns are not Jupiters: Imprints of\n pressure-bump planet formation on planetary architectures: In protoplanetary disks, sufficiently massive planets excite pressure bumps,\nwhich can then be preferred locations for forming new planet cores. We discuss\nhow this loop may affect the architecture of multi-planet systems, and compare\nour predictions with observation. Our main prediction is that low-mass planets\nand giant planets can each be divided into two subpopulations with different\nlevels of mass uniformity. Low-mass planets that can and cannot reach the\npebble isolation mass (the minimum mass required to produce a pressure bump)\ndevelop into intra-similar \"Super-Earths\" and more diverse \"Earths\",\nrespectively. Gas giants that do and do not accrete envelope quickly develop\ninto intra-similar \"Jupiters\" and more diverse \"Saturns\", respectively.\nSuper-Earths prefer to form long chains via repeated pressure-bump planet\nformation, while Jupiter formation is usually terminated at pairs or triplets\ndue to dynamical instability. These predictions are broadly consistent with\nobservations. In particular, we discover a previously overlooked mass\nuniformity dichotomy among the observed populations of both low-mass planets\n(Earths vs. Super-Earths) and gas giants (Saturns vs. Jupiters). For low-mass\nplanets, planets well below the pebble isolation mass ($\\lesssim 3M_\\oplus$ or\n$\\lesssim 1.5 R_\\oplus$ for sun-like stars) show significantly higher\nintra-system pairwise mass difference than planets around the pebble isolation\nmass. For gas giants, the period ratios of intra-system pairs show a bimodal\ndistribution, which can be interpreted as two subpopulations with different\nlevels of mass uniformity. These findings suggest that pressure-bump planet\nformation could be an important ingredient in shaping planetary architectures.", "category": "astro-ph_EP" }, { "text": "Finding regions of bounded motion in binary asteroid environment using\n Lagrangian descriptors: Trajectory design in highly-perturbed environments like binary asteroids is\nchallenging. It typically requires using realistic, non-autonomous dynamical\nmodels in which periodic solutions derived in autonomous systems vanish. In\nthis work, Lagrangian descriptors are employed in the perturbed planar\nbi-elliptic restricted four-body problem to find regions of bounded motion over\na finite horizon about Dimorphos, the secondary body of the (65803) Didymos\nbinary system. Results show that Lagrangian descriptors successfully reveal\nphase space organizing structures both in the unperturbed and perturbed planar\nbi-elliptic restricted four-body problem. With no solar radiation pressure,\nregions of bounded motion are visually identified, so granting access to a vast\nselection of bounded orbits about Dimorphos. Conversely, the presence of solar\nradiation pressure breaks down the majority of structures, leading to a large\nregion of unstable motion with rare exceptions. Lagrangian descriptors are\ncomputationally inexpensive dynamical indicators that could be conveniently\napplied to astrodynamics.", "category": "astro-ph_EP" }, { "text": "Fate of the runner in hit-and-run collisions: In similar-sized planetary collisions, a significant part of the impactor\noften misses the target and continues downrange. We follow the dynamical\nevolution of \"runners\" from giant impacts to determine their ultimate fate.\nSurprisingly, runners re-impact their target planets only about half of the\ntime, for realistic collisional and dynamical scenarios. Otherwise they remain\nin orbit for tens of millions of years (the limit of our N-body calculations)\nand longer, or sometimes collide with a different planet than the first one.\nWhen the runner does return to collide again with the same arget planet, its\nimpact velocity is mainly constrained by the outcome of the prior collision.\nImpact angle and orientation, however, are unconstrained by the prior\ncollision.", "category": "astro-ph_EP" }, { "text": "Characterization of the HD 108236 system with CHEOPS and TESS.\n Confirmation of a fifth transiting planet: The HD108236 system was first announced with the detection of four small\nplanets based on TESS data. Shortly after, the transit of an additional planet\nwith a period of 29.54d was serendipitously detected by CHEOPS. In this way,\nHD108236 (V=9.2) became one of the brightest stars known to host five small\ntransiting planets (R$_p$<3R$_{\\oplus}$). We characterize the planetary system\nby using all the data available from CHEOPS and TESS space missions. We use the\nflexible pointing capabilities of CHEOPS to follow up the transits of all the\nplanets in the system, including the fifth transiting body. After updating the\nhost star parameters by using the results from Gaia eDR3, we analyzed 16 and 43\ntransits observed by CHEOPS and TESS, respectively, to derive the planets\nphysical and orbital parameters. We carried out a timing analysis of the\ntransits of each of the planets of HD108236 to search for the presence of\ntransit timing variations. We derived improved values for the radius and mass\nof the host star (R$_{\\star}$=0.876$\\pm$0.007 R$_{\\odot}$ and\nM$_{\\star}$=0.867$_{-0.046}^{+0.047}$ M$_{\\odot}$). We confirm the presence of\nthe fifth transiting planet f in a 29.54d orbit. Thus, the system consists of\nfive planets of R$_b$=1.587$\\pm$0.028, R$_c$=2.122$\\pm$0.025,\nR$_d$=2.629$\\pm$0.031, R$_e$=3.008$\\pm$0.032, and R$_f$=1.89$\\pm$0.04\n[R$_{\\oplus}$]. We refine the transit ephemeris for each planet and find no\nsignificant transit timing variations for planets c, d, and e. For planets b\nand f, instead, we measure significant deviations on their transit times (up to\n22 and 28 min, respectively) with a non-negligible dispersion of 9.6 and 12.6\nmin in their time residuals. We confirm the presence of planet f and find no\nsignificant evidence for a potential transiting planet in a 10.9d orbital\nperiod, as previously suggested. Full abstract in the PDF file.", "category": "astro-ph_EP" }, { "text": "Prospecting for exo-Earths in multiple planet systems with a gas giant: In this work, we hunt for the best places to find exo-Earths in the currently\nknown exoplanet population. While it is still unclear whether Jupiter had a\nbeneficial or detrimental effect on the creation of the right environment for a\nhabitable Earth to develop, we focus on the 51 multiple planet systems that\nhave at least one Jupiter-like planet and aim to identify which would be good\ncandidates to host an exo-Earth. We conduct a series of numerical simulations\nto identify dynamically stable regions of the habitable zone of the multiple\nexoplanet systems capable of hosting an Earth-mass planet. We produce a\ncandidate list of 16 systems that could host such a stable exo-Earth in their\nhabitable zone, and for which the induced radial velocity signal of a\nhypothetical one, two or four Earth-mass planet on the host star would be\ndetectable with the ESPRESSO spectrograph. We find that whilst the\ngravitational interactions with the massive planet nearest the habitable zone\nare critical in determining stability, the secular resonant interactions\nbetween multiple planets can also have a dramatic influence on the overall\nstability of the habitable zone.", "category": "astro-ph_EP" }, { "text": "On the coexistence of the streaming instability and the vertical shear\n instability in protoplanetary disks: The streaming instability is a leading candidate mechanism to explain the\nformation of planetesimals. Yet, the role of this instability in the driving of\nturbulence in protoplanetary disks, given its fundamental nature as a linear\nhydrodynamical instability, has so far not been investigated in detail. We\nstudy the turbulence that is induced by the streaming instability as well as\nits interaction with the vertical shear instability. For this purpose, we\nemploy the FLASH Code to conduct two-dimensional axisymmetric global disk\nsimulations spanning radii from $1$ au to $100$ au, including the mutual drag\nbetween gas and dust as well as the radial and vertical stellar gravity. If the\nstreaming instability and the vertical shear instability start their growth at\nthe same time, we find the turbulence in the dust mid-plane layer to be\nprimarily driven by the streaming instability. It gives rise to vertical gas\nmotions with a Mach number of up to ${\\sim}10^{-2}$. The dust scale height is\nset in a self-regulatory manner to about $1\\%$ of the gas scale height. In\ncontrast, if the vertical shear instability is allowed to saturate before the\ndust is introduced into our simulations, then it continues to be the main\nsource of the turbulence in the dust layer. The vertical shear instability\ninduces turbulence with a Mach number of ${\\sim}10^{-1}$ and thus impedes dust\nsedimentation. Nonetheless, we find the vertical shear instability and the\nstreaming instability in combination to lead to radial dust concentration in\nlong-lived accumulations which are significantly denser than those formed by\nthe streaming instability alone. Thus, the vertical shear instability may\npromote planetesimal formation by creating weak overdensities that act as seeds\nfor the streaming instability.", "category": "astro-ph_EP" }, { "text": "Stellar Spin-Orbit Misalignment in a Multiplanet System: Stars hosting hot Jupiters are often observed to have high obliquities,\nwhereas stars with multiple co-planar planets have been seen to have low\nobliquities. This has been interpreted as evidence that hot-Jupiter formation\nis linked to dynamical disruption, as opposed to planet migration through a\nprotoplanetary disk. We used asteroseismology to measure a large obliquity for\nKepler-56, a red giant star hosting two transiting co-planar planets. These\nobservations show that spin-orbit misalignments are not confined to hot-Jupiter\nsystems. Misalignments in a broader class of systems had been predicted as a\nconsequence of torques from wide-orbiting companions, and indeed\nradial-velocity measurements revealed a third companion in a wide orbit in the\nKepler-56 system.", "category": "astro-ph_EP" }, { "text": "Latitudinal Variation of Clouds' Structure Responsible for Venus' Cold\n Collar: Global Climate Models (GCM) are very useful tools to study theoretically the\ngeneral dynamics and specific phenomena in planetary atmospheres. In the case\nof Venus, several GCMs succeeded in reproducing the atmosphere's superrotation\nand the global temperature field. However, the highly variable polar\ntemperature and the permanent cold collar have not been reproduced\nsatisfactorily yet. Here we improve the radiative transfer scheme of the\nInstitut Pierre Simon Laplace Venus GCM in order to numerically simulate the\npolar thermal features in Venus atmosphere. The main difference with the\nprevious model is that we now take into account the latitudinal variation of\nthe cloud structure. Both solar heating rates and infrared cooling rates have\nbeen modified to consider the cloud top's altitude decrease toward the poles\nand the variation in latitude of the different particle modes' abundances. A\nnew structure that closely resembles the observed cold collar appears in the\naverage temperature field at $2\\times10^{4} - 4\\times10^{3}$~Pa ($\\sim62 -\n66$~km) altitude range and $60^{\\circ} - 90^{\\circ}$ latitude band. It is not\nisolated from the pole as in the observation-based maps, but the obtained\ntemperature values (220~K) are in good agreement with observed values.\nTemperature polar maps across this region show an inner warm region where the\npolar vortex is observed, but the obtained 230~K average value is colder than\nthe observed mean value and the simulated horizontal structure does not show\nthe fine-scale features present within the vortex. Our study shows that the\ncloud structure is essential in the cold collar formation. Although our\nanalysis focuses on the improvement of the radiative forcing and the variations\nit causes in the thermal structure, polar dynamics is definitely affected by\nthis modified environment and a noteworthy upwelling motion is found in the\ncold collar area.", "category": "astro-ph_EP" }, { "text": "Inner Boundary Condition in Quasi-Lagrangian Simulations of Accretion\n Disks: In simulations of viscously evolving accretion disks, the inner boundary\ncondition is particularly important. If treated incorrectly, it induces\nincorrect behavior very quickly, because the viscous time is shortest near the\ninner boundary. Recent work has determined the correct inner boundary in\nEulerian simulations. But in quasi-Lagrangian simulations (e.g., SPH, moving\nmesh, and mesh-less), where the inner boundary is modeled by removing mass\nwithin a finite zone, the inner density profile typically becomes anomalously\ndepleted. Here we show how the boundary condition should be applied in such\ncodes, via a simple modification of the usual approach: when one removes mass,\none must speed up the remaining material so that the disk's angular momentum is\nunchanged. We show with both 1D and 2D moving-mesh (AREPO) simulations that\nthis scheme works as desired in viscously evolving disks. It produces no\nspurious density depletions and is independent of the mass removal rate,\nprovided that the disk is adequately resolved and that the mass removal rate is\nnot so extreme as to trigger instabilities. This \"torque-free\" mass removal\ntechnique permits the use of quasi-Lagrangian codes to simulate viscously\nevolving disks, while including a variety of additional effects. As an example,\nwe apply our scheme to a 2D simulation of an accretion disk perturbed by a very\nmassive planet, in which the disk is evolved to viscous steady state.", "category": "astro-ph_EP" }, { "text": "Constraining the gap size in the disk around HD 100546 in the\n mid-infrared: We refine the gap size measurements of the disk surrounding the Herbig Ae\nstar HD 100546 in the N band. Our new mid-infrared interferometric (MIDI) data\nhave been taken with the UT baselines and span the full range of orientations.\nThe correlated fluxes show a wavy pattern in which the minima separation links\nto a geometrical structure in the disk. We fit each correlated flux measurement\nwith a spline function, deriving the corresponding spatial scale, while\nassuming that the pattern arises interferometrically due to the bright emission\nfrom the inner disk and the opposing sides of the wall of the outer disk. We\nthen fit an ellipse to the derived separations at their corresponding position\nangles, thereby using the observations to constrain the disk inclination to i\n=47 +/- 1 degree and the disk position angle to PA =135.0 +/- 2.5 degree East\nof North, both of which are consistent with the estimated values in previous\nstudies. We also derive the radius of the ellipse to 15.7 +/- 0.8 au. To\nconfirm that the minima separations translate to a geometrical structure in the\ndisk, we model the disk of HD 100546 using a semi-analytical approach taking\ninto account the temperature and optical depth gradients. Using this model, we\nsimultaneously reproduce the level and the minima of the correlated fluxes and\nconstrain the gap size of the disk for each observation. The values obtained\nfor the projected gap size in different orientations are consistent with the\nseparation found by the geometrical model.", "category": "astro-ph_EP" }, { "text": "Five key exoplanet questions answered via the analysis of 25 hot Jupiter\n atmospheres in eclipse: Population studies of exoplanets are key to unlocking their statistical\nproperties. So far the inferred properties have been mostly limited to\nplanetary, orbital and stellar parameters extracted from, e.g., Kepler, radial\nvelocity, and GAIA data. More recently an increasing number of exoplanet\natmospheres have been observed in detail from space and the ground. Generally,\nhowever, these atmospheric studies have focused on individual planets, with the\nexception of a couple of works which have detected the presence of water vapor\nand clouds in populations of gaseous planets via transmission spectroscopy.\nHere, using a suite of retrieval tools, we analyse spectroscopic and\nphotometric data of 25 hot Jupiters, obtained with the Hubble and Spitzer Space\nTelescopes via the eclipse technique. By applying the tools uniformly across\nthe entire set of 25 planets, we extract robust trends in the thermal structure\nand chemical properties of hot Jupiters not obtained in past studies. With the\nrecent launch of JWST and the upcoming missions Twinkle, and Ariel, population\nbased studies of exoplanet atmospheres, such as the one presented here, will be\na key approach to understanding planet characteristics, formation, and\nevolution in our galaxy.", "category": "astro-ph_EP" }, { "text": "Debris Disks: Seeing Dust, Thinking of Planetesimals and Planets: Debris disks are optically thin, almost gas-free dusty disks observed around\na significant fraction of main-sequence stars older than about 10 Myr. Since\nthe circumstellar dust is short-lived, the very existence of these disks is\nconsidered as evidence that dust-producing planetesimals are still present in\nmature systems, in which planets have formed - or failed to form - a long time\nago. It is inferred that these planetesimals orbit their host stars at asteroid\nto Kuiper-belt distances and continually supply fresh dust through mutual\ncollisions. This review outlines observational techniques and results on debris\ndisks, summarizes their essential physics and theoretical models, and then\nplaces them into the general context of planetary systems, uncovering\ninterrelations between the disks, dust parent bodies, and planets. It is shown\nthat debris disks can serve as tracers of planetesimals and planets and shed\nlight on the planetesimal and planet formation processes that operated in these\nsystems in the past.", "category": "astro-ph_EP" }, { "text": "Tidal Evolution of the Evection Resonance/Quasi-Resonance and the\n Angular Momentum of the Earth-Moon System: Forming the Moon by a high-angular momentum impact may explain the Earth-Moon\nisotopic similarities, however, the post-impact angular momentum needs to be\nreduced by a factor of 2 or more to the current value (1 L_EM) after the Moon\nforms. Capture into the evection resonance, occurring when the lunar perigee\nprecession period equals one year, could remove the angular momentum excess.\nHowever the appropriate angular momentum removal appears sensitive to the tidal\nmodel and chosen tidal parameters. In this work, we use a constant-time delay\ntidal model to explore the Moon's orbital evolution through evection. We find\nthat exit from formal evection occurs early and that subsequently, the Moon\nenters a quasi-resonance regime, in which evection still regulates the lunar\neccentricity even though the resonance angle is no longer librating. Although\nnot in resonance proper, during quasi-resonance angular momentum is\ncontinuously removed from the Earth-Moon system and transferred to Earth's\nheliocentric orbit. The final angular momentum, set by the timing of\nquasi-resonance escape, is a function of the ratio of tidal strength in the\nMoon and Earth and the absolute rate of tidal dissipation in the Earth. We\nconsider a physically-motivated model for tidal dissipation in the Earth as the\nmantle cools from a molten to a partially molten state. We find that as the\nmantle solidifies, increased terrestrial dissipation drives the Moon out of\nquasi-resonance. For post-impact systems that contain >2 L_EM, final angular\nmomentum values after quasi-resonance escape remain significantly higher than\nthe current Earth-Moon value.", "category": "astro-ph_EP" }, { "text": "UV Surface Environment of Earth-like Planets Orbiting FGKM Stars Through\n Geological Evolution: The UV environment of a host star affects the photochemistry in the\natmosphere, and ultimately the surface UV environment for terrestrial planets\nand therefore the conditions for the origin and evolution of life. We model the\nsurface UV radiation environment for Earth-sized planets orbiting FGKM stars at\nthe 1AU equivalent distance for Earth through its geological evolution. We\nexplore four different types of atmospheres corresponding to an early Earth\natmosphere at 3.9 Gyr ago and three atmospheres covering the rise of oxygen to\npresent day levels at 2.0 Gyr ago, 0.8 Gyr ago and modern Earth (Following\nKaltenegger et al. 2007). In addition to calculating the UV flux on the surface\nof the planet, we model the biologically effective irradiance, using DNA damage\nas a proxy for biological damage. We find that a pre-biotic Earth (3.9 Gyr ago)\norbiting an F0V star receives 6 times the biologically effective radiation as\naround the early Sun and 3520 times the modern Earth-Sun levels. A pre-biotic\nEarth orbiting GJ 581 (M3.5V) receives 300 times less biologically effective\nradiation, about 2 times modern Earth-Sun levels. The UV fluxes calculated here\nprovide a grid of model UV environments during the evolution of an Earth-like\nplanet orbiting a range of stars. These models can be used as inputs into\nphoto-biological experiments and for pre-biotic chemistry and early life\nevolution experiments.", "category": "astro-ph_EP" }, { "text": "Kelvin-Helmholtz Instabilities in Multi-Sized Dust Layers: We examine the effect of the dust size distribution on Kelvin-Helmholtz\ninstabilities in the protoplanetary disk with dust sedimentation. With newly\ntaking into account the dust size distribution, the growth rate of the\nKelvin-Helmholtz instability is calculated using the linear stability analysis\nwith the dust density distribution consistent with sedimentation. Dust\nabundance required for gravitational instabilities before the Kelvin-Helmholtz\ninstability is derived from the linear stability analysis, and it is found that\nthe required dust abundance significantly coincides with that estimated from\nthe Richardson number. It is also found that when the dust size distribution is\ntaken into account, the critical Richardson number for the onset of the\nKelvin-Helmholtz instability tends to increase with dust abundance. This result\nis different from that in the case without the dust size distribution.", "category": "astro-ph_EP" }, { "text": "Orbital Evolution of Moons in Weakly Accreting Circumplanetary Disks: We investigate the formation of hot and massive circumplanetary disks (CPDs)\nand the orbital evolution of satellites formed in these disks. Because of the\ncomparatively small size-scale of the sub-disk, quick magnetic diffusion\nprevents the magnetorotational instability (MRI) from being well-developed at\nionization levels that would allow MRI in the parent protoplanetary disk. In\nthe absence of significant angular momentum transport, continuous mass supply\nfrom the parental protoplanetary disk leads to the formation of a massive CPD.\nWe have developed an evolutionary model for this scenario and have estimated\nthe orbital evolution of satellites within the disk. We find, in a certain\ntemperature range, that inward migration of a satellite can be stopped by a\nchange in the structure due to the opacity transitions. Moreover, by capturing\nsecond and third migrating satellites in mean motion resonances, a compact\nsystem in Laplace resonance can be formed in our disk models.", "category": "astro-ph_EP" }, { "text": "Eccentric Companions to Kepler-448b and Kepler-693b: Clues to the\n Formation of Warm Jupiters: I report the discovery of non-transiting close companions to two transiting\nwarm Jupiters (WJs), Kepler-448/KOI-12b (orbital period\n$P=17.9\\,\\mathrm{days}$, radius $R_{\\rm p}=1.23^{+0.06}_{-0.05}\\,R_{\\rm Jup}$)\nand Kepler-693/KOI-824b ($P=15.4\\,\\mathrm{days}$, $R_{\\rm\np}=0.91\\pm0.05\\,R_{\\rm Jup}$), via dynamical modeling of their transit timing\nand duration variations (TTVs and TDVs). The companions have masses of\n$22^{+7}_{-5}\\,M_{\\rm Jup}$ (Kepler-448c) and $150^{+60}_{-40}\\,M_{\\rm Jup}$\n(Kepler-693c), and both are on eccentric orbits ($e=0.65^{+0.13}_{-0.09}$ for\nKepler-448c and $e=0.47^{+0.11}_{-0.06}$ for Kepler-693c) with periastron\ndistances of $1.5\\,\\mathrm{au}$. Moderate eccentricities are detected for the\ninner orbits as well ($e=0.34^{+0.08}_{-0.07}$ for Kepler-448b and\n$e=0.2^{+0.2}_{-0.1}$ for Kepler-693b). In the Kepler-693 system, a large\nmutual inclination between the inner and outer orbits\n($53^{+7}_{-9}\\,\\mathrm{deg}$ or $134^{+11}_{-10}\\,\\mathrm{deg}$) is also\nrevealed by the TDVs. This is likely to induce a secular oscillation of the\ninner WJ's eccentricity that brings its periastron close enough to the host\nstar for tidal star-planet interactions to be significant. In the Kepler-448\nsystem, the mutual inclination is weakly constrained and such an eccentricity\noscillation is possible for a fraction of the solutions. Thus these WJs may be\nundergoing tidal migration to become hot Jupiters (HJs), although the migration\nvia this process from beyond the snow line is disfavored by the close-in and\nmassive nature of the companions. This may indicate that WJs can be formed in\nsitu and could even evolve into HJs via high-eccentricity migration inside the\nsnow line.", "category": "astro-ph_EP" }, { "text": "Orbit classification in the planar circular Pluto-Charon system: We numerically investigate the orbital dynamics of a spacecraft, or a comet,\nor an asteroid in the Pluto-Charon system in a scattering region around Charon\nusing the planar circular restricted three-body problem. The test particle can\nmove in bounded orbits around Charon or escape through the necks around the\nLagrangian points $L_1$ and $L_2$ or even collide with the surface of Charon.\nWe explore four of the five possible Hill's regions configurations depending on\nthe value of the Jacobi constant which is of course related with the total\norbital energy. We conduct a thorough numerical analysis on the phase space\nmixing by classifying initial conditions of orbits and distinguishing between\nthree types of motion: (i) bounded, (ii) escaping and (iii) collisional. In\nparticular, we locate the different basins and we relate them with the\ncorresponding spatial distributions of the escape and collision times. Our\nresults reveal the high complexity of this planetary system. Furthermore, the\nnumerical analysis shows a strong dependence of the properties of the\nconsidered basins with the total orbital energy, with a remarkable presence of\nfractal basin boundaries along all the regimes. Our results are compared with\nearlier ones regarding the Saturn-Titan planetary system.", "category": "astro-ph_EP" }, { "text": "Planet populations inferred from debris discs: insights from 178 debris\n systems in the ISPY, LEECH and LIStEN planet-hunting surveys: We know little about the outermost exoplanets in planetary systems, because\nour detection methods are insensitive to moderate-mass planets on wide orbits.\nHowever, debris discs can probe the outer-planet population, because dynamical\nmodelling of observed discs can reveal properties of perturbing planets. We use\nfour sculpting and stirring arguments to infer planet properties in 178\ndebris-disc systems from the ISPY, LEECH and LIStEN planet-hunting surveys.\nSimilar analyses are often conducted for individual discs, but we consider a\nlarge sample in a consistent manner. We aim to predict the population of\nwide-separation planets, gain insight into the formation and evolution\nhistories of planetary systems, and determine the feasibility of detecting\nthese planets in the near future. We show that a `typical' cold debris disc\nlikely requires a Neptune- to Saturn-mass planet at 10-100 au, with some\nneeding Jupiter-mass perturbers. Our predicted planets are currently\nundetectable, but modest detection-limit improvements (e.g. from JWST) should\nreveal many such perturbers. We find that planets thought to be perturbing\ndebris discs at late times are similar to those inferred to be forming in\nprotoplanetary discs, so these could be the same population if newly formed\nplanets do not migrate as far as currently thought. Alternatively, young\nplanets could rapidly sculpt debris before migrating inwards, meaning that the\nresponsible planets are more massive (and located further inwards) than\ndebris-disc studies assume. We combine self-stirring and size-distribution\nmodelling to show that many debris discs cannot be self-stirred without having\nunreasonably high masses; planet- or companion-stirring may therefore be the\ndominant mechanism in many (perhaps all) debris discs. Finally, we provide\ncatalogues of planet predictions, and identify promising targets for future\nplanet searches.", "category": "astro-ph_EP" }, { "text": "Dust Growth and Magnetic Fields: from Cores to Disks (even down to\n Planets): The recent rapid progress in observations of circumstellar disks and\nextrasolar planets has reinforced the importance of understanding an intimate\ncoupling between star and planet formation. Under such a circumstance, it may\nbe invaluable to attempt to specify when and how planet formation begins in\nstar-forming regions and to identify what physical processes/quantities are the\nmost significant to make a link between star and planet formation. To this end,\nwe have recently developed a couple of projects. These include an observational\nproject about dust growth in Class 0 YSOs and a theoretical modeling project of\nthe HL Tauri disk. For the first project, we utilize the archive data of radio\ninterferometric observations, and examine whether dust growth, a first step of\nplanet formation, occurs in Class 0 YSOs. We find that while our observational\nresults can be reproduced by the presence of large ($\\sim$ mm) dust grains for\nsome of YSOs under the single-component modified blackbody formalism, an\ninterpretation of no dust growth would be possible when a more detailed model\nis used. For the second project, we consider an origin of the disk\nconfiguration around HL Tauri, focusing on magnetic fields. We find that\nmagnetically induced disk winds may play an important role in the HL Tauri\ndisk. The combination of these attempts may enable us to move towards a\ncomprehensive understanding of how star and planet formation are intimately\ncoupled with each other.", "category": "astro-ph_EP" }, { "text": "SWEET-Cat updated. New homogenous spectroscopic parameters: Context: Exoplanets have now been proven to be very common. The number of its\ndetections continues to grow following the development of better instruments\nand missions. One key step for the understanding of these worlds is their\ncharacterization, which mostly depend on their host stars. Aims:We perform a\nsignificant update of the Stars With ExoplanETs CATalog (SWEET-Cat), a unique\ncompilation of precise stellar parameters for planet-host stars provided for\nthe exoplanet community. Methods: We made use of high-resolution spectra for\nplanet-host stars, either observed by our team or found in several public\narchives. The new spectroscopic parameters were derived for the spectra\nfollowing the same homogeneous process (ARES+MOOG). The host star parameters\nwere then merged together with the planet properties listed in exoplanet.eu to\nperform simple data analysis. Results: We present new spectroscopic homogeneous\nparameters for 106 planet-host stars. Sixty-three planet hosts are also\nreviewed with new parameters. We also show that there is a good agreement\nbetween stellar parameters derived for the same star but using spectra obtained\nfrom different spectrographs. The planet-metallicity correlation is reviewed\nshowing that the metallicity distribution of stars hosting low-mass planets\n(below 30 M$_{\\oplus}$) is indistinguishable from that from the solar\nneighborhood sample in terms of metallicity distribution.", "category": "astro-ph_EP" }, { "text": "\"TNOs are Cool\": A survey of the trans-Neptunian region XIV. Size/albedo\n characterization of the Haumea family observed with Herschel and Spitzer: A group of trans-Neptunian objects (TNO) are dynamically related to the dwarf\nplanet 136108 Haumea. Ten of them show strong indications of water ice on their\nsurfaces, are assumed to have resulted from a collision, and are accepted as\nthe only known TNO collisional family. Nineteen other dynamically similar\nobjects lack water ice absorptions and are hypothesized to be dynamical\ninterlopers. We have made observations to determine sizes and geometric albedos\nof six of the accepted Haumea family members and one dynamical interloper. Ten\nother dynamical interlopers have been measured by previous works. We compare\nthe individual and statistical properties of the family members and\ninterlopers, examining the size and albedo distributions of both groups. We\nalso examine implications for the total mass of the family and their ejection\nvelocities. We use far-infrared space-based telescopes to observe the target\nTNOs near their thermal peak and combine these data with optical magnitudes to\nderive sizes and albedos using radiometric techniques. We determine the\npower-law slope of ejection velocity as a function of effective diameter. The\ndetected Haumea family members have a diversity of geometric albedos $\\sim$\n0.3-0.8, which are higher than geometric albedos of dynamically similar objects\nwithout water ice. The median geometric albedo for accepted family members is\n$p_V=0.48_{-0.18}^{+0.28}$, compared to 0.08$_{-0.05}^{+0.07}$ for the\ndynamical interlopers. In the size range $D=175-300$ km, the slope of the\ncumulative size distribution is $q$=3.2$_{-0.4}^{+0.7}$ for accepted family\nmembers, steeper than the $q$=2.0$\\pm$0.6 slope for the dynamical interlopers\nwith D$< $500 km. The total mass of Haumea's moons and family members is 2.4%\nof Haumea's mass. The ejection velocities required to emplace them on their\ncurrent orbits show a dependence on diameter, with a power-law slope of\n0.21-0.50.", "category": "astro-ph_EP" }, { "text": "Thermophysical Characteristics of OSIRIS-REx Target Asteroid (101955)\n Bennu: In this work, we investigate the thermophysical properties, including thermal\ninertia, roughness fraction and surface grain size of OSIRIS-REx target\nasteroid (101955) Bennu by using a thermophysical model with the recently\nupdated 3D radar-derived shape model (\\cite[Nolan et al., 2013]{Nolan2013}) and\nmid-infrared observations (\\cite[M$\\ddot{u}$ller et al, 2012]{Muller2012},\n\\cite[Emery et al., 2014]{Emery2014}). We find that the asteroid bears an\neffective diameter of $510^{+6}_{-40}$ m, a geometric albedo of\n$0.047^{+0.0083}_{-0.0011}$, a roughness fraction of $0.04^{+0.26}_{-0.04}$,\nand thermal inertia of $240^{+440}_{-60}\\rm~Jm^{-2}s^{-0.5}K^{-1}$ for our\nbest-fit solution. The best-estimate thermal inertia suggests that fine-grained\nregolith may cover a large portion of Bennu's surface, where a grain size may\nvary from $1.3$ to $31$~mm. Our outcome suggests that Bennu is suitable for the\nOSIRIS-REx mission to return samples to Earth.", "category": "astro-ph_EP" }, { "text": "A Distinct Population of Small Planets: Sub-Earths: The sizes of small planets have been known to be bi-modal, with a gap\nseparating planets that have lost their primordial atmospheres (super-Earths),\nand the ones that retain them (mini-Neptunes). Here, we report evidences for\nanother distinct population at smaller sizes. By focussing on planets orbiting\naround GK-dwarfs inward of 16 days, and correcting for observational\ncompleteness, we find that the number of super-Earths peak around 1.4 Earth\nradii and disappear shortly below this size. Instead, a new population of\nplanets (sub-Earths) appear to dominate at sizes below ~ 1 Earth radius, with\nan occurrence that rises with decreasing size. This pattern is also observed in\nultra-short-period planets.\n The end of super-Earths supports earlier claims that super-Earths and\nmini-Neptunes, planets that likely form in gaseous proto-planetary disks, have\na narrow mass distribution. The sub-Earths, in contrast, can be described by a\npower-law mass distribution and may be explained by the theory of terrestrial\nplanet formation. We therefore speculate that they are formed well after the\ngaseous disks have dissipated. The extension of these sub-Earths towards longer\norbital periods, currently invisible, may be the true terrestrial analogues.\nThis strongly motivates new searches.", "category": "astro-ph_EP" }, { "text": "Topographic Constraints on the Origin of the Equatorial Ridge on Iapetus: Saturn's moon Iapetus has an equatorial ridge system, which may be as high as\n20 km, that may have formed by endogenic forces, such as tectonic and\nconvective forces, or exogenic processes such as debris infall. We use\nhigh-resolution topographic data to conduct a topographic analysis of the\nridge, which suggests a predominantly triangular morphology, with some ridge\nface slopes reaching 40 degrees, allowing for an exogenic formation mechanism.", "category": "astro-ph_EP" }, { "text": "Ring Formation in Protoplanetary Disks Driven by an Eccentric\n Instability: We find that, under certain conditions, protoplanetary disks may\nspontaneously generate multiple, concentric gas rings without an embedded\nplanet through an eccentric cooling instability. Using both linear theory and\nnon-linear hydrodynamics simulations, we show that a variety of background\nstates may trap a slowly precessing, one-armed spiral mode that becomes\nunstable when a gravitationally-stable disk rapidly cools. The angular momentum\nrequired to excite this spiral comes at the expense of non-uniform mass\ntransport that generically results in multiple rings. For example, one\nlong-term hydrodynamics simulation exhibits four long-lived, axisymmetric gas\nrings. We verify the instability evolution and ring formation mechanism from\nfirst principles with our linear theory, which shows remarkable agreement with\nthe simulation results. Dust trapped in these rings may produce observable\nfeatures consistent with observed disks. Additionally, direct detection of the\neccentric gas motions may be possible when the instability saturates, and any\nresidual eccentricity leftover in the rings at later times may also provide\ndirect observational evidence of this mechanism.", "category": "astro-ph_EP" }, { "text": "A Simple Phenomenological Model for Grain Clustering in Turbulence: We propose a simple model for density fluctuations of aerodynamic grains,\nembedded in a turbulent, gravitating gas disk. The model combines a calculation\nfor the behavior of a group of grains encountering a single turbulent eddy,\nwith a hierarchical approximation of the eddy statistics. This makes analytic\npredictions for a range of quantities including: distributions of grain\ndensities, power spectra and correlation functions of fluctuations, and maximum\ngrain densities reached. We predict how these scale as a function of grain drag\ntime t_stop, spatial scale, grain-to-gas mass ratio, strength of turbulence\n(alpha), and detailed disk properties. We test these against numerical\nsimulations with various turbulence-driving mechanisms. The simulations agree\nwell with the predictions, spanning t_stop*Omega ~ 1e-4 - 10, alpha ~ 1e-10 -\n1e-2, and grain-to-gas mass ratio ~0-3. Results from 'turbulent concentration'\nsimulations and laboratory experiments are also predicted as a special case.\nVortices on a wide range of scales disperse and concentrate grains\nhierarchically. For small grains this is most efficient in eddies with turnover\ntime comparable to the stopping time, but fluctuations are also damped by local\ngas-grain drift. For large grains, shear and gravity lead to a much broader\nrange of eddy scales driving fluctuations, with most power on the largest\nscales. The grain density distribution has a log-Poisson shape, with\nfluctuations for large grains up to factors >1000. We provide simple analytic\nexpressions for the predictions, and discuss implications for planetesimal\nformation, grain growth, and the structure of turbulence.", "category": "astro-ph_EP" }, { "text": "Climate Modeling of a Potential ExoVenus: The planetary mass and radius sensitivity of exoplanet discovery capabilities\nhas reached into the terrestrial regime. The focus of such investigations is to\nsearch within the Habitable Zone where a modern Earth-like atmosphere may be a\nviable comparison. However, the detection bias of the transit and radial\nvelocity methods lies close to the host star where the received flux at the\nplanet may push the atmosphere into a runaway greenhouse state. One such\nexoplanet discovery, Kepler-1649b, receives a similar flux from its star as\nmodern Venus does from the Sun, and so was categorized as a possible exoVenus.\nHere we discuss the planetary parameters of Kepler-1649b with relation to Venus\nto establish its potential as a Venus analog. We utilize the general\ncirculation model ROCKE-3D to simulate the evolution of the surface temperature\nof Kepler-1649b under various assumptions, including relative atmospheric\nabundances. We show that in all our simulations the atmospheric model rapidly\ndiverges from temperate surface conditions towards a runaway greenhouse with\nrapidly escalating surface temperatures. We calculate transmission spectra for\nthe evolved atmosphere and discuss these spectra within the context of the\nJames Webb Space Telescope (JWST) Near-Infrared Spectrograph (NIRSpec)\ncapabilities. We thus demonstrate the detectability of the key atmospheric\nsignatures of possible runaway greenhouse transition states and outline the\nfuture prospects of characterizing potential Venus analogs.", "category": "astro-ph_EP" }, { "text": "Physical properties, transmission and emission spectra of the WASP-19\n planetary system from multi-colour photometry: We present new ground-based, multi-colour, broad-band photometric\nmeasurements of the physical parameters, transmission and emission spectra of\nthe transiting extrasolar planet WASP-19b. The measurements are based on\nobservations of 8 transits and four occultations using the 1.5m Danish\nTelescope, 14 transits at the PEST observatory, and 1 transit observed\nsimultaneously through four optical and three near-infrared filters, using the\nGROND instrument on the ESO 2.2m telescope. We use these new data to measure\nrefined physical parameters for the system. We find the planet to be more\nbloated and the system to be twice as old as initially thought. We also used\npublished and archived datasets to study the transit timings, which do not\ndepart from a linear ephemeris. We detected an anomaly in the GROND transit\nlight curve which is compatible with a spot on the photosphere of the parent\nstar. The starspot position, size, spot contrast and temperature were\nestablished. Using our new and published measurements, we assembled the\nplanet's transmission spectrum over the 370-2350 nm wavelength range and its\nemission spectrum over the 750-8000 nm range. By comparing these data to\ntheoretical models we investigated the theoretically-predicted variation of the\napparent radius of WASP-19b as a function of wavelength and studied the\ncomposition and thermal structure of its atmosphere. We conclude that: there is\nno evidence for strong optical absorbers at low pressure, supporting the common\nidea that the planet's atmosphere lacks a dayside inversion; the temperature of\nthe planet is not homogenized, because the high warming of its dayside causes\nthe planet to be more efficient in re-radiating than redistributing energy to\nthe night side; the planet seems to be outside of any current classification\nscheme.", "category": "astro-ph_EP" }, { "text": "Outbursting Comet P/2010 V1 (Ikeya-Murakami): A Miniature Comet Holmes: Short-period comet P/2010 V1 (Ikeya-Murakami, hereafter V1) was discovered\nvisually by two amateur astronomers. The appearance of the comet was peculiar,\nconsisting of an envelope, a spherical coma near the nucleus and a tail\nextending in the anti-solar direction. We investigated the brightness and the\nmorphological development of the comet by taking optical images with\nground-based telescopes. Our observations show that V1 experienced a\nlarge-scale explosion between UT 2010 October 31 and November 3. The color of\nthe comet was consistent with the Sun (g'-RC=0.61+-0.20, RC-IC=0.20+-0.20, and\nB-RC=0.93+-0.25), suggesting that dust particles were responsible for the\nbrightening. We used a dynamical model to understand the peculiar morphology,\nand found that the envelope consisted of small grains (0.3-1 micron) expanding\nat a maximum speed of 500+-40 m/s, while the tail and coma were composed of a\nwider range of dust particle sizes (0.4-570 micron) and expansion speeds 7-390\nm/s. The total mass of ejecta is ~5x10^8 kg and kinetic energy ~5x10^12 J.\nThese values are much smaller than in the historic outburst of 17P/Holmes in\n2007, but the energy per unit mass (1x10^4 J/kg) is comparable. The energy per\nunit mass is about 10% of the energy released during the crystallization of\namorphous water ice suggesting that crystallization of buried amorphous ice can\nsupply the mass and energy of the outburst ejecta.", "category": "astro-ph_EP" }, { "text": "Results from a set of three-dimensional numerical experiments of a hot\n Jupiter atmosphere: We present highlights from a large set of simulations of a hot Jupiter\natmosphere, nominally based on HD 209458b, aimed at exploring both the\nevolution of the deep atmosphere, and the acceleration of the zonal flow or\njet. We find the occurrence of a super-rotating equatorial jet is robust to\nchanges in various parameters, and over long timescales, even in the absence of\nstrong inner or bottom boundary drag. This jet is diminished in one simulation\nonly, where we strongly force the deep atmosphere equator-to-pole temperature\ngradient over long timescales. Finally, although the eddy momentum fluxes in\nour atmosphere show similarities with the proposed mechanism for accelerating\njets on tidally-locked planets, the picture appears more complex. We present\ntentative evidence for a jet driven by a combination of eddy momentum transport\nand mean flow.", "category": "astro-ph_EP" }, { "text": "An ATCA survey of debris disks at 7 millimeters: We present ATCA continuum observations at a wavelength of 6.8 mm of five\ndebris disks: $\\beta$ Pictoris, q$^1$ Eridani, HD 107146, HD 181327, and HD\n95086. These observations provide the detection at the longest wavelengths\nobtained to date for all these debris disks. By combining our 6.8 mm data with\nprevious detections at shorter sub-millimeter/millimeter wavelengths we measure\nthe long wavelength spectral index of these sources. We then use previous\nestimates for the temperature of the emitting dust to derive the spectral index\nof the dust emissivity. Under the assumption that all the detected flux comes\nfrom dust only, we constrain the slope of the solid size distribution, assumed\nto be a power-law. The values that we infer for the slope of the size\ndistribution range between about 3.36 and 3.50. We compare our findings with\nthe case of the Fomalhaut debris disk and use these results to test the\npredictions of collisional cascades of planetesimal belts.", "category": "astro-ph_EP" }, { "text": "Refined stellar, orbital and planetary parameters of the eccentric\n HAT-P-2 planetary system: We present refined parameters for the extrasolar planetary system HAT-P-2\n(also known as HD 147506), based on new radial velocity and photometric data.\nHAT-P-2b is a transiting extrasolar planet that exhibits an eccentric orbit. We\npresent a detailed analysis of the planetary and stellar parameters, yielding\nconsistent results for the mass and radius of the star, better constraints on\nthe orbital eccentricity, and refined planetary parameters. The improved\nparameters for the host star are M_star = 1.36 +/- 0.04 M_sun and R_star = 1.64\n+/- 0.08 R_sun, while the planet has a mass of M_p = 9.09 +/- 0.24 M_Jup and\nradius of R_p = 1.16 +/- 0.08 R_Jup. The refined transit epoch and period for\nthe planet are E = 2,454,387.49375 +/- 0.00074 (BJD) and P = 5.6334729 +/-\n0.0000061 (days), and the orbital eccentricity and argument of periastron are e\n= 0.5171 +/- 0.0033 and omega = 185.22 +/- 0.95 degrees. These orbital elements\nallow us to predict the timings of secondary eclipses with a reasonable\naccuracy of ~15 minutes. We also discuss the effects of this significant\neccentricity including the characterization of the asymmetry in the transit\nlight curve. Simple formulae are presented for the above, and these, in turn,\ncan be used to constrain the orbital eccentricity using purely photometric\ndata. These will be particularly useful for very high precision, space-borne\nobservations of transiting planets.", "category": "astro-ph_EP" }, { "text": "Searching for the HR 8799 Debris Disk with HST/STIS: We present a new algorithm for space telescope high contrast imaging of\nclose-to-face-on planetary disks called Optimized Spatially Filtered (OSFi)\nnormalization. This algorithm is used on HR 8799 Hubble Space Telescope (HST)\ncoronagraphic archival data, showing an over-luminosity after reference star\npoint spread function (PSF) subtraction that may be from the inner disk and/or\nplanetesimal belt components of this system. The PSF-subtracted radial profiles\nin two separate epochs from 2011 and 2012 are consistent with one another, and\nself-subtraction shows no residual in both epochs. We explore a number of\npossible false-positive scenarios that could explain this residual flux,\nincluding telescope breathing, spectral differences between HR 8799 and the\nreference star, imaging of the known warm inner disk component, OSFi algorithm\nthroughput and consistency with the standard spider normalization HST PSF\nsubtraction technique, and coronagraph misalignment from pointing accuracy. In\ncomparison to another similar STIS dataset, we find that the over-luminosity is\nlikely a result of telescope breathing and spectral difference between HR 8799\nand the reference star. Thus, assuming a non-detection, we derive upper limits\non the HR 8799 dust belt mass in small grains. In this scenario, we find that\nthe flux of these micron-sized dust grains leaving the system due to radiation\npressure is small enough to be consistent with measurements of other debris\ndisk halos.", "category": "astro-ph_EP" }, { "text": "High precision Symplectic Integrators for the Solar System: Using a Newtonian model of the Solar System with all 8 planets, we perform\nextensive tests on various symplectic integrators of high orders, searching for\nthe best splitting scheme for long term studies in the Solar System. These\ncomparisons are made in Jacobi and Heliocentric coordinates and the\nimplementation of the algorithms is fully detailed for practical use. We\nconclude that high order integrators should be privileged, with a preference\nfor the new $(10,6,4)$ method of (Blanes et al., 2012)", "category": "astro-ph_EP" }, { "text": "Collision detection for N-body Kepler systems: In a Keplerian system, a large number of bodies orbit a central mass.\nAccretion disks, protoplanetary disks, asteroid belts, and planetary rings are\nexamples. Simulations of these systems require algorithms that are\ncomputationally efficient. The inclusion of collisions in the simulations is\nchallenging but important. We intend to calculate the time of collision of two\nastronomical bodies in intersecting Kepler orbits as a function of the orbital\nelements. The aim is to use the solution in an analytic propagator ($N$-body\nsimulation) that jumps from one collision event to the next. We outline an\nalgorithm that maintains a list of possible collision pairs ordered\nchronologically. At each step (the soonest event on the list), only the\nparticles created in the collision can cause new collision possibilities. We\nestimate the collision rate, the length of the list, and the average change in\nthis length at an event, and study the efficiency of the method used. We find\nthat the collision-time problem is equivalent to finding the grid point between\ntwo parallel lines that is closest to the origin. The solution is based on the\ncontinued fraction of the ratio of orbital periods. Due to the large jumps in\ntime, the algorithm can beat tree codes (octree and $k$-d tree codes can\nefficiently detect collisions) for specific systems such as the Solar System\nwith $N<10^8$. However, the gravitational interactions between particles can\nonly be treated as gravitational scattering or as a secular perturbation, at\nthe cost of reducing the time-step or at the cost of accuracy. While\nsimulations of this size with high-fidelity propagators can already span vast\ntimescales, the high efficiency of the collision detection allows many runs\nfrom one initial state or a large sample set, so that one can study statistics.", "category": "astro-ph_EP" }, { "text": "Revisiting the Full Sets of Orbital Parameters for the XO-3 System: No\n evidence for Temporal Variation of the Spin-Orbit Angle: We present 12 new transit light curves and 16 new out-of-transit radial\nvelocity measurements for the XO-3 system. By modelling our newly collected\nmeasurements together with archival photometric and Doppler velocimetric data,\nwe confirmed the unusual configuration of the XO-3 system, which contains a\nmassive planet ($M_P=11.92^{+0.59}_{-0.63} M_J$) on a relatively eccentric\n($e=0.2853^{+0.0027}_{-0.0026}$) and short-period ($3.19152 \\pm 0.00145\\,$day)\norbit around a massive star ($M_*=1.219^{+0.090}_{-0.095} M_{\\odot}$).\nFurthermore, we find no strong evidence for a temporal change of either $V\\sin\ni_{*}$ (and by extension, the stellar spin vector of XO-3), or the transit\nprofile (and thus orbital angular momentum vector of XO-3b). We conclude that\nthe discrepancy in previous Rossiter-McLaughlin measurements ($70.0^{\\circ} \\pm\n15.0^{\\circ}$ (Hebrard et al. 2008); $37.3^{\\circ} \\pm 3.7^{\\circ}$ (Winn et\nal. 2009); $37.3^{\\circ} \\pm 3.0^{\\circ}$ (Hirano et al. 2011)) may have\nstemmed from systematic noise sources.", "category": "astro-ph_EP" }, { "text": "Multiband Optical Observation of P/2010 A2 Dust Tail: An inner main-belt asteroid, P/2010 A2, was discovered on January 6th, 2010.\nBased on its orbital elements, it is considered that the asteroid belongs to\nthe Flora collisional family, where S-type asteroids are common, whilst showing\na comet-like dust tail. Although analysis of images taken by the Hubble Space\nTelescope and Rosetta spacecraft suggested that the dust tail resulted from a\nrecent head-on collision between asteroids (Jewitt et al. 2010; Snodgrass et\nal. 2010), an alternative idea of ice sublimation was suggested based on the\nmorphological fitting of ground-based images (Moreno et al. 2010). Here, we\nreport a multiband observation of P/2010 A2 made on January 2010 with a 105 cm\ntelescope at the Ishigakijima Astronomical Observatory. Three broadband\nfilters, $g'$, $R_c$, and $I_c$, were employed for the observation. The unique\nmultiband data reveals that the reflectance spectrum of the P/2010 A2 dust tail\nresembles that of an Sq-type asteroid or that of ordinary chondrites rather\nthan that of an S-type asteroid. Due to the large error of the measurement, the\nreflectance spectrum also resembles the spectra of C-type asteroids, even\nthough C-type asteroids are uncommon in the Flora family. The reflectances\nrelative to the $g'$-band (470 nm) are 1.096$\\pm$0.046 at the $R_c$-band (650\nnm) and 1.131$\\pm$0.061 at the $I_c$-band (800 nm). We hypothesize that the\nparent body of P/2010 A2 was originally S-type but was then shattered upon\ncollision into scaterring fresh chondritic particles from the interior, thus\nforming the dust tail.", "category": "astro-ph_EP" }, { "text": "Coupling thermal evolution of planets and hydrodynamic atmospheric\n escape in MESA: The long-term evolution of hydrogen-dominated atmospheres of sub-Neptune-like\nplanets is mostly controlled by two factors: a slow dissipation of the\ngravitational energy acquired at the formation (known as thermal evolution) and\natmospheric mass loss. Here, we use MESA to self-consistently couple the\nthermal evolution model of lower atmospheres with a realistic hydrodynamical\natmospheric evaporation prescription. To outline the main features of such\ncoupling, we simulate planets with a range of core masses (5-20 Mearth) and\ninitial atmospheric mass fractions (0.5-30%), orbiting a solar-like star at 0.1\nau. In addition to our computed evolutionary tracks, we also study the\nstability of planetary atmospheres, showing that the atmospheres of light\nplanets can be completely removed within 1 Gyr, and that compact atmospheres\nhave a better survival rate. From a detailed comparison between our results and\nthe output of the previous-generation models, we show that coupling between\nthermal evolution and atmospheric evaporation considerably affects the thermal\nstate of atmospheres for low-mass planets and, consequently, changes the\nrelationship between atmospheric mass fraction and planetary parameters. We,\ntherefore, conclude that self-consistent consideration of the thermal evolution\nand atmospheric evaporation is of crucial importance for evolutionary modeling\nand a better characterization of planetary atmospheres. From our simulations,\nwe derive an analytical expression between the planetary radius and atmospheric\nmass fraction at different ages. In particular, we find that, for a given\nobserved planetary radius, the predicted atmospheric mass fraction changes as\nage^0.11.", "category": "astro-ph_EP" }, { "text": "A Giant Planet Around a Metal-poor Star of Extragalactic Origin: Stars in their late stage of evolution, such as Horizontal Branch stars, are\nstill largely unexplored for planets. We report the detection of a planetary\ncompanion around HIP 13044, a very metal-poor star on the red Horizontal\nBranch, based on radial velocity observations with a high-resolution\nspectrograph at the 2.2-m MPG/ESO telescope. The star's periodic radial\nvelocity variation of P=16.2 days caused by the planet can be distinguished\nfrom the periods of the stellar activity indicators. The minimum mass of the\nplanet is 1.25 Jupiter masses and its orbital semi-major axis 0.116 AU. Because\nHIP 13044 belongs to a group of stars that have been accreted from a disrupted\nsatellite galaxy of the Milky Way, the planet most likely has an extragalactic\norigin.", "category": "astro-ph_EP" }, { "text": "Aqueous alteration on main belt primitive asteroids: results from\n visible spectroscopy: This work focuses on the study of the aqueous alteration process which acted\nin the main belt and produced hydrated minerals on the altered asteroids. The\naqueous alteration is particularly important for unraveling the processes\noccurring during the earliest times of the Solar System history, as it can give\ninformation both on the asteroids thermal evolution and on the localization of\nwater sources in the asteroid belt. We present new spectral observations in the\nvisible region of 80 asteroids belonging to the primitive classes C, G, F, B\nand P. We combine the present observations with the visible spectra of\nasteroids available in the literature for a total of 600 primitive main belt\nasteroids. Our analysis shows that the aqueous alteration sequence starts from\nthe P-type objects, practically unaltered, and increases through the F, B, C,\nand G asteroids. Around 50% of the observed C-type asteroids show absorption\nfeatures in the vis. range due to hydrated silicates, implying that more than\n70% of them will have a 3 $\\mu$m absorption band and thus hydrated minerals on\ntheir surfaces. The process dominates in primitive asteroids located between\n2.3 and 3.1 AU, that is at smaller heliocentric distances than previously\nsuggested. The aqueous alteration process dominates in the 50--240 km sized\nprimitive asteroids, while it is less effective for bodies smaller than 50 km.\nNo correlation is found between the aqueous alteration process and the\nasteroids albedo or orbital elements. Comparing the $\\sim$ 0.7 $\\mu$m band\nparameters of hydrated silicates and CM2 carbonaceous chondrites, we see that\nthe band center of meteorites is at longer wavelengths than that of asteroids.\nThis difference on center positions may be attributed to different minerals\nabundances, and to the fact that CM2 available on Earth might not be\nrepresentative of the whole aqueous altered asteroids population.", "category": "astro-ph_EP" }, { "text": "Molecular Outgassing in Centaur 29P/Schwassmann-Wachmann 1 During Its\n Exceptional 2021 Outburst: Coordinated Multi-Wavelength Observations Using\n nFLASH at APEX and iSHELL at the NASA-IRTF: The extraordinary 2021 September-October outburst of Centaur\n29P/Schwassmann-Wachmann 1 afforded an opportunity to test the composition of\nprimitive Kuiper disk material at high sensitivity. We conducted nearly\nsimultaneous multi-wavelength spectroscopic observations of\n29P/Schwassmann-Wachmann 1 using iSHELL at the NASA Infrared Telescope Facility\nand nFLASH at the Atacama Pathfinder EXperiment (APEX) on 2021 October 6, with\nfollow-up APEX/nFLASH observations on 2021 October 7 and 2022 April 3. This\ncoordinated campaign between near-infrared and radio wavelengths enabled us to\nsample molecular emission from a wealth of coma molecules and to perform\nmeasurements that cannot be accomplished with either wavelength alone. We\nsecurely detected CO emission on all dates with both facilities, including\nvelocity-resolved spectra of the CO (J=2-1) transition with APEX/nFLASH and\nmultiple CO (v=1-0) rovibrational transitions with IRTF/iSHELL. We report\nrotational temperatures, coma kinematics, and production rates for CO and\nstringent (3-sigma) upper limits on abundance ratios relative to CO for CH4,\nC2H6, CH3OH, H2CO, CS, and OCS. Our upper limits for CS/CO and OCS/CO represent\ntheir first values in the literature for this Centaur. Upper limits for CH4,\nC2H6, CH3OH, and H2CO are the most stringent reported to date, and are most\nsimilar to values found in ultra CO-rich Oort cloud comet C/2016 R2\n(PanSTARRS), which may have implications for how ices are preserved in cometary\nnuclei. We demonstrate the superb synergy of coordinated radio and\nnear-infrared measurements, and advocate for future small body studies that\njointly leverage the capabilities of each wavelength.", "category": "astro-ph_EP" }, { "text": "Cooling-Induced Vortex Decay in Keplerian Disks: Vortices are readily produced by hydrodynamical instabilities, such as the\nRossby wave instability, in protoplanetary disks. However, large-scale\nasymmetries indicative of dust-trapping vortices are uncommon in sub-millimeter\ncontinuum observations. One possible explanation is that vortices have short\nlifetimes. In this paper, we explore how radiative cooling can lead to vortex\ndecay. Elliptical vortices in Keplerian disks go through adiabatic heating and\ncooling cycles. Radiative cooling modifies these cycles and generates\nbaroclinicity that changes the potential vorticity of the vortex. We show that\nthe net effect is typically a spin down, or decay, of the vortex for a\nsub-adiabatic radial stratification. We perform a series of two-dimensional\nshearing box simulations, varying the gas cooling (or relaxation) time, $t_{\\rm\ncool}$, and initial vortex strength. We measure the vortex decay half-life,\n$t_{\\rm half}$, and find that it can be roughly predicted by the timescale\nratio $t_{\\rm cool}/t_{\\rm turn}$, where $t_{\\rm turn}$ is the vortex\nturnaround time. Decay is slow in both the isothermal ($t_{\\rm cool}\\ll t_{\\rm\nturn}$) and adiabatic ($t_{\\rm cool}\\gg t_{\\rm turn}$) limits; it is fastest\nwhen $t_{\\rm cool}\\sim0.1\\,t_{\\rm turn}$, where $t_{\\rm half}$ is as short as\n$\\sim300$ orbits. At tens of au where disk rings are typically found, $t_{\\rm\nturn}$ is likely much longer than $t_{\\rm cool}$, potentially placing vortices\nin the fast decay regime.", "category": "astro-ph_EP" }, { "text": "An analytic solution to measure the gas size in protoplanetary discs in\n the viscous self-similar scenario: In order to understand which mechanism is responsible for accretion in\nprotoplanetary discs, a robust knowledge of the observed disc radius using gas\ntracers such as $^{12}$CO and other CO isotopologues is pivotal. Indeed, the\ntwo main theories proposed, viscous accretion and wind-driven accretion,\npredict different time evolution for the disc radii. In this Letter, we present\nan analytical solution for the evolution of the disc radii in viscously\nevolving protoplanetary discs using $^{12}$CO as a tracer, under the assumption\nthat the $^{12}$CO radius is the radius where the surface density of the disc\nis equal to the threshold for CO photo-dissociation. We discuss the properties\nof the solution and the limits of its applicability as a simple numerical\nprescription to evaluate the observed disc radii of populations of discs. Our\nresults suggest that, in addition to photo-dissociation, also freeze out plays\nan important role in setting the disc size. We find an effective reduction of\nthe CO abundance by about two orders of magnitude at the location of CO\nphoto-dissociation, which however should not be interpreted as the bulk\nabundance of CO in the disc. The use of our analytical solution will allow to\ncompute disc sizes for large quantities of models without using expensive\ncomputational resources such as radiative transfer calculations.", "category": "astro-ph_EP" }, { "text": "Physical Characterization of Metal-rich Near-Earth Asteroids 6178 (1986\n DA) and 2016 ED85: Metal-rich near-Earth asteroids (NEAs) represent a small fraction of the NEA\npopulation that is mostly dominated by S- and C-type asteroids. Because of\nthis, their identification and study provide us with a unique opportunity to\nlearn more about the formation and evolution of this particular type of bodies,\nas well as their relationship with meteorites found on Earth. We present\nnear-infrared (NIR) spectroscopic data of NEAs 6178 (1986 DA) and 2016 ED85. We\nfound that the spectral characteristics of these objects are consistent with\nthose of metal-rich asteroids, showing red slopes, convex shapes, and a weak\npyroxene absorption band at $\\sim$0.93 $\\mu$m. The compositional analysis\nshowed that they have a pyroxene chemistry of Fs$_{40.6\\pm3.3}$Wo$_{8.9\\pm1.1}$\nand a mineral abundance of $\\sim$15% pyroxene and 85% metal. We determined that\nthese objects were likely transported to the near-Earth space via the 5:2 mean\nmotion resonance with Jupiter. Asteroid spectra were compared with the spectra\nof mesosiderites and bencubbinites. Differences in the NIR spectra and pyroxene\nchemistry suggest that bencubbinites are not good meteorite analogs.\nMesosiderites were found to have a similar pyroxene chemistry and produced a\ngood spectral match when metal was added to the silicate component. We\nestimated that the amounts of Fe, Ni, Co, and the platinum group metals present\nin 1986 DA could exceed the reserves worldwide.", "category": "astro-ph_EP" }, { "text": "A dearth of small particles in the transiting material around the white\n dwarf WD 1145+017: White dwarf WD 1145+017 is orbited by several clouds of dust, possibly\nemanating from actively disintegrating bodies. These dust clouds reveal\nthemselves through deep, broad, and evolving transits in the star's light\ncurve. Here, we report two epochs of multi-wavelength photometric observations\nof WD 1145+017, including several filters in the optical, K$_\\mathrm{s}$ and\n4.5 $\\mu$m bands in 2016 and 2017. The observed transit depths are different at\nthese wavelengths. However, after correcting for excess dust emission at\nK$_\\mathrm{s}$ and 4.5 $\\mu$m, we find the transit depths for the white dwarf\nitself are the same at all wavelengths, at least to within the observational\nuncertainties of $\\sim$5%-10%. From this surprising result, and under the\nassumption of low optical depth dust clouds, we conclude that there is a\ndeficit of small particles (with radii $s \\lesssim$ 1.5 $\\mu$m) in the\ntransiting material. We propose a model wherein only large particles can\nsurvive the high equilibrium temperature environment corresponding to 4.5 hr\norbital periods around WD 1145+017, while small particles sublimate rapidly. In\naddition, we evaluate dust models that are permitted by our measurements of\ninfrared emission.", "category": "astro-ph_EP" }, { "text": "Ks band secondary eclipses of WASP-19b and WASP-43b with the\n Anglo-Australian Telescope: We report new Ks band secondary eclipse observations for the hot-Jupiters\nWASP-19b and WASP-43b. Using the IRIS2 infrared camera on the Anglo-Australian\nTelescope (AAT), we measured significant secondary eclipses for both planets,\nwith depths of 0.287 -0.020/+0.020% and 0.181 -0.027/+0.027% for WASP-19b and\nWASP-43b respectively. We compare the observations to atmosphere models from\nthe VSTAR line-by-line radiative transfer code, and examine the effect of C/O\nabundance, top layer haze, and metallicities on the observed spectra. We\nperformed a series of signal injection and recovery exercises on the observed\nlight curves to explore the detection thresholds of the AAT+IRIS2 facility. We\nfind that the optimal photometric precision is achieved for targets brighter\nthan Kmag = 9, for which eclipses as shallow as 0.05% are detectable at >5\nsigma significance.", "category": "astro-ph_EP" }, { "text": "Asteroid thermal modeling in the presence of reflected sunlight with an\n application to WISE/NEOWISE observational data: This study addresses thermal modeling of asteroids with a new derivation of\nthe Near Earth Asteroid Thermal (NEATM) model which correctly accounts for the\npresence of reflected sunlight in short wave IR bands. Kirchhoff's law of\nthermal radiation applies to this case and has important implications. New\ninsight is provided into the eta parameter in the NEATM model and it is\nextended to thermal models besides NEATM. The role of surface material\nproperties on eta is examined using laboratory spectra of meteorites and other\nasteroid compositional proxies; the common assumption that emissivity e = 0.9\nin asteroid thermal models may not be justified and can lead to misestimating\nphysical parameters. In addition, indeterminacy in thermal modeling can limit\nits ability to uniquely determine temperature and other physical properties. A\nnew curve fitting approach allows thermal modeling to be done independent of\nvisible band observational parameters such as the absolute magnitude H. These\nnew thermal modeling techniques are applied to observational data for selected\nasteroids from the WISE/NEOWISE mission. The previous NEOWISE analysis assumes\nKirchhoff's law does not apply. It also deviates strongly from established\nstatistical practice and systematically underestimates the sampling error\ninherent in observing potentially irregular asteroids from a finite sample of\nobservations. As a result, the new analysis finds asteroid diameter and other\nphysical properties that have large differences from published NEOWISE results,\nwith greatly increased error estimates. NEOWISE results have a claimed +/-10%\naccuracy for diameter estimates, but this is unsupported. ABSTRACT CONTINUED IN\nPDF...", "category": "astro-ph_EP" }, { "text": "Early formation of planetary building blocks inferred from Pb isotopic\n ages of chondrules: The most abundant components of primitive meteorites (chondrites) are\nmillimeter-sized glassy spherical chondrules formed by transient melting events\nin the solar protoplanetary disk. Using Pb-Pb dates of 22 individual\nchondrules, we show that primary production of chondrules in the early solar\nsystem was restricted to the first million years after formation of the Sun and\nthat these existing chondrules were recycled for the remaining lifetime of the\nprotoplanetary disk. This is consistent with a primary chondrule formation\nepisode during the early high-mass accretion phase of the protoplanetary disk\nthat transitions into a longer period of chondrule reworking. An abundance of\nchondrules at early times provides the precursor material required to drive the\nefficient and rapid formation of planetary objects via chondrule accretion.", "category": "astro-ph_EP" }, { "text": "Kepler-91b: a planet at the end of its life. Planet and giant host star\n properties via light-curve variations: The evolution of planetary systems is intimately linked to the evolution of\ntheir host star. Our understanding of the whole planetary evolution process is\nbased on the large planet diversity observed so far. To date, only few tens of\nplanets have been discovered orbiting stars ascending the Red Giant Branch.\nAlthough several theories have been proposed, the question of how planets die\nremains open due to the small number statistics. In this work we study the\ngiant star Kepler-91 (KOI-2133) in order to determine the nature of a\ntransiting companion. This system was detected by the Kepler Space Telescope.\nHowever, its planetary confirmation is needed. We confirm the planetary nature\nof the object transiting the star Kepler-91 by deriving a mass of $\nM_p=0.88^{+0.17}_{-0.33} ~M_{\\rm Jup}$ and a planetary radius of\n$R_p=1.384^{+0.011}_{-0.054} ~R_{\\rm Jup}$. Asteroseismic analysis produces a\nstellar radius of $R_{\\star}=6.30\\pm 0.16 ~R_{\\odot}$ and a mass of\n$M_{\\star}=1.31\\pm 0.10 ~ M_{\\odot} $. We find that its eccentric orbit\n($e=0.066^{+0.013}_{-0.017}$) is just $1.32^{+0.07}_{-0.22} ~ R_{\\star}$ away\nfrom the stellar atmosphere at the pericenter. Kepler-91b could be the previous\nstage of the planet engulfment, recently detected for BD+48 740. Our\nestimations show that Kepler-91b will be swallowed by its host star in less\nthan 55 Myr. Among the confirmed planets around giant stars, this is the\nplanetary-mass body closest to its host star. At pericenter passage, the star\nsubtends an angle of $48^{\\circ}$, covering around 10% of the sky as seen from\nthe planet. The planetary atmosphere seems to be inflated probably due to the\nhigh stellar irradiation.", "category": "astro-ph_EP" }, { "text": "The Habitable Zones of Pre-Main-Sequence Stars: We calculate the pre-main-sequence HZ for stars of spectral classes F to M.\nThe spatial distribution of liquid water and its change during the\npre-main-sequence phase of protoplanetary systems is important in understanding\nhow planets become habitable. Such worlds are interesting targets for future\nmissions because the coolest stars could provide habitable conditions for up to\n2.5 billion years post-accretion. Moreover, for a given star type, planetary\nsystems are more easily resolved because of higher pre-main-sequence stellar\nluminosities, resulting in larger planet to star separation for cool stars than\nis the case for the traditional main-sequence (MS) habitable zone (HZ). We use\n1D radiative-convective climate and stellar evolutionary models to calculate\npre-main-sequence HZ distances for F1 to M8 stellar types. We also show that\naccreting planets that are later located in the traditional MS HZ orbiting\nstars cooler than a K5 (including the full range of M-stars) receive stellar\nfluxes that exceed the runaway greenhouse threshold, and thus may lose\nsubstantial amounts of water initially delivered to them. We predict that\nM-star planets need to initially accrete more water than Earth did or,\nalternatively, have additional water delivered later during the long\npre-main-sequence phase to remain habitable. Our findings are also consistent\nwith recent claims that Venus lost its water during accretion.", "category": "astro-ph_EP" }, { "text": "Phase Diagram for the Methane-Ethane System and its Implications for\n Titan's Lakes: On Titan, methane (CH4) and ethane (C2H6) are the dominant species found in\nthe lakes and seas. In this study, we have combined laboratory work and\nmodeling to refine the methane-ethane binary phase diagram at low temperatures\nand probe how the molecules interact at these conditions. We used visual\ninspection for the liquidus and Raman spectroscopy for the solidus. Through\nthese methods we determined a eutectic point of 71.15$\\pm$0.5 K at a\ncomposition of 0.644$\\pm$0.018 methane - 0.356$\\pm$0.018 ethane mole fraction\nfrom the liquidus data. Using the solidus data, we found a eutectic isotherm\ntemperature of 72.2 K with a standard deviation of 0.4 K. In addition to\nmapping the binary system, we looked at the solid-solid transitions of pure\nethane and found that, when cooling, the transition of solid I-III occurred at\n89.45$\\pm$0.2 K. The warming sequence showed transitions of solid III-II\noccurring at 89.85$\\pm$0.2 K and solid II-I at 89.65$\\pm$0.2 K. Ideal\npredictions were compared to molecular dynamics simulations to reveal that the\nmethane-ethane system behaves almost ideally, and the largest deviations occur\nas the mixing ratio approaches the eutectic composition.", "category": "astro-ph_EP" }, { "text": "A Northern Ecliptic Survey for Solar System Science: Making an inventory of the Solar System is one of the four fundamental\nscience requirements for the Large Synoptic Survey Telescope (LSST). The\ncurrent baseline footprint for LSST's main Wide-Fast-Deep (WFD) Survey observes\nthe sky below 0$^\\circ$ declination, which includes only half of the ecliptic\nplane. Critically, key Solar System populations are asymmetrically distributed\non the sky: they will be entirely missed, or only partially mapped, if only the\nWFD occurs. We propose a Northern Ecliptic Spur (NES) mini survey, observing\nthe northern sky up to +10$^\\circ$ ecliptic latitude, to maximize Solar System\nscience with LSST. The mini survey comprises a total area of $\\sim$5800\ndeg$^2$/604 fields, with 255 observations/field over the decade, split between\ng,r, and z bands. Our proposed survey will 1) obtain a census of main-belt\ncomets; 2) probe Neptune's past migration history, by exploring the resonant\nstructure of the Kuiper belt and the Neptune Trojan population; 3) explore the\norigin of Inner Oort cloud objects and place significant constraints on the\nexistence of a hypothesized planet beyond Neptune; and 4) enable precise\npredictions of KBO stellar occultations. These high-ranked science goals of the\nSolar System Science Collaboration are only achievable with this proposed\nnorthern survey.", "category": "astro-ph_EP" }, { "text": "The multi-wavelength phase curves of small bodies: Phase coloring: Context. Small bodies change their brightness due to different motives:\nRotation along their axis or axes, combined with irregular shapes and/or\nchanging surface properties, or changes in the geometry of observations. In\nthis work, we tackle the problem of Phase curves, which show the change in\nbrightness due to changes in the fraction of illuminated surface as seen by the\nobserver. Aims. We aim to study the effect of the phase curves in the five\nwavelengths of the Sloan Digital Sky Survey in scores of objects (several tens\nof thousands), focusing particularly on the spectral slopes and the colors and\ntheir changes with phase angle. Methods. We used a Bayesian inference method\nand Monte Carlo techniques to retrieve the absolute magnitudes in five\nwavelengths, using the results to study the phase coloring effect in different\nbins of the semi-major axis. Results. We obtained absolute magnitudes in the\nfive filters for over 40 000 objects. Although some outliers are identified,\nmost of the usual color-color space is recovered by the data presented. We also\ndetect a dual behavior in the spectral slopes, with a change at\n${\\alpha\\approx}$ 5 deg.", "category": "astro-ph_EP" }, { "text": "Meteor observations with Mini-MegaTORTORA wide-field monitoring system: Here we report on the results of meteor observations with 9-channel\nMini-MegaTORTORA (MMT-9) wide-field optical monitoring system with high\ntemporal resolution. During first 1.5 years of operation more than 90 thousands\nof meteors have been detected, at a rate of 300-350 per night, with durations\nfrom 0.1 to 2.5 seconds and angular velocities up to 38 degrees per second. The\nfaintest detected meteors has the peak brightness about 10 mag, while the\nmajority - from 4 to 8 mag. Some of the meteors have been observed in BVR\nfilters simultaneously. Color variations along the trail for them are\ndetermined. All parameters of detected meteors are published online. The\ndatabase also includes the information on 10 thousands meteors detected by our\nprevious FAVOR camera in 2006-2009 years.", "category": "astro-ph_EP" }, { "text": "Precession due to a close binary system: An alternative explanation for\n \u03bd-Octantis?: We model the secular evolution of a star's orbit when it has a nearby binary\nsystem. We assume a hierarchical triple system where the inter-binary distance\nis small in comparison with the distance to the star. We show that the major\nsecular effect is precession of the star's orbit around the binary system's\ncentre of mass. We explain how we can obtain this precession rate from the\nstar's radial velocity data, and thus infer the binary system's parameters. We\nshow that the secular effect of a nearby binary system on the star's radial\nvelocity can sometimes mimic a planet. We analyze the radial velocity data for\n{\\nu}-octantis A which has a nearby companion ({\\nu}-octantis B) and we obtain\nretrograde precession of (-0.86 \\pm 0.02)\\degree/yr. We show that if\n{\\nu}-octantis B was itself a double star, it could mimic a signal with\nsimilarities to that previously identified as a planet of {\\nu}-octantis A.\nNevertheless, we need more observations in order to decide in favor of the\ndouble star hypothesis.", "category": "astro-ph_EP" }, { "text": "Detection of He I $\\lambda10830$ \u00c5 absorption on HD 189733 b with\n CARMENES high-resolution transmission spectroscopy: We present three transit observations of HD 189733 b obtained with the\nhigh-resolution spectrograph CARMENES at Calar Alto. A strong absorption signal\nis detected in the near-infrared He I triplet at 10830 \\AA{} in all three\ntransits. During mid-transit, the mean absorption level is $0.88\\pm0.04$ %\nmeasured in a $\\pm$10 km s$^{-1}$ range at a net blueshift of $-3.5\\pm0.4$ km\ns$^{-1}$ (10829.84--10830.57 \\AA{}). The absorption signal exhibits radial\nvelocities of $+6.5\\pm3.1$ km s$^{-1}$ and $-12.6\\pm1.0$ km s$^{-1}$ during\ningress and egress, respectively; measured in the planetary rest frame. We show\nthat stellar activity related pseudo-signals interfere with the planetary\natmospheric absorption signal. They could contribute as much as 80% of the\nobserved signal and might also affect the radial velocity signature, but\npseudo-signals are very unlikely to explain the entire signal. The observed\nline ratio between the two unresolved and the third line of the He I triplet is\n$2.8\\pm0.2$, which strongly deviates from the value expected for an optically\nthin atmospheres. When interpreted in terms of absorption in the planetary\natmosphere, this favors a compact helium atmosphere with an extent of only 0.2\nplanetary radii and a substantial column density on the order of $4\\times\n10^{12}$ cm$^{-2}$. The observed radial velocities can be understood either in\nterms of atmospheric circulation with equatorial superrotation or as a sign of\nan asymmetric atmospheric component of evaporating material. We detect no clear\nsignature of ongoing evaporation, like pre- or post-transit absorption, which\ncould indicate material beyond the planetary Roche lobe, or radial velocities\nin excess of the escape velocity. These findings do not contradict planetary\nevaporation, but only show that the detected helium absorption in HD 189733 b\ndoes not trace the atmospheric layers that show pronounced escape signatures.", "category": "astro-ph_EP" }, { "text": "ACCESS: An optical transmission spectrum of the high-gravity, hot\n Jupiter HAT-P-23b: We present a new ground-based visible transmission spectrum of the\nhigh-gravity, hot Jupiter HAT-P-23b, obtained as part of the ACCESS project. We\nderive the spectrum from five transits observed between 2016 and 2018, with\ncombined wavelength coverage between 5200 {\\AA} - 9269 {\\AA} in 200 {\\AA} bins,\nand with a median precision of 247 ppm per bin. HAT-P-23b's relatively high\nsurface gravity (g ~ 30 m/s^2), combined with updated stellar and planetary\nparameters from Gaia DR2, gives a 5-scale-height signal of 384 ppm for a\nhydrogen-dominated atmosphere. Bayesian models favor a clear atmosphere for the\nplanet with the tentative presence of TiO, after simultaneously modeling\nstellar contamination, using spots parameter constraints from photometry. If\nconfirmed, HAT-P-23b would be the first example of a high-gravity gas giant\nwith a clear atmosphere observed in transmission at optical/NIR wavelengths;\ntherefore, we recommend expanding observations to the UV and IR to confirm our\nresults and further characterize this planet. This result demonstrates how\ncombining transmission spectroscopy of exoplanet atmospheres with long-term\nphotometric monitoring of the host stars can help disentangle the exoplanet and\nstellar activity signals.", "category": "astro-ph_EP" }, { "text": "Protons in the near-lunar wake observed by the Sub-keV Atom Reflection\n Analyzer on board Chandrayaan-1: Significant proton fluxes were detected in the near wake region of the Moon\nby an ion mass spectrometer on board Chandrayaan-1. The energy of these\nnightside protons is slightly higher than the energy of the solar wind protons.\nThe protons are detected close to the lunar equatorial plane at a $140^{\\circ}$\nsolar zenith angle, i.e., ~50$^{\\circ}$ behind the terminator at a height of\n100 km. The protons come from just above the local horizon, and move along the\nmagnetic field in the solar wind reference frame. We compared the observed\nproton flux with the predictions from analytical models of an electrostatic\nplasma expansion into a vacuum. The observed velocity was higher than the\nvelocity predicted by analytical models by a factor of 2 to 3. The simple\nanalytical models cannot explain the observed ion dynamics along the magnetic\nfield in the vicinity of the Moon.", "category": "astro-ph_EP" }, { "text": "Making hot Jupiters in stellar clusters II: efficient formation in\n binary systems: Observations suggested that the occurrence rate of hot Jupiters (HJs) in open\nclusters is largely consistent with the field ($\\sim1\\%$) but in the\nbinary-rich cluster M67, the rate is $\\sim5\\%$. How does the cluster\nenvironment boost HJ formation via the high-eccentricity tidal migration\ninitiated by the extreme-amplitude von Zeipel-Lidov-Kozai (XZKL) mechanism\nforced by a companion star? Our analytical treatment shows that the cluster's\ncollective gravitational potential alters the companion's orbit slowly, which\nmay render the star-planet-companion configuration XZKL-favourable, a\nphenomenon only possible for very wide binaries. We have also performed direct\nGyr $N$-body simulations of the star cluster evolution and XZKL of planets'\norbit around member stars. We find that an initially-single star may acquire a\ncompanion star via stellar scattering and the companion may enable XZKL in the\nplanets' orbit. Planets around an initially-binary star may also be\nXZKL-activated by the companion. In both scenarios, the companion's orbit has\nlikely been significantly changed by star scattering and the cluster potential\nbefore XZKL occurs in the planets' orbits. Across different cluster models,\n0.8\\%-3\\% of the planets orbiting initially-single stars have experienced XZKL\nwhile the fraction is 2\\%-26\\% for initially-binary stars. Notably, the\nejection fraction is similar to or appreciably smaller than XZKL. Around a star\nthat is binary at 1 Gyr, 13\\%-32\\% of its planets have undergone XZKL, and\ncombined with single stars, the overall XZKL fraction is 3\\%-21\\%, most\naffected by the cluster binarity. If 10\\% of the stars in M67 host a giant\nplanet, our model predicts an HJ occurrence rate of $\\sim1\\%$. We suggest that\nHJ surveys target old, high-binarity, not-too-dense open clusters and\nprioritise wide binaries to maximise HJ yield.", "category": "astro-ph_EP" }, { "text": "X-ray irradiation and evaporation of the four young planets around V1298\n Tau: Planets around young stars are thought to undergo atmospheric evaporation due\nto the high magnetic activity of the host stars. Here we report on X-ray\nobservations of V1298 Tau, a young star with four transiting exoplanets. We use\nX-ray observations of the host star with Chandra and ROSAT to measure the\ncurrent high-energy irradiation level of the planets, and employ a model for\nthe stellar activity evolution together with exoplanetary mass loss to estimate\nthe possible evolution of the planets. We find that V1298 Tau is X-ray bright\nwith $\\log L_X$ [erg/s] $=30.1$ and has a mean coronal temperature of $\\approx\n9$ MK. This places the star amongst the more X-ray luminous ones at this\nstellar age. We estimate the radiation-driven mass loss of the exoplanets, and\nfind that it depends sensitively on the possible evolutionary spin-down tracks\nof the star as well as on the current planetary densities. Assuming the planets\nare of low density due to their youth, we find that the innermost two planets\ncan lose significant parts of their gaseous envelopes, and could be evaporated\ndown to their rocky cores depending on the stellar spin evolution. However, if\nthe planets are heavier and follow the mass-radius relation of older planets,\nthen even in the highest XUV irradiation scenario none of the planets is\nexpected to cross the radius gap into the rocky regime until the system reaches\nan age of 5 Gyr.", "category": "astro-ph_EP" }, { "text": "Thermosphere and exosphere of Hot-Jupiters: Here we describe the observations and the resulting constraints on the upper\natmosphere (thermosphere and exosphere) of the \"Hot-Jupiters\". In particular,\nobservations and theoretical modeling of Hot-Jupiter evaporation are described.\nThe observations allowed the discovery that the planet orbiting HD209458 has an\nextended atmosphere of escaping hydrogen and showed the presence of oxygen and\ncarbon at very high altitude. These observations give unique constraints on the\nescape rate and mechanism in the atmosphere of these planets. The most recent\nLyman-alpha HST observations of HD189733b allows for the first time to compare\nthe evaporation from two different planets in different environments. Models to\nquantify the escape rate from the measured occultation depths, and an energy\ndiagram to describe the evaporation state of Hot-Jupiters are presented. Using\nthis diagram, it is shown that few already known planets could be remnants of\nformerly giant planets.", "category": "astro-ph_EP" }, { "text": "Applying the perturbative integral in aeromaneuvers around Mars to\n calculate the cost: The perturbative integral method was applied to quantify the contribution of\nexternal forces during a specific interval of time in trajectories of\nspacecraft around asteroids and under the Luni-solar influence. However, this\nmethod has not been used to quantify the contributions of drag in aerocapture\nand aerobraking. For this reason, the planet Mars is selected to apply this\nmethod during an aerogravity-assisted maneuver. Several trajectories are\nanalyzed, making use of a drag device with area to mass ratios varying from 0.0\nto 20.0 m2/kg, simulating solar sails or de-orbit devices. The mathematical\nmodel is based in the restricted three-body problem. The use of this maneuver\nmakes it possible to obtain the variations of energy in the trajectory,\nreplacing expensive maneuvers based on fuel consumption. To observe the effects\nof the maneuvers, different values of pericenter velocity and altitude were\nselected for prograde and retrograde orbits. The innovation of this research is\nthe application of an integral method to quantify the delta-V of the aero\ngravity maneuver, comparing the cost of the maneuver with the traditional\nmethods of space propulsion. The results allow the identification of orbits\nwith conditions to capture, and the perturbative maps show the velocity\nvariations.", "category": "astro-ph_EP" }, { "text": "Methane on Mars: New insights into the sensitivity of CH4 with the\n NOMAD/ExoMars spectrometer through its first in-flight calibration: The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the\nExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in\nsolar occultation, nadir, and limb geometries, and will be able to produce an\noutstanding amount of diverse data, mostly focused on properties of the\natmosphere. The infrared channels of the instrument operate by combining an\nechelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF).\nUsing in-flight data, we characterized the instrument performance and\nparameterized its calibration. In particular: an accurate frequency calibration\nwas achieved, together with its variability due to thermal effects on the\ngrating. The AOTF properties and transfer function were also quantified, and we\ndeveloped and tested a realistic method to compute the spectral continuum\ntransmitted through the coupled grating + AOTF system. The calibration results\nenabled unprecedented insights into the important problem of the sensitivity of\nNOMAD to methane abundances in the atmosphere. We also deeply characterized its\nperformance under realistic conditions of varying aerosol abundances, diverse\nalbedos and changing illumination conditions as foreseen over the nominal\nmission. The results show that, in low aerosol conditions, NOMAD single\nspectrum, 1-sigma sensitivity to CH4 is around 0.33 ppbv at 20 km of altitude\nwhen performing solar occultations, and better than 1 ppbv below 30 km. In\ndusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir\ngeometry, results demonstrate that NOMAD will be able to produce seasonal maps\nof CH4 with a sensitivity around 5 ppbv over most of planet's surface with\nspatial integration over 5x5 degrees bins. Results show also that such numbers\ncan be improved by a factor of 10 to 30 by data binning. Overall, our results\nquantify NOMAD's capability to address the variable aspects of Martian climate.", "category": "astro-ph_EP" }, { "text": "A census of $\u03c1$ Oph candidate members from Gaia DR2: The Ophiuchus cloud complex is one of the best laboratories to study the\nearlier stages of the stellar and protoplanetary disc evolution. The wealth of\naccurate astrometric measurements contained in the Gaia Data Release 2 can be\nused to update the census of Ophiuchus member candidates. We seek to find\npotential new members of Ophiuchus and identify those surrounded by a\ncircumstellar disc. We constructed a control sample composed of 188 bona fide\nOphiuchus members. Using this sample as a reference we applied three different\ndensity-based machine learning clustering algorithms (DBSCAN, OPTICS, and\nHDBSCAN) to a sample drawn from the Gaia catalogue centred on the Ophiuchus\ncloud. The clustering analysis was applied in the five astrometric dimensions\ndefined by the three-dimensional Cartesian space and the proper motions in\nright ascension and declination. The three clustering algorithms systematically\nidentify a similar set of candidate members in a main cluster with astrometric\nproperties consistent with those of the control sample. The increased\nflexibility of the OPTICS and HDBSCAN algorithms enable these methods to\nidentify a secondary cluster. We constructed a common sample containing 391\nmember candidates including 166 new objects, which have not yet been discussed\nin the literature. By combining the Gaia data with 2MASS and WISE photometry,\nwe built the spectral energy distributions from 0.5 to $22\\microm$ for a subset\nof 48 objects and found a total of 41 discs, including 11 Class II and 1 Class\nIII new discs. Density-based clustering algorithms are a promising tool to\nidentify candidate members of star forming regions in large astrometric\ndatabases. If confirmed, the candidate members discussed in this work would\nrepresent an increment of roughly 40% of the current census of Ophiuchus.", "category": "astro-ph_EP" }, { "text": "Bayesian constraints on the origin and geology of exo-planetary material\n using a population of externally polluted white dwarfs: White dwarfs that have accreted planetary bodies are a powerful probe of the\nbulk composition of exoplanetary material. In this paper, we present a Bayesian\nmodel to explain the abundances observed in the atmospheres of 202 DZ white\ndwarfs by considering the heating, geochemical differentiation, and collisional\nprocesses experienced by the planetary bodies accreted, as well as\ngravitational sinking. The majority (>60%) of systems are consistent with the\naccretion of primitive material. We attribute the small spread in refractory\nabundances observed to a similar spread in the initial planet-forming material,\nas seen in the compositions of nearby stars. A range in Na abundances in the\npollutant material is attributed to a range in formation temperatures from\nbelow 1,000K to higher than 1,400K, suggesting that pollutant material arrives\nin white dwarf atmospheres from a variety of radial locations. We also find\nthat Solar System-like differentiation is common place in exo-planetary\nsystems. Extreme siderophile (Fe, Ni or Cr) abundances in 8 systems require the\naccretion of a core-rich fragment of a larger differentiated body to at least a\n3sigma significance, whilst one system shows evidence that it accreted a\ncrust-rich fragment. In systems where the abundances suggest that accretion has\nfinished (13/202), the total mass accreted can be calculated. The 13 systems\nare estimated to have accreted masses ranging from the mass of the Moon to half\nthat of Vesta. Our analysis suggests that accretion continues for 11Myrs on\naverage.", "category": "astro-ph_EP" }, { "text": "Cool Jupiters greatly outnumber their toasty siblings: Occurrence rates\n from the Anglo-Australian Planet Search: Our understanding of planetary systems different to our own has grown\ndramatically in the past 30 years. However, our efforts to ascertain the degree\nto which the Solar system is abnormal or unique have been hindered by the\nobservational biases inherent to the methods that have yielded the greatest\nexoplanet hauls. On the basis of such surveys, one might consider our planetary\nsystem highly unusual - but the reality is that we are only now beginning to\nuncover the true picture. In this work, we use the full eighteen-year archive\nof data from the Anglo-Australian Planet Search to examine the abundance of\n'Cool Jupiters' - analogs to the Solar system's giant planets, Jupiter and\nSaturn. We find that such planets are intrinsically far more common through the\ncosmos than their siblings, the hot Jupiters. We find that the occurrence rate\nof such 'Cool Jupiters' is $6.73^{+2.09}_{-1.13}$\\%, almost an order of\nmagnitude higher than the occurrence of hot Jupiters (at\n$0.84^{+0.70}_{-0.20}$\\%). We also find that the occurrence rate of giant\nplanets is essentially constant beyond orbital distances of $\\sim$1\\,au. Our\nresults reinforce the importance of legacy radial velocity surveys for the\nunderstanding of the Solar system's place in the cosmos.", "category": "astro-ph_EP" }, { "text": "Six newly-discovered hot Jupiters transiting F/G stars: WASP-87b,\n WASP-108b, WASP-109b, WASP-110b, WASP-111b & WASP-112b: We present the discoveries of six transiting hot Jupiters: WASP-87b,\nWASP-108b, WASP-109b, WASP-110b, WASP-111b and WASP-112b. The planets have\nmasses of 0.51--2.2 $M_{\\rm Jup}$ and radii of 1.19--1.44 $R_{\\rm Jup}$ and are\nin orbits of 1.68--3.78 d around stars with masses 0.81--1.50 $M_{\\rm \\odot}$.\n WASP-111b is in a prograde, near-aligned ($\\lambda = -5 \\pm 16^\\circ$),\nnear-circular ($e < 0.10$ at 2 $\\sigma$) orbit around a mid-F star. As tidal\nalignment around such a hot star is thought to be inefficient, this suggests\nthat either the planet migrated inwards through the protoplanetary disc or that\nscattering processes happened to leave it in a near-aligned orbit. WASP-111\nappears to have transitioned from an active to a quiescent state between the\n2012 and 2013 seasons, which makes the system a candidate for studying the\neffects of variable activity on a hot-Jupiter atmosphere. We find evidence that\nthe mid-F star WASP-87 is a visual binary with a mid-G star. Two host stars are\nmetal poor: WASP-112 has [Fe/H] = $-0.64 \\pm 0.15$ and WASP-87 has [Fe/H] =\n$-0.41 \\pm 0.10$. The low density of WASP-112 (0.81 $M_{\\rm \\odot}$, $0.80 \\pm\n0.04$ $\\rho_{\\rm \\odot}$) cannot be matched by standard models for any\nreasonable value of the age of the star, suggesting it to be affected by the\n\"radius anomaly\".", "category": "astro-ph_EP" }, { "text": "Some Comments on Possible Preferred Directions for the SETI Search: The search for extraterrestrial intelligence by looking for signals from\nadvanced technological civilizations has been ongoing for some decades. We\nsuggest that it could possibly be made more efficient by focusing on stars from\nwhich the solar system can be observed via mini-eclipsings of the Sun by\ntransiting planets.", "category": "astro-ph_EP" }, { "text": "Physical Characterization of Warm Spitzer-observed Near-Earth Objects: Near-infrared spectroscopy of Near-Earth Objects (NEOs) connects diagnostic\nspectral features to specific surface mineralogies. The combination of\nspectroscopy with albedos and diameters derived from thermal infrared\nobservations can increase the scientific return beyond that of the individual\ndatasets. To that end, we have completed a spectroscopic observing campaign to\ncomplement the ExploreNEOs Warm Spitzer program that obtained albedos and\ndiameters of nearly 600 NEOs (Trilling et al. 2010). Here we present the\nresults of observations using the low-resolution prism mode (~0.7-2.5 microns)\nof the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We also\ninclude near-infrared observations of ExploreNEOs targets from the MIT-UH-IRTF\nJoint Campaign for Spectral Reconnaissance. Our dataset includes near-infrared\nspectra of 187 ExploreNEOs targets (125 observations of 92 objects from our\nsurvey and 213 observations of 154 objects from the MIT survey). We identify a\ntaxonomic class for each spectrum and use band parameter analysis to\ninvestigate the mineralogies for the S-, Q-, and V-complex objects. Our\nanalysis suggests that for spectra that contain near-infrared data but lack the\nvisible wavelength region, the Bus-DeMeo system misidentifies some S-types as\nQ-types. We find no correlation between spectral band parameters and\nExploreNEOs albedos and diameters. We find slightly negative Band Area Ratio\n(BAR) correlations with phase angle for Eros and Ivar, but a positive BAR\ncorrelation with phase angle for Ganymed. We find evidence for spectral phase\nreddening for Eros, Ganymed, and Ivar. We identify the likely ordinary\nchondrite type analog for a subset of our sample. Our resulting proportions of\nH, L, and LL ordinary chondrites differ from those calculated for meteorite\nfalls and in previous studies of ordinary chondrite-like NEOs.", "category": "astro-ph_EP" }, { "text": "New and updated convex shape models of asteroids based on optical data\n from a large collaboration network: Asteroid modeling efforts in the last decade resulted in a comprehensive\ndataset of almost 400 convex shape models and their rotation states. This\namount already provided a deep insight into physical properties of main-belt\nasteroids or large collisional families. We aim to increase the number of\nasteroid shape models and rotation states. Such results are an important input\nfor various further studies such as analysis of asteroid physical properties in\ndifferent populations, including smaller collisional families, thermophysical\nmodeling, and scaling shape models by disk-resolved images, or stellar\noccultation data. This provides, in combination with known masses, bulk density\nestimates, but constrains also theoretical collisional and evolutional models\nof the Solar System. We use all available disk-integrated optical data (i.e.,\nclassical dense-in-time photometry obtained from public databases and through a\nlarge collaboration network as well as sparse-in-time individual measurements\nfrom a few sky surveys) as an input for the convex inversion method, and derive\n3D shape models of asteroids, together with their rotation periods and\norientations of rotation axes. The key ingredient is the support of more that\none hundred observers who submit their optical data to publicly available\ndatabases. We present updated shape models for 36 asteroids, for which mass\nestimates are currently available in the literature or their masses will be\nmost likely determined from their gravitational influence on smaller bodies,\nwhich orbital deflection will be observed by the ESA Gaia astrometric mission.\nThis was achieved by using additional optical data from recent apparitions for\nthe shape optimization. Moreover, we also present new shape model\ndeterminations for 250 asteroids, including 13 Hungarias and 3 near-Earth\nasteroids.", "category": "astro-ph_EP" }, { "text": "An Early Look of Comet C/2013 A1 (Siding Spring): Breathtaker or\n Nightmare?: The dynamically new comet, C/2013 A1 (Siding Spring), is to make a close\napproach to Mars on 2014 October 19 at 18:30 UT at a distance of 40+/-1 Martian\nradius. Such extremely rare event offers a precious opportunity for the\nspacecrafts on Mars to closely study a dynamically new comet itself as well as\nthe planet-comet interaction. Meanwhile, the high speed meteoroids released\nfrom C/Siding Spring also pose a threat to physically damage the spacecrafts.\nHere we present our observations and modeling results of C/Siding Spring to\ncharacterize the comet and assess the risk posed to the spacecrafts on Mars. We\nfind that the optical tail of C/Siding Spring is dominated by larger particles\nat the time of the observation. Synchrone simulation suggests that the comet\nwas already active in late 2012 when it was more than 7 AU from the Sun. By\nparameterizing the dust activity with a semi-analytic model, we find that the\nejection speed of C/Siding Spring is comparable to comets such as the target of\nthe Rosetta mission, 67P/Churyumov-Gerasimenko. Under nominal situation, the\nsimulated dust cone will miss the planet by about 20 Martian radius. At the\nextreme ends of uncertainties, the simulated dust cone will engulf Mars, but\nthe meteoric influx at Mars is still comparable to the nominal sporadic influx,\nseemly indicating that intense and enduring meteoroid bombardment due to\nC/Siding Spring is unlikely. Further simulation also suggests that\ngravitational disruption of the dust tail may be significant enough to be\nobservable at Earth.", "category": "astro-ph_EP" }, { "text": "A Hibonite-Pyroxene Spherule in Allan Hills 77307 (CO3.03): Petrography\n and Mineralogy: Hibonite-pyroxene spherules are an extremely rare kind of refractory\ninclusion that show a wide range of exotic isotopic properties despite their\ndefining similarity and simplicity in morphology and mineralogy. One such,\nrelatively large (about 120 micron diameter), inclusion has been found in one\nof the most pristine meteorites, Allan Hills 77307 (a carbonaceous chondrite of\nthe Ornans group; Petrologic type 3.03). The inclusion consists of two central\nhibonite laths of about 30x15 micron surrounded by Al, Ca-rich pyroxene. The\nhibonite laths have uniform composition. The composition of pyroxene\nsurrounding the hibonite is radially homogenously Al,-Ca rich up to about 50-60\nmicrons which transitions to Mg, -Ti rich at the outer boundary.\nHibonite-pyroxene spherule found in ALHA 77307 shares many similarities with\nthe other previously found hibonite-pyroxene spherules. A distinguishing\nfeature of the inclusion in ALHA77307 is the presence of two slivers/ wedges at\nthe opposite outer edge of the hibonite- pyroxene spherule that consist of\nrapidly, poorly crystalized, sub-micron minerals with pristine textures. The\npristine petrography and mineralogy of this inclusion allow discernment of the\nexpected general trend of formation and alteration amongst hibonite-pyroxene\nspherules.", "category": "astro-ph_EP" }, { "text": "Forthcoming mutual events of planets and astrometric radio sources: Radio astronomy observations of close approaches of the Solar system planets\nto compact radio sources as well as radio source occultations by planets may be\nof large interest for planetary sciences, dynamical astronomy, and testing\ngravity theories. In this paper, we present extended lists of occultations of\nastrometric radio sources observed in the framework of various astrometric and\ngeodetic VLBI programs by planets, and close approaches of planets to radio\nsources expected in the nearest years. Computations are made making use of the\nEPOS software package.", "category": "astro-ph_EP" }, { "text": "WEIRD: Wide-orbit Exoplanet search with InfraRed Direct imaging: We report results from the Wide-orbit Exoplanet search with InfraRed Direct\nimaging (WEIRD), a survey designed to search for Jupiter-like companions on\nvery wide orbits (1000 to 5000 AU) around young stars ($<$120 Myr) that are\nknown members of moving groups in the solar neighborhood ($<$70 pc). Sharing\nthe same age, distance, and metallicity as their host while being on large\nenough orbits to be studied as \"isolated\" objects make such companions prime\ntargets for spectroscopic observations and valuable benchmark objects for\nexoplanet atmosphere models. The search strategy is based on deep imaging in\nmultiple bands across the near-infrared domain. For all 177 objects of our\nsample, $z_{ab}^\\prime$, $J$, [3.6] and [4.5] images were obtained with\nCFHT/MegaCam, GEMINI/GMOS, CFHT/WIRCam, GEMINI/Flamingos-2, and $Spitzer$/IRAC.\nUsing this set of 4 images per target, we searched for sources with red\n$z_{ab}^\\prime$ and $[3.6]-[4.5]$ colors, typically reaching good completeness\ndown to 2Mjup companions, while going down to 1Mjup for some targets, at\nseparations of $1000-5000$ AU. The search yielded 4 candidate companions with\nthe expected colors, but they were all rejected through follow-up proper motion\nobservations. Our results constrain the occurrence of 1-13 Mjup planetary-mass\ncompanions on orbits with a semi-major axis between 1000 and 5000 AU at less\nthan 0.03, with a 95\\% confidence level.", "category": "astro-ph_EP" }, { "text": "Trace Elemental Behavior in the Solar Nebula: Synchrotron X-ray\n Fluorescence Analyses of CM and CR Chondritic Iron Sulfides and Associated\n Metal: We have performed a coordinated focused ion beam (FIB)-scanning and\ntransmission electron microscopy (S/TEM), electron probe microanalysis\n(EMPA)-synchrotron X-ray fluorescence (SXRF) microprobe study to determine\nphase-specific microstructural characteristics and high-resolution in situ\ntrace element concentrations of primary pyrrhotite, pentlandite, and associated\nmetal grains from chondrules in CM2 and CR2 carbonaceous chondrites. This work\nis the first of its kind to link trace element chemical and microstructural\nobservations in chondritic sulfides in an attempt to determine formation\nmechanisms and conditions of primary sulfides in these meteorite groups. SXRF\nmicroprobe analyses allowed the concentrations of the minor and trace elements,\nCo, Cu, Ge, Zn, and Se to be quantified, in addition to Fe and Ni, at a spatial\nresolution of 2 microns. The similarity between the CM and CR PPI sulfide trace\nelement patterns provides evidence for a common formation mechanism for this\ntype of sulfide grain in both meteorite groups. In addition, the SRM sulfide\nand metal have comparable trace element patterns that indicates a genetic\nrelationship between the two, such as sulfidization of metal. Enrichments in\nNi, Co, Cu, and Se are consistent with the chalcophile/siderophile behavior of\nthese elements. The observed depletions in Ge suggest that it may have been\nlost by evaporation or else was never incorporated into the metal or sulfide\nprecursor materials. The depletion in Zn may also be attributable to\nevaporation, but, being partially lithophile, may also have been preferentially\nincorporated into silicates during chondrule formation. Trace element\nconcentrations support crystallization from an immiscible sulfide melt in\nchondrules for formation of the PPI grains and sulfidization of metal for the\norigin of the SRM grains.", "category": "astro-ph_EP" }, { "text": "AMD-stability in presence of first order Mean Motion Resonances: The AMD-stability criterion allows to discriminate between a-priori stable\nplanetary systems and systems for which the stability is not granted and needs\nfurther investigations. AMD-stability is based on the conservation of the\nAngular Momentum Deficit (AMD) in the averaged system at all orders of\naveraging. While the AMD criterion is rigorous, the conservation of the AMD is\nonly granted in absence of mean-motion resonances (MMR). Here we extend the\nAMD-stability criterion to take into account mean-motion resonances, and more\nspecifically the overlap of first order MMR. If the MMR islands overlap, the\nsystem will experience generalized chaos leading to instability. The\nHamiltonian of two massive planets on coplanar quasi-circular orbits can be\nreduced to an integrable one degree of freedom problem for period ratios close\nto a first order MMR. We use the reduced Hamiltonian to derive a new overlap\ncriterion for first order MMR. This stability criterion unifies the previous\ncriteria proposed in the literature and admits the criteria obtained for\ninitially circular and eccentric orbits as limit cases. We then improve the\ndefinition of AMD-stability to take into account the short term chaos generated\nby MMR overlap. We analyze the outcome of this improved definition of\nAMD-stability on selected multi-planet systems from the Extrasolar Planets\nEncyclopeadia.", "category": "astro-ph_EP" }, { "text": "Lunar-like silicate material forms the Earth quasisatellite (469219)\n 2016 HO3 Kamo`oalewa: Little is known about Earth quasi-satellites, a class of near-Earth small\nsolar system bodies that orbit the sun but remain close to the Earth, because\nthey are faint and difficult to observe. Here we use the Large Binocular\nTelescope (LBT) and the Lowell Discovery Telescope (LDT) to conduct a\ncomprehensive physical characterization of quasi-satellite (469219) Kamo`oalewa\nand assess its affinity with other groups of near-Earth objects. We find that\n(469219) Kamo`oalewa rotates with a period of 28.3 (+1.8/-1.3) minutes and\ndisplays a reddened reflectance spectrum from 0.4-2.2 microns. This spectrum is\nindicative of a silicate-based composition, but with reddening beyond what is\ntypically seen amongst asteroids in the inner solar system. We compare the\nspectrum to those of several material analogs and conclude that the best match\nis with lunar-like silicates. This interpretation implies extensive space\nweathering and raises the prospect that Kamo`oalewa could comprise lunar\nmaterial.", "category": "astro-ph_EP" }, { "text": "Modeling the flyby anomalies with dark matter scattering: update with\n additional data and further predictions: We continue our exploration of whether the flyby anomalies can be explained\nby scattering of spacecraft nucleons from dark matter gravitationally bound to\nthe earth, with the addition of data from five new flybys to that from the\noriginal six. We continue to use our model in which inelastic and elastic\nscatterers populate shells generated by the precession of circular orbits with\nnormals tilted with respect to the earth's axis. With 11 data points and 8\nparameters in the model, a statistically meaningful fit is obtained with a\nchi-squared of 2.7. We give plots of the anomalous acceleration along the\nspacecraft trajectory, and the cumulative velocity change, for the five flybys\nwhich exhibit a significant nonzero anomaly. We also discuss implications of\nthe fit for dark matter-nucleon cross sections, give the prediction of our fit\nfor the anomaly to be expected from the future Juno flyby, and give predictions\nof our fit for flyby orbit orientation changes. In addition we give formulas\nfor estimating the flyby temperature increase caused by dark matter inelastic\nscattering, and for the fraction of flyby nucleons undergoing such scatters.\nFinally, for circular satellite orbits, we give a table of predicted secular\nchanges in orbit radius. These are much too large to be reasonable -- comparing\nwith data for COBE and GP-B supplied to us by Edward Wright (after the first\nversion of this paper was posted), we find that our model predicts changes in\norbit radius that are too large by many orders of magnitude. So the model\nstudied here is ruled out. We conclude that further modeling of the flyby\nanomalies must simultaneously attempt to fit constraints coming from satellite\norbits.", "category": "astro-ph_EP" }, { "text": "Direct Imaging Search for Extrasolar Planets in the Pleiades: We carried out an imaging survey for extrasolar planets around stars in the\nPleiades (125 Myr, 135 pc) in the $H$ and $K_{S}$ bands using HiCIAO combined\nwith the adaptive optics, AO188, on the Subaru telescope. We found 13 companion\ncandidates fainter than 14.5 mag in the $H$ band around 9 stars. Five of these\n13 were confirmed to be background stars by measurement of their proper motion.\nOne was not found in the second epoch observation, and thus was not a\nbackground or companion object. One had multi-epoch image, but the precision of\nits proper motion was not sufficient to conclude whether it was background\nobject. Four other candidates are waiting for second epoch observations to\ndetermine their proper motion. Finally, the remaining 2 were confirmed to be 60\n$M_{J}$ brown dwarf companions orbiting around HD 23514 (G0) and HII 1348 (K5)\nrespectively, as had been reported in previous studies. In our observations,\nthe average detection limit for a point source was 20.3 mag in the $H$ band\nbeyond 1''.5 from the central star. On the basis of this detection limit, we\ncalculated the detection efficiency to be 90% for a planet with 6 to 12 Jovian\nmasses and a semi-major axis of 50--1000 AU. For this we extrapolated the\ndistribution of planet mass and semi-major axis derived from RV observations\nand adopted the planet evolution model of Baraffe et al. (2003). As there was\nno detection of a planet, we estimated the frequency of such planets to be less\nthan 17.9% ($2\\sigma$) around one star of the Pleiades cluster.", "category": "astro-ph_EP" }, { "text": "Reconnaissance of the HR 8799 Exosolar System I: Near IR Spectroscopy: We obtained spectra, in the wavelength range \\lambda = 995 - 1769 nm, of all\nfour known planets orbiting the star HR 8799. Using the suite of\ninstrumentation known as Project 1640 on the Palomar 5-m Hale Telescope, we\nacquired data at two epochs. This allowed for multiple imaging detections of\nthe companions and multiple extractions of low-resolution (R ~ 35) spectra.\nData reduction employed two different methods of speckle suppression and\nspectrum extraction, both yielding results that agree. The spectra do not\ndirectly correspond to those of any known objects, although similarities with L\nand T-dwarfs are present, as well as some characteristics similar to planets\nsuch as Saturn. We tentatively identify the presence of CH_4 along with NH_3\nand/or C_2H_2, and possibly CO_2 or HCN in varying amounts in each component of\nthe system. Other studies suggested red colors for these faint companions, and\nour data confirm those observations. Cloudy models, based on previous\nphotometric observations, may provide the best explanation for the new data\npresented here. Notable in our data is that these presumably co-eval objects of\nsimilar luminosity have significantly different spectra; the diversity of\nplanets may be greater than previously thought. The techniques and methods\nemployed in this paper represent a new capability to observe and rapidly\ncharacterize exoplanetary systems in a routine manner over a broad range of\nplanet masses and separations. These are the first simultaneous spectroscopic\nobservations of multiple planets in a planetary system other than our own.", "category": "astro-ph_EP" }, { "text": "Evidence of fast pebble growth near condensation fronts in the HL Tau\n protoplanetary disk: Water and simple organic molecular ices dominate the mass of solid materials\navailable for planetesimal and planet formation beyond the water snow line.\nHere we analyze ALMA long baseline 2.9, 1.3 and 0.87 mm continuum images of the\nyoung star HL Tau, and suggest that the emission dips observed are due to rapid\npebble growth around the condensation fronts of abundant volatile species.\nSpecifically, we show that the prominent innermost dip at 13 AU is spatially\nresolved in the 0.87 mm image, and its center radius is coincident with the\nexpected mid-plane condensation front of water ice. In addition, two other\nprominent dips, at distances of 32 and 63 AU, cover the mid-plane condensation\nfronts of pure ammonia or ammonia hydrates and clathrate hydrates (especially\nwith CO and N$_2$) formed from amorphous water ice. The spectral index map of\nHL Tau between 1.3 and 0.87 mm shows that the flux ratios inside the dips are\nstatistically larger than those of nearby regions in the disk. This variation\ncan be explained by a model with two dust populations, where most of solid mass\nresides in a component that has grown into decimeter size scales inside the\ndips. Such growth is in accord with recent numerical simulations of volatile\ncondensation, dust coagulation and settling.", "category": "astro-ph_EP" }, { "text": "The spin-orbit angles of the transiting exoplanets WASP-1b, WASP-24b,\n WASP-38b and HAT-P-8b from Rossiter-McLaughlin observations: We present observations of the Rossiter-McLaughlin effect for the transiting\nexoplanet systems WASP-1, WASP-24, WASP-38 and HAT-P-8, and deduce the\norientations of the planetary orbits with respect to the host stars' rotation\naxes. The planets WASP-24b, WASP-38b and HAT-P-8b appear to move in prograde\norbits and be well aligned, having sky-projected spin orbit angles consistent\nwith zero: {\\lambda} = -4.7 \\pm 4.0{\\deg}, {\\lambda} = 15 + 33{\\deg}/-43{\\deg}\nand {\\lambda} = -9.7 +9.0{\\deg}/-7.7{\\deg}, respectively. The host stars have\nTeff < 6250 K and conform with the trend of cooler stars having low\nobliquities. WASP-38b is a massive planet on a moderately long period,\neccentric orbit so may be expected to have a misaligned orbit given the high\nobliquities measured in similar systems. However, we find no evidence for a\nlarge spin-orbit angle. By contrast, WASP-1b joins the growing number of\nmisaligned systems and has an almost polar orbit, {\\lambda} = -79\n+4.5{\\deg}/-4.3{\\deg}. It is neither very massive, eccentric nor orbiting a hot\nhost star, and therefore does not share the properties of many other misaligned\nsystems.", "category": "astro-ph_EP" }, { "text": "The CORALIE survey for southern extrasolar planets XIX. Brown dwarfs and\n stellar companions unveiled by radial velocity and astrometry: A historical planet-search on a sample of 1647 nearby southern main sequence\nstars has been ongoing since 1998 with the CORALIE spectrograph at La Silla\nObservatory, with a backup subprogram dedicated to the monitoring of binary\nstars. We review 25 years of CORALIE measurements and search for Doppler\nsignals consistent with stellar or brown dwarf companions to produce an updated\ncatalog of both known and previously unpublished binary stars in the\nplanet-search sample, assessing the binarity fraction of the stellar population\nand providing perspective for more precise planet-search in the binary sample.\nWe perform new analysis on the CORALIE planet-search sample radial velocity\nmeasurements, searching for stellar companions and obtaining orbital solutions\nfor both known and new binary systems. We perform simultaneous radial velocity\nand proper motion anomaly fits on the subset of these systems for which\nHipparcos and Gaia astrometry measurements are available, obtaining accurate\nestimates of true mass for the companions. We find 218 stars in the CORALIE\nsample to have at least one stellar companion, 130 of which are not yet\npublished in the literature and for which we present orbital solutions. The use\nof proper motion anomaly allow us to derive true masses for the stellar\ncompanions in 132 systems, which we additionally use to estimate stability\nregions for possible planetary companions on circumprimary or circumbinary\norbits. Finally, we produce detection limit maps for each star in the sample\nand obtain occurrence rates of $0.43^{+0.23}_{-0.11}\\%$ and\n$12.69^{+0.87}_{-0.77}\\%$ for brown dwarf and stellar companions respectively\nin the CORALIE sample.", "category": "astro-ph_EP" }, { "text": "Transiting Planet Candidates Beyond the Snow Line Detected by Visual\n Inspection of 7557 Kepler Objects of Interest: We visually inspected the light curves of 7557 Kepler Objects of Interest\n(KOIs) to search for single transit events (STEs) possibly due to long-period\ngiant planets. We identified 28 STEs in 24 KOIs, among which 14 events are\nnewly reported in this paper. We estimate the radius and orbital period of the\nobjects causing STEs by fitting the STE light curves simultaneously with the\ntransits of the other planets in the system or with the prior information on\nthe host star density. As a result, we found that STEs in seven of those\nsystems are consistent with Neptune- to Jupiter-sized objects of orbital\nperiods ranging from a few to $\\sim$ $20\\,\\mathrm{yr}$. We also estimate that\n$\\gtrsim20\\%$ of the compact multi-transiting systems host cool giant planets\nwith periods $\\gtrsim 3\\,\\mathrm{yr}$ on the basis of their occurrence in the\nKOIs with multiple candidates, assuming the small mutual inclination between\ninner and outer planetary orbits.", "category": "astro-ph_EP" }, { "text": "Moderate-Resolution $K$-Band Spectroscopy of Substellar Companion\n $\u03ba$ Andromedae b: We present moderate-resolution ($R\\sim4000$) $K$ band spectra of the\n\"super-Jupiter,\" $\\kappa$ Andromedae b. The data were taken with the OSIRIS\nintegral field spectrograph at Keck Observatory. The spectra reveal resolved\nmolecular lines from H$_{2}$O and CO. The spectra are compared to a custom\n$PHOENIX$ atmosphere model grid appropriate for young planetary-mass objects.\nWe fit the data using a Markov Chain Monte Carlo forward modeling method. Using\na combination of our moderate-resolution spectrum and low-resolution, broadband\ndata from the literature, we derive an effective temperature of\n$T_\\mathrm{eff}$ = 1950 - 2150 K, a surface gravity of $\\log g=3.5 - 4.5$, and\na metallicity of [M/H] = $-0.2 - 0.0$. These values are consistent with\nprevious estimates from atmospheric modeling and the currently favored young\nage of the system ($<$50 Myr). We derive a C/O ratio of 0.70$_{-0.24}^{+0.09}$\nfor the source, broadly consistent with the solar C/O ratio. This, coupled with\nthe slightly subsolar metallicity, implies a composition consistent with that\nof the host star, and is suggestive of formation by a rapid process. The\nsubsolar metallicity of $\\kappa$ Andromedae b is also consistent with\npredictions of formation via gravitational instability. Further constraints on\nformation of the companion will require measurement of the C/O ratio of\n$\\kappa$ Andromedae A. We also measure the radial velocity of $\\kappa$\nAndromedae b for the first time, with a value of\n$-1.4\\pm0.9\\,\\mathrm{km}\\,\\mathrm{s}^{-1}$ relative to the host star. We find\nthat the derived radial velocity is consistent with the estimated high\neccentricity of $\\kappa$ Andromedae b.", "category": "astro-ph_EP" }, { "text": "Non-adiabatic tidal oscillations induced by a planetary companion: We calculate the dynamical tides raised by a close planetary companion on\nnon-rotating stars of $1$ $\\text{M}_{\\odot}$ and $1.4$ $\\text{M}_{\\odot}$.\nUsing the Henyey method, we solve the fully non-adiabatic equations throughout\nthe star. The horizontal Lagrangian displacement is found to be 10 to 100 times\nlarger than the equilibrium tide value in a thin region near the surface of the\nstar. This is because non--adiabatic effects dominate in a region that extends\nfrom below the outer edge of the convection zone up to the stellar surface, and\nthe equilibrium tide approximation is inconsistent with non--adiabaticity.\nAlthough this approximation generally applies in the low frequency limit, it\nalso fails in the parts of the convection zone where the forcing frequency is\nsmall but larger than the Brunt-V\\\"ais\\\"al\\\"a frequency. We derive analytical\nestimates which give a good approximation to the numerical values of the\nmagnitude of the ratio of the horizontal and radial displacements at the\nsurface. The relative surface flux perturbation is also significant, on the\norder of 0.1 % for a system modelled on 51 Pegasi b. Observations affected by\nthe horizontal displacement may therefore be more achievable than previously\nthought, and brightness perturbations may be the result of flux perturbations\nrather than due to the radial displacement. We discuss the implication of this\non the possibility of detecting such tidally excited oscillations, including\nthe prospect of utilising the large horizontal motion for observations of\nsystems such as 51 Pegasi.", "category": "astro-ph_EP" }, { "text": "Asteroid 2017 FZ2 et al.: signs of recent mass-shedding from YORP?: The first direct detection of the asteroidal YORP effect, a phenomenon that\nchanges the spin states of small bodies due to thermal reemission of sunlight\nfrom their surfaces, was obtained for (54509) YORP 2000 PH5. Such an alteration\ncan slowly increase the rotation rate of asteroids, driving them to reach their\nfission limit and causing their disruption. This process can produce binaries\nand unbound asteroid pairs. Secondary fission opens the door to the eventual\nformation of transient but genetically-related groupings. Here, we show that\nthe small near-Earth asteroid (NEA) 2017 FZ2 was a co-orbital of our planet of\nthe quasi-satellite type prior to their close encounter on 2017 March 23.\nBecause of this flyby with the Earth, 2017 FZ2 has become a non-resonant NEA.\nOur N-body simulations indicate that this object may have experienced\nquasi-satellite engagements with our planet in the past and it may return as a\nco-orbital in the future. We identify a number of NEAs that follow similar\npaths, the largest named being YORP, which is also an Earth's co-orbital. An\napparent excess of NEAs moving in these peculiar orbits is studied within the\nframework of two orbit population models. A possibility that emerges from this\nanalysis is that such an excess, if real, could be the result of mass shedding\nfrom YORP itself or a putative larger object that produced YORP. Future\nspectroscopic observations of 2017 FZ2 during its next visit in 2018 (and of\nrelated objects when feasible) may be able to confirm or reject this\ninterpretation.", "category": "astro-ph_EP" }, { "text": "The birth environment of the solar system constrained by the relative\n abundances of the solar radionuclides: The relative abundances of the radionuclides in the solar system at the time\nof its birth are crucial arbiters for competing hypotheses regarding the birth\nenvironment of the Sun. The presence of short-lived radionuclides, as evidenced\nby their decay products in meteorites, has been used to suggest that\nparticular, sometimes exotic, stellar sources were proximal to the Sun's birth\nenvironment. The recent confirmation of neutron star - neutron star (NS-NS)\nmergers and associated kilonovae as potentially dominant sources of r-process\nnuclides can be tested in the case of the solar birth environment using the\nrelative abundances of the longer-lived nuclides. Critical analysis of the 15\nradionuclides and their stable partners for which abundances and production\nratios are well known suggests that the Sun formed in a typical massive\nstar-forming region (SFR). The apparent overabundances of short-lived\nradionuclides (e.g.\\, $^{26} {\\rm Al}$, $^{41}{\\rm Ca}$, $^{36}{\\rm Cl}$) in\nthe early solar system appears to be an artifact of a heretofore\nunder-appreciation for the important influences of enrichment by Wolf-Rayet\nwinds in SFRs. The long-lived nuclides (e.g.\\, $^{238}{\\rm U}$, $^{244}{\\rm\nPu}$, $^{247}{\\rm Cr}$, $^{129}{\\rm I}$) are consistent with an average time\ninterval between production events of $10^8$ years, seemingly too short to be\nthe products of NS-NS mergers alone. The relative abundances of all of these\nnuclides can be explained by their mean decay lifetimes and an average\nresidence time in the ISM of $\\sim200$ Myr. This residence time evidenced by\nthe radionuclides is consistent with the average lifetime of dust in the ISM\nand the timescale for converting molecular cloud mass to stars.", "category": "astro-ph_EP" }, { "text": "ALMA Observations of the DART Impact: Characterizing the Ejecta at\n Sub-Millimeter Wavelengths: We report observations of the Didymos-Dimorphos binary asteroid system using\nthe Atacama Large Millimeter/Submillimeter Array (ALMA) and the Atacama Compact\nArray (ACA) in support of the Double Asteroid Redirection Test (DART) mission.\nOur observations on UT 2022 September 15 provided a pre-impact baseline and the\nfirst measure of Didymos-Dimorphos' spectral emissivity at $\\lambda=0.87$ mm,\nwhich was consistent with the handful of siliceous and carbonaceous asteroids\nmeasured at millimeter wavelengths. Our post-impact observations were conducted\nusing four consecutive executions each of ALMA and the ACA spanning from\nT$+$3.52 to T$+$8.60 hours post-impact, sampling thermal emission from the\nasteroids and the impact ejecta. We scaled our pre-impact baseline measurement\nand subtracted it from the post-impact observations to isolate the flux density\nof mm-sized grains in the ejecta. Ejecta dust masses were calculated for a\nrange of materials that may be representative of Dimorphos' S-type asteroid\nmaterial. The average ejecta mass over our observations is consistent with\n1.3--6.4$\\times10^7$ kg, with the lower and higher values calculated for\namorphous silicates and for crystalline silicates, respectively. Owing to the\nlikely crystalline nature of S-type asteroid material, the higher value is\nfavored. These ejecta masses represent 0.3--1.5\\% of Dimorphos' total mass and\nare in agreement with lower limits on the ejecta mass based on measurements at\noptical wavelengths. Our results provide the most sensitive measure of mm-sized\nmaterial in the ejecta and demonstrate the power of ALMA for providing\nsupporting observations to spaceflight missions.", "category": "astro-ph_EP" }, { "text": "Sending a Spacecraft to Interstellar Comet 2I/Borisov: In August 2019, a second interstellar object 2I/Borisov was discovered 2\nyears after the discovery of the first known interstellar object, 1I/'Oumuamua.\nCan we send a spacecraft to this object, using existing technologies? In this\npaper we assess the technical feasibility of a near-term mission to 2I/Borisov.\nWe apply the Optimum Interplanetary Trajectory Software (OITS) tool to generate\ntrajectories to 2I/Borisov. As results, we get the minimal $\\Delta V$\ntrajectory with a launch date in July 2018. For this trajectory, a Falcon Heavy\nlauncher could have hauled an 8 ton spacecraft to 2I/Borisov. For a later\nlaunch date, results for a combined powered Jupiter flyby with a Solar Oberth\nmaneuver are presented. For a launch in 2027, we could reach 2I/Borisov in\n2052, using the Space Launch System (SLS), up-scaled Parker probe heat shield\ntechnology, and solid propulsion engines. Using a SLS a spacecraft with a mass\nof 765 kg could be sent to 2I/Borisov. A Falcon Heavy could deliver 202 kg to\n2I/Borisov. Arrival times sooner than 2052 can potentially be achieved but with\nhigher $\\Delta V$ requirements and lower spacecraft payload masses.\n2I/Borisov's discovery shortly after the discovery of 1I/'Oumuamua implies that\nthe next interstellar object might be discovered in the near future. The\nfeasibility of a mission to both, 1I/'Oumuamua and 2I/Borisov using existing\ntechnologies indicates that missions to at least some future interstellar\nobjects are feasible as well.", "category": "astro-ph_EP" }, { "text": "Hydrogen Greenhouse Planets Beyond the Habitable Zone: We show that collision-induced absorption allows molecular hydrogen to act as\nan incondensible greenhouse gas, and that bars or tens of bars of primordial\nH2-He mixtures can maintain surface temperatures above the freezing point of\nwater well beyond the \"classical\" habitable zone defined for CO2 greenhouse\natmospheres. Using a 1-D radiative-convective model we find that 40 bars of\npure H2 on a 3 Earth-mass planet can maintain a surface temperature of 280K out\nto 1.5AU from an early-type M dwarf star and 10 AU from a G-type star.\nNeglecting the effects of clouds and of gaseous absorbers besides H2, the flux\nat the surface would be sufficient for photosynthesis by cyanobacteria (in the\nG star case) or anoxygenic phototrophs (in the M star case). We argue that\nprimordial atmospheres of one to several hundred bars of H2-He are possible,\nand use a model of hydrogen escape to show that such atmospheres are likely to\npersist further than 1.5 AU from M stars, and 2 AU from G stars, assuming these\nplanets have protecting magnetic fields. We predict that the microlensing\nplanet OGLE-05-390L could have retained a H2-He atmosphere and be habitable at\n~2.6 AU from its host M star.", "category": "astro-ph_EP" }, { "text": "Peering into the formation history of beta Pictoris b with VLTI/GRAVITY\n long baseline interferometry: Our objective is to estimate the C/O ratio in the atmosphere of beta Pictoris\nb and obtain an estimate of the dynamical mass of the planet, as well as to\nrefine its orbital parameters using high-precision astrometry. We used the\nGRAVITY instrument with the four 8.2 m telescopes of the Very Large Telescope\nInterferometer to obtain K-band spectro-interferometric data on $\\beta$ Pic b.\nWe extracted a medium resolution (R=500) K-band spectrum of the planet and a\nhigh-precision astrometric position. We estimated the planetary C/O ratio using\ntwo different approaches (forward modeling and free retrieval) from two\ndifferent codes (ExoREM and petitRADTRANS, respectively). Finally, we used a\nsimplified model of two formation scenarios (gravitational collapse and\ncore-accretion) to determine which can best explain the measured C/O ratio. Our\nnew astrometry disfavors a circular orbit for $\\beta$ Pic b\n($e=0.15^{+0.05}_{-0.04}$). Combined with previous results and with\nHipparcos/GAIA measurements, this astrometry points to a planet mass of $M =\n12.7\\pm{}2.2\\,M_\\mathrm{Jup}$. This value is compatible with the mass derived\nwith the free-retrieval code petitRADTRANS using spectral data only. The\nforward modeling and free-retrieval approches yield very similar results\nregarding the atmosphere of beta Pic b. In particular, the C/O ratios derived\nwith the two codes are identical ($0.43\\pm{}0.05$ vs $0.43^{+0.04}_{-0.03}$).\nWe argue that if the stellar C/O in $\\beta$ Pic is Solar, then this combination\nof a very high mass and a low C/O ratio for the planet suggests a formation\nthrough core-accretion, with strong planetesimal enrichment.", "category": "astro-ph_EP" }, { "text": "Chemical consequences of the C/O ratio on hot Jupiters: Examples from\n WASP-12b,CoRoT-2b, XO-1b, and HD 189733b: Motivated by recent spectroscopic evidence for carbon-rich atmospheres on\nsome transiting exoplanets, we investigate the influence of the C/O ratio on\nthe chemistry, composition, and spectra of extrasolar giant planets both from a\nthermochemical-equilibrium perspective and from consideration of disequilibrium\nprocesses like photochemistry and transport-induced quenching. We find that\nalthough CO is predicted to be a major atmospheric constituent on hot Jupiters\nfor all C/O ratios, other oxygen-bearing molecules like H2O and CO2 are much\nmore abundant when C/O < 1, whereas CH4, HCN, and C2H2 gain significantly in\nabundance when C/O > 1. Disequilibrium processes tend to enhance the abundance\nof CH4, NH3, HCN, and C2H2 over a wide range of C/O ratios. We compare the\nresults of our models with secondary-eclipse photometric data from the Spitzer\nSpace Telescope and conclude that (1) disequilibrium models with C/O ~ 1 are\nconsistent with spectra of WASP-12b, XO-1b, and CoRoT-2b, confirming the\npossible carbon-rich nature of these planets, (2) spectra from HD 189733b are\nconsistent with C/O ~< 1, but as the assumed metallicity is increased above\nsolar, the required C/O ratio must increase toward 1 to prevent too much H2O\nabsorption, (3) species like HCN can have a significant influence on spectral\nbehavior in the 3.6 and 8.0 um Spitzer channels, potentially providing even\nmore opacity than CH4 when C/O > 1, and (4) the very high CO2 abundance\ninferred for HD 189733b from near-infrared observations cannot be explained\nthrough equilibrium or disequilibrium chemistry in a H2-dominated atmosphere.\nWe discuss possible formation mechanisms for carbon-rich hot Jupiters. The C/O\nratio and bulk atmospheric metallicity provide important clues regarding the\nformation and evolution of the giant planets.", "category": "astro-ph_EP" }, { "text": "On the frequency of planetary systems around G-dwarfs: We determine the fraction of G-dwarf stars that could host stable planetary\nsystems based on the observed properties of binaries in the Galactic field, and\nin various postulated primordial binary populations, which assume that the\nprimordial binary fraction is higher than that in the field. We first consider\nthe frequency of Solar System analogues - planetary systems that form either\naround a single G-dwarf star, or a binary containing a G-dwarf where the binary\nseparation exceeds 100-300au. If the primordial binary fraction and period\ndistribution is similar to that in the field, then up to 63 per cent of G-dwarf\nsystems could potentially host a Solar System analogue. However, if the\nprimordial binary fraction is higher, the fraction of G-dwarf systems that\ncould host a planetary system like our own is lowered to 38 per cent.\n We extend our analysis to consider the fraction of G-dwarf systems (both\nsingle and binary) that can host either circumprimary planets (orbiting the\nprimary star of the binary) or circumbinary planets (orbiting both stars in the\nbinary) for fiducial planetary separations between 1 - 100au. Depending on the\nassumed binary population, in the circumprimary case between 65 and 95 per cent\nof systems can host a planet at 1au, decreasing to between 20 and 65 per cent\nof systems that can host a planet at 100au. In the circumbinary case, between 5\nand 59 per cent of systems can host a planet at 1au, increasing to between 34\nand 75 per cent of systems that can host a planet at 100au.\n Our results suggest that the assumed binary fraction is the key parameter in\ndetermining the fraction of potentially stable planetary systems in G-dwarf\nsystems and that using the present-day value may lead to significant\noverestimates if the binary fraction was initially higher.", "category": "astro-ph_EP" }, { "text": "High-temperature Dust Condensation around an AGB Star: Evidence from a\n Highly Pristine Presolar Corundum: Corundum ($\\alpha$-Al$_{2}$O$_{3}$) and amorphous or metastable\nAl$_{2}$O$_{3}$ are common components of circumstellar dust observed around\nO-rich asymptotic giant branch (AGB) stars and found in primitive meteorites.\nWe report a detailed isotopic and microstructural investigation of a unique\npresolar corundum grain, QUE060, identified in an acid residue of the Queen\nAlexandra Range 97008 (LL3.05) meteorite. Based on its O and Mg isotopic\ncompositions, this 1.4 $\\mu$m diameter grain formed in a low- or\nintermediate-mass AGB star. It has four developed rhombohedral $\\{$011$\\}$\nfaces of corundum and a rough, rounded face with cavities. High Mg contents\n(Mg/Al $>$ 0.004) are due to the decay of radioactive $^{26}$Al. No spinel\n(MgAl$_{2}$O$_{4}$) inclusions that might have exsolved from the corundum are\nobserved, but there are several high-Mg domains with modulated structures. The\nsubhedral shape of grain QUE060 is the first clear evidence that corundum\ncondenses and grows to micrometer sizes in the extended atmospheres around AGB\nstars. The flat faces indicate that grain QUE060 experienced little\nmodification by gas-grain and grain-grain collisions in the interstellar medium\n(ISM) and solar nebula. The Mg distribution in its structure indicates that\ngrain QUE060 has not experienced any severe heating events since the exhaustion\nof $^{26}$Al. However, it underwent at least one very transient heating event\nto form the high-Mg domains. A possible mechanism for producing this transient\nevent, as well as the one rough surface and cavity, is a single grain-grain\ncollision in the ISM. These results indicate that grain QUE060 is the most\npristine circumstellar corundum studied to date.", "category": "astro-ph_EP" }, { "text": "Detection of Na in WASP-21b's lower and upper atmosphere: Optical transmission spectroscopy provides crucial constraints on the\nreference pressure levels and scattering properties for hot Jupiter\natmospheres. For certain planets, where alkali atoms are detected in the\natmosphere, their line profiles could serve as a good probe to link upper and\nlower atmospheric layers. WASP-21b is a Saturn-mass hot Jupiter orbiting a\nthick disc star, with a low density and an equilibrium temperature of 1333 K,\nwhich makes it a good target for transmission spectroscopy. Here, we present a\nlow-resolution transmission spectrum for WASP-21b based in one transit observed\nby the OSIRIS spectrograph at the 10.4 m Gran Telescopio Canarias (GTC), and a\nhigh-resolution transmission spectrum based in three transits observed by\nHARPS-N at Telescopio Nazinale Galileo (TNG) and HARPS at the ESO 3.6 m\ntelescope. We performed spectral retrieval analysis on GTC's low-resolution\ntransmission spectrum and report the detection of Na at a confidence level of\n$>$3.5-$\\sigma$. The Na line exhibits a broad line profile that can be\nattributed to pressure broadening, indicating a mostly clear planetary\natmosphere. The spectrum shows a tentative excess absorption at the K D$_1$\nline. Using HARPS-N and HARPS, we spectrally resolved the Na doublet\ntransmission spectrum. An excess absorption at the Na doublet is detected\nduring the transit, and shows a radial velocity shift consistent with the\nplanet orbital motion. We proposed a metric to quantitatively distinguish hot\nJupiters with relatively clear atmospheres from others, and WASP-21b has the\nlargest metric value among all the characterized hot Jupiters. The detection of\nNa at both lower and upper atmosphere of WASP-21b reveals that it is an ideal\ntarget for future follow-up observations, providing the opportunity to\nunderstand the nature of its atmosphere across a wide range of pressure levels.", "category": "astro-ph_EP" }, { "text": "Orbital evolution of potentially habitable planets of tidally\n interacting binary stars: We simulate the coupled stellar and tidal evolution of short-period binary\nstars (orbital period $P_{orb} \\lsim$8 days) to investigate the orbital\noscillations, instellation cycles, and orbital stability of circumbinary\nplanets (CBPs). We consider two tidal models and show that both predict an\noutward-then-inward evolution of the binary's semi-major axis $a_{bin}$ and\neccentricity $e_{bin}$. This orbital evolution drives a similar evolution of\nthe minimum CBP semi-major axis for orbital stability. By expanding on previous\nmodels to include the evolution of the mass concentration, we show that the\nmaximum in the CBP orbital stability limit tends to occur 100 Myr after the\nplanets form, a factor of 100 longer than previous investigations. This result\nprovides further support for the hypothesis that the early stellar-tidal\nevolution of binary stars has removed CBPs from short-period binaries. We then\napply the models to Kepler-47 b, a CBP orbiting close to its host stars'\nstability limit, to show that if the binary's initial $e_{bin} \\gsim$0.24, the\nplanet would have been orbiting within the instability zone in the past and\nprobably wouldn't have survived. For stable, hypothetical cases in which the\nstability limit does not reach a planet's orbit, we find that the amplitudes of\n$a_{bin}$ and $e_{bin}$ oscillations can damp by up to 10\\% and 50\\%,\nrespectively. Finally, we consider equal-mass stars with $P_{orb} =$ 7.5 days\nand compare the HZ to the stability limit. We find that for stellar masses\n$\\lsim0.12M_{\\odot}$, the HZ is completely unstable, even if the binary orbit\nis circular. For $e_{bin} \\lsim$0.5, that limit increases to $0.17M_{\\odot}$,\nand the HZ is partially destabilized for stellar masses up to $0.45M_{\\odot}$.\nThese results may help guide searches for potentially habitable CBPs, as well\nas characterize their evolution and likelihood to support life after they are\nfound.", "category": "astro-ph_EP" }, { "text": "The DRAKE mission: finding the frequency of life in the Cosmos: In the search for life in the Universe, exoplanets represent numerous natural\nexperiments in planet formation, evolution, and the emergence of life. This\nraises the fascinating prospect of evaluating cosmic life on a statistical\nbasis. One key statistic is the occurrence rate of life-bearing worlds, $f_{\\rm\nL}$, the 'frequency of life' term in the famous Drake Equation. Measuring\n$f_{\\rm L}$ would give profound insight into how common life is and may help to\nconstrain origin-of-life theories. I propose $f_{\\rm L}$ as the goal for the\nDRAKE mission (Dedicated Research for Advancing Knowledge of Exobiology): a\ntransit spectroscopy survey of M-dwarf habitable zone terrestrial planets. I\ninvestigate how the uncertainty on the observed value of $f_{\\rm L}$ scales\nwith sample size. I determine that sampling error dominates over observational\nerror and that the uncertainty is a function of the observed $f_{\\rm L}$ value.\nI show that even small sample sizes can provide significant constraints on\n$f_{\\rm L}$, boding well for the transit spectroscopy approach. I perform a\nfeasibility study of the DRAKE mission using a nominal instrument design and\nmission plan. Due to low observing efficiencies, DRAKE may need to be\nincorporated into a wider-ranging deep-space or lunar observatory. A 50-planet\nsurvey could constrain $f_{\\rm L}$ to $\\leq$ 0.06 (at 95% confidence) if the\nsample $f_{\\rm L}$ = 0, or 0.03-0.2 if the sample $f_{\\rm L}$ = 0.1. This can\nbe achieved (on average) in 10 years using a 17-m telescope with an\nunrestricted field-of-regard. DRAKE is a viable approach to attempting the\nfirst experimental measurement of $f_{\\rm L}$.", "category": "astro-ph_EP" }, { "text": "TOI-1468: A system of two transiting planets, a super-Earth and a\n mini-Neptune, on opposite sides of the radius valley: We report the discovery and characterization of two small transiting planets\norbiting the bright M3.0V star TOI-1468 (LSPM J0106+1913), whose transit\nsignals were detected in the photometric time series in three sectors of the\nTESS mission. We confirm the e planetary nature of both of them using precise\nradial velocity measurements from the CARMENES and MAROON-X spectrographs, and\nsupplement them with ground-based transit photometry. A joint analysis of all\nthese data reveals that the shorter-period planet, TOI-1468 b ($P_{\\rm b}$ =\n1.88 d), has a planetary mass of $M_{\\rm b} = 3.21\\pm0.24$ $M_{\\oplus}$ and a\nradius of $R_{\\rm b} =1.280^{+0.038}_{-0.039} R_{\\oplus}$, resulting in a\ndensity of $\\rho_{\\rm b} = 8.39^{+ 1.05}_{- 0.92}$ g cm$^{-3}$, which is\nconsistent with a mostly rocky composition. For the outer planet, TOI-1468 c\n($P_{\\rm c} = 15.53$ d), we derive a mass of $M_{\\rm c} = 6.64^{+ 0.67}_{-\n0.68}$ $M_{\\oplus}$, a radius of $R_{\\rm c} = 2.06\\pm0.04\\,R_{\\oplus}$, and a\nbulk density of $\\rho_{c} = 2.00^{+ 0.21}_{- 0.19}$ g cm$^{-3}$, which\ncorresponds to a rocky core composition with a H/He gas envelope. These planets\nare located on opposite sides of the radius valley, making our system an\ninteresting discovery as there are only a handful of other systems with the\nsame properties. This discovery can further help determine a more precise\nlocation of the radius valley for small planets around M dwarfs and, therefore,\nshed more light on planet formation and evolution scenarios.", "category": "astro-ph_EP" }, { "text": "The fragmentation criteria in local vertically stratified\n self-gravitating disk simulations: Massive circumstellar disks are prone to gravitational instabilities, which\ntrigger the formation of spiral arms that can fragment into bound clumps under\nthe right conditions. Two dimensional simulations of self-gravitating disks are\nuseful starting points for studying fragmentation, allowing for high-resolution\nsimulations of thin disks. However, convergence issues can arise in 2D from\nvarious sources. One of these sources is the 2D approximation of self-gravity,\nwhich exaggerates the effect of self-gravity on small scales when the potential\nis not smoothed to account for the assumed vertical extent of the disk. This\neffect is enhanced by increased resolution, resulting in fragmentation at\nlonger cooling timescales $\\beta$. If true, it suggests that the 3D simulations\nof disk fragmentation may not have the same convergence problem and could be\nused to examine the nature of fragmentation without smoothing self-gravity on\nscales similar to the disk scale height. To that end, we have carried out local\n3D self-gravitating disk simulations with simple $\\beta$ cooling with fixed\nbackground irradiation to determine if 3D is necessary to properly describe\ndisk fragmentation. Above a resolution of $\\sim 40$ grid cells per scale\nheight, we find that our simulations converge with respect to the cooling\ntimescale. This result converges in agreement with analytic expectations which\nplace a fragmentation boundary at $\\beta_\\mathrm{crit} = 3$.", "category": "astro-ph_EP" }, { "text": "Korean-Japanese Planet Search Program: Substellar Companions around\n Intermediate-Mass Giants: A Korean-Japanese planet search program has been carried out using the 1.8m\ntelescope at Bohyunsan Optical Astronomy Observatory (BOAO) in Korea, and the\n1.88m telescope at Okayama Astrophysical Observatory (OAO) in Japan to search\nfor planets around intermediate-mass giant stars. The program aims to show the\nproperties of planetary systems around such stars by precise Doppler survey of\nabout 190 G or K type giants together with collaborative surveys of the\nEast-Asian Planet Search Network. So far, we detected two substellar companions\naround massive intermediate-mass giants in the Korean-Japanese planet search\nprogram. One is a brown dwarf-mass companion with 37.6 $M_{\\mathrm{J}}$\norbiting a giant HD 119445 with 3.9 $M_{\\odot}$, which is the most massive\nbrown dwarf companion among those found around intermediate-mass giants. The\nother is a planetary companion with 1.8 $M_{\\mathrm{J}}$ orbiting a giant star\nwith 2.4 $M_{\\odot}$, which is the lowest-mass planetary companion among those\ndetected around giant stars with $>$ 1.9 $M_{\\odot}$. Plotting these systems on\ncompanion mass vs. stellar mass diagram, there seem to exist two unpopulated\nregions of substellar companions around giants with 1.5--3 $M_{\\odot}$ and\nplanetary companions orbiting giants with 2.4--4 $M_{\\odot}$. The existence of\nthese possible unpopulated regions supports a current characteristic view that\nmore massive substellar companions tend to exist around more massive stars.", "category": "astro-ph_EP" }, { "text": "HAT-P-54b: A hot jupiter transiting a 0.64 Msun star in field 0 of the\n K2 mission: We report the discovery of HAT-P-54b, a planet transiting a late K dwarf star\nin field 0 of the NASA K2 mission. We combine ground-based photometric light\ncurves with radial velocity measurements to determine the physical parameters\nof the system. HAT-P-54b has a mass of 0.760 $\\pm$ 0.032 $M_J$, a radius of\n0.944 $\\pm$ 0.028 $R_J$, and an orbital period of 3.7998 d. The star has V =\n13.505 $\\pm$ 0.060, a mass of 0.645 $\\pm$ 0.020 $M_{\\odot}$, a radius of 0.617\n$\\pm$ 0.013 $R_{\\odot}$, an effective temperature of Teff = 4390 $\\pm$ 50K, and\na subsolar metallicity of [Fe/H] = -0.127 $\\pm$ 0.080. HAT-P-54b has a radius\nthat is smaller than 92% of the known transiting planets with masses greater\nthan that of Saturn, while HAT-P-54 is one of the lowest-mass stars known to\nhost a hot Jupiter. Follow-up high-precision photometric observations by the K2\nmission promise to make this a well-studied planetary system.", "category": "astro-ph_EP" }, { "text": "The Formation Mechanism of Gas Giants on Wide Orbits: The recent discoveries of massive planets on ultra-wide orbits of HR 8799\n(Marois et al. 2008) and Fomalhaut (Kalas et al. 2008) present a new challenge\nfor planet formation theorists. Our goal is to figure out which of three giant\nplanet formation mechanisms--core accretion (with or without migration),\nscattering from the inner disk, or gravitational instability--could be\nresponsible for Fomalhaut b, HR 8799 b, c and d, and similar planets discovered\nin the future. This paper presents the results of numerical experiments\ncomparing the long-period planet formation efficiency of each possible\nmechanism in model A star, G star and M star disks.\n First, a simple core accretion simulation shows that planet cores forming\nbeyond 35 AU cannot reach critical mass, even under the most favorable\nconditions one can construct. Second, a set of N-body simulations demonstrates\nthat planet-planet scattering does not create stable, wide-orbit systems such\nas HR 8799. Finally, a linear stability analysis verifies previous work showing\nthat global spiral instabilities naturally arise in high-mass disks. We\nconclude that massive gas giants on stable orbits with semimajor axes greater\nthan 35 AU form by gravitational instability in the disk. We recommend that\nobservers examine the planet detection rate as a function of stellar age,\ncontrolling for planet dimming with time. If planet detection rate is found to\nbe independent of stellar age, it would confirm our prediction that\ngravitational instability is the dominant mode of producing detectable planets\non wide orbits. We also predict that the occurrence ratio of long-period to\nshort-period gas giants should be highest for M dwarfs due to the inefficiency\nof core accretion and the expected small fragment mass in their disks.", "category": "astro-ph_EP" }, { "text": "Circular periodic orbits, resonance capture and inclination excitation\n during type II migration: We consider planetary systems evolving under the effect of a Stokes-type\ndissipative force mimicking the outcome of a type II migration process. As\ninward migration proceeds and the planets follow the circular family (they\nstart on circular orbits) and even though they are initially almost coplanar,\nresonance capture can be realized. Then, at the \\textit{vertical critical\norbits} (VCOs), that the circular family possesses, the inclination excitation\ncan abruptly take place. The planets are now guided by the spatial elliptic\nfamilies, which bifurcate from those critical orbits. We herein, perform a\ndirect link of mutually inclined stable planetary systems on circular orbits\ntrapped in \\textit{mean-motion resonance} (MMR) with the existence of VCOs of\nhigh values of multiplicity. It is shown that the more the multiplicity of the\nperiodic orbits of the circular family increases, the more VCOs (corresponding\nto more MMRs) appear. In this way, we can provide a justification for the\nexistence of resonant planets on circular orbits, which could, even further to\nthat, evolve stably if they were mutually inclined.", "category": "astro-ph_EP" }, { "text": "The Atmosphere and Interior Structure of HAT-P-13b from Spitzer\n Secondary Eclipses: We present {\\em Spitzer} secondary-eclipse observations of the hot Jupiter\nHAT-P-13 b in the 3.6 {\\micron} and 4.5 {\\micron} bands. HAT-P-13 b inhabits a\ntwo-planet system with a configuration that enables constraints on the planet's\nsecond Love number, \\math{k\\sb{2}}, from precise eccentricity measurements,\nwhich in turn constrains models of the planet's interior structure. We exploit\nthe direct measurements of \\math{e \\cos \\omega} from our secondary-eclipse data\nand combine them with previously published radial velocity data to generate a\nrefined model of the planet's orbit and thus an improved estimate on the\npossible interval for \\math{k\\sb{2}}. We report eclipse phases of \\math{0.49154\n\\pm 0.00080} and \\math{0.49711 \\pm 0.00083} and corresponding \\math{e \\cos\n\\omega} estimates of \\math{-0.0136 \\pm 0.0013} and \\math{-0.0048 \\pm 0.0013}.\nUnder the assumptions of previous work, our estimate of \\math{k\\sb{2}} of 0.81\n{\\pm} 0.10 is consistent with the lower extremes of possible core masses found\nby previous models, including models with no solid core. This anomalous result\nchallenges both interior models and the dynamical assumptions that enable them,\nincluding the essential assumption of apsidal alignment. We also report eclipse\ndepths of 0.081\\% {\\pm} 0.008\\% in the 3.6 {\\micron} channel and 0.088 \\% {\\pm}\n0.028 \\% in the 4.5 {\\micron} channel. These photometric results are\nnon-uniquely consistent with solar-abundance composition without any thermal\ninversion.", "category": "astro-ph_EP" }, { "text": "An extensive radial velocity survey toward NGC 6253: The old and metal rich open cluster NGC 6253 was observed with the FLAMES\nmulti-object spectrograph during an extensive radial velocity campaign\nmonitoring 317 stars with a median of 15 epochs per object. All the targeted\nstars are located along the upper main sequence of the cluster between 14.8 $<$\nV $<$ 16.5. Fifty nine stars are confirmed cluster members both by radial\nvelocities and proper motions and do not show evidence of variability. We\ndetected 45 variable stars among which 25 belong to NGC 6253. We were able to\nderive an orbital solution for 4 cluster members (and for 2 field stars)\nyielding minimum masses in between $\\sim$90 M$\\rm_J$ and $\\sim$460 M$\\rm_J$ and\nperiods between 3 and 220 days. Simulations demonstrated that this survey was\nsensitive to objects down to 30 M$\\rm_J$ at 10 days orbital periods with a\ndetection efficiency equal to 50%. On the basis of these results we concluded\nthat the observed frequency of binaries down to the hydrogen burning limit and\nup to 20 days orbital period is around (1.5$\\pm$1.3)% in NGC 6253. The overall\nobserved frequency of binaries around the sample of cluster stars is\n(13$\\pm$3)%. The median radial velocity precision achieved by the GIRAFFE\nspectrograph in this magnitude range was around $\\sim$240m$\\rm\\,s^{-1}$\n($\\sim$180 m$\\rm\\,s^{-1}$ for UVES). Based on a limited follow-up analysis of 7\nstars in our sample with the HARPS spectrograph we determined that a precision\nof 35 m $\\rm s^{-1}$ can be reached in this magnitude range, offering the\npossibility to further extend the variability analysis into the substellar\ndomain. Prospects are even more favourable once considering the upcoming\nESPRESSO spectrograph at VLT.", "category": "astro-ph_EP" }, { "text": "A sub-Neptune sized planet transiting the M2.5-dwarf G 9-40: Validation\n with the Habitable-zone Planet Finder: We validate the discovery of a 2 Earth radii sub-Neptune-size planet around\nthe nearby high proper motion M2.5-dwarf G 9-40 (EPIC 212048748), using\nhigh-precision near-infrared (NIR) radial velocity (RV) observations with the\nHabitable-zone Planet Finder (HPF), precision diffuser-assisted ground-based\nphotometry with a custom narrow-band photometric filter, and adaptive optics\nimaging. At a distance of $d=27.9\\mathrm{pc}$, G 9-40b is the second closest\ntransiting planet discovered by K2 to date. The planet's large transit depth\n($\\sim$3500ppm), combined with the proximity and brightness of the host star at\nNIR wavelengths (J=10, K=9.2) makes G 9-40b one of the most favorable\nsub-Neptune-sized planet orbiting an M-dwarf for transmission spectroscopy with\nJWST, ARIEL, and the upcoming Extremely Large Telescopes. The star is\nrelatively inactive with a rotation period of $\\sim$29 days determined from the\nK2 photometry. To estimate spectroscopic stellar parameters, we describe our\nimplementation of an empirical spectral matching algorithm using the\nhigh-resolution NIR HPF spectra. Using this algorithm, we obtain an effective\ntemperature of $T_{\\mathrm{eff}}=3404\\pm73$K, and metallicity of\n$\\mathrm{[Fe/H]}=-0.08\\pm0.13$. Our RVs, when coupled with the orbital\nparameters derived from the transit photometry, exclude planet masses above\n$11.7 M_\\oplus$ with 99.7% confidence assuming a circular orbit. From its\nradius, we predict a mass of $M=5.0^{+3.8}_{-1.9} M_\\oplus$ and an RV\nsemi-amplitude of $K=4.1^{+3.1}_{-1.6}\\mathrm{m\\:s^{-1}}$, making its mass\nmeasurable with current RV facilities. We urge further RV follow-up\nobservations to precisely measure its mass, to enable precise transmission\nspectroscopic measurements in the future.", "category": "astro-ph_EP" }, { "text": "HIFI Observations of Water in the Atmosphere of Comet C/2008 Q3\n (Garradd): High-resolution far-infrared and sub-millimetre spectroscopy of water lines\nis an important tool to understand the physical and chemical properties of\ncometary atmospheres. We present observations of several rotational ortho- and\npara-water transitions in comet C/2008 Q3 (Garradd) performed with HIFI on\nHerschel. These observations have provided the first detection of the\n2_{12}-1_{01} (1669 GHz) ortho and 1_{11}-0_{00} (1113 GHz) para transitions of\nwater in a cometary spectrum. In addition, the ground-state transition\n1_{10}-1_{01} at 557 GHz is detected and mapped. By detecting several water\nlines quasi-simultaneously and mapping their emission we can constrain the\nexcitation parameters in the coma. Synthetic line profiles are computed using\nexcitation models which include excitation by collisions, solar infrared\nradiation, and radiation trapping. We obtain the gas kinetic temperature,\nconstrain the electron density profile, and estimate the coma expansion\nvelocity by analyzing the map and line shapes. We derive water production rates\nof 1.7-2.8 x 10^{28} s^{-1} over the range r_h = 1.83-1.85 AU.", "category": "astro-ph_EP" }, { "text": "Exoplanets Beyond the Solar Neighbourhood: Galactic Tidal Perturbations: The majority of Milky Way extrasolar planets likely reside within a few kpc\nof the Galactic centre. The Galactic tidal forces acting on planets scale\ninversely with radius in the Galaxy and so are much greater in the inner Galaxy\nthan in the Solar neighbourhood. Within a range of 3.5 to 10 kpc, the vertical\ntide from the Galactic disc is predominant. Interior to 3.5 kpc, the effects of\nthe Galactic bulge cannot be neglected and the in-plane tidal components are as\nimportant as the vertical ones. Here, we quantify the orbital changes induced\nby these tides. We find that the greatest perturbations occur when the\nplanetary orbit is severely misaligned to the parent star's orbit. When both\nplanes are perpendicular, the eccentricity of the planet is driven to unity,\nalthough the semimajor axis is secularly unaffected. When both planes are\ncoincident, the effect from Galactic tides is minimized, but remains non-zero.\nIn these cases, we provide estimates for the survival times, as well as the\nminimum baseline eccentricity variation for all Milky Way exoplanets as a\nfunction of Galactic parameters. Inclinations similar to the Solar System's\n(about 60 degrees) can easily cause eccentric Neptunes (at about 30 AU) around\nhost stars deep within the Galactic bulge (within 50 pc) to experience\neccentricity variations of several tenths, and cause the exoplanets with the\nwidest-known separations (at about 1000 AU) to experience similar variations in\nthe Galactic disc. These variations occur on timescales of a few Gyr, a\nfraction of a typical main sequence lifetime.", "category": "astro-ph_EP" }, { "text": "Silicon isotopes reveal recycled altered oceanic crust in the mantle\n sources of Ocean Island Basalts: The study of silicon (Si) isotopes in ocean island basalts (OIB) has the\npotential to discern between different models for the origins of geochemical\nheterogeneities in the mantle. Relatively large (several per mil per atomic\nmass unit) Si isotope fractionation occurs in low-temperature environments\nduring biochemical and geochemical precipitation of dissolved Si, where the\nprecipitate is preferentially enriched in the lighter isotopes relative to the\ndissolved Si. In contrast, only a limited range (tenths of a per mil) of Si\nisotope fractionation has been observed from high-temperature igneous\nprocesses. Therefore, Si isotopes may be useful as tracers for the presence of\ncrustal material within OIB mantle source regions that experienced relatively\nlow-temperature surface processes in a manner similar to other stable isotope\nsystems, such as oxygen. Characterizing the isotopic composition of the mantle\nis also of central importance to the use of the Si isotope system as a basis\nfor comparisons with other planetary bodies (e.g., Moon, Mars, asteroids).\n Here we present the first comprehensive suite of high-precision Si isotope\ndata obtained by MC-ICP-MS for a diverse suite of OIB. Samples originate from\nocean islands in the Pacific, Atlantic, and Indian Ocean basins and include\nrepresentative end-members for the EM-1, EM-2, and HIMU mantle components. On\naverage, Si isotope compositions of OIB are in general agreement with previous\nestimates for the Si isotope composition of bulk silicate Earth. Nonetheless,\nsome small systematic variations are present; specifically, most HIMU-type\n(Mangaia; Cape Verde; La Palma, Canary Islands) and Iceland OIB are enriched in\nthe lighter isotopes of Si, consistent with recycled altered oceanic crust and\nlithospheric mantle in their mantle sources.", "category": "astro-ph_EP" }, { "text": "A linear distribution of orbits in compact planetary systems?: We report a linear ordering of orbits in a sample of multiple extrasolar\nplanetary systems with super-Earth planets. We selected 20 cases, mostly\ndiscovered by the Kepler mission, hosting at least four planets within \\sim 0.5\nau. The semi-major axis a_n of an n-th planet in each system of this sample\nobeys a(n) = a_1 + (n-1) \\Delta a, where a_1 is the semi-major axis of the\ninnermost orbit and \\Delta a is a spacing between subsequent planets, which are\nspecific for a particular system. For instance, the Kepler-33 system hosting\nfive super-Earth planets exhibits the relative deviations between the observed\nand linearly predicted semi-major axes of only a few percent. At least half of\nsystems in the sample fulfill the linear law with a similar accuracy. We\nexplain the linear distribution of semi-major axes as a natural implication of\nmultiple chains of mean motion resonances between subsequent planets, which\nemerge due to planet--disk interactions and convergent migration at early\nstages of their evolution.", "category": "astro-ph_EP" }, { "text": "Detecting Transits of Planetary Companions to Giant Stars: Of the approximately 350 extrasolar planets currently known, of order 10%\norbit evolved stars with radii R >~ 2.5 R_sun. These planets are of particular\ninterest because they tend to orbit more massive hosts, and have been subjected\nto variable stellar insolation over their recent histories as their primaries\nevolved off the main sequence. Unfortunately, we have limited information about\nthe physical properties of these planets, as they were all detected by the\nradial velocity method and none have been observed to transit. Here we evaluate\nthe prospects for detecting transits of planetary companions to giant stars. We\nshow that several of the known systems have a priori transit probabilities of\n>~ 10%, and about one transiting system is expected for the sample of host\nstars with R >= 2.5 R_sun. Although the transits are expected to have very\nsmall amplitudes (~few x 10^-4) and long durations (>~ 50 hrs), we argue that\nthe difficulty with detecting these signals in broadband light is one of\nsystematic errors and practicality rather than photon noise, even for modest\naperture ~1m telescopes. We propose a novel method that may overcome these\ndifficulties, which uses narrow-band measurements to isolate the thin ring of\nchromospheric emission expected at the limb of giant stars. The transit signals\nin these narrow bands are expected to be larger in magnitude and briefer in\nduration than in broad-band emission, and thus alleviating many of the\ndifficulties with transit detection in broad-band emission. Finally, we point\nout that it may be possible to discover planetary companions to giant stars\nusing Kepler, provided that a sufficient number of such targets are monitored.", "category": "astro-ph_EP" }, { "text": "Formation of eccentric gas discs from sublimating or partially disrupted\n asteroids orbiting white dwarfs: Of the 21 known gaseous debris discs around white dwarfs, a large fraction of\nthem display observational features that are well described by an eccentric\ndistribution of gas. In the absence of embedded objects or additional forces,\nthese discs should not remain eccentric for long timescales, and should instead\ncircularise due to viscous spreading. The metal pollution and infrared excess\nwe observe from these stars is consistent with the presence of tidally\ndisrupted sub-stellar bodies. We demonstrate, using smoothed particle\nhydrodynamics, that a sublimating or partially disrupting planet on an\neccentric orbit around a white dwarf will form and maintain a gas disc with an\neccentricity within 0.1 of, and lower than, that of the orbiting body. We also\ndemonstrate that the eccentric gas disc observed around the white dwarf SDSS\nJ1228+1040 can be explained by the same hypothesis.", "category": "astro-ph_EP" }, { "text": "A possible flyby anomaly for Juno at Jupiter: In the last decades there have been an increasing interest in improving the\naccuracy of spacecraft navigation and trajectory data. In the course of this\nplan some anomalies have been found that cannot, in principle, be explained in\nthe context of the most accurate orbital models including all known effects\nfrom classical dynamics and general relativity. Of particular interest for its\npuzzling nature, and the lack of any accepted explanation for the moment, is\nthe flyby anomaly discovered in some spacecraft flybys of the Earth over the\ncourse of twenty years. This anomaly manifest itself as the impossibility of\nmatching the pre and post-encounter Doppler tracking and ranging data within a\nsingle orbit but, on the contrary, a difference of a few mm$/$s in the\nasymptotic velocities is required to perform the fitting.\n Nevertheless, no dedicated missions have been carried out to elucidate the\norigin of this phenomenon with the objective either of revising our\nunderstanding of gravity or to improve the accuracy of spacecraft Doppler\ntracking by revealing a conventional origin.\n With the occasion of the Juno mission arrival at Jupiter and the close flybys\nof this planet, that are currently been performed, we have developed an orbital\nmodel suited to the time window close to the perijove. This model shows that an\nanomalous acceleration of a few mm$/$s$^2$ is also present in this case. The\nchance for overlooked conventional or possible unconventional explanations is\ndiscussed.", "category": "astro-ph_EP" }, { "text": "Excitation Properties of Photopigments and Their Possible Dependence on\n the Host Star: Photosynthesis is a plausible pathway for the sustenance of a substantial\nbiosphere on an exoplanet. In fact, it is also anticipated to create\ndistinctive biosignatures detectable by next-generation telescopes. In this\nwork, we explore the excitation features of photopigments that harvest\nelectromagnetic radiation by constructing a simple quantum-mechanical model.\nOur analysis suggests that the primary Earth-based photopigments for\nphotosynthesis may not function efficiently at wavelengths $> 1.1$ $\\mu$m. In\nthe context of (hypothetical) extrasolar photopigments, we calculate the\npotential number of conjugated $\\pi$-electrons ($N_\\star$) in the relevant\nmolecules, which can participate in the absorption of photons. By hypothesizing\nthat the absorption maxima of photopigments are close to the peak spectral\nphoton flux of the host star, we utilize the model to estimate $N_\\star$. As\nper our formalism, $N_\\star$ is modulated by the stellar temperature, and is\nconceivably higher (lower) for planets orbiting stars cooler (hotter) than the\nsun; exoplanets around late-type M-dwarfs might require an $N_\\star$ twice that\nof the Earth. We conclude the analysis with a brief exposition of how our model\ncould be empirically tested by future observations.", "category": "astro-ph_EP" }, { "text": "Mineralogical Characterization and Phase Angle Study of Two Binary\n Near-Earth Asteroids, Potential Targets for NASA's Janus Mission: Ground-based characterization of spacecraft targets prior to mission\noperations is critical to properly plan and execute measurements. Understanding\nsurface properties, like mineralogical composition and phase curves (expected\nbrightness at different viewing geometries) informs data acquisition during the\nflybys. Binary near-Earth asteroids (NEA) (35107) 1991 VH and (175706) 1996 FG3\nwere selected as potential targets of the National Aeronautics and Space\nAdministration's (NASA) dual spacecraft Janus mission. We observed 1991 VH\nusing the 3-m NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, on\nJuly 26, 2008. 1996 FG3 was observed with the IRTF for seven nights during the\nspring of 2022. Compositional analysis of 1991 VH revealed that this NEA is\nclassified as an Sq-type in the Bus-DeMeo taxonomy classification, with a\ncomposition consistent with LL ordinary chondrites. Using thermal modeling, we\ncomputed the thermally corrected spectra for 1996 FG3 and the corresponding\nbest fit albedo of about 2-3% for the best spectra averaged for each night. Our\nspectral analysis indicates that this NEA is a Ch-type. The best possible\nmeteorite analogs for 1996 FG3, based on curve matching, are two carbonaceous\nchondrites, Y-86789 and Murchison. No rotational variation was detected in the\nspectra of 1996 FG3, which means there may not be any heterogeneities on the\nsurface of the primary. However, a clear phase reddening effect was observed in\nour data, confirming findings from previous ground-based studies.", "category": "astro-ph_EP" }, { "text": "Twenty years of SpeX: Accuracy limits of spectral slope measurements in\n asteroid spectroscopy: We examined two decades of SpeX/NASA Infrared Telescope Facility observations\nfrom the Small Main-Belt Asteroid Spectroscopic Survey (SMASS) and the\nMIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS) to investigate\nuncertainties and systematic errors in reflectance spectral slope measurements\nof asteroids. From 628 spectra of 11 solar analogs used for calibration of the\nasteroid spectra, we derived an uncertainty of 4.2%/micron on slope\nmeasurements over 0.8 to 2.4 micron. Air mass contributes to -0.92%/micron per\n0.1 unit air mass difference between the asteroid and the solar analog, and\ntherefore for an overall 2.8%/micron slope variability in SMASS and MITHNEOS\ndesigned to operate within 1.0 to 1.3 air mass. No additional observing\nconditions (including parallactic angle, seeing and humidity) were found to\ncontribute systematically to slope change. We discuss implications for asteroid\ntaxonomic classification works. Uncertainties provided in this study should be\naccounted for in future compositional investigation of small bodies to\ndistinguish intrinsic heterogeneities from possible instrumental effects.", "category": "astro-ph_EP" }, { "text": "Elliptical instability in terrestrial planets and moons: The presence of celestial companions means that any planet may be subject to\nthree kinds of harmonic mechanical forcing: tides, precession/nutation, and\nlibration. These forcings can generate flows in internal fluid layers, such as\nfluid cores and subsurface oceans, whose dynamics then significantly differ\nfrom solid body rotation. In particular, tides in non-synchronized bodies and\nlibration in synchronized ones are known to be capable of exciting the\nso-called elliptical instability, i.e. a generic instability corresponding to\nthe destabilization of two-dimensional flows with elliptical streamlines,\nleading to three-dimensional turbulence. We aim here at confirming the\nrelevance of such an elliptical instability in terrestrial bodies by\ndetermining its growth rate, as well as its consequences on energy dissipation,\non magnetic field induction, and on heat flux fluctuations on planetary scales.\nPrevious studies and theoretical results for the elliptical instability are\nre-evaluated and extended to cope with an astrophysical context. In particular,\ngeneric analytical expressions of the elliptical instability growth rate are\nobtained using a local WKB approach, simultaneously considering for the first\ntime (i) a local temperature gradient due to an imposed temperature contrast\nacross the considered layer or to the presence of a volumic heat source and\n(ii) an imposed magnetic field along the rotation axis, coming from an external\nsource. The theoretical results are applied to the telluric planets and moons\nof the solar system as well as to three Super-Earths: 55 CnC e, CoRoT-7b, and\nGJ 1214b. For the tide-driven elliptical instability in non-synchronized\nbodies, only the Early Earth core is shown to be clearly unstable. For the\nlibration-driven elliptical instability in synchronized bodies, the core of Io\nis shown to be stable, contrary to previously thoughts, whereas Europa, 55 CnC\ne, CoRoT-7b and GJ 1214b cores can be unstable. The subsurface ocean of Europa\nis slightly unstable}. However, these present states do not preclude more\nunstable situations in the past.", "category": "astro-ph_EP" }, { "text": "Forward and Inverse Modeling of the Emission and Transmission Spectrum\n of GJ 436b: Investigating Metal Enrichment, Tidal Heating, and Clouds: The Neptune-mass GJ 436b is one of the most-studied transiting exoplanets\nwith repeated measurements of both its thermal emission and transmission\nspectra. We build on previous studies to answer outstanding questions about\nthis planet, including its potentially high metallicity and tidal heating of\nits interior. We present new observations of GJ 436b's thermal emission at 3.6\nand 4.5 micron, which reduce uncertainties in estimates of GJ 436b's flux at\nthose wavelengths and demonstrate consistency between Spitzer observations\nspanning more than 7 years. We analyze the Spitzer thermal emission photometry\nand Hubble WFC3 transmission spectrum in tandem. We use a powerful dual-pronged\nmodeling approach, comparing these data to both self-consistent and retrieval\nmodels. We vary the metallicity, intrinsic luminosity from tidal heating,\ndisequilibrium chemistry, and heat redistribution. We also study the effect of\nclouds and photochemical hazes on the spectra, but do not find strong evidence\nfor either. The self-consistent and retrieval modeling combine to suggest that\nGJ 436b has a high atmospheric metallicity, with best fits at or above several\nhundred times solar metallicity, tidal heating warming its interior with\nbest-fit intrinsic effective effective temperatures around 300--350 K, and\ndisequilibrium chemistry. High metal-enrichments (>600x solar) can only occur\nfrom the accretion of rocky, rather than icy, material. Assuming Tint~300--350\nK, we find that Q'~2x10^5--10^6, larger than Neptune's Q', and implying a long\ntidal circularization timescale for the planet's orbit. We suggest that\nNeptune-mass planets may be a more diverse class than previously imagined, with\nmetal-enhancements potentially spanning several orders of magnitude, to perhaps\nover 1000x solar metallicity. High fidelity observations with instruments like\nJWST will be critical for characterizing this diversity.", "category": "astro-ph_EP" }, { "text": "MOA-2010-BLG-073L: An M-Dwarf with a Substellar Companion at the\n Planet/Brown Dwarf Boundary: We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073,\nannounced by the Microlensing Observations in Astrophysics survey on\n2010-03-18.\n This event was remarkable because the source was previously known to be\nphotometrically variable. Analyzing the pre-event source lightcurve, we\ndemonstrate that it is an irregular variable over time scales >200d. Its\ndereddened color, $(V-I)_{S,0}$, is 1.221$\\pm$0.051mag and from our lens model\nwe derive a source radius of 14.7$\\pm$1.3 $R_{\\odot}$, suggesting that it is a\nred giant star.\n We initially explored a number of purely microlensing models for the event\nbut found a residual gradient in the data taken prior to and after the event.\nThis is likely to be due to the variability of the source rather than part of\nthe lensing event, so we incorporated a slope parameter in our model in order\nto derive the true parameters of the lensing system.\n We find that the lensing system has a mass ratio of q=0.0654$\\pm$0.0006. The\nEinstein crossing time of the event, $T_{\\rm{E}}=44.3$\\pm$0.1d, was\nsufficiently long that the lightcurve exhibited parallax effects. In addition,\nthe source trajectory relative to the large caustic structure allowed the\norbital motion of the lens system to be detected. Combining the parallax with\nthe Einstein radius, we were able to derive the distance to the lens,\n$D_L$=2.8$\\pm$0.4kpc, and the masses of the lensing objects. The primary of the\nlens is an M-dwarf with $M_{L,p}$=0.16$\\pm0.03M_{\\odot}$ while the companion\nhas $M_{L,s}$=11.0$\\pm2.0M_{\\rm{J}}$ putting it in the boundary zone between\nplanets and brown dwarfs.", "category": "astro-ph_EP" }, { "text": "Hot Exoplanet Atmospheres Resolved with Transit Spectroscopy (HEARTS)\n VI. Non-detection of sodium with HARPS on the bloated super-Neptune WASP-127b: WASP-127b is one of the puffiest exoplanets found to date, with a mass only\n$3.4$ Neptune masses, but a radius larger than Jupiter. It is also located at\nthe border of the Neptune desert, which describes the lack of highly-irradiated\nNeptune-sized planets, and which remains poorly understood. Its large scale\nheight and bright host star make the transiting WASP-127b a valuable target to\ncharacterise in transmission spectroscopy. We use combined EulerCam and TESS\nlight curves to recalculate the system's parameters. Additionally, we present\nan in-depth search for sodium in four transit observations of WASP-127b,\nobtained as part of the Hot Exoplanet Atmosphere Resolved with Transit\nSpectroscopy (HEARTS) survey with the High Accuracy Radial velocity Planet\nSearcher (HARPS) spectrograph. Two nights from this dataset were analysed\nindependently by another team, claiming a detection of sodium incompatible with\nprevious studies of data from both ground and space. We show that this large\nsodium detection is actually due to contamination from telluric sodium\nemissions and the low S/N in the core of the deep stellar sodium lines. When\nproperly accounting for these effects, the previous sodium signal is reduced to\nan absorption of $0.46\\pm0.20\\%$ ($2.3\\sigma$), which is compatible with\nanalyses of WASP-127b transits carried out with other instruments. We can fit a\nGaussian to the D2 line, however, the D1 line was not detected, indicating an\nunusual line ratio if sodium exists in the atmosphere. Follow-up of WASP-127 at\nboth high-resolution and with high sensitivity will be required to firmly\nestablish the presence of sodium and analyse its line shape.", "category": "astro-ph_EP" }, { "text": "Hydrothermal formation of Clay-Carbonate alteration assemblages in the\n Nili Fossae region of Mars: The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has returned\nobservations of the Nili Fossae region indicating the presence of Mg- carbonate\nin small (<10km sq2), relatively bright rock units that are commonly fractured\n(Ehlmann et al., 2008b). We have analyzed spectra from CRISM images and used\nco-located HiRISE images in order to further characterize these\ncarbonate-bearing units. We applied absorption band mapping techniques to\ninvestigate a range of possible phyllosilicate and carbonate minerals that\ncould be present in the Nili Fossae region. We also describe a clay-carbonate\nhydrothermal alteration mineral assemblage in the Archean Warrawoona Group of\nWestern Australia that is a potential Earth analog to the Nili Fossae\ncarbonate-bearing rock units. We discuss the geological and biological\nimplications for hydrothermal processes on Noachian Mars.", "category": "astro-ph_EP" }, { "text": "Discovery and characterization of the exoplanets WASP-148b and c. A\n transiting system with two interacting giant planets: We present the discovery and characterization of WASP-148, a new extrasolar\nsystem that includes at least two giant planets. The host star is a slowly\nrotating inactive late-G dwarf with a V=12 magnitude. The planet WASP-148b is a\nhot Jupiter of 0.72 R_Jup and 0.29 M_Jup that transits its host with an orbital\nperiod of 8.80 days. We found the planetary candidate with the SuperWASP\nphotometric survey, then characterized it with the SOPHIE spectrograph. Our\nradial velocity measurements subsequently revealed a second planet in the\nsystem, WASP-148c, with an orbital period of 34.5 days and a minimum mass of\n0.40 M_Jup. No transits of this outer planet were detected. The orbits of both\nplanets are eccentric and fall near the 4:1 mean-motion resonances. This\nconfiguration is stable on long timescales, but induces dynamical interactions\nso that the orbits differ slightly from purely Keplerian orbits. In particular,\nWASP-148b shows transit-timing variations of typically 15 minutes, making it\nthe first interacting system with transit-timing variations that is detected on\nground-based light curves. We establish that the mutual inclination of the\norbital plane of the two planets cannot be higher than 35 degrees, and the true\nmass of WASP-148c is below 0.60 M_Jup. We present photometric and spectroscopic\nobservations of this system that cover a time span of ten years. We also\nprovide their Keplerian and Newtonian analyses; these analyses should be\nsignificantly improved through future TESS~observations.", "category": "astro-ph_EP" }, { "text": "The Role of Disc Self-Gravity in Circumbinary Planet Systems: II. Planet\n Evolution: We present the results of hydrodynamic simulations examining migration and\ngrowth of planets embedded in self-gravitating circumbinary discs. The binary\nstar parameters are chosen to mimic those of the Kepler-16, -34 and -35\nsystems; the aim of this study is to examine the role of disc mass in\ndetermining the stopping locations of migrating planets at the edge of the\ncavity created by the central binary. Disc self-gravity can cause significant\nshrinkage of the cavity for disc masses in excess of 5--10 $\\times$ the minimum\nmass solar nebula model. Planets forming early in the disc lifetime can migrate\nthrough the disc and stall at locations closer to the central star than is\nnormally the case for lower mass discs, resulting in closer agreement between\nsimulated and observed orbital architecture. The presence of a planet orbiting\nin the cavity of a massive disc can prevent the cavity size from expanding to\nthe size of a lower mass disc. As the disc mass reduces over long time scales,\nthis indicates that circumbinary planet systems retain memory of their initial\nconditions. Our simulations produce planetary orbits in good agreement with\nKepler-16b without the need for self-gravity; Kepler-34 analogue systems\nproduce wide and highly eccentric cavities, and self-gravity improves the\nagreement between simulations and data. Kepler-35b is more difficult to explain\nin detail due to it's relatively low mass, which results in the simulated\nstopping location being at a larger radius than that observed.", "category": "astro-ph_EP" }, { "text": "Alfnoor: assessing the information content of Ariel's low resolution\n spectra with planetary population studies: The ARIEL Space Telescope will provide a large and diverse sample of\nexoplanet spectra, performing spectroscopic observations of about 1000\nexoplanets in the wavelength range $0.5 \\to 7.8 \\; \\mu m$. In this paper, we\ninvestigate the information content of ARIEL's Reconnaissance Survey low\nresolution transmission spectra. Among the goals of the ARIEL Reconnaissance\nSurvey is also to identify planets without molecular features in their\natmosphere. In this work, (1) we present a strategy that will allow to select\ncandidate planets to be reobserved in a ARIEL's higher resolution Tier; (2) we\npropose a metric to preliminary classify exoplanets by their atmospheric\ncomposition without performing an atmospheric retrieval; (3) we introduce the\npossibility to find other methods to better exploit the data scientific\ncontent.", "category": "astro-ph_EP" }, { "text": "The Great Saturn Storm of 2010-2011: In December 2010, a major storm erupted in Saturn's northern hemisphere near\n37 degree planetographic latitude. This rather surprising event, occurring at\nan unexpected latitude and time, is the sixth \"Great White Spot\" (GWS) storm\nobserved over the last century and a half. Such GWS events are planetary-scale\natmospheric phenomena that dramatically change the typically bland appearance\nof the planet. Occurring while the Cassini mission was on-orbit at Saturn, the\nGreat Storm of 2010-2011 was well-suited for intense scrutiny by the suite of\nsophisticated instruments onboard the Cassini spacecraft as well by modern\ninstrumentation on ground-based telescopes and onboard the Hubble Space\nTelescope. This GWS erupted on December 5th and generated a major dynamical\ndisturbance that affected the whole latitude band from 25 deg to 48 deg N.\nLightning events were prominent and detected as outbursts and flashes at both\noptical and radio wavelengths. The activity of the head ceased after about\nseven months, leaving the cloud structure and ambient winds perturbed. The tops\nof the optically dense clouds of the storm's head reached the 300 mbar altitude\nlevel where a mixture of ices was detected. The energetics of the frequency and\npower of lightning, as well as the estimated power generated by the latent heat\nreleased in the water-based convection, both indicate that the power released\nfor the storm was a significant fraction of Saturn's total radiated power. The\neffects of the storm propagated into the stratosphere forming two warm\nairmasses at the 0.5-5 mbar pressure level altitude. Related to the\nstratospheric disturbance, hydrocarbon composition excesses were found. The\ndecades-long interval between storms is probably related to the insolation\ncycle and the long radiative time constant of Saturn's atmosphere, and several\ntheories for temporarily storing energy have been proposed.", "category": "astro-ph_EP" }, { "text": "Resolved near-UV hydrogen emission lines at 40-Myr super-Jovian\n protoplanet Delorme 1 (AB)b: Indications of magnetospheric accretion: We have followed up on our observations of the ~ 40-Myr, and still accreting,\nPMC Delorme 1 (AB)b. We used high-resolution spectroscopy to characterise the\naccretion process further by accessing the wealth of emission lines in the\nnear-UV. With VLT/UVES, we obtained R ~ 50000 spectroscopy at 330--452 nm.\nAfter separating the emission of the companion from that of the M5 low-mass\nbinary, we performed a detailed emission-line analysis, which included\nplanetary accretion shock modelling. We reaffirm ongoing accretion in Delorme 1\n(AB)b and report the first detections in a (super-Jovian) protoplanet of\nresolved hydrogen line emission in the near-UV (H-gamma, H-delta, H-epsilon, H8\nand H9). We tentatively detect H11, H12, He I and Ca II H/K. The analysis\nstrongly favours a planetary accretion shock with a line-luminosity-based\naccretion rate dMp/dt = 2e-8 MJ/yr. The lines are asymmetric and well described\nby sums of narrow and broad components with different velocity shifts. Overall\nline shapes are best explained by a pre-shock velocity v0 = 170+-30 km/s,\nimplying a planetary mass Mp = 13+-5 MJ, and number densities n0 ~ 1e13/cc or\nn0 ~ 1e11/cc. The higher density implies a small line-emitting area of ~ 1%\nrelative to the planetary surface. This favours magnetospheric accretion, a\ncase potentially strengthened by the presence of blueshifted emission in the\nasymmetrical profiles.High-resolution spectroscopy offers the opportunity to\nresolve line profiles, crucial for studying the accretion process in depth. The\nsuper-Jovian protoplanet Delorme 1 (AB)b is still accreting at ~ 40 Myr. Thus,\nDelorme 1 belongs to the growing family of Peter Pan disc systems with\nprotoplanetary and/or circumplanetary disc(s) far beyond the typically assumed\ndisc lifetimes. Further observations of this benchmark companion, and its\npresumed disc(s), will help answer key questions about the accretion geometry\nin PMCs.", "category": "astro-ph_EP" }, { "text": "Solving the Alhazen-Ptolemy Problem: Determining Specular Points on\n Spherical Surfaces for Radiative Transfer of Titan's Seas: Given a light source, a spherical reflector, and an observer, where on the\nsurface of the sphere will the light be directly reflected to the observer,\ni.e. where is the the specular point? This is known as the Alhazen-Ptolemy\nproblem, and finding this specular point for spherical reflectors is useful in\napplications ranging from computer rendering to atmospheric modeling to GPS\ncommunications. Existing solutions rely upon finding the roots of a quartic\nequation and evaluating numerically which root provides the real specular\npoint. We offer a formulation, and two solutions thereof, for which the correct\nroot is predeterminable, thereby allowing the construction of the fully\nanalytical solutions we present. Being faster to compute, our solutions should\nprove useful in cases which require repeated calculation of the specular point,\nsuch as Monte-Carlo radiative transfer, including reflections off of Titan's\nhydrocarbon seas.", "category": "astro-ph_EP" }, { "text": "Dynamical effects on the classical Kuiper Belt during the\n excited-Neptune model: The link between the dynamical evolution of the giant planets and the Kuiper\nBelt orbital structure can provide clues and insight about the dynamical\nhistory of the Solar System. The classical region of the Kuiper Belt has two\npopulations (the cold and hot populations) with completely different physical\nand dynamical properties. These properties have been explained in the framework\nof a subset of the simulations of the Nice Model, in which Neptune remained on\na low-eccentricity orbit (Neptune's eccentricity is never larger than 0.1)\nthroughout the giant planet instability. However, recent simulations have\nshowed that the remaining Nice model simulations, in which Neptune temporarily\nacquires a large-eccentricity orbit (larger than 0.1), are also consistent with\nthe preservation of the cold population (inclination smaller than 4 degrees),\nif the latter formed in situ. However, the resulting a cold population showed\nin many of the simulations eccentricities larger than those observed for the\nreal population. We focus on a short period of time which is characterized by\nNeptune's large eccentricity and a slow precession of Neptune's perihelion. We\nshow that if self-gravity is considered in the disk, the precession rate of the\nparticles longitude of perihelion is slowed down. This, combined with the\neffect of mutual scattering among the bodies, which spreads all orbital\nelements, allows some objects to return to low eccentricities. However, we show\nthat if the cold population originally had a small total mass, this effect is\nnegligible. Thus, we conclude that the only possibilities to keep at low\neccentricity some cold-population objects during a high-eccentricity phase of\nNeptune are that (i) either Neptune's precession was rapid, as suggested by\nBatygin et al. (2011) or (ii) Neptune's slow precession phase was long enough\nto allow some particles to experience a full secular cycle.", "category": "astro-ph_EP" }, { "text": "OGLE-2017-BLG-1434Lb: Confirmation of a Cold Super-Earth using Keck\n Adaptive Optics: The microlensing event OGLE-2017-BLG-1434 features a cold super-Earth planet\nwhich is one of eleven microlensing planets with a planet-host star mass ratio\n$q < 1 \\times 10^{-4}$. We provide an additional mass-distance constraint on\nthe lens host using near-infrared adaptive optics photometry from Keck/NIRC2.\nWe are able to determine a flux excess of $K_L = 16.96 \\pm 0.11$ which most\nlikely comes entirely from the lens star. Combining this with constraints from\nthe large Einstein ring radius, $\\theta_E=1.40 \\pm 0.09\\;mas$ and OGLE parallax\nwe confirm this event as a super-Earth with mass $m_p = 4.43 \\pm 0.25M_\\odot$.\nThis system lies at a distance of $D_L = 0.86 \\pm 0.05\\,kpc$ from Earth and the\nlens star has a mass of $M_L=0.234\\pm0.012M_\\odot$. We confirm that with a\nstar-planet mass ratio of $q=0.57 \\times 10^{-4}$, OGLE-2017-BLG-1434 lies near\nthe inflexion point of the planet-host mass-ratio power law.", "category": "astro-ph_EP" }, { "text": "New transit timing observations for GJ 436 b, HAT-P-3 b, HAT-P-19 b,\n WASP-3 b, and XO-2 b: We present new transit observations acquired between 2014 and 2018 for the\nhot exoplanets GJ 436 b, HAT-P-3 b, HAT-P-19 b, WASP-3 b, and XO-2 b. New\nmid-transit times extend the timespan covered by observations of these\nexoplanets and allow us to refine their transit ephemerides. All new transits\nare consistent with linear ephemerides.", "category": "astro-ph_EP" }, { "text": "The role of the general relativity on icy body reservoirs under the\n effects of an inner eccentric Jupiter: Recent studies have analyzed the dynamical evolution of outer small body\npopulations under the effects of an eccentric inner massive perturber. Such\nouter reservoirs are composed of particles on prograde and retrograde orbits,\nas well as particles whose orbit flips from prograde to retrograde and back\nagain showing a coupling between the inclination i and the ascending node\nlongitude \\Omega (Type-F particles). We analyze the role of the General\nRelativity (GR) on the dynamics of outer particles under the influence of an\ninner eccentric Jupiter-mass planet produced by a planetary scattering event.\nIn particular, we study how the GR affects the dynamical evolution of the outer\nType-F particles, which experience an eccentric Lidov-Kozai mechanism. We carry\nout N-body simulations with and without GR effects. When the GR is included,\nthe extreme values of \\Omega are obtained for retrograde inclinations, while\nthe minimum and maximum inclinations allowed for Type-F particles increase in\ncomparison with that derived without GR effects. According to this, if the GR\nis included in the simulations, the range of prograde (retrograde) inclinations\nof the libration region is reduced (increased) respect to that obtained in\nabsence of GR. We find two new class of particles when the GR effects are\nincluded in the simulations. On the one hand, particles whose orbital plane\nflips from prograde to retrograde and back again without experiencing a\ncoupling between i and \\Omega. On the other hand, retrograde particles that\nshow a strong coupling between i and \\Omega. We infer that the GR may\nsignificantly modify the dynamical properties of the outer reservoirs that\nevolve under the effects of an eccentric inner perturber.", "category": "astro-ph_EP" }, { "text": "Properties of CO$_2$ clathrate hydrates formed in the presence of\n MgSO$_4$ solutions with implications for icy moons: There is evidence to suggest that clathrate hydrates have a significant\neffect on the surface geology of icy bodies in the Solar System. However the\naqueous environments believed to be present on these bodies are likely to be\nsaline rather than pure water. Laboratory work to underpin the properties of\nclathrates in such environments is lacking. We fill this gap by carrying out a\nlaboratory investigation of the physical properties of CO$_2$ clathrates\nproduced in weak aqueous solutions of MgSO$_4$. We use synchrotron X-ray powder\ndiffraction to investigate clathrates formed at high CO$_2$ pressure in ice\nthat has formed from aqueous solutions of MgSO$_4$. We measure the thermal\nexpansion, density and dissociation properties of the clathrates under\ntemperature conditions similar to those on icy Solar System bodies. We find\nthat the sulphate solution inhibits the formation of clathrates by lowering\ntheir dissociation temperatures. Hysteresis is found in the thermal expansion\ncoefficients as clathrates are cooled and heated; we attribute this to the\npresence of the salt in solution. The density derived from X-ray powder\ndiffraction is temperature and pressure dependent. When comparing the density\nof CO$_2$ clathrates to that of the solution in which they formed, we conclude\nthat they sink in the oceans in which they form. We also find that the\npolymorph of ice present at low temperatures is Ih rather than Ic, which we\nattribute to the presence of the MgSO$_4$. We 1) conclude that the clathrate\ndensity has implications for their behaviour in satellite oceans as their\nsinking and floating capabilities are temperature and pressure dependent, 2)\nconclude that the presence of MgSO$_4$ inhibits the formation of clathrates and\nin some cases may even affect their structure and 3) report the dominance of Ih\nthroughout the experimental procedure despite Ic being the stable phase at low\ntemperature.", "category": "astro-ph_EP" }, { "text": "A Bayesian Analysis of Technological Intelligence in Land and Oceans: Current research indicates that (sub)surface ocean worlds essentially devoid\nof subaerial landmasses (e.g., continents) are common in the Milky Way, and\nthat these worlds could host habitable conditions, thence raising the\npossibility that life and technological intelligence (TI) may arise in such\naquatic settings. It is known, however, that TI on Earth (i.e., humans) arose\non land. Motivated by these considerations, we present a Bayesian framework to\nassess the prospects for the emergence of TIs in land- and ocean-based habitats\n(LBHs and OBHs). If all factors are equally conducive for TIs to arise in LBHs\nand OBHs, we demonstrate that the evolution of TIs in LBHs (which includes\nhumans) might have very low odds of roughly $1$-in-$10^3$ to $1$-in-$10^4$,\nthus outwardly contradicting the Copernican Principle. Hence, we elucidate\nthree avenues whereby the Copernican Principle can be preserved: (i) the\nemergence rate of TIs is much lower in OBHs, (ii) the habitability interval for\nTIs is much shorter in OBHs, and (iii) only a small fraction of worlds with\nOBHs comprise appropriate conditions for effectuating TIs. We also briefly\ndiscuss methods for empirically falsifying our predictions, and comment on the\nfeasibility of supporting TIs in aerial environments.", "category": "astro-ph_EP" }, { "text": "RISTRETTO: high-resolution spectroscopy at the diffraction limit of the\n VLT: RISTRETTO is a visible high-resolution spectrograph fed by an extreme\nadaptive optics (XAO) system, to be proposed as a visitor instrument on ESO\nVLT. The main science goal of RISTRETTO is the detection and atmospheric\ncharacterization of exoplanets in reflected light, in particular the temperate\nrocky planet Proxima b. RISTRETTO will be able to measure albedos and detect\natmospheric features in a number of exoplanets orbiting nearby stars for the\nfirst time. It will do so by combining a high-contrast AO system working at the\ndiffraction limit of the telescope to a high-resolution spectrograph, via a\n7-spaxel integral-field unit (IFU) feeding single-mode fibers. Further science\ncases for RISTRETTO include the study of accreting protoplanets such as PDS 70\nb & c through spectrally-resolved H-alpha emission; and spatially-resolved\nstudies of Solar System objects such as icy moons and the ice giants Uranus and\nNeptune. The project is in an advanced design phase for the spectrograph and\nIFU/fiber-link sub-systems, and a preliminary design phase for the AO\nfront-end. Construction of the spectrograph and IFU/fiber-link will start at\nthe end of 2022. RISTRETTO is a pathfinder instrument in view of similar\ndevelopments at ESO ELT, in particular the SCAO-IFU mode of ELT-ANDES and the\nfuture ELT-PCS instrument.", "category": "astro-ph_EP" }, { "text": "Titan organic aerosols: molecular composition and structure of\n laboratory analogues inferred from systematic pyrolysis gas chromatography\n mass spectrometry analysis: Numerous studies have been carried out to characterize the chemical\ncomposition of laboratory analogues of Titan aerosols (tholins), but their\nmolecular composition as well as their structure are still poorly known. If\npyrolysis gas chromatography mass spectrometry (pyr-GCMS) has been used for\nyears to give clues about this composition, the highly disparate results\nobtained can be attributed to the analytical conditions used and/or to\ndifferences in the nature of the analogues studied. In order to have a better\ndescription of Titan tholins molecular composition, we led a systematic\nanalysis of these materials using pyr-GCMS with two major objectives: (i)\nexploring the analytical parameters to estimate the biases this technique can\ninduce and to find an optimum for analyses allowing the detection of a wide\nrange of compounds and thus a characterization of the tholins composition as\ncomprehensive as possible, and (ii) highlighting the role of the CH4 ratio in\nthe gaseous reactive medium on the tholins molecular structure. With this aim,\nwe used a radio-frequency plasma discharge to synthetize tholins with different\nconcentrations of CH4 diluted in N2. The samples were systematically pyrolyzed\nfrom 200 to 600{\\deg}C. The extracted gases were then analyzed by GCMS for\ntheir molecular identification.", "category": "astro-ph_EP" }, { "text": "Atmospheres as a Window to Rocky Exoplanet Surfaces: As the characterization of exoplanet atmospheres proceeds, providing insights\ninto atmospheric chemistry and composition, a key question is how much deeper\ninto the planet we might be able to see from its atmospheric properties alone.\nFor small planets with modest atmospheres and equilibrium temperatures, the\nfirst layer below the atmosphere will be their rocky surface. For such warm\nrocky planets, broadly Venus-like planets, the high temperatures and moderate\npressures at the base of their atmospheres may enable thermochemical\nequilibrium between rock and gas. This links the composition of the surface to\nthat of the observable atmosphere. Using an equilibrium chemistry code, we find\na boundary in surface pressure-temperature space which simultaneously separates\ndistinct mineralogical regimes and atmospheric regimes, potentially enabling\ninference of surface mineralogy from spectroscopic observations of the\natmosphere. Weak constraints on the surface pressure and temperature also\nemerge. This regime boundary corresponds to conditions under which SO2 is\noxidized and absorbed by calcium-bearing minerals in the crust, thus the two\nregimes reflect the sulphidation of the crust. The existence of these\natmospheric regimes for Venus-like planets is robust to plausible changes in\nthe elemental composition. Our results pave the way to the prospect of\ncharacterizing exoplanetary surfaces as new data for short period rocky planet\natmospheres emerge.", "category": "astro-ph_EP" }, { "text": "On the Low False Positive Probabilities of Kepler Planet Candidates: We present a framework to conservatively estimate the probability that any\nparticular planet-like transit signal observed by the Kepler mission is in fact\na planet, prior to any ground-based follow-up efforts. We use Monte Carlo\nmethods based on stellar population synthesis and Galactic structure models,\nand report a priori false positive probabilities for every Kepler Object of\nInterest in tabular form, assuming a 20% intrinsic occurrence rate of close-in\nplanets in the radius range 0.5 Rearth < Rp < 20 Rearth. Almost every candidate\nhas FPP <10%, and over half have FPP <5%. This probability varies most strongly\nwith the magnitude and Galactic latitude of the Kepler target star, and more\nweakly with transit depth. We establish that a single deep high-resolution\nimage will be an extremely effective follow-up tool for the shallowest\n(Earth-sized) transits, providing the quickest route towards probabilistically\n\"validating\" the smallest candidates by potentially decreasing the false\npositive probability of an earth-sized transit around a faint star from >10% to\n<1%. On the other hand, we show that the most useful follow-up observations for\nmoderate-depth (super-Earth and Neptune-sized) candidates are shallower AO\nimaging and high S/N spectroscopy. Since Kepler has detected many more\nplanetary signals than can be positively confirmed with ground-based follow-up\nefforts in the near term, these calculations will be crucial to using the\nensemble of Kepler data to determine population characteristics of planetary\nsystems. We also describe how our analysis complements the Kepler team's more\ndetailed BLENDER false positive analysis for planet validation.", "category": "astro-ph_EP" }, { "text": "Bayesian Model Testing of Ellipsoidal Variations on Stars due to Hot\n Jupiters: A massive planet closely orbiting its host star creates tidal forces that\ndistort the typically spherical stellar surface. These distortions, known as\nellipsoidal variations, result in changes in the photometric flux emitted by\nthe star, which can be detected within the data from the Kepler Space\nTelescope. Currently, there exist several models describing such variations and\ntheir effect on the photometric flux. By using Bayesian model testing in\nconjunction with the Bayesian-based exoplanet characterization software package\nEXONEST, the most probable representation for ellipsoidal variations was\ndetermined for synthetic data and the confirmed hot Jupiter exoplanet\nKepler-13Ab.The most preferred model for ellipsoidal variations observed in the\nKepler-13 light curve was determined to be EVIL-MC. Among the trigonometric\nmodels, the Modified Kane & Gelino model provided the best representation of\nellipsoidal variations for the Kepler-13 system and may serve as a fast\nalternative to the more computationally intensive EVIL-MC. The computational\nfeasibility of directly modeling the ellipsoidal variations of a star are\nexamined and future work is outlined. Providing a more accurate model of\nellipsoidal variations is expected to result in better planetary mass\nestimations.", "category": "astro-ph_EP" }, { "text": "Marginalising instrument systematics in HST WFC3 transit lightcurves: Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) infrared observations\nat 1.1-1.7$\\mu$m probe primarily the H$_2$O absorption band at 1.4$\\mu$m, and\nhas provided low resolution transmission spectra for a wide range of\nexoplanets. We present the application of marginalisation based on Gibson\n(2014) to analyse exoplanet transit lightcurves obtained from HST WFC3, to\nbetter determine important transit parameters such as R$_p$/R$_*$, important\nfor accurate detections of H$_2$O. We approximate the evidence, often referred\nto as the marginal likelihood, for a grid of systematic models using the Akaike\nInformation Criterion (AIC). We then calculate the evidence-based weight\nassigned to each systematic model and use the information from all tested\nmodels to calculate the final marginalised transit parameters for both the\nband-integrated, and spectroscopic lightcurves to construct the transmission\nspectrum. We find that a majority of the highest weight models contain a\ncorrection for a linear trend in time, as well as corrections related to HST\norbital phase. We additionally test the dependence on the shift in spectral\nwavelength position over the course of the observations and find that\nspectroscopic wavelength shifts $\\delta_\\lambda(\\lambda)$, best describe the\nassociated systematic in the spectroscopic lightcurves for most targets, while\nfast scan rate observations of bright targets require an additional level of\nprocessing to produce a robust transmission spectrum. The use of\nmarginalisation allows for transparent interpretation and understanding of the\ninstrument and the impact of each systematic evaluated statistically for each\ndataset, expanding the ability to make true and comprehensive comparisons\nbetween exoplanet atmospheres.", "category": "astro-ph_EP" }, { "text": "Lunar eclipse induces disturbance in the lunar exosphere: Given the renewed scientific interest in lunar exploration missions, complete\nunderstanding of lunar near surface environment and its exosphere under\ndifferent conditions is of paramount importance. Lunar exosphere has been\nextensively studied by ground based observations [18,19,20,21,22,23] and\nhypothesized by different models[1,2,3,4,5,6,7,8,9,10,11,12,13]. In present\nwork, we have discussed overlooked possible sources behind changes in the lunar\nexosphere when the Moon passes through the penumbra and umbra of the Earth\nduring a lunar eclipse. The dusty turbulent environment due to planetary shadow\nis not only confined to lunar studies and exploration, but it can also be\nextended to all terrestrial airless bodies in the universe with a dusty surface\ne.g. some planets, planetary satellites, asteroids etc.", "category": "astro-ph_EP" }, { "text": "Differences in the gas and dust distribution in the transitional disk of\n a sun-like young star, PDS 70: We present ALMA 0.87 mm continuum, HCO+ J=4--3 emission line, and CO J=3--2\nemission line data of the disk of material around the young, Sun-like star PDS\n70. These data reveal the existence of a possible two component transitional\ndisk system with a radial dust gap of 0.\"2 +/- 0.\"05, an azimuthal gap in the\nHCO+ J=4--3 moment zero map, as well as two bridge-like features in the gas\ndata. Interestingly these features in the gas disk have no analogue in the dust\ndisk making them of particular interest. We modeled the dust disk using the\nMonte Carlo radiative transfer code HOCHUNK3D (Whitney et al. 2013) using a two\ndisk components. We find that there is a radial gap that extends from 15-60 au\nin all grain sizes which differs from previous work.", "category": "astro-ph_EP" }, { "text": "No evidence for radius inflation in hot Jupiters from vertical advection\n of heat: Understanding the radiative-dynamical coupling between upper photosphere and\ndeeper atmosphere is a key in understanding the abnormal large radii of hot\nJupiters. One needs very long integration times of 3D general circulation\nmodels (GCMs) with self consistent radiative transfer to achieve a better\nunderstanding of the feedback process between dynamics and radiation. We here\npresent the longest 3D non-gray GCM study (86000 d) of an ultra hot Jupiter\n(WASP-76 b) published to this date that reached a final converged state.\nFurthermore, we present a method that can be used to accelerate the path\ntowards temperature convergence in the deep atmospheric layers. We find that\nthe final converged temperature profile is cold in the deep atmospheric layers,\nlacking any sign of vertical transport of potential temperature by large scale\natmospheric motions. We thus conclude that the coupling between radiation and\ndynamics alone is not sufficient to explain the abnormal large radii of\ninflated hot gas giants.", "category": "astro-ph_EP" }, { "text": "First Near-IR Spectroscopic Survey of Neptune Trojans with JWST:\n Distinct Surface Compositions of Red vs Ultra-Red Neptune Trojans: Neptune's Trojan asteroids have been observed to have a variety of optical\ncolors, most notably red (g $-$ r < 0.75) vs. ultra-red (g $-$ r > 0.75), but\nthe underlying cause of these different color classifications is unknown.\nNear-IR spectroscopy can be used as a probe of the surface composition of these\nobjects, as broad ice bands for a variety of materials are present in the\nnear-IR. Here, we present the first results of a spectroscopic survey of\nNeptune's Trojan asteroids using the NIRSpec instrument on JWST. We compare the\nnear-IR spectra of eight Neptune Trojans (NTs) based on different optical color\nclassifications and with model spectra of different ices. We find that most of\nour targets are consistent with a surface covered in a thin layer of H$_2$O and\nCO$_2$ ices, while the only NT to reliably be classified as ultra-red is\ncovered in ice tholins in addition to CO$_2$. Ice tholins are a known reddening\nagent when subjected to irradiation, so these results support the hypothesis\nthat differences in optical color are due to differences in irradiation of the\nsurfaces of these bodies. Since NTs have very similar orbits and therefore\ngenerally similar levels of irradiation at the current time, our results\nsuggest that these objects have unique origins or there is ongoing processing\nof the surfaces of these objects through stochastic disturbances such as\nimpacts.", "category": "astro-ph_EP" }, { "text": "ExoMol line lists IV: The rotation-vibration spectrum of methane up to\n 1500 K: A new hot line list is calculated for $^{12}$CH$_4$ in its ground electronic\nstate. This line list, called 10to10, contains 9.8 billion transitions and\nshould be complete for temperatures up to 1500 K. It covers the wavelengths\nlonger than 1 $\\mu$m and includes all transitions to upper states with energies\nbelow $hc \\cdot 18\\,000$ cm$^{-1}$ and rotational excitation up to $J=39$. The\nline list is computed using the eigenvalues and eigenfunctions of CH$_4$\nobtained by variational solution of the Schr\\\"{o}dinger equation for the\nrotation-vibration motion of nuclei employing program TROVE. An ab initio\ndipole moment surface and a new 'spectroscopic' potential energy surface are\nused. Detailed comparisons with other available sources of methane transitions\nincluding HITRAN, experimental compilations and other theoretical line lists\nshow that these sources lack transitions both higher temperatures and near\ninfrared wavelengths. This line list is suitable for modelling atmospheres of\ncool stars and exoplanets. It is available from the CDS database as well as at\nwww.exomol.com.", "category": "astro-ph_EP" }, { "text": "Asteroid models from generalised projections: Essential facts for\n asteroid modellers and geometric inverse problem solvers: We present a review of the problem of asteroid shape and spin reconstruction\nfrom generalised projections; i.e., from lightcurves, disk-resolved images,\noccultation silhouettes, radar range-Doppler data, and interferometry. The aim\nof this text is to summarize all important mathematical facts and proofs\nrelated to this inverse problem, to describe their implications to observers\nand modellers, and to provide the reader with all relevant references.", "category": "astro-ph_EP" }, { "text": "Trajectory Optimisation of a Swarm Orbiting 67P/Churyumov-Gerasimenko\n Maximising Gravitational Signal: Proper modelling of the gravitational fields of irregularly shaped asteroids\nand comets is an essential yet challenging part of any spacecraft visit and\nflyby to these bodies. Accurate density representations provide crucial\ninformation for proximity missions which rely heavily on it to design safe and\nefficient trajectories. This work explores using a spacecraft swarm to maximise\nthe measured gravitational signal in a hypothetical mission around the comet\n67P/Churyumov-Gerasimenko. Spacecraft trajectories are simultaneously\npropagated with an evolutionary optimisation approach to maximise overall\nsignal return. The propagation is based on an open-source polyhedral gravity\nmodel using a detailed mesh of 67P and considers the comet's sidereal rotation.\nWe compare performance on a mission scenario using one and four spacecraft. The\nresults show that the swarm achieved almost twice the single spacecraft\ncoverage over a fixed mission duration. However, optimising for a single\nspacecraft results in a more effective trajectory. Overall, this work serves as\na testbed for efficiently designing a set of trajectories in this complex\ngravitational environment balancing measured signals and risks in a swarm\nscenario.\n The codebase and results are publicly available at\nhttps://github.com/rasmusmarak/TOSS", "category": "astro-ph_EP" }, { "text": "Sub-Saturn Planet MOA-2008-BLG-310Lb: Likely To Be In The Galactic Bulge: We report the detection of sub-Saturn-mass planet MOA-2008-BLG-310Lb and\nargue that it is the strongest candidate yet for a bulge planet. Deviations\nfrom the single-lens fit are smoothed out by finite-source effects and so are\nnot immediately apparent from the light curve. Nevertheless, we find that a\nmodel in which the primary has a planetary companion is favored over the\nsingle-lens model by \\Delta\\chi^2 ~ 880 for an additional three degrees of\nfreedom. Detailed analysis yields a planet/star mass ratio\nq=(3.3+/-0.3)x10^{-4} and an angular separation between the planet and star\nwithin 10% of the angular Einstein radius. The small angular Einstein radius,\n\\theta_E=0.155+/-0.011 mas, constrains the distance to the lens to be D_L>6.0\nkpc if it is a star (M_L>0.08 M_sun). This is the only microlensing exoplanet\nhost discovered so far that must be in the bulge if it is a star. By analyzing\nVLT NACO adaptive optics images taken near the baseline of the event, we detect\nadditional blended light that is aligned to within 130 mas of the lensed\nsource. This light is plausibly from the lens, but could also be due to a\ncompanion to lens or source, or possibly an unassociated star. If the blended\nlight is indeed due to the lens, we can estimate the mass of the lens,\nM_L=0.67+/-0.14 M_sun, planet mass m=74+/-17 M_Earth, and projected separation\nbetween the planet and host, 1.25+/-0.10 AU, putting it right on the \"snow\nline\". If not, then the planet has lower mass, is closer to its host and is\ncolder. To distinguish among these possibilities on reasonable timescales would\nrequire obtaining Hubble Space Telescope images almost immediately, before the\nsource-lens relative motion of \\mu=5 mas yr^{-1} causes them to separate\nsubstantially.", "category": "astro-ph_EP" }, { "text": "Efficient Follow-Up of Exoplanet Transits Using Small Telescopes: This paper is to introduce an online tool for the prediction of exoplanet\ntransit light curves. Small telescopes can readily capture exoplanet transits\nunder good weather conditions when the combination of a bright star and a large\ntransiting exoplanet results in a significant depth of transit. However, in\nreality there are many considerations that need to be made in order to obtain\nuseful measurements. This paper and accompanying website layout a procedure\nbased on time series differential photometry that has been successfully\nemployed using 0.4m aperture telescopes to predict the expected precision for a\nwhole light curve. This enables robust planning to decide whether the\nobservation of a particular exoplanet transit should be attempted and in\nparticular to be able to readily see when it should not to be attempted. This\nmay result in a significant increase in the number of transit observations\ncaptured by non-specialists. The technique and website are also appropriate for\nplanning a variety of variable star observations where a prediction of the\nlight curve can be made.", "category": "astro-ph_EP" }, { "text": "Long-Term Stability of Tightly Packed Multi-Planet Systems in Prograde,\n Coplanar, Circumstellar Orbits within the $\u03b1$ Centauri AB System: We perform long-term simulations, up to ten billion years, of closely-spaced\nconfigurations of 2 -- 6 planets, each as massive as the Earth, traveling on\nnested orbits about either stellar component in $\\alpha$ Centauri AB. The\ninnermost planet initially orbits at either the inner edge of its star's\nempirical habitable zone (HZ) or the inner edge of its star's conservative HZ.\nAlthough individual planets on low inclination, low eccentricity, orbits can\nsurvive throughout the habitable zones of both stars, perturbations from the\ncompanion star require that the minimum spacing of planets in multi-planet\nsystems within the habitable zones of each star must be significantly larger\nthan the spacing of similar multi-planet systems orbiting single stars in order\nto be long-lived. The binary companion induces a forced eccentricity upon the\norbits of planets in orbit around either star. Planets on appropriately-phased\ncircumstellar orbits with initial eccentricities equal to their forced\neccentricities can survive on more closely spaced orbits than those with\ninitially circular orbits, although the required spacing remains higher than\nfor planets orbiting single stars. A total of up to nine planets on nested\nprograde orbits can survive for the current age of the system within the\nempirical HZs of the two stars, with five of these orbiting $\\alpha$ Centauri B\nand four orbiting $\\alpha$ Centauri A.", "category": "astro-ph_EP" }, { "text": "The Magellan PFS Planet Search Program: Radial Velocity and Stellar\n Abundance Analyses of the 360 AU, Metal-Poor Binary \"Twins\" HD 133131A & B: We present a new precision radial velocity (RV) dataset that reveals multiple\nplanets orbiting the stars in the $\\sim$360 AU, G2$+$G2 \"twin\" binary HD\n133131AB. Our 6 years of high-resolution echelle observations from MIKE and 5\nyears from PFS on the Magellan telescopes indicate the presence of two\neccentric planets around HD 133131A with minimum masses of 1.43$\\pm$0.03 and\n0.63$\\pm$0.15 $\\mathcal{M}_{\\rm J}$ at 1.44$\\pm$0.005 and 4.79$\\pm$0.92 AU,\nrespectively. Additional PFS observations of HD 133131B spanning 5 years\nindicate the presence of one eccentric planet of minimum mass 2.50$\\pm$0.05\n$\\mathcal{M}_{\\rm J}$ at 6.40$\\pm$0.59 AU, making it one of the longest period\nplanets detected with RV to date. These planets are the first to be reported\nprimarily based on data taken with PFS on Magellan, demonstrating the\ninstrument's precision and the advantage of long-baseline RV observations. We\nperform a differential analysis between the Sun and each star, and between the\nstars themselves, to derive stellar parameters and measure a suite of 21\nabundances across a wide range of condensation temperatures. The host stars are\nold (likely $\\sim$9.5 Gyr) and metal-poor ([Fe/H]$\\sim$-0.30), and we detect a\n$\\sim$0.03 dex depletion in refractory elements in HD 133131A versus B (with\nstandard errors $\\sim$0.017). This detection and analysis adds to a small but\ngrowing sample of binary \"twin\" exoplanet host stars with precise abundances\nmeasured, and represents the most metal-poor and likely oldest in that sample.\nOverall, the planets around HD 133131A and B fall in an unexpected regime in\nplanet mass-host star metallicity space and will serve as an important\nbenchmark for the study of long period giant planets.", "category": "astro-ph_EP" }, { "text": "TOI-222: a single-transit TESS candidate revealed to be a 34-day\n eclipsing binary with CORALIE, EulerCam and NGTS: We report the period, eccentricity, and mass determination for the TESS\nsingle-transit event candidate TOI-222, which displayed a single 3000 ppm\ntransit in the TESS two-minute cadence data from Sector 2. We determine the\norbital period via radial velocity measurements (P=33.9,days), which allowed\nfor ground-based photometric detection of two subsequent transits. Our data\nshow that the companion to TOI-222 is a low mass star, with a radius of\n$0.18_{-0.10}^{+0.39}$ Rsun and a mass of $0.23\\pm0.01$ Msun. This discovery\nshowcases the ability to efficiently discover long-period systems from TESS\nsingle transit events using a combination of radial velocity monitoring coupled\nwith high precision ground-based photometry.", "category": "astro-ph_EP" }, { "text": "An ultra-short period rocky super-Earth orbiting the G2-star HD 80653: Ultra-short period (USP) planets are a class of exoplanets with periods\nshorter than one day. The origin of this sub-population of planets is still\nunclear, with different formation scenarios highly dependent on the composition\nof the USP planets. A better understanding of this class of exoplanets will,\ntherefore, require an increase in the sample of such planets that have accurate\nand precise masses and radii, which also includes estimates of the level of\nirradiation and information about possible companions. Here we report a\ndetailed characterization of a USP planet around the solar-type star HD 80653\n$\\equiv$ EP 251279430 using the K2 light curve and 108 precise radial\nvelocities obtained with the HARPS-N spectrograph, installed on the Telescopio\nNazionale Galileo. From the K2 C16 data, we found one super-Earth planet\n($R_{b}=1.613\\pm0.071 R_{\\oplus}$) transiting the star on a short-period orbit\n($P_{\\rm b}=0.719573\\pm0.000021$ d). From our radial velocity measurements, we\nconstrained the mass of HD 80653 b to $M_{b}=5.60\\pm0.43 M_{\\oplus}$. We also\ndetected a clear long-term trend in the radial velocity data. We derived the\nfundamental stellar parameters and determined a radius of\n$R_{\\star}=1.22\\pm0.01 R_{\\odot}$ and mass of $M_{\\star}=1.18\\pm0.04\nM_{\\odot}$, suggesting that HD 80653, has an age of $2.7\\pm1.2$ Gyr. The bulk\ndensity ($\\rho_{b} = 7.4 \\pm 1.1$ g cm$^{-3}$) of the planet is consistent with\nan Earth-like composition of rock and iron with no thick atmosphere. Our\nanalysis of the K2 photometry also suggests hints of a shallow secondary\neclipse with a depth of 8.1$\\pm$3.7 ppm. Flux variations along the orbital\nphase are consistent with zero. The most important contribution might come from\nthe day-side thermal emission from the surface of the planet at $T\\sim3480$ K.", "category": "astro-ph_EP" }, { "text": "KMT-2018-BLG-1990Lb: A Nearby Jovian Planet From A Low-Cadence\n Microlensing Field: We report the discovery and characterization of KMT-2018-BLG-1990Lb, a Jovian\nplanet $(m_p=0.57_{-0.25}^{+0.79}\\,M_J)$ orbiting a late M dwarf\n$(M=0.14_{-0.06}^{+0.20}\\,M_\\odot)$, at a distance\n$(D_L=1.23_{-0.43}^{+1.06}\\,\\kpc)$, and projected at $2.6\\pm 0.6$ times the\nsnow line distance, i.e., $a_{\\rm snow}\\equiv 2.7\\,\\au (M/M_\\odot)$, This is\nthe second Jovian planet discovered by KMTNet in its low cadence ($0.4\\,{\\rm\nhr}^{-1}$) fields, demonstrating that this population will be well\ncharacterized based on survey-only microlensing data.", "category": "astro-ph_EP" }, { "text": "Correction to: Effect of the rotation and tidal dissipation history of\n stars on the evolution of close-in planets: This is an erratum for the publication Bolmont & Mathis 2016 (Celestial\nMechanics and Dynamical Astronomy, 126, 275-296,\nhttps://doi.org/10.1007/s10569-016-9690-3). There was a small mistake for the\nspin integration of our code which we corrected and we take advantage of this\nerratum to investigate a bit further the influence of a planet on the spin of\nits host star.", "category": "astro-ph_EP" }, { "text": "Asteroid Surface Geophysics: The regolith-covered surfaces of asteroids preserve records of geophysical\nprocesses that have occurred both at their surfaces and sometimes also in their\ninteriors. As a result of the unique micro-gravity environment that these\nbodies posses, a complex and varied geophysics has given birth to fascinating\nfeatures that we are just now beginning to understand. The processes that\nformed such features were first hypothesised through detailed spacecraft\nobservations and have been further studied using theoretical, numerical and\nexperimental methods that often combine several scientific disciplines. These\nmultiple approaches are now merging towards a further understanding of the\ngeophysical states of the surfaces of asteroids. In this chapter we provide a\nconcise summary of what the scientific community has learned so far about the\nsurfaces of these small planetary bodies and the processes that have shaped\nthem. We also discuss the state of the art in terms of experimental techniques\nand numerical simulations that are currently being used to investigate regolith\nprocesses occurring on small-body surfaces and that are contributing to the\ninterpretation of observations and the design of future space missions.", "category": "astro-ph_EP" }, { "text": "Circumbinary Chaos: Using Pluto's Newest Moon to Constrain the Masses of\n Nix & Hydra: The Pluto system provides a unique local laboratory for the study of binaries\nwith multiple low mass companions. In this paper, we study the orbital\nstability of P4, the most recently discovered moon in the Pluto system. This\nnewfound companion orbits near the plane of the Pluto-Charon binary, roughly\nhalfway between the two minor moons Nix and Hydra. We use a suite of few body\nintegrations to constrain the masses of Nix and Hydra, and the orbital\nparameters of P4. For the system to remain stable over the age of the Solar\nSystem, the masses of Nix and Hydra likely do not exceed 5e16 kg and 9e16 kg,\nrespectively. These upper limits assume a fixed mass ratio between Nix and\nHydra at the value implied by their median optical brightness. Our study finds\nthat stability is more sensitive to their total mass and that a downward\nrevision of Charon's eccentricity (from our adopted value of 0.0035) is\nunlikely to significantly affect our conclusions. Our upper limits are an order\nof magnitude below existing astrometric limits on the masses of Nix and Hydra.\nFor a density at least that of ice, the albedos of Nix and Hydra would exceed\n0.3. This constraint implies they are icy, as predicted by giant impact models.\nEven with these low masses, P4 only remains stable if its eccentricity e <\n0.02. The 5:1 commensurability with Charon is particularly unstable, Combining\nstability constraints with the observed mean motion places the preferred orbit\nfor P4 just exterior to the 5:1 resonance. These predictions will be tested\nwhen the New Horizons satellite visits Pluto. Based on the results for the\nPluto-Charon system, we expect that circumbinary, multi-planet systems will be\nmore widely spaced than their singleton counterparts. Further, circumbinary\nexoplanets close to the three-body stability boundary, such as those found by\nKepler, are less likely to have other companions nearby.", "category": "astro-ph_EP" }, { "text": "Spin and orbital dynamics of planets undergoing thermal atmospheric\n tides using a vectorial approach: Earth-mass planets are expected to have atmospheres and experience thermal\ntides raised by the host star. These tides transfer energy to the planet that\ncan counter the dissipation from bodily tides. Indeed, even a relatively thin\natmosphere can drive the rotation of these planets away from the synchronous\nstate. Here we revisit the dynamical evolution of planets undergoing thermal\natmospheric tides. We use a novel approach based on a vectorial formalism,\nwhich is frame independent and valid for any configuration of the system,\nincluding any eccentricity and obliquity values. We provide the secular\nequations of motion after averaging over the mean anomaly and the argument of\nthe pericenter, which are suitable to model the long-term spin and orbital\nevolution of the planet.", "category": "astro-ph_EP" }, { "text": "Long-term Orbital Period Variation of Hot Jupiters from Transiting Time\n Analysis using TESS Survey Data: Many hot Jupiters may experience orbital decays, which are manifested as\nlong-term transit timing variations. We have analyzed 7068 transits from the\nTransiting Exoplanet Survey Satellite (TESS) for a sample of 326 hot Jupiters.\nThese new mid-transit time data allow us to update ephemerides for these\nsystems. By combining the new TESS transit timing data with archival data, we\nsearch for possible long-term orbital period variations in these hot Jupiters\nusing a linear and a quadratic ephemeris model. We identified 26 candidates\nthat exhibit possible long-term orbital period variations, including 18\ncandidates with decreasing orbital periods and 8 candidates with increasing\norbital periods. Among them, 12 candidates have failed in our leave-one-out\ncross-validation (LOOCV) test and thus should be considered as marginal\ncandidates. In addition to tidal interaction, alternative mechanisms such as\napsidal precession, R{\\o}mer effect, and Applegate effect could also contribute\nto the observed period variations. The ephemerides derived in this work are\nuseful for scheduling follow-up observations for these hot Jupiters in the\nfuture. The Python code used to generate the ephemerides is made available\nonline.", "category": "astro-ph_EP" }, { "text": "Breakup of the Synchronous State of Binary Asteroid Systems: This paper continues the authors' previous work and presents a coplanar\naveraged ellipsoid-ellipsoid model of synchronous binary asteroid system (BAS)\nplus thermal and tidal effects. Using this model, we analyze the breakup\nmechanism of the synchronous BAS. Different from the classical spin-orbit\ncoupling model which neglects the rotational motion's influence on the orbital\nmotion, our model considers simultaneously the orbital motion and the\nrotational motions. Our findings are following. (1) Stable region of the\nsecondary's synchronous state is mainly up to the secondary's shape. The\nprimary's shape has little influence on it. (2) The stable region shrinks\ncontinuously with the increasing value of the secondary's shape parameter\n$a_B/b_B$. Beyond the value of $a_B/b_B=\\sqrt{2}$, the planar stable region for\nthe secondary's synchronous rotation is small but not zero. (3) Considering the\nBYORP torque, our model shows agreement with the 1-degree of freedom adiabatic\ninvariance theory in the outwards migration process, but an obvious difference\nin the inwards migration process. In particular, our studies show that the\nso-called 'long-term' stable equilibrium between the BYORP torque and the tidal\ntorque is never a real equilibrium state, although the binary asteroid system\ncan be captured in this state for quite a long time. (4) In case that the\nprimary's angular velocity gradually reduces due to the YORP effect, the\nsecondary's synchronous state may be broken when the primary's rotational\nmotion crosses some major spin-orbit resonances.", "category": "astro-ph_EP" }, { "text": "A condensed matter analogy of impact crater formation: Impact craters exist on various solid objects in the planetary system. A\nsimplified analogy of the process of their formation is here analyzed by\nstandard solid state physics and the so called dynamic quantized fracture\nmechanics. An expression which links the crater volume to the parameters of the\nimpactor and the target is obtained within the two approaches. For low impactor\nenergy, this expression is of the same mathematical form as the one resulting\nfrom recent experiments.It is shown that the formation of an impact crater is\npossible even without heating of the target, if the critical stress in the\ntarget satisfies certain conditions. The critical value of the stress needed\nfor the occurence of a fracture is calculated for three craters: two\nterrestrial and one lunar crater. The approach presented here uses only\nmeasurable material parameters, and is therefore more realistic than the\ntreatement of the same problem using the cohesive energy of materials.", "category": "astro-ph_EP" }, { "text": "Structure, variability, and origin of the low-latitude nightglow\n continuum between 300 and 1,800 nm: Evidence for HO$_2$ emission in the\n near-infrared: The Earth's mesopause region between about 75 and 105 km is characterised by\nchemiluminescent emission from various lines of different molecules and atoms.\nThis emission was and is important for the study of the chemistry and dynamics\nin this altitude region at nighttime. However, our understanding of molecular\nemissions with low intensities and high line densities is still very limited.\nBased on 10 years of data from the astronomical X-shooter echelle spectrograph\nat Cerro Paranal in Chile, we have characterised in detail this nightglow\n(pseudo-)continuum in the wavelength range from 300 to 1,800 nm. We studied the\nspectral features, derived continuum components with similar variability,\ncalculated climatologies, studied the response to solar activity, and even\nestimated the effective emission heights. The results indicate that the\nnightglow continuum at Cerro Paranal essentially consists of only two\ncomponents, which exhibit very different properties. The main structures of\nthese components peak at 595 and 1,510 nm. While the former was previously\nidentified as the main peak of the FeO 'orange arc' bands, the latter is a new\ndiscovery. Laboratory data and theory indicate that this feature and other\nstructures between about 800 and at least 1,800 nm are caused by emission from\nHO$_2$. We performed runs with the Whole Atmosphere Community Climate Model\n(WACCM) with modified chemistry and found that the total intensity, layer\nprofile, and variability indeed support this interpretation, where the excited\nHO$_2$ radicals are mostly produced from the termolecular recombination of H\nand O$_2$. The WACCM results for the continuum at visual wavelengths show good\nagreement for FeO from the reaction of Fe and O$_3$. However, the simulated\ntotal emission appears to be too low, which would require additional mechanisms\nwhere the variability is dominated by O$_3$.", "category": "astro-ph_EP" }, { "text": "Monitoring polarization in comet 46P/Wirtanen: We measure the degree of linear polarization of comet 46P/Wirtanen during two\nmonths, embracing the perihelion passage in 2018 December with phase angles\nranging from {\\alpha}=18.1 to 46.4 deg. The polarimetric response PQ obtained\nresembles what was previously found in comet C/1975 V1 (West). This suggests\n46P/Wirtanen belongs to a group of comets with high maximum positive\npolarization. We conducted BVRI photometry of 46P and found either neutral or\nblue colour of its dust which is in good accordance with measurements of C/1975\nV1 (West). While aperture-average polarimetry of 46P/Wirtanen reveals a nearly\nzero polarization PQ at the lowest phase angle {\\alpha} = 18.1 deg,\nsimultaneous imaging polarimetry suggests that the negative polarization (PQ<0)\narises in a region of within 5000 km of the nucleus, where the negative\npolarization could be as strong as PQ=-(1.44 +/- 0.15) percent. This\nobservation suggests the existence of the circumnucleus halo and that the coma\nis populated by at least two types of dust particles. One of those reveals a\nlow positive polarization at side scattering and high negative polarization\nnear backscattering. Both polarimetric features are simultaneously produced by\nweakly absorbing Mg-rich silicate particles. Another type of dust produces\nsolely positive polarization that could be attributed to carbonaceous\nparticles. This composition of 46P/Wirtanen coma appears to be similar with\nwhat was previously found in comet C/1975 V1 (West).", "category": "astro-ph_EP" }, { "text": "Detection Efficiency of Asteroid Surveys: A comprehensive characterization of the detection efficiency of nine of the\nmajor asteroid surveys that have been active over the past two decades is\npresented. The detection efficiency is estimated on a nightly basis by\ncomparing the detected asteroids with the complete catalog of known asteroids\npropagated to the same observing epoch. Results include a nightly estimate of\nthe detection efficiency curves as a function of apparent magnitude and\napparent velocity of the asteroids, as well as a cumulative analysis to\nestimate the overall performance of each survey. The limiting magnitude\ndistribution is estimated for each survey, and it is then modeled as a function\nof telescope aperture to obtain an estimate over a wide range of apertures.", "category": "astro-ph_EP" }, { "text": "On possible types of magnetospheres of hot Jupiters: We show that the orbits of exoplanets of the \"hot Jupiter\" type, as a rule,\nare located close to the Alf\\'{v}en point of the stellar wind of the parent\nstar. At this, many hot Jupiters can be located in the sub-Alf\\'{v}en zone in\nwhich the magnetic pressure of the stellar wind exceeds its dynamic pressure.\nTherefore, magnetic field of the wind must play an extremely important role for\nthe flow of the stellar wind around the atmospheres of the hot Jupiters. This\nfactor must be considered both in theoretical models and in the interpretation\nof observational data. The analysis shows that many typical hot Jupiters should\nhave shock-less intrinsic magnetospheres, which, apparently, do not have\ncounterparts in the Solar System. Such magnetospheres are characterized,\nprimarily, by the absence of the bow shock, while the magnetic barrier\n(ionopause) is formed by the induced currents in the upper layers of the\nionosphere. We confirmed this inference by the three-dimensional numerical\nsimulation of the flow of the parent star stellar wind around the hot Jupiter\nHD 209458b in which we took into account both proper magnetic field of the\nplanet and magnetic field of the wind.", "category": "astro-ph_EP" }, { "text": "Solid accretion onto planetary cores in radiative disks: The solid accretion rate, necessary to grow gas giant planetary cores within\nthe disk lifetime, has been a major constraint for theories of planet\nformation. We tested the solid accretion rate efficiency on planetary cores of\ndifferent masses embedded in their birth disk, by means of 3D\nradiation-hydrodynamics, where we followed the evolution of a swarm of embedded\nsolids of different sizes. We found that using a realistic equation of state\nand radiative cooling, the disk at 5 au is able to cool efficiently and reduce\nits aspect ratio. As a result, the pebble isolation mass is reached before the\ncore grows to 10 Earth masses, stopping efficiently the pebble flux and\ncreating a transition disk. Moreover, the reduced isolation mass halts the\nsolid accretion before the core reaches the critical mass, leading to a barrier\nto giant planet formation, and it explains the large abundance of super-Earth\nplanets in the observed population.", "category": "astro-ph_EP" }, { "text": "Combining Gaia and GRAVITY: Characterising Five New Directly Detected\n Substellar Companions: Precise mass constraints are vital for the characterisation of brown dwarfs\nand exoplanets. Here, we present how the combination of data obtained by Gaia\nand GRAVITY can help enlarge the sample of substellar companions with measured\ndynamical masses. We show how the Non-Single-Star (NSS) two-body orbit\ncatalogue contained in Gaia DR3 can be used to inform high angular resolution\nfollow-up observations with GRAVITY. Applying the method presented in this work\nfor eight Gaia candidate systems, we detect all eight predicted companions,\nseven of which being previously unknown and five of substellar nature. Among\nthe sample is Gaia DR3 2728129004119806464 B, which - detected at a angular\nseparation of (34.01 $\\pm$ 0.15) mas from the host - is the closest substellar\ncompanion ever imaged. In combination with the system's distance this\ntranslates to a physical separation of (1.054 $\\pm$ 0.002) AU. The GRAVITY data\nare then used to break the host-companion mass degeneracy inherent to the Gaia\nNSS orbit solutions as well as to constrain the orbital solutions of the\nrespective target systems. Knowledge of the companion masses enables us to\nfurther characterise them in terms of their age, effective temperature and\nradius by the application of evolutionary models. The results serve as an\nindependent validation of the orbital solutions published in the NSS two-body\norbit catalogue and show that the combination of astrometric survey missions\nand high-angular resolution direct imaging hold great promise for efficiently\nincreasing the sample of directly-imaged companions in the future, especially\nin the light of the Gaia's upcoming DR4 and the advent of GRAVITY+.", "category": "astro-ph_EP" }, { "text": "Valence-shell photoionization of chlorine-like Ar$^{+}$ ions: Absolute cross-section measurements for valence-shell photoionization of\nAr$^{+}$ ions are reported for photon energies ranging from 27.4 eV to 60.0 eV.\nThe data, taken by merging beams of ions and synchrotron radiation at a photon\nenergy resolution of 10 meV, indicate that the primary ion beam was a\nstatistically weighted mixture of the $^2P^o_{3/2}$ ground state and the\n$^2P^o_{1/2}$ metastable state of Ar$^{+}$. Photoionization of this\nC$\\ell$-like ion is characterized by multiple Rydberg series of autoionizing\nresonances superimposed on a direct photoionization continuum. Observed\nresonance lineshapes indicate interference between indirect and direct\nphotoionization channels. Resonance features are spectroscopically assigned and\ntheir energies and quantum defects are tabulated. The measurements are\nsatisfactorily reproduced by theoretical calculations based on an intermediate\ncoupling semi-relativistic Breit-Pauli approximation.", "category": "astro-ph_EP" }, { "text": "Debris Disks in Multi-Planet Systems: Are Our Inferences Compromised by\n Unseen Planets?: Resolved debris disk features (e.g., warps, offsets, edges and gaps,\nazimuthal asymmetries, radially thickened rings, scale heights) contain\nvaluable information about the underlying planetary systems, such as the\nposited planet's mass, semi-major axis, and other orbital parameters. Most\nexisting models assume a single planet is sculpting the disk feature, but\nrecent observations of mature planetary systems (e.g., by radial velocity\nsurveys or \\textit{Kepler}) have revealed that many planets reside in\nmulti-planet systems. Here we investigate if/how planet properties inferred\nfrom single-planet models are compromised when multiple planets reside in the\nsystem. For each disk feature, we build a two-planet model that includes a\nplanet b with fixed parameters and a planet c with a full range of possible\nparameters. We investigate these two-planet systems and summarize the\nconfigurations for which assuming a single planet (i.e., planet b) leads to\nsignificantly flawed inferences of that planet's properties. We find that\nalthough disk features are usually primarily dominated by a single planet, when\nusing single-planet models we are at risk of misinterpreting planet properties\nby orders of magnitude in extreme cases. Specifically, we are at high risk of\nmisinterpreting planet properties from disk warps; at moderate risk from disk\nedges and gaps, radially thickened rings, and scale height features; and at low\nrisk from host star-disk center offsets and azimuthal asymmetries. We summarize\nsituations where we can infer the need to use a multi-planet model instead of a\nsingle-planet one from disk morphology dissimilarities.", "category": "astro-ph_EP" }, { "text": "A new statistical method for characterizing the atmospheres of\n extrasolar planets: By detecting light from extrasolar planets,we can measure their compositions\nand bulk physical properties. The technologies used to make these measurements\nare still in their infancy, and a lack of self-consistency suggests that\nprevious observations have underestimated their systemic errors.We demonstrate\na statistical method, newly applied to exoplanet characterization, which uses a\nBayesian formalism to account for underestimated errorbars. We use this method\nto compare photometry of a substellar companion, GJ 758b, with custom\natmospheric models. Our method produces a probability distribution of\natmospheric model parameters including temperature, gravity, cloud model\n(fsed), and chemical abundance for GJ 758b. This distribution is less sensitive\nto highly variant data, and appropriately reflects a greater uncertainty on\nparameter fits.", "category": "astro-ph_EP" }, { "text": "Computing Apparent Planetary Magnitudes for The Astronomical Almanac: Improved equations for computing planetary magnitudes are reported. These\nformulas model V-band observations acquired from the time of the earliest\nfilter photometry in the 1950s up to the present era. The new equations\nincorporate several terms that have not previously been used for generating\nphysical ephemerides. These include the rotation and revolution angles of Mars,\nthe sub-solar and sub-Earth latitudes of Uranus, and the secular time\ndependence of Neptune. Formulas for use in The Astronomical Almanac cover the\nplanetary phase angles visible from Earth. Supplementary equations cover those\nphase angles beyond the geocentric limits. Geocentric magnitudes were computed\nover a span of at least 50 years and the results were statistically analyzed.\nThe mean, variation and extreme magnitudes for each planet are reported. Other\nbands besides V on the Johnson-Cousins and Sloan photometric systems are\nbriefly discussed. The planetary magnitude data products available from the\nU.S. Naval Observatory are also listed. An appendix describes source code and\ntest data sets that are available on-line for computing planetary magnitudes\naccording to the equations and circumstances given in this paper. The files are\nposted as supplementary material for this paper. They are also available at\nSourceForge under project\nhttps://sourceforge.net/projects/planetary-magnitudes/ under the 'Files' tab in\nthe folder 'Ap_Mag_Current_Version'.", "category": "astro-ph_EP" }, { "text": "Modeling the Historical Flux of Planetary Impactors: The impact cratering record of the Moon and the terrestrial planets provides\nimportant clues about the formation and evolution of the Solar System.\nEspecially intriguing is the epoch 3.8-3.9 Gyr ago (Ga), known as the Late\nHeavy Bombardment (LHB), when the youngest lunar basins such as Imbrium and\nOrientale formed. The LHB was suggested to originate from a slowly declining\nimpactor flux or from a late dynamical instability. Here we develop a model for\nthe historical flux of large asteroid impacts and discuss how it depends on\nvarious parameters, including the time and nature of the planetary\nmigration/instability. We find that the asteroid impact flux dropped by 1 to 2\norders of magnitude during the first 1 Gyr and remained relatively unchanged\nover the last 3 Gyr. The early impacts were produced by asteroids whose orbits\nbecame excited during the planetary migration/instability, and by those\noriginating from the inner extension of the main belt (E-belt; semimajor axis\n1.6 5000K. The\nwhole atmosphere may couple to a global, large-scale magnetic field, and\nlightning may occur on the nightside.", "category": "astro-ph_EP" }, { "text": "The Architecture of the Cassini Division: The Cassini Division in Saturn's rings contains a series of eight named gaps,\nthree of which contain dense ringlets. Observations of stellar occultations by\nthe Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft\nhave yielded ~40 accurate and precise measurements of the radial position of\nthe edges of all of these gaps and ringlets. These data reveal suggestive\npatterns in the shapes of many of the gap edges: the outer edges of the 5 gaps\nwithout ringlets are circular to within 1 km, while the inner edges of 6 of the\ngaps are eccentric, with apsidal precession rates consistent with those\nexpected for eccentric orbits near each edge. Intriguingly, the pattern speeds\nof these eccentric inner gap edges, together with that of the eccentric Huygens\nringlet,form a series with a characteristic spacing of 0.06 degrees/day. The\ntwo gaps with non-eccentric inner edges lie near first-order Inner Lindblad\nResonances (ILRs) with moons. One such edge is close to the 5:4 ILR with\nPrometheus. The other resonantly confined edge is the outer edge of the B ring,\nwhich lies near the 2:1 Mimas ILR. Detailed investigation of the B-ring-edge\ndata confirm the presence of an m=2 perturbation on the B-ring edge, but also\nsuggest that this pattern moves or librates relative to Mimas. The B-ring edge\nalso has an m=1 component that rotates around the planet at a rate close to the\nexpected apsidal precession rate. The pattern speeds of the eccentric edges in\nthe Cassini Division can potentially be generated from various combinations of\nthe pattern speeds of structures observed on the edge of the B ring. We\ntherefore suggest that the locations of most of the gaps in the Cassini\nDivision may be determined by resonances involving a combination of\nperturbations from Mimas and the massive edge of the B ring.", "category": "astro-ph_EP" }, { "text": "Hybrid methods in planetesimal dynamics (I) : Description of a new\n composite algorithm: The formation and evolution of protoplanetary systems, the breeding grounds\nof planet formation, is a complex dynamical problem that involves many orders\nof magnitudes. To serve this purpose, we present a new hybrid algorithm that\ncombines a Fokker-Planck approach with the advantages of a pure\ndirect-summation N-body scheme, with a very accurate integration of close\nencounters for the orbital evolution of the larger bodies with a statistical\nmodel, envisaged to simulate the very large number of smaller planetesimals in\nthe disc. Direct-summation techniques have been historically developped for the\nstudy of dense stellar systems such as open and globular clusters and, within\nsome limits imposed by the number of stars, of galactic nuclei. The number of\nmodifications to adapt direct-summation N-body techniques to planetary dynamics\nis not undemanding and requires modifications. These include the way close\nencounters are treated, as well as the selection process for the \"neighbour\nradius\" of the particles and the extended Hermite scheme, used for the very\nfirst time in this work, as well as the implementation of a central potential,\ndrag forces and the adjustment of the regularisation treatment. For the\nstatistical description of the planetesimal disc we employ a Fokker-Planck\napproach. We include dynamical friction, high- and low-speed encounters, the\nrole of distant encounters as well as gas and collisional damping and then\ngeneralise the model to inhomogenous discs. We then describe the combination of\nthe two techniques to address the whole problem of planetesimal dynamics in a\nrealistic way via a transition mass to integrate the evolution of the particles\naccording to their masses.", "category": "astro-ph_EP" }, { "text": "No hydrogen exosphere detected around the super-Earth HD97658 b: The exoplanet HD97658b provides a rare opportunity to probe the atmospheric\ncomposition and evolution of moderately irradiated super-Earths. It transits a\nbright K star at a moderate orbital distance of 0.08 au. Its low density is\ncompatible with a massive steam envelope that could photodissociate at high\naltitudes and become observable as escaping hydrogen. Our analysis of 3\ntransits with HST/STIS at Ly-alpha reveals no such signature, suggesting that\nthe thermosphere is not hydrodynamically expanding and is subjected to a low\nescape of neutral hydrogen (<10^8 g/s at 3 sigma). Using HST Ly-alpha and\nChandra & XMM-Newton observations at different epochs, we find that HD97658 is\na weak and soft X-ray source with signs of chromospheric variability in the\nLy-alpha line core. We determine an average reference for the intrinsic\nLy-alpha line and XUV spectrum of the star, and show that HD97658 b is in mild\nconditions of irradiation compared to other known evaporating exoplanets with\nan XUV irradiation about 3 times lower than the evaporating warm Neptune GJ436\nb. This could be why the thermosphere of HD97658b is not expanding: the low XUV\nirradiation prevents an efficient photodissociation of any putative steam\nenvelope. Alternatively, it could be linked to a low hydrogen content or\ninefficient conversion of the stellar energy input. The HD97658 system provides\nclues for understanding the stability of low-mass planet atmospheres. Our study\nof HD97658 b can be seen as a control experiment of our methodology, confirming\nthat it does not bias detections of atmospheric escape and underlining its\nstrength and reliability. Our results show that stellar activity can be\nefficiently discriminated from absorption signatures by a transiting exospheric\ncloud. They also highlight the potential of observing the upper atmosphere of\nsmall transiting planets to probe their physical and chemical properties", "category": "astro-ph_EP" }, { "text": "Disk Accretion Driven by Spiral Shocks: Spiral density waves are known to exist in many astrophysical disks,\npotentially affecting disk structure and evolution. We conduct a numerical\nstudy of the effects produced by a density wave, evolving into a shock, on the\ncharacteristics of the underlying disk. We measure the deposition of angular\nmomentum in the disk by spiral shocks of different strength and verify the\nanalytical prediction of Rafikov (2016) for the behavior of this quantity,\nusing shock amplitude (which is potentially observable) as the input variable.\nGood agreement between the theory and numerics is found as we vary shock\namplitude (including highly nonlinear shocks), disk aspect ratio, equation of\nstate, radial profiles of the background density and temperature, and pattern\nspeed of the wave. We show that high numerical resolution is required to\nproperly capture shock-driven transport, especially at low wave amplitudes. We\nalso demonstrate that relating local mass accretion rate to shock dissipation\nin rapidly evolving disks requires accounting for the time-dependent\ncontribution to the angular momentum budget, caused by the time dependence of\nthe radial pressure support. We provide a simple analytical prescription for\nthe behavior of this contribution and demonstrate its excellent agreement with\nthe simulation results. Using these findings we formulate a theoretical\nframework for studying one-dimensional (in radius) evolution of the\nshock-mediated accretion disks, which can be applied to a variety of\nastrophysical systems.", "category": "astro-ph_EP" }, { "text": "Kepler's Orbits and Special Relativity in Introductory Classical\n Mechanics: Kepler's orbits with corrections due to Special Relativity are explored using\nthe Lagrangian formalism. A very simple model includes only relativistic\nkinetic energy by defining a Lagrangian that is consistent with both the\nrelativistic momentum of Special Relativity and Newtonian gravity. The\ncorresponding equations of motion are solved in a Keplerian limit, resulting in\nan approximate relativistic orbit equation that has the same form as that\nderived from General Relativity in the same limit and clearly describes three\ncharacteristics of relativistic Keplerian orbits: precession of perihelion;\nreduced radius of circular orbit; and increased eccentricity. The prediction\nfor the rate of precession of perihelion is in agreement with established\ncalculations using only Special Relativity. All three characteristics are\nqualitatively correct, though suppressed when compared to more accurate\ngeneral-relativistic calculations. This model is improved upon by including\nrelativistic gravitational potential energy. The resulting approximate\nrelativistic orbit equation has the same form and symmetry as that derived\nusing the very simple model, and more accurately describes characteristics of\nrelativistic orbits. For example, the prediction for the rate of precession of\nperihelion of Mercury is one-third that derived from General Relativity. These\nLagrangian formulations of the special-relativistic Kepler problem are\nequivalent to the familiar vector calculus formulations. In this Keplerian\nlimit, these models are supposed to be physical based on the likeness of the\nequations of motion to those derived using General Relativity. The derivation\nof this orbit equation is approachable by undergraduate physics majors and\nnonspecialists whom have not had a course dedicated to relativity.", "category": "astro-ph_EP" }, { "text": "Evidence For A Vertical Dependence on the Pressure Structure in AS 209: We present an improved method to measure the rotation curves for disks with\nnon-axisymmetric brightness profiles initially published in Teague et al.\n(2018a). Application of this method to the well studied AS$~$209 system shows\nsubstantial deviations from Keplerian rotation of up to $\\pm 5\\%$. These\ndeviations are most likely due to perturbations in the gas pressure profile,\nincluding a perturbation located at $\\approx 250~$au and spanning up to\n$\\approx 50~$au which is only detected kinematically. Modelling the required\ntemperature and density profiles required to recover the observed rotation\ncurve we demonstrate that the rings observed in $\\mu$m scattered light are\ncoincident with the pressure maxima, and are radially offset from the rings\nobserved in mm continuum emission. This suggests that if rings in the NIR are\ndue to sub-$\\mu$m grains trapped in pressure maxima that there is a vertical\ndependence on the radius of the pressure minima.", "category": "astro-ph_EP" }, { "text": "The Old and New Meanings of Cloud 'Belt' and 'Zone': A Study of Jovian\n and Saturnian Atmospheric Banding: The brightness of cloud bands on Jupiter and Saturn as a function of latitude\nis reported. Bright Jovian bands near the equator are located in regions of\nanti-cyclonic circulation of the atmosphere. By contrast, bright equatorial\nbands on Saturn are associated with cyclonic motion. Modern definitions of the\ncloud band terms 'zone' and 'belt' are distinguished from their old meanings.", "category": "astro-ph_EP" }, { "text": "Extreme trans-Neptunian objects and the Kozai mechanism: signalling the\n presence of trans-Plutonian planets: The existence of an outer planet beyond Pluto has been a matter of debate for\ndecades and the recent discovery of 2012 VP113 has just revived the interest\nfor this controversial topic. This Sedna-like object has the most distant\nperihelion of any known minor planet and the value of its argument of\nperihelion is close to 0 degrees. This property appears to be shared by almost\nall known asteroids with semimajor axis greater than 150 au and perihelion\ngreater than 30 au (the extreme trans-Neptunian objects or ETNOs), and this\nfact has been interpreted as evidence for the existence of a super-Earth at 250\nau. In this scenario, a population of stable asteroids may be shepherded by a\ndistant, undiscovered planet larger than the Earth that keeps the value of\ntheir argument of perihelion librating around 0 degrees as a result of the\nKozai mechanism. Here, we study the visibility of these ETNOs and confirm that\nthe observed excess of objects reaching perihelion near the ascending node\ncannot be explained in terms of any observational biases. This excess must be a\ntrue feature of this population and its possible origin is explored in the\nframework of the Kozai effect. The analysis of several possible scenarios\nstrongly suggest that at least two trans-Plutonian planets must exist.", "category": "astro-ph_EP" }, { "text": "The Manifold Of Variations: impact location of short-term impactors: The interest in the problem of small asteroids observed shortly before a deep\nclose approach or an impact with the Earth has grown a lot in recent years.\nSince the observational dataset of such objects is very limited, they deserve\ndedicated orbit determination and hazard assessment methods. The currently\navailable systems are based on the systematic ranging, a technique providing a\n2-dimensional manifold of orbits compatible with the observations, the\nso-called Manifold Of Variations. In this paper we first review the Manifold Of\nVariations method, to then show how this set of virtual asteroids can be used\nto predict the impact location of short-term impactors, and compare the results\nwith those of already existent methods.", "category": "astro-ph_EP" }, { "text": "Determining fireball fates using the $\u03b1$-$\u03b2$ criterion: As fireball networks grow, the number of events observed becomes unfeasible\nto manage by manual efforts. Reducing and analysing big data requires automated\ndata pipelines. Triangulation of a fireball trajectory can swiftly provide\ninformation on positions and, with timing information, velocities. However,\nextending this pipeline to determine the terminal mass estimate of a meteoroid\nis a complex next step. Established methods typically require assumptions to be\nmade of the physical meteoroid characteristics (such as shape and bulk\ndensity). To determine which meteoroids may have survived entry there are\nempirical criteria that use a fireball's final height and velocity - low and\nslow final parameters are likely the best candidates. We review the more\nelegant approach of the dimensionless coefficient method. Two parameters,\n$\\alpha$ (ballistic coefficient) and $\\beta$ (mass-loss), can be calculated for\nany event with some degree of deceleration, given only velocity and height\ninformation. $\\alpha$ and $\\beta$ can be used to analytically describe a\ntrajectory with the advantage that they are not mere fitting coefficients; they\nalso represent the physical meteoroid properties. This approach can be applied\nto any fireball network as an initial identification of key events and\ndetermine on which to concentrate resources for more in depth analyses. We used\na set of 278 events observed by the Desert Fireball Network to show how\nvisualisation in an $\\alpha$ - $\\beta$ diagram can quickly identify which\nfireballs are likely meteorite candidates.", "category": "astro-ph_EP" }, { "text": "A Possible Mechanism for Overcoming the Electrostatic Barrier Against\n Dust Growth in Protoplanetary disks: The coagulation of dust particles under the conditions in protoplanetary\ndisks is investigated. The study focuses on the repulsive electrostatic barrier\nagainst growth of charged dust grains. Taking into account the photoelectric\neffect leads to the appearance of a layer at intermediate heights where the\ndust has a close to zero charge, enabling the dust grains to grow efficiently.\nAn increase in the coagulation rate comes about not only due to the lowering of\nthe Coulomb barrier, but also because of the electrostatic attraction between\ngrains of opposite charge due to the non-zero dispersion of the near-zero\ncharge. Depending on the efficiency of mixing in the disk, the acceleration of\nthe evolution of the dust in this layer could be important, both in the\nquasi-stationary stage of the disk evolution and during its dispersal.", "category": "astro-ph_EP" }, { "text": "Lightcurve Survey of V-type Asteroids. I. Observations until Spring 2004: To examine the distribution of rotational rates for chips of asteroid 4\nVesta, lightcurve observation of seven V-type asteroids (2511 Patterson, 2640\nHallstorm, 2653 Principia, 2795 Lapage, 3307 Athabasca, 4147 Lennon, and 4977\nRauthgundis) were performed from fall 2003 to spring 2004. Distribution of spin\nrates of V-type main-belt asteroids from the past and our observations have\nthree peaks. This result implies that age of catastrophic impact making Vesta\nfamily may be not as young as Karin and Iannini families but as old as Eos and\nKoronis families.", "category": "astro-ph_EP" }, { "text": "Precise Dynamical Masses and Orbital Fits for $\u03b2$ Pic b and $\u03b2$\n Pic c: We present a comprehensive orbital analysis to the exoplanets $\\beta$\nPictoris b and c that resolves previously reported tensions between the\ndynamical and evolutionary mass constraints on $\\beta$ Pic b. We use the MCMC\norbit code orvara to fit fifteen years of radial velocities and relative\nastrometry (including recent GRAVITY measurements), absolute astrometry from\nHipparcos and Gaia, and a single relative radial velocity measurement between\n$\\beta$ Pic A and b. We measure model-independent masses of\n$9.3^{+2.6}_{-2.5}\\, M_{\\rm Jup}$ for $\\beta$ Pic b and $8.3\\pm 1.0\\,M_{\\rm\nJup}$ for $\\beta$ Pic c. These masses are robust to modest changes to the input\ndata selection. We find a well-constrained eccentricity of $0.119 \\pm 0.008$\nfor $\\beta$ Pic b, and an eccentricity of $0.21^{+0.16}_{-0.09}$ for $\\beta$\nPic c, with the two orbital planes aligned to within $\\sim$0.5$^\\circ$. Both\nplanets' masses are within $\\sim$1$\\sigma$ of the predictions of hot-start\nevolutionary models and exclude cold starts. We validate our approach on\n$N$-body synthetic data integrated using REBOUND. We show that orvara can\naccount for three-body effects in the $\\beta$ Pic system down to a level\n$\\sim$5 times smaller than the GRAVITY uncertainties. Systematics in the masses\nand orbital parameters from orvara's approximate treatment of multiplanet\norbits are a factor of $\\sim$5 smaller than the uncertainties we derive here.\nFuture GRAVITY observations will improve the constraints on $\\beta$ Pic c's\nmass and (especially) eccentricity, but improved constraints on the mass of\n$\\beta$ Pic b will likely require years of additional RV monitoring and\nimproved precision from future Gaia data releases.", "category": "astro-ph_EP" }, { "text": "Detecting extrasolar moons akin to solar system satellites with an\n orbital sampling effect: Despite years of high accuracy observations, none of the available\ntheoretical techniques has yet allowed the confirmation of a moon beyond the\nsolar system. Methods are currently limited to masses about an order of\nmagnitude higher than the mass of any moon in the solar system. I here present\na new method sensitive to exomoons similar to the known moons. Due to the\nprojection of transiting exomoon orbits onto the celestial plane, satellites\nappear more often at larger separations from their planet. After about a dozen\nrandomly sampled observations, a photometric orbital sampling effect (OSE)\nstarts to appear in the phase-folded transit light curve, indicative of the\nmoons' radii and planetary distances. Two additional outcomes of the OSE emerge\nin the planet's transit timing variations (TTV-OSE) and transit duration\nvariations (TDV-OSE), both of which permit measurements of a moon's mass. The\nOSE is the first effect that permits characterization of multi-satellite\nsystems. I derive and apply analytical OSE descriptions to simulated transit\nobservations of the Kepler space telescope assuming white noise only. Moons as\nsmall as Ganymede may be detectable in the available data, with M stars being\ntheir most promising hosts. Exomoons with the 10-fold mass of Ganymede and a\nsimilar composition (about 0.86 Earth radii in radius) can most likely be found\nin the available Kepler data of K stars, including moons in the stellar\nhabitable zone. A future survey with Kepler-class photometry, such as Plato\n2.0, and a permanent monitoring of a single field of view over 5 years or more\nwill very likely discover extrasolar moons via their OSEs.", "category": "astro-ph_EP" }, { "text": "Probing exoplanet clouds with optical phase curves: Kepler-7b is to date the only exoplanet for which clouds have been inferred\nfrom the optical phase curve -- from visible-wavelength whole-disk brightness\nmeasurements as a function of orbital phase. Added to this, the fact that the\nphase curve appears dominated by reflected starlight makes this close-in giant\nplanet a unique study case. Here we investigate the information on coverage and\noptical properties of the planet clouds contained in the measured phase curve.\nWe generate cloud maps of Kepler-7b and use a multiple-scattering approach to\ncreate synthetic phase curves, thus connecting postulated clouds with\nmeasurements. We show that optical phase curves can help constrain the\ncomposition and size of the cloud particles. Indeed, model fitting for\nKepler-7b requires poorly absorbing particles that scatter with low-to-moderate\nanisotropic efficiency, conclusions consistent with condensates of silicates,\nperovskite, and silica of submicron radii. We also show that we are limited in\nour ability to pin down the extent and location of the clouds. These\nconsiderations are relevant to the interpretation of optical phase curves with\ngeneral circulation models. Finally, we estimate that the spherical albedo of\nKepler-7b over the Kepler passband is in the range 0.4--0.5.", "category": "astro-ph_EP" }, { "text": "Photoevaporative Dispersal of Protoplanetary Disks around Evolving\n Intermediate-mass Stars: We aim to understand the effect of stellar evolution on the evolution of\nprotoplanetary disks. We focus in particular on the disk evolution around\nintermediate-mass (IM) stars, which evolve more rapidly than low-mass ones. We\nnumerically solve the long-term evolution of disks around 0.5-5 solar-mass\nstars considering viscous accretion and photoevaporation (PE) driven by stellar\nfar-ultraviolet (FUV), extreme-ultraviolet (EUV), and X-ray emission. We also\ntake stellar evolution into account and consider the time evolution of the PE\nrate. We find that the FUV, EUV, and X-ray luminosities of IM stars evolve by\norders of magnitude within a few Myr along with the time evolution of stellar\nstructure, stellar effective temperature, or accretion rate. Therefore, the PE\nrate also evolves with time by orders of magnitude, and we conclude that\nstellar evolution is crucial for the disk evolution around IM stars.", "category": "astro-ph_EP" }, { "text": "Spectroscopic Time-series Performance of JWST/NIRSpec from Commissioning\n Observations: We report on JWST commissioning observations of the transiting exoplanet\nHAT-P-14 b, obtained using the Bright Object Time Series (BOTS) mode of the\nNIRSpec instrument with the G395H/F290LP grating/filter combination\n($3-5\\mu$m). While the data were used primarily to verify that the NIRSpec BOTS\nmode is working as expected, and to enable it for general scientific use, they\nyield a precise transmission spectrum which we find is featureless down to the\nprecision level of the instrument, consistent with expectations given\nHAT-P-14~b's small scale-height and hence expected atmospheric features. The\nexquisite quality and stability of the \\emph{JWST/NIRSpec} transit spectrum --\nalmost devoid of any systematic effects -- allowed us to obtain median\nuncertainties of 50-60 ppm in this wavelength range at a resolution of $R=100$\nin a single exposure, which is in excellent agreement with pre-flight\nexpectations and close to the (or at the) photon-noise limit for a $J = 9.094$,\nF-type star like HAT-P-14. These observations showcase the ability of\nNIRSpec/BOTS to perform cutting-edge transiting exoplanet atmospheric science,\nsetting the stage for observations and discoveries to be made in Cycle 1 and\nbeyond.", "category": "astro-ph_EP" }, { "text": "Structured Distributions of Gas and Solids in Protoplanetary Disks: Recent spatially-resolved observations of protoplanetary disks revealed a\nplethora of substructures, including concentric rings and gaps, inner cavities,\nmisalignments, spiral arms, and azimuthal asymmetries. This is the major\nbreakthrough in studies of protoplanetary disks since Protostars and Planets VI\nand is reshaping the field of planet formation. However, while the capability\nof imaging substructures in protoplanetary disks has been steadily improving,\nthe origin of many substructures are still largely debated. The structured\ndistributions of gas and solids in protoplanetary disks likely reflect the\noutcome of physical processes at work, including the formation of planets. Yet,\nthe diverse properties among the observed protoplanetary disk population, for\nexample, the number and radial location of rings and gaps in the dust\ndistribution, suggest that the controlling process may differ between disks\nand/or the outcome may be sensitive to stellar or disk properties. In this\nreview, we (1) summarize the existing observations of protoplanetary disk\nsubstructures collected from the literature; (2) provide a comprehensive\ntheoretical review of various processes proposed to explain observed\nprotoplanetary disk substructures; (3) compare current theoretical predictions\nwith existing observations and highlight future research directions to\ndistinguish between different origins; and (4) discuss implications of\nstate-of-the-art protoplanetary disk observations to protoplanetary disk and\nplanet formation theory.", "category": "astro-ph_EP" }, { "text": "Thermal properties of Rhea's Poles: Evidence for a Meter-Deep\n Unconsolidated Subsurface Layer: Cassini's Composite Infrared Spectrometer (CIRS) observed both of Rhea's\npolar regions during two flybys on 2013/03/09 and 2015/02/10. The results show\nRhea's southern winter pole is one of the coldest places directly observed in\nour solar system: temperatures of 25.4+/-7.4 K and 24.7+/-6.8 K are inferred.\nThe surface temperature of the northern summer pole is warmer: 66.6+/-0.6 K.\nAssuming the surface thermophysical properties of both polar regions are\ncomparable then these temperatures can be considered a summer and winter\nseasonal temperature constraint for the polar region. These observations\nprovide solar longitude coverage at 133 deg and 313 deg for the summer and\nwinter poles respectively, with additional winter temperature constraint at 337\ndeg. Seasonal models with bolometric albedos of 0.70-0.74 and thermal inertias\nof 1-46 MKS can provide adequate fits to these temperature constraints. Both\nthese albedo and thermal inertia values agree (within error) with those\npreviously observed on both Rhea's leading and trailing hemispheres.\nInvestigating the seasonal temperature change of Rhea's surface is particularly\nimportant, as the seasonal wave is sensitive to deeper surface temperatures\n(~10cm to m) than the more commonly reported diurnal wave (<1cm). The low\nthermal inertia derived here implies that Rhea's polar surfaces are highly\nporous even at great depths. Analysis of a CIRS 10 to 600 cm-1 stare\nobservation, taken between 16:22:33 and 16:23:26 UT on 2013/03/09 centered on\n71.7 W, 58.7 S provides the first analysis of a thermal emissivity spectrum on\nRhea. The results show a flat emissivity spectrum with negligible emissivity\nfeatures. A few possible explanations exist for this flat emissivity spectrum,\nbut the most likely for Rhea is that the surface is both highly porous and\ncomposed of small particles (less than approximately 50 um).", "category": "astro-ph_EP" }, { "text": "A Planetary Companion around a Metal-Poor Star with Extragalactic Origin: We report the detection of a planetary companion around HIP 13044, a\nmetal-poor star on the red Horizontal Branch. The detection is based on radial\nvelocity observations with FEROS, a high-resolution spectrograph at the 2.2-m\nMPG/ESO telescope, located at ESO La Silla observatory in Chile. The periodic\nradial velocity variation of P = 16.2 days can be distinguished from the\nperiods of the stellar activity indicators. We computed a minimum planetary\nmass of 1.25 MJup and an orbital semi-major axis of 0.116 AU for the planet.\nThis discovery is unique in three aspects: First, it is the first planet\ndetection around a star with a metallicity much lower than few percent of the\nsolar value; second, the planet host star resides in a stellar evolutionary\nstage that is still unexplored in the exoplanet surveys; third, the star HIP\n13044 belongs to one of the most significant stellar halo streams in the solar\nneighborhood, implying an extragalactic origin of the planetary system HIP\n13044 in a disrupted former satellite of the Milky Way.", "category": "astro-ph_EP" }, { "text": "New transit timing observations for GJ 436 b, HAT-P-3 b, HAT-P-19 b,\n WASP-3 b, and XO-2 b: We present new transit observations acquired between 2014 and 2018 for the\nhot exoplanets GJ 436 b, HAT-P-3 b, HAT-P-19 b, WASP-3 b, and XO-2 b. New\nmid-transit times extend the timespan covered by observations of these\nexoplanets and allow us to refine their transit ephemerides. All new transits\nare consistent with linear ephemerides.", "category": "astro-ph_EP" }, { "text": "Autonomous Rapid Exploration in Close-Proximity of an Asteroid: The increasing number of space missions may overwhelm ground support\ninfrastructure, prompting the need for autonomous deep-space guidance,\nnavigation, and control (GN\\&C) systems. These systems offer sustainable and\ncost-effective solutions, particularly for asteroid missions that deal with\nuncertain environments. This study proposes a paradigm shift from the proposals\ncurrently found in the literature for autonomous asteroid exploration, which\ninherit the conservative architecture from the ground-in-the-loop approach that\nrelies heavily on reducing uncertainties before close-proximity operations.\nInstead, it advocates for robust guidance and control to handle uncertainties\ndirectly, without extensive navigation campaigns. From a series of conservative\nassumptions, we demonstrate the feasibility of this autonomous GN\\&C for\nrobotic spacecraft by using existing technology. It is shown that a bolder\noperational approach enables autonomous spacecraft to significantly reduce\nexploration time by weeks or months. This paradigm shift holds great potential\nfor reducing costs and saving time in autonomous missions of the future.", "category": "astro-ph_EP" }, { "text": "Planet Shadows in Protoplanetary Disks. II: Observable Signatures: We calculate simulated images of disks perturbed by embedded small planets.\nThese 10-50 M_Earth bodies represent the growing cores of giant planets. We\nexamine scattered light and thermal emission from these disks over a range of\nwavelengths, taking into account the wavelength-dependent opacity of dust in\nthe disk. We also examine the effect of inclination on the observed\nperturbations. We find that the perturbations are best observed in the visible\nto mid-infrared. Scattered light images reflect shadows produced at the surface\nof perturbed disks, while the infrared images follow thermal emission from the\nsurface of the disk, showing cooled/heated material in the shadowed/brightened\nregions. At still longer wavelengths in the sub-millimeter, the perturbation\nfades as the disk becomes optically thin and surface features become\noverwhelmed by emission closer toward the midplane of the disk. With the\nconstruction of telescopes such as TMT, GMT and ALMA due in the next decade,\nthere is a real possibility of observing planets forming in disks in the\noptical and sub-millimeter. However, having the angular resolution to observe\nthe features in the mid-infrared will remain a challenge.", "category": "astro-ph_EP" }, { "text": "Kepler-1656b's Extreme Eccentricity: Signature of a Gentle Giant: Highly eccentric orbits are one of the major surprises of exoplanets relative\nto the Solar System and indicate rich and tumultuous dynamical histories. One\nsystem of particular interest is Kepler-1656, which hosts a sub-Jovian planet\nwith an eccentricity of 0.8. Sufficiently eccentric orbits will shrink in\nsemi-major axis due to tidal dissipation of orbital energy during periastron\npassage. Here our goal was to assess whether Kepler-1656b is currently\nundergoing such high-eccentricity migration, and to further understand the\nsystem's origins and architecture. We confirm a second planet in the system\nwith $M_{\\rm c}= 0.40 \\pm 0.09M_{\\rm jup}$ and P$_{\\rm c}= 1919\\pm 27\\,$days.\nWe simulated the dynamical evolution of planet b in the presence of planet c\nand find a variety of possible outcomes for the system, such as tidal migration\nand engulfment. The system is consistent with an in situ dynamical origin of\nplanet b followed by subsequent Eccentric Kozai Lidov (EKL) perturbations that\nexcite Kepler-1656b's eccentricity gently, i.e. without initiating tidal\nmigration. Thus, despite its high eccentricity, we find no evidence that planet\nb is or has migrated through the high-eccentricity channel. Finally, we predict\nthe outer orbit to be mutually inclined in a nearly perpendicular configuration\nwith respect to the inner planet orbit based on the outcomes of our\nsimulations, and make observable predictions for the inner planet's spin-orbit\nangle. Our methodology can be applied to other eccentric or tidally locked\nplanets to constrain their origins, orbital configurations and properties of a\npotential companion.", "category": "astro-ph_EP" }, { "text": "Spectral signature of atmospheric winds in high resolution transit\n observations: The study of exoplanet atmospheres showed large diversity compared to the\nplanets in our solar system. Especially Jupiter type exoplanets orbiting their\nhost star in close orbits, the so-called hot and ultra-hot Jupiters, have been\nstudied in detail due to their enhanced atmospheric signature. Due to their\ntidally locked status, the temperature difference between the day- and\nnightside triggers atmospheric winds which can lead to various fingerprints in\nthe observations. Spatially resolved absorption lines during transit such as\nsodium (Na) could be a good tracer for such winds. Different works resolved the\nNa$^-$ absorption lines on different exoplanets which show different line\nwidths. Assuming that this could be attributed to such zonal jet streams, this\nwork models the effect of such winds on synthetic absorption lines. For this,\ntransiting Jupiter type planets with rotational velocities similar to hot and\nultra-hot Jupiter are considered. The investigation shows that high wind\nvelocities could reproduce the broadening of Na-line profiles inferred in\ndifferent high-resolution transit observations. There is a tendency that the\nbroadening values decrease for planets with lower equilibrium temperature. This\ncould be explained by atmospheric drag induced by the ionization of alkali\nlines which slow down the zonal jet streams, favoring their existence on hot\nJupiter rather than ultra-hot Jupiter.", "category": "astro-ph_EP" }, { "text": "Possible formation pathways for the low density Neptune-mass planet\n HAT-P-26b: We investigate possible pathways for the formation of the low density\nNeptune-mass planet HAT-P-26b. We use two formation different models based on\npebbles and planetesimals accretion, and includes gas accretion, disk migration\nand simple photoevaporation. The models tracks the atmospheric oxygen\nabundance, in addition to the orbital period, and mass of the forming planets,\nthat we compare to HAT-P-26b. We find that pebbles accretion can explain this\nplanet more naturally than planetesimals accretion that fails completely unless\nwe artificially enhance the disk metallicity significantly. Pebble accretion\nmodels can reproduce HAT-P-26b with either a high initial core mass and low\namount of envelope enrichment through core erosion or pebbles dissolution, or\nthe opposite, with both scenarios being possible. Assuming a low envelope\nenrichment factor as expected from convection theory and comparable to the\nvalues we can infer from the D/H measurements in Uranus and Neptune, our most\nprobable formation pathway for HAT-P-26b is through pebble accretion starting\naround 10 AU early in the disk's lifetime.", "category": "astro-ph_EP" }, { "text": "Stochastic orbital migration of small bodies in Saturn's rings: Many small moonlets, creating propeller structures, have been found in\nSaturn's rings by the Cassini spacecraft. We study the dynamical evolution of\nsuch 20-50m sized bodies which are embedded in Saturn's rings. We estimate the\nimportance of various interaction processes with the ring particles on the\nmoonlet's eccentricity and semi-major axis analytically. For low ring surface\ndensities, the main effects on the evolution of the eccentricity and the\nsemi-major axis are found to be due to collisions and the gravitational\ninteraction with particles in the vicinity of the moonlet. For large surface\ndensities, the gravitational interaction with self-gravitating wakes becomes\nimportant.\n We also perform realistic three dimensional, collisional N-body simulations\nwith up to a quarter of a million particles. A new set of pseudo shear periodic\nboundary conditions is used which reduces the computational costs by an order\nof magnitude compared to previous studies. Our analytic estimates are confirmed\nto within a factor of two.\n On short timescales the evolution is always dominated by stochastic effects\ncaused by collisions and gravitational interaction with self-gravitating ring\nparticles. These result in a random walk of the moonlet's semi-major axis. The\neccentricity of the moonlet quickly reaches an equilibrium value due to\ncollisional damping. The average change in semi-major axis of the moonlet after\n100 orbital periods is 10-100m. This translates to an offset in the azimuthal\ndirection of several hundred kilometres. We expect that such a shift is easily\nobservable.", "category": "astro-ph_EP" }, { "text": "Vortex Formation and Survival in Protoplanetary Disks subject to\n Vertical Shear Instability: Several protoplanetary disks observed by ALMA show dust concentrations\nconsistent with particle trapping in giant vortices. The formation and survival\nof vortices is of major importance for planet formation, because vortices act\nas particle traps and are therefore preferred locations of planetesimal\nformation. Recent studies showed that the vertical shear instability (VSI) is\ncapable of generating turbulence and small vortices in protoplanetary disks\nthat have the proper radial and vertical stratification and thermally relax on\nsufficiently short time scales. But the effect of the azimuthal extend of the\ndisk is often neglected as the disks azimuth is limited to $\\Delta \\phi \\leq\n\\pi/2$. We aim to investigate the influence of the azimuthal extent of the disk\non the long-term evolution of a protoplanetary disk and the possibility of\nlarge vortices forming. To this end, we perform 3-dimensional simulations for\nup to 1000 local orbits using different values of $\\Delta \\phi = \\pi/2 $ to\n$2\\pi$ for VSI in disks with a prescribed radial density and temperature\ngradient cooling on short timescales. We find the VSI capable of forming large\nvortices which can exist at least several hundred orbits in simulations\ncovering a disk with $\\Delta \\phi \\geq \\pi$. This suggests the VSI to be\ncapable to form vortices or at least to trigger vortex formation via a\nsecondary instability, e.g. Rossby Wave Instability or Kelvin Helmholtz\nInstability.", "category": "astro-ph_EP" }, { "text": "Orbital structure of the GJ876 extrasolar planetary system, based on the\n latest Keck and HARPS radial velocity data: We use full available array of radial velocity data, including recently\npublished HARPS and Keck observatory sets, to characterize the orbital\nconfiguration of the planetary system orbiting GJ876. First, we propose and\ndescribe in detail a fast method to fit perturbed orbital configuration, based\non the integration of the sensitivity equations inferred by the equations of\nthe original $N$-body problem. Further, we find that it is unsatisfactory to\ntreat the available radial velocity data for GJ876 in the traditional white\nnoise model, because the actual noise appears autocorrelated (and demonstrates\nnon-white frequency spectrum). The time scale of this correlation is about a\nfew days, and the contribution of the correlated noise is about 2 m/s (i.e.,\nsimilar to the level of internal errors in the Keck data). We propose a\nvariation of the maximum-likelihood algorithm to estimate the orbital\nconfiguration of the system, taking into account the red noise effects. We\nshow, in particular, that the non-zero orbital eccentricity of the innermost\nplanet \\emph{d}, obtained in previous studies, is likely a result of\nmisinterpreted red noise in the data. In addition to offsets in some orbital\nparameters, the red noise also makes the fit uncertainties systematically\nunderestimated (while they are treated in the traditional white noise model).\nAlso, we show that the orbital eccentricity of the outermost planet is actually\nill-determined, although bounded by $\\sim 0.2$. Finally, we investigate\npossible orbital non-coplanarity of the system, and limit the mutual\ninclination between the planets \\emph{b} and \\emph{c} orbits by\n$5^\\circ-15^\\circ$, depending on the angular position of the mutual orbital\nnodes.", "category": "astro-ph_EP" }, { "text": "Radial Drift of Dust in Protoplanetary Disks: The Evolution of Ice lines\n and Dead zones: We have developed a new model for the astrochemical structure of a viscously\nevolving protoplanetary disk that couples an analytic description of the disk's\ntemperature and density profile, chemical evolution, and an evolving dust\ndistribution. We compute evolving radial distributions for a range of dust\ngrain sizes, which depend on coagulation, fragmentation and radial drift\nprocesses. In particular we find that the water ice line plays an important\nrole in shaping the radial distribution of the maximum grain size because ice\ncoated grains are significantly less susceptible to fragmentation than their\ndry counterparts. This in turn has important effects on disk ionization and\ntherefore on the location of dead zones. In comparison to a simple constant\ngas-to-dust ratio model for the dust as an example, we find that the new model\npredicts an outer dead zone edge that moves in by a factor of about 3 at 1 Myr\n(to 5 AU) and by a factor of about 14 by 3 Myr (to 0.5 AU). We show that the\nchanging position of the dead zone and heat transition traps have important\nimplications for the formation and trapping of planets in protoplanetary disks.\nFinally, we consider our results in light of recent ALMA observations of HL Tau\nand TW Hya.", "category": "astro-ph_EP" }, { "text": "Effect of Non-Adiabatic Thermal Profiles on the Inferred Compositions of\n Uranus and Neptune: It has been a common assumption of interior models that the outer planets of\nour solar system are convective, and that the internal temperature\ndistributions are therefore adiabatic. This assumption is also often applied to\nexoplanets. However, if a large portion of the thermal flux can be transferred\nby conduction, or if convection is inhibited, the thermal profile could be\nsubstantially different and would therefore affect the inferred planetary\ncomposition. Here we investigate how the assumption of non-adiabatic\ntemperature profiles in Uranus and Neptune affects their internal structures\nand compositions. We use a set of plausible temperature profiles together with\ndensity profiles that match the measured gravitational fields to derive the\nplanets' compositions. We find that the inferred compositions of both Uranus\nand Neptune are quite sensitive to the assumed thermal profile in the outer\nlayers, but relatively insensitive to the thermal profile in the central, high\npressure region. The overall value of the heavy element mass fraction, $Z$, for\nthese planets is between 0.8 and 0.9. Finally, we suggest that large parts of\nUranus' interior might be conductive, a conclusion that is consistent with\nUranus dynamo models and a hot central inner region.", "category": "astro-ph_EP" }, { "text": "Predicting the magnetic vectors within coronal mass ejections arriving\n at Earth: 1. Initial Architecture: The process by which the Sun affects the terrestrial environment on short\ntimescales is predominately driven by the amount of magnetic reconnection\nbetween the solar wind and Earth's magnetosphere. Reconnection occurs most\nefficiently when the solar wind magnetic field has a southward component. The\nmost severe impacts are during the arrival of a coronal mass ejection (CME)\nwhen the magnetosphere is both compressed and magnetically connected to the\nheliospheric environment. Unfortunately, forecasting magnetic vectors within\ncoronal mass ejections remains elusive. Here we report how, by combining a\nstatistically robust helicity rule for a CME's solar origin with a simplified\nflux rope topology the magnetic vectors within the Earth-directed segment of a\nCME can be predicted. In order to test the validity of this proof-of-concept\narchitecture for estimating the magnetic vectors within CMEs, a total of eight\nCME events (between 2010 and 2014) have been investigated. With a focus on the\nlarge false alarm of January 2014, this work highlights the importance of\nincluding the early evolutionary effects of a CME for forecasting purposes. The\nangular rotation in the predicted magnetic field closely follows the broad\nrotational structure seen within the in situ data. This time-varying field\nestimate is implemented into a process to quantitatively predict a time-varying\nKp index that is described in detail in paper II. Future statistical work,\nquantifying the uncertainties in this process, may improve the more heuristic\napproach used by early forecasting systems.", "category": "astro-ph_EP" }, { "text": "Ground- and Space-based Detection of the Thermal Emission Spectrum of\n the Transiting Hot Jupiter KELT-2Ab: We describe the detection of water vapor in the atmosphere of the transiting\nhot Jupiter KELT-2Ab by treating the star-planet system as a spectroscopic\nbinary with high-resolution, ground-based spectroscopy. We resolve the signal\nof the planet's motion with deep combined flux observations of the star and the\nplanet. In total, six epochs of Keck NIRSPEC $L$-band observations were\nobtained, and the full data set was subjected to a cross correlation analysis\nwith a grid of self-consistent atmospheric models. We measure a radial\nprojection of the Keplerian velocity, $K_P$, of 148 $\\pm$ 7 km s$^{-1}$,\nconsistent with transit measurements, and detect water vapor at 3.8$\\sigma$. We\ncombine NIRSPEC $L$-band data with $Spitzer$ IRAC secondary eclipse data to\nfurther probe the metallicity and carbon-to-oxygen ratio of KELT-2Ab's\natmosphere. While the NIRSPEC analysis provides few extra constraints on the\n$Spitzer$ data, it does provide roughly the same constraints on metallicity and\ncarbon-to-oxygen ratio. This bodes well for future investigations of the\natmospheres of non-transiting hot Jupiters.", "category": "astro-ph_EP" }, { "text": "Multi-Output Random Forest Regression to Emulate the Earliest Stages of\n Planet Formation: In the current paradigm of planet formation research, it is believed that the\nfirst step to forming massive bodies (such as asteroids and planets) requires\nthat small interstellar dust grains floating through space collide with each\nother and grow to larger sizes. The initial formation of these pebbles is\ngoverned by an integro-differential equation known as the Smoluchowski\ncoagulation equation, to which analytical solutions are intractable for all but\nthe simplest possible scenarios. While brute-force methods of approximation\nhave been developed, they are computationally costly, currently making it\ninfeasible to simulate this process including other physical processes relevant\nto planet formation, and across the very large range of scales on which it\noccurs. In this paper, we take a machine learning approach to designing a\nsystem for a much faster approximation. We develop a multi-output random forest\nregression model trained on brute-force simulation data to approximate\ndistributions of dust particle sizes in protoplanetary disks at different\npoints in time. The performance of our random forest model is measured against\nthe existing brute-force models, which are the standard for realistic\nsimulations. Results indicate that the random forest model can generate highly\naccurate predictions relative to the brute-force simulation results, with an\n$R^{2}$ of 0.97, and do so significantly faster than brute-force methods.", "category": "astro-ph_EP" }, { "text": "Concentrating small particles in protoplanetary disks through the\n streaming instability: Laboratory experiments indicate that direct growth of silicate grains via\nmutual collisions can only produce particles up to roughly millimeters in size.\nOn the other hand, recent simulations of the streaming instability have shown\nthat mm/cm-sized particles require an excessively high metallicity for dense\nfilaments to emerge. Using a numerical algorithm for stiff mutual drag force,\nwe perform simulations of small particles with significantly higher resolutions\nand longer simulation times than in previous investigations. We find that\nparticles of dimensionless stopping time $\\tau_\\mathrm{s} = 10^{-2}$ and\n$10^{-3}$ -- representing mm- and cm-sized particles interior of the water ice\nline -- concentrate themselves via the streaming instability at a solid\nabundance of a few percent. We thus revise a previously published critical\nsolid abundance curve for the regime of $\\tau_\\mathrm{s} \\ll 1$. The solid\ndensity in the concentrated regions reaches values higher than the Roche\ndensity, indicating that direct collapse of particles down to mm sizes into\nplanetesimals is possible. Our results hence bridge the gap in particle size\nbetween direct dust growth limited by bouncing and the streaming instability.", "category": "astro-ph_EP" }, { "text": "KIC 8462852: Transit of a Large Comet Family: We investigate the plausibility of a cometary source of the unusual transits\nobserved in the KIC 8462852 light curve. A single comet of similar size to\nthose in our solar system produces a transit depth of the order of $10^{-3}$\nlasting less than a day which is much smaller and shorter than the largest dip\nobserved ($\\sim20\\%$ for $\\sim3$ days), but a large, closely traveling cluster\nof comets can fit the observed depths and durations. We find that a series of\nlarge comet swarms, with all but one on the same orbit, provides a good fit for\nthe KIC 8462852 data during Quarters 16 and 17, but does not explain the large\ndip observed during Quarter 8. However, the transit dips only loosely constrain\nthe orbits and can be fit by swarms with periastrons differing by a factor of\n10. To reach a transit depth of $\\sim0.2$, the comets need to be in a close\ngroup of $\\sim30$, if they are $\\sim100$ km in radius or in a group of\n$\\sim300$ if they are $\\sim10$ km in radius. The total number of comets\nrequired to fit all of the dips is $\\sim70$ $\\sim$100 km or $\\sim700$ $\\sim10$\nkm comets. A single comet family from a tidally disrupted Ceres-sized\nprogenitor or the start of a Late Heavy Bombardment period explains the last\n$\\sim60$ days of the unusual KIC 8462852 light curve.", "category": "astro-ph_EP" }, { "text": "A grid of upper atmosphere models for 1--40 MEARTH planets: application\n to CoRoT-7 b and HD219134 b,c: There is growing observational and theoretical evidence suggesting that\natmospheric escape is a key driver of planetary evolution. Commonly, planetary\nevolution models employ simple analytic formulae (e.g., energy limited escape)\nthat are often inaccurate, and more detailed physical models of atmospheric\nloss usually only give snapshots of an atmosphere's structure and are difficult\nto use for evolutionary studies. To overcome this problem, we upgrade and\nemploy an already existing upper atmosphere hydrodynamic code to produce a\nlarge grid of about 7000 models covering planets with masses 1 - 39 Earth mass\nwith hydrogen-dominated atmospheres and orbiting late-type stars. The modeled\nplanets have equilibrium temperatures ranging between 300 and 2000 K. For each\nconsidered stellar mass, we account for three different values of the\nhigh-energy stellar flux (i.e., low, moderate, and high activity). For each\ncomputed model, we derive the atmospheric temperature, number density, bulk\nvelocity, X-ray and EUV (XUV) volume heating rates, and abundance of the\nconsidered species as a function of distance from the planetary center. From\nthese quantities, we estimate the positions of the maximum dissociation and\nionisation, the mass-loss rate, and the effective radius of the XUV absorption.\nWe show that our results are in good agreement with previously published\nstudies employing similar codes. We further present an interpolation routine\ncapable to extract the modelling output parameters for any planet lying within\nthe grid boundaries. We use the grid to identify the connection between the\nsystem parameters and the resulting atmospheric properties. We finally apply\nthe grid and the interpolation routine to estimate atmospheric evolutionary\ntracks for the close-in, high-density planets CoRoT-7 b and HD219134 b,c...", "category": "astro-ph_EP" }, { "text": "Teegarden's Star revisited: A nearby planetary system with at least\n three planets: The two known planets in the planetary system of Teegarden's Star are among\nthe most Earth-like exoplanets currently known. Revisiting this nearby\nplanetary system with two planets in the habitable zone aims at a more complete\ncensus of planets around very low-mass stars. A significant number of new\nradial velocity measurements from CARMENES, ESPRESSO, MAROON-X, and HPF, as\nwell as photometry from TESS motivated a deeper search for additional planets.\nWe confirm and refine the orbital parameters of the two know planets\nTeegarden's Star b and c. We also report the detection of a third planet d with\nan orbital period of 26.13+-0.04 d and a minimum mass of 0.82+-0.17 M_Earth. A\nsignal at 96 d is attributed to the stellar rotation period. The interpretation\nof a signal at 172 d remains open. The TESS data exclude transiting\nshort-period planets down to about half an Earth radius. We compare the\nplanetary system architecture of very low-mass stars. In the currently known\nconfiguration, the planetary system of Teegarden's star is dynamically quite\ndifferent from that of TRAPPIST-1, which is more compact, but dynamically\nsimilar to others such as GJ 1002.", "category": "astro-ph_EP" }, { "text": "Effects of Dust Evolution on the Vertical Shear Instability in the Outer\n Regions of Protoplanetary Disks: The vertical shear instability (VSI) is a hydrodynamical instability that\nrequires rapid gas cooling and has been suggested to operate in outer regions\nof protoplanetary disks. The VSI drives turbulence with strong vertical\nmotions, which could regulate the dust growth and settling. However, dust\ngrowth and settling can regulate the VSI because dust depletion makes gas\ncooling inefficient in outer disk regions that are optically thin to their own\nthermal emission. In this study, we quantify this potentially stabilizing\neffects of dust evolution on the VSI based on the linear analysis. We construct\na model for calculating the cooling timescale, taking into account dust growth\nbeyond micron sizes and size-dependent settling. Combining the model with the\nlinear stability analysis, we map the region where the VSI operates, which we\ncall the VSI zone, and estimate the maximum growth rate at each radial\nposition. We find that dust growth as well as settling makes the VSI zone more\nconfined around the midplane. This causes a decrease in the growth rate because\nthe vertical shear of the rotation velocity, which is the source of the\ninstability, is weaker at lower altitude. In our default disk model with 0.01\nsolar masses, dust growth from 10 micron to 1 mm causes a decrease in the\ngrowth rate by a factor of more than 10. The suppression of VSI-driven\nturbulence by dust evolution may promote further dust evolution in the outer\nregions and also explain a high degree of dust settling observed in the disk\naround HL Tau.", "category": "astro-ph_EP" }, { "text": "High contrast imaging at 10 microns, a search for exoplanets around: Eps\n Indi A, Eps Eri, Tau Ceti, Sirius A and Sirius B: The direct imaging of rocky exoplanets is one of the major science goals for\nupcoming large telescopes. The contrast requirement for imaging such planets is\nchallenging. However, the mid-IR (InfraRed) regime provides the optimum\ncontrast to directly detect the thermal signatures of exoplanets in our solar\nneighbourhood. We aim to exploit novel fast chopping techniques newly developed\nfor astronomy with the aid of adaptive optics to look for thermal signatures of\nexoplanets around bright stars in the solar neighbourhood. We use the upgraded\nVISIR (Very Large Telescope Imager and Spectrometer for the mid-InfraRed)\ninstrument with high contrast imaging (HCI) capability optimized for\nobservations at 10~$\\mu$m to look for exoplanets around five nearby ($d$ < 4\npc) stars. The instrument provides an improved signal-to-noise (S/N) by a\nfactor of $\\sim$4 in the N-band compared to standard VISIR for a given S/N and\ntime. In this work we achieve a detection sensitivity of sub-mJy, which is\nsufficient to detect few Jupiter mass planets in nearby systems. Although no\ndetections are made we achieve most sensitive limits within $<2''$ for all the\nobserved targets compared to previous campaigns. For $\\epsilon$ Indi A and\n$\\epsilon$ Eri we achieve detection limits very close to the giant planets\ndiscovered by RV, with the limits on $\\epsilon$ Indi A being the most sensitive\nto date. Our non-detection therefore supports an older age for $\\epsilon$ Indi\nA. The results presented here show the promise for high contrast imaging and\nexoplanet detections in the mid-IR regime.", "category": "astro-ph_EP" }, { "text": "Tidal dissipation in a homogeneous spherical body. I. Methods: A formula for the tidal dissipation rate in a spherical body is derived from\nfirst principles, to correct some mathematical inaccuracies found in the\nliterature. The development is combined with the Darwin-Kaula formalism for\ntides. Our intermediate results are compared with those by Zschau (1978) and\nPlatzman (1984). When restricted to the special case of an incompressible\nspherical planet spinning synchronously without libration, our final formula\ncan be compared with the commonly used expression from Peale & Cassen (1978,\nEqn. 31). The two turn out to differ. In our expression, the contributions from\nall Fourier modes are positive-definite, this not being the case of the formula\nfrom Ibid. (The presence of negative terms in their formula was noticed by\nMakarov 2013.) Examples of application of our expression for the tidal damping\nrate are provided in the work by Makarov and Efroimsky (2014).", "category": "astro-ph_EP" }, { "text": "Insights on the dynamical history of the Fomalhaut system -\n Investigating the Fom c hypothesis: The eccentric shape of the debris disk observed around Fomalhaut was first\nattributed to Fom b, a companion detected near the belt inner-edge, but new\nconstraints on its orbit revealed that it is belt-crossing, highly eccentric\n$(e \\sim 0.6-0.9)$, and can hardly account for the shape of the belt. The best\nscenario to explain this paradox is that there is another massive body in this\nsystem, Fom c, which drives the debris disk shape. The resulting planetary\nsystem is highly unstable, which hints at a dynamical scenario involving a\nrecent scattering of Fom b on its current orbit, potentially with the putative\nFom c.\n Our goal is to give insights on the probability for Fom b to have been set on\nits highly eccentric orbit by a close-encounter with the putative Fom c. We aim\nto study in particular the part played by mean-motion resonances with Fom c,\nwhich could have brought Fom b sufficiently close to Fom c for it to be\nscattered on its current orbit, but also delay this scattering event.\n Using N-body simulations, we found that the generation of orbits similar to\nthat of Fom b, either in term of dimensions or orientation, is a robust process\ninvolving a scattering event and a further secular evolution of inner material\nwith an eccentric massive body such as the putative Fom c. We found in\nparticular that mean-motion resonances can delay scattering events, and thus\nthe production of Fom b-like orbits, on timescales comparable to the age of the\nsystem, thus explaining the witnessing of an unstable configuration.\n We conclude that Fom b probably originated from an inner resonance with Fom\nc, which is at least Neptune-Saturn size, and was set on its current orbit by a\nscattering event with Fom c. Since Fom b could not have formed from material in\nresonance, our scenario also hints at former migration processes in this\nplanetary system.", "category": "astro-ph_EP" }, { "text": "A multiplicity study of transiting exoplanet host stars. I.\n High-contrast imaging with VLT/SPHERE: We study the multiplicity of host stars to known transiting extra-solar\nplanets to test competing theories on the formation mechanisms of hot Jupiters.\nWe observed 45 exoplanet host stars using VLT/SPHERE/IRDIS to search for\npotential companions. For each identified candidate companion we determined the\nprobability that it is gravitationally bound to its host by performing common\nproper motion checks and modelling of synthetic stellar populations around the\nhost. We detected new candidate companions around K2-38, WASP-72, WASP-80,\nWASP-87, WASP-88, WASP-108, WASP-118, WASP-120, WASP-122, WASP123, WASP-130,\nWASP-131 and WASP-137. The closest candidates were detected at separations of\n$0.124''\\pm0.007''$ and $0.189''\\pm0.003''$ around WASP-108 and WASP-131; the\nmeasured $K$ band contrasts indicate that these are stellar companions of\n$0.35\\pm0.02\\,M_{\\odot}$ and $0.62^{+0.05}_{-0.04}\\,M_{\\odot}$, respectively.\nIncluding the re-detection and confirmation of previously known companions in\n13 other systems we derived a multiplicity fraction of\n$55.4^{+5.9}_{-9.4}\\,\\%$. For the representative sub-sample of 40 hot Jupiter\nhost stars among our targets, the derived multiplicity rate is\n$54.8^{+6.3}_{-9.9}\\,\\%$. Our data do not confirm any trend that systems with\neccentric planetary companions are preferably part of multiple systems. On\naverage, we reached a magnitude contrast of $8.5\\pm0.9$ mag at an angular\nseparation of 0.5''. This allows to exclude additional stellar companions with\nmasses larger than $0.08$ M$_\\odot$ for almost all observed systems; around the\nclosest and youngest systems this sensitivity is achieved at physical\nseparations as small as 10 au. The presented study shows that SPHERE is an\nideal instrument to detect and characterize close companions to exoplanetary\nhost stars.", "category": "astro-ph_EP" }, { "text": "Dynamics of Planetary Systems Within Star Clusters: Aspects of the Solar\n System's Early Evolution: Most planetary systems -- including our own -- are born within stellar\nclusters, where interactions with neighboring stars can help shape the system\narchitecture. This paper develops an orbit-averaged formalism to characterize\nthe cluster's mean-field effects as well as the physics of long-period stellar\nencounters. Our secular approach allows for an analytic description of the\ndynamical consequences of the cluster environment on its constituent planetary\nsystems. We analyze special cases of the resulting Hamiltonian, corresponding\nto eccentricity evolution driven by planar encounters, as well as hyperbolic\nperturbations upon dissipative disks. We subsequently apply our results to the\nearly evolution of our solar system, where the cluster's collective potential\nperturbs the solar system's plane, and stellar encounters act to increase the\nvelocity dispersion of the Kuiper belt. Our results are two-fold: first, we\nfind that cluster effects can alter the mean plane of the solar system by\n$\\lesssim1\\deg$, and are thus insufficient to explain the $\\psi\\approx6\\deg$\nobliquity of the sun. Second, we delineate the extent to which stellar flybys\nexcite the orbital dispersion of the cold classical Kuiper belt, and show that\nwhile stellar flybys may grow the cold belt's inclination by the observed\namount, the resulting distribution is incompatible with the data.\nCorrespondingly, our calculations place an upper limit on the product of the\nstellar number density and residence time of the sun in its birth cluster,\n$\\eta\\,\\tau\\lesssim2\\times10^4\\,$Myr/pc$^3$.", "category": "astro-ph_EP" }, { "text": "ExoData: A python package to handle large exoplanet catalogue data: Exoplanet science often involves using the system parameters of real\nexoplanets for tasks such as simulations, fitting routines, and target\nselection for proposals. Several exoplanet catalogues are already well\nestablished but often lack a version history and code friendly interfaces.\nSoftware that bridges the barrier between the catalogues and code enables users\nto improve the specific repeatability of results by facilitating the retrieval\nof exact system parameters used in an articles results along with unifying the\nequations and software used. As exoplanet science moves towards large data,\ngone are the days where researchers can recall the current population from\nmemory. An interface able to query the population now becomes invaluable for\ntarget selection and population analysis. ExoData is a Python interface and\nexploratory analysis tool for the Open Exoplanet Catalogue. It allows the\nloading of exoplanet systems into Python as objects (Planet, Star, Binary etc)\nfrom which common orbital and system equations can be calculated and measured\nparameters retrieved. This allows researchers to use tested code of the common\nequations they require (with units) and provides a large science input\ncatalogue of planets for easy plotting and use in research. Advanced querying\nof targets are possible using the database and Python programming language.\nExoData is also able to parse spectral types and fill in missing parameters\naccording to programmable specifications and equations. Examples of use cases\nare integration of equations into data reduction pipelines, selecting planets\nfor observing proposals and as an input catalogue to large scale simulation and\nanalysis of planets.", "category": "astro-ph_EP" }, { "text": "Preview of Comet C/2021 A1 (Leonard) and Its Encounter with Venus: Long period comet C/2021 A1 (Leonard) will approach Venus to within 0.029 au\non 2021 December 18 and may subsequently graze the planet with its dust trail\nless than two days later. We observed C/2021 A1 with the Lowell Discovery\nTelescope on 2021 January 13 and March 3, as well as with the Palomar Hale\nTelescope on 2021 March 20, while the comet was inbound at heliocentric\ndistances of r=4.97 au, 4.46 au, and 4.28 au, respectively. Tail morphology\nsuggests that the dust is optically dominated by ~0.1-1 mm radius grains\nproduced in the prior year. Neither narrowband imaging photometry nor\nspectrophotometry reveal any definitive gas emission, placing 3-sigma upper\nbounds on CN production of <1e23 molec/s at both of the latter two epochs.\nTrajectory analysis indicates that large (>1 mm) grains ejected at extremely\nlarge heliocentric distances (r>30 au) are most strongly favored to reach\nVenus. The flux of such meteors on Venus, and thus their potential direct or\nindirect observability, is highly uncertain as the comet's dust production\nhistory is poorly constrained at these distances, but will likely fall well\nbelow the meteor flux from comet C/2013 A1 (Siding Spring)'s closer encounter\nto Mars in 2014, and thus poses negligible risk to any spacecraft in orbit\naround Venus. Dust produced in previous apparitions will not likely contribute\nsubstantially to the meteor flux, nor will dust from any future activity apart\nfrom an unlikely high speed (>0.5 km/s) dust outburst prior to the comet\nreaching r~2 au in 2021 September.", "category": "astro-ph_EP" }, { "text": "Detectability of Life Using Oxygen on Pelagic Planets and Water Worlds: The search for life on exoplanets is one of the grand scientific challenges\nof our time. The strategy to date has been to find (e.g., through transit\nsurveys like Kepler) Earth-like exoplanets in their stars habitable zone, then\nuse transmission spectroscopy to measure biosignature gases, especially oxygen,\nin the planets atmospheres (e.g., using JWST, the James Webb Space Telescope).\nAlready there are more such planets than can be observed by JWST, and missions\nlike the Transiting Exoplanet Survey Satellite and others will find more. A\nbetter understanding of the geochemical cycles relevant to biosignature gases\nis needed, to prioritize targets for costly follow-up observations and to help\ndesign future missions. We define a Detectability Index to quantify the\nlikelihood that a biosignature gas could be assigned a biological vs.\nnon-biological origin. We apply this index to the case of oxygen gas, O2, on\nEarth-like planets with varying water contents. We demonstrate that on\nEarth-like exoplanets with 0.2 weight percent (wt%) water (i.e., no exposed\ncontinents) a reduced flux of bioessential phosphorus limits the export of\nphotosynthetically produced atmospheric O2 to levels indistinguishable from\ngeophysical production by photolysis of water plus hydrogen escape. Higher\nwater contents >1wt% that lead to high-pressure ice mantles further slow\nphosphorus cycling. Paradoxically, the maximum water content allowing use of O2\nas a biosignature, 0.2wt%, is consistent with no water based on mass and\nradius. Thus, the utility of an O2 biosignature likely requires the direct\ndetection of both water and land on a planet.", "category": "astro-ph_EP" }, { "text": "The Tidal-Thermal Evolution of the Pluto-Charon System: Existence of subsurface oceans on the satellites of the giant planets and\nTrans-Neptunian objects has been predicted for some time. Oceans on icy worlds\nexert a considerable influence on the dynamics of the ice-ocean system and,\nbecause of the astrobiological potential, represent an important objective for\nfuture missions. The Pluto-Charon system is representative of an icy moon\norbiting a dwarf planet formed from the remnants of a giant impact. Evolution\nof icy moons is primarily controlled by the mode and efficiency of heat\ntransfer through the outer ice shell, which is influenced by the presence of\nimpurities, by tidal dissipation in the ice shell, and the radioactive element\nbudget in the core. Previous studies on the evolution of the Pluto-Charon\nsystem considered either only the thermal or the tidal evolution, and in the\ncases where both were considered, the important effect of the presence of\nimpurities in the liquid oceans was not addressed. We consider the joint\ntidal-thermal evolution of the system by combining a comprehensive tidal model\nthat incorporates a viscoelastic tidal response with a parameterized convection\nmodel developed for icy worlds. This approach enables an extensive analysis of\nthe conditions required for formation and maintenance of subsurface liquid\noceans to the present. Our results show that because of fast circularization\nand synchronization of the orbits, tidal heating is only important during the\nearly stages of evolution (<1 Myr). We test the sensitivity of our results to\nthe initial orbital and thermal parameters. In all the cases, oceans on Pluto\nare always predicted to remain liquid to the present, ranging from 40 km to\n150-km thick, whereas oceans on Charon have solidified. This is supported by\nNew Horizons observations of extensional faults on Pluto and both extensional\nand compressional faults on Charon.", "category": "astro-ph_EP" }, { "text": "The 1998 November 14 Occultation of GSC 0622-00345 by Saturn. I.\n Techniques for Ground-Based Stellar Occultations: On 1998 November 14, Saturn and its rings occulted the star GSC 0622-00345.\nWe observed atmospheric immersion with NSFCAM at the National Aeronautics and\nSpace Administration's Infrared Telescope Facility on Mauna Kea, Hawaii.\nImmersion occurred at 55.5\\circ S planetocentric latitude. A 2.3 {\\mu}m,\nmethane-band filter suppressed reflected sunlight. Atmospheric emersion and\nring data were not successfully obtained. We describe our observation,\nlight-curve production, and timing techniques, including improvements in\naperture positioning, removal of telluric scintillation effects, and timing.\nMany of these techniques are known within the occultation community, but have\nnot been described in the reviewed literature. We present a light curve whose\nsignal-to-noise ratio per scale height is 267, among the best ground-based\nsignals yet achieved, despite a disadvantage of up to 8 mag in the stellar flux\ncompared to prior work.", "category": "astro-ph_EP" }, { "text": "Short-term variability of comet C/2012 S1 (ISON) at 4.8 AU from the Sun: We observed comet C/2012 S1 (ISON) during six nights in February 2013 when it\nwas at 4.8 AU from the sun. At this distance and time the comet was not very\nactive and it was theoretically possible to detect photometric variations\nlikely due to the rotation of the cometary nucleus. The goal of this work is to\nobtain differential photometry of the comet inner coma using different aperture\nradii in order to derive a possible rotational period. Large field of view\nimages were obtained with a 4k x 4k CCD at the f/3 0.77m telescope of La Hita\nObservatory in Spain. Aperture photometry was performed in order to get\nrelative magnitude variation versus time. Using calibrated star fields we also\nobtained ISON's R-magnitudes versus time. We applied a Lomb-Scargle periodogram\nanalysis to get possible periodicities for the observed brightness variations,\ndirectly related with the rotation of the cometary nucleus. The comet light\ncurve obtained is very shallow, with a peak-to-peak amplitude of 0.03 $\\pm$\n0.02 mag. A tentative synodic rotational period (single-peaked) of 14.4 $\\pm$\n1.2 hours for ISON's nucleus is obtained from our analysis, but there are other\npossibilities. We studied the possible effect of the seeing variations in the\nobtained periodicities during the same night, and from night to night. These\nseeing variations had no effect on the derived periodicity. We discuss and\ninterpret all possible solutions for the rotational period of ISON's nucleus.", "category": "astro-ph_EP" }, { "text": "ALMA Observations of Asymmetric Molecular Gas Emission from a\n Protoplanetary Disk in the Orion Nebula: We present Atacama Large Millimeter/submillimeter Array (ALMA) observations\nof molecular line emission from d216-0939, one of the largest and most massive\nprotoplanetary disks in the Orion Nebula Cluster (ONC). We model the spectrally\nresolved HCO$^+$ (4--3), CO (3--2), and HCN (4--3) lines observed at 0\\farcs5\nresolution to fit the temperature and density structure of the disk. We also\nweakly detect and spectrally resolve the CS (7--6) line but do not model it.\nThe abundances we derive for CO and HCO$^+$ are generally consistent with\nexpected values from chemical modeling of protoplanetary disks, while the HCN\nabundance is higher than expected. We dynamically measure the mass of the\ncentral star to be $2.17\\pm0.07\\,M_\\odot$ which is inconsistent with the\npreviously determined spectral type of K5. We also report the detection of a\nspatially unresolved high-velocity blue-shifted excess emission feature with a\nmeasurable positional offset from the central star, consistent with a Keplerian\norbit at $60\\pm20\\,\\mathrm{au}$. Using the integrated flux of the feature in\nHCO$^+$ (4--3), we estimate the total H$_2$ gas mass of this feature to be at\nleast $1.8-8\\,M_\\mathrm{Jupiter}$, depending on the assumed temperature. The\nfeature is due to a local temperature and/or density enhancement consistent\nwith either a hydrodynamic vortex or the expected signature of the envelope of\na forming protoplanet within the disk.", "category": "astro-ph_EP" }, { "text": "HAT-P-58b -- HAT-P-64b: Seven Planets Transiting Bright Stars: We report the discovery and characterization of 7 transiting exoplanets from\nthe HATNet survey. The planets, which are hot Jupiters and Saturns transiting\nbright sun-like stars, include: HAT-P-58b (with mass Mp = 0.37 MJ, radius Rp =\n1.33 RJ, and orbital period P = 4.0138 days), HAT-P-59b (Mp = 1.54 MJ, Rp =\n1.12 RJ, P = 4.1420 days), HAT-P-60b (Mp = 0.57 MJ, Rp = 1.63 RJ, P = 4.7948\ndays), HAT-P-61b (Mp = 1.06 MJ, Rp = 0.90 RJ, P = 1.9023 days), HAT-P-62b (Mp =\n0.76 MJ, Rp = 1.07 RJ, P = 2.6453 days), HAT-P-63b (Mp = 0.61 MJ, Rp = 1.12 RJ,\nP = 3.3777 days), and HAT-P-64b (Mp = 0.58 MJ, Rp = 1.70 RJ, P = 4.0072 days).\nThe typical errors on these quantities are 0.06 MJ, 0.03 RJ, and 0.2seconds,\nrespectively. We also provide accurate stellar parameters for each of the hosts\nstars. With V = 9.710+/-0.050mag, HAT-P-60 is an especially bright transiting\nplanet host, and an excellent target for additional follow-up observations.\nWith Rp = 1.703+/-0.070 RJ, HAT-P-64b is a highly inflated hot Jupiter around a\nstar nearing the end of its main-sequence lifetime, and is among the largest\nknown planets. Five of the seven systems have long-cadence observations by TESS\nwhich are included in the analysis. Of particular note is HAT-P-59\n(TOI-1826.01) which is within the Northern continuous viewing zone of the TESS\nmission, and HAT-P-60, which is the TESS candidate TOI-1580.01.", "category": "astro-ph_EP" }, { "text": "A particle-based hybrid code for planet formation: We introduce a new particle-based hybrid code for planetary accretion. The\ncode uses an $N$-body routine for interactions with planetary embryos while it\ncan handle a large number of planetesimals using a super-particle\napproximation, in which a large number of small planetesimals are represented\nby a small number of tracers. Tracer-tracer interactions are handled by a\nstatistical routine which uses the phase-averaged stirring and collision rates.\nWe compare hybrid simulations with analytic predictions and pure $N$-body\nsimulations for various problems in detail and find good agreements for all\ncases. The computational load on the portion of the statistical routine is\ncomparable to or less than that for the $N$-body routine. The present code\nincludes an option of hit-and-run bouncing but not fragmentation, which remains\nfor future work.", "category": "astro-ph_EP" }, { "text": "The Complex Rotational Light Curve of (385446) Manw\u00eb-Thorondor, a\n Multi-Component Eclipsing System in the Kuiper Belt: Kuiper Belt Object (385446) Manw\\\"e-Thorondor is a multi-object system with\nmutual events predicted to occur from 2014 to 2019. To detect the events, we\nobserved the system at 4 epochs (UT 2016 Aug 25 and 26, 2017 Jul 22 and 25,\n2017 Nov 9, and 2018 Oct 6) in g, r, and VR bands using the 4-m SOAR and the\n8.1-m Gemini South telescopes at Cerro Pach\\'on, Chile and Lowell Observatory '\ns 4.3-m Discovery Channel Telescope at Happy Jack, Arizona. These dates overlap\nthe uncertainty range (+/- 0.5 d) for four inferior events (Thorondor eclipsing\nManw\\\"e). We clearly observe variability for the unresolved system with a\ndouble-peaked period 11.88190 +/- 0.00005 h and ~0.5 mag amplitude together\nwith much longer-term variability. Using a multi-component model, we\nsimultaneously fit our observations and earlier photometry measured separately\nfor Manw\\\"e and Thorondor with the Hubble Space Telescope. Our fit suggests\nManw\\\"e is bi-lobed, close to the barbell shape expected for a strengthless\nbody with density ~0.8 g/cm3 in hydrostatic equilibrium. For Manw\\\"e, we\nthereby derive maximum width to length ratio ~0.30, surface area equivalent to\na sphere of diameter 190 km, geometric albedo 0.06, mass 1.4x1018 kg, and spin\naxis oriented ~75 deg from Earth ' s line of sight. Changes in Thorondor ' s\nbrightness by ~0.6 mag with ~300-d period may account for the system ' s\nlong-term variability. Mutual events with unexpectedly shallow depth and short\nduration may account for residuals to the fit. The system is complex, providing\na challenging puzzle for future modeling efforts.", "category": "astro-ph_EP" }, { "text": "An Ultra-Hot Neptune in the Neptune desert: About one out of 200 Sun-like stars has a planet with an orbital period\nshorter than one day: an ultra-short-period planet (Sanchis-ojeda et al. 2014;\nWinn et al. 2018). All of the previously known ultra-short-period planets are\neither hot Jupiters, with sizes above 10 Earth radii (Re), or apparently rocky\nplanets smaller than 2 Re. Such lack of planets of intermediate size (the \"hot\nNeptune desert\") has been interpreted as the inability of low-mass planets to\nretain any hydrogen/helium (H/He) envelope in the face of strong stellar\nirradiation. Here, we report the discovery of an ultra-short-period planet with\na radius of 4.6 Re and a mass of 29 Me, firmly in the hot Neptune desert. Data\nfrom the Transiting Exoplanet Survey Satellite (Ricker et al. 2015) revealed\ntransits of the bright Sun-like star \\starname\\, every 0.79 days. The planet's\nmean density is similar to that of Neptune, and according to thermal evolution\nmodels, it has a H/He-rich envelope constituting 9.0^(+2.7)_(-2.9)% of the\ntotal mass. With an equilibrium temperature around 2000 K, it is unclear how\nthis \"ultra-hot Neptune\" managed to retain such an envelope. Follow-up\nobservations of the planet's atmosphere to better understand its origin and\nphysical nature will be facilitated by the star's brightness (Vmag=9.8).", "category": "astro-ph_EP" }, { "text": "AcuA: the AKARI/IRC Mid-infrared Asteroid Survey: We present the results of an unbiased asteroid survey in the mid-infrared\nwavelength with the Infrared Camera (IRC) onboard the Japanese infrared\nsatellite AKARI. About 20% of the point source events recorded in the AKARI\nAll-Sky Survey observations are not used for the IRC Point Source Catalog\n(IRC-PSC) in its production process because of the lack of multiple detection\nby position. Asteroids, which are moving objects on the celestial sphere,\nremain in these \"residual events\". We identify asteroids out of the residual\nevents by matching them with the positions of known asteroids. For the\nidentified asteroids, we calculate the size and albedo based on the Standard\nThermal Model. Finally we have a brand-new catalog of asteroids, named the\nAsteroid Catalog Using Akari (AcuA), which contains 5,120 objects, about twice\nas many as the IRAS asteroid catalog. The catalog objects comprise 4,953 main\nbelt asteroids, 58 near Earth asteroids, and 109 Jovian Trojan asteroids. The\ncatalog will be publicly available via the Internet.", "category": "astro-ph_EP" }, { "text": "The apparent tidal decay of WASP-4 b can be explained by the R\u00f8mer\n effect: Tidal orbital decay plays a vital role in the evolution of hot Jupiter\nsystems. As of now, this was only observationally confirmed for the WASP-12\nsystem. There are a few other candidates, including WASP-4 b, but no conclusive\nresult could be obtained for these systems as of yet. In this study, we present\nan analysis of new TESS data of WASP-4 b together with archival data, taking\nthe light-time effect (LTE), induced by the second planetary companion, into\naccount as well. We make use of three different Markov-Chain-Monte-Carlo\nmodels; a circular orbit with a constant orbital period, a circular orbit with\na decaying orbit, and an elliptical orbit with apsidal precession. This\nanalysis is repeated for four cases. The first case features no LTE correction,\nwith the remaining three cases featuring three different timing correction\napproaches. Comparison of these models yields no conclusive answer to the cause\nof WASP-4\\,b's apparent transit timing variations. A broad range of values of\nthe orbital decay and apsidal precession parameters are possible, depending on\nthe LTE correction. This work highlights the importance of continued\nphotometric and spectroscopic monitoring of hot Jupiters.", "category": "astro-ph_EP" }, { "text": "Do we need to consider electron kinetic effects to properly model a\n planetary magnetosphere: the case of Mercury: The magnetosphere of Mercury is studied using an implicit full particle in\ncell simulation (PIC). We use a hybrid simulation where ions are full particles\nand electrons are considered as a fluid to start a full PIC simulation where\nelectrons are also particles and follow their distribution function. This\napproach allows us to estimate the changes introduced by the electron kinetic\nphysics. We find that the overall macroscopic state of the magnetosphere of\nMercury is little affected but several physical processes are significantly\nmodified in the full PIC simulation: the foreshock region is more active with\nmore intense shock reformation, the Kelvin-Helmholtz rippling effects on the\nnightside magnetopause are sharper, and the magnetotail current sheet becomes\nthinner than those predicted by the hybrid simulation. The greatest effect of\nthe electron physics, comes from the processes of particle energization. Both\nspecies, not just the electrons, are found to gain more energy when kinetic\nelectron processes are taken into account. The region with the most energetic\nplasma is found on the dusk side of the tail where magnetic flux ropes are\nformed due to reconnection. We find that the ion and electron energization is\nassociated with the regions of reconnection and the development of kinetic\ninstabilities caused by counter-streaming electron populations. The resulting\nelectron distributions are highly non Maxwellian, a process that neither MHD\nnor hybrid models can describe.", "category": "astro-ph_EP" }, { "text": "Dynamical evolution and end states of active and inactive Centaurs: We numerically study the dynamical evolution of observed samples of active\nand inactive Centaurs and clones that reach the Jupiter-Saturn region. Our aim\nis to compare the evolution between active and inactive Centaurs, their end\nstates and their transfer to Jupiter family comets and Halley-type comets. We\nfind that the median lifetime of inactive Centaurs is about twice longer than\nthat for active Centaurs, suggesting that activity is related to the residence\ntime in the region. This view is strengthened by the observation that\nhigh-inclination and retrograde Centaurs (Tisserand parameters with respect to\nJupiter $T_J < 2$) which have the longest median dynamical lifetime ($=1.37\n\\times 10^6$ yr) are all inactive. We also find that the perihelion distances\nof some active, comet-like Centaurs have experienced drastic drops of a few au\nin the recent past ($\\sim 10^2-10^3$ yr), while such drops are not found among\ninactive Centaurs. Inactive Centaurs with $T_J \\lsim 2.5$ usually evolve to\nHalley-type comets, whereas inactive Centaurs with $T_J \\gsim 2.5$ and active\nCentaurs (that also have $T_J \\gsim 2.5$) evolve almost always to Jupiter\nfamily comets and very seldom to Halley type comets. Inactive Centaurs are also\nmore prone to end up as sungrazers, and both inactive and active Centaurs\ntransit through different mean motion resonances (generally with Jupiter)\nduring their evolution.", "category": "astro-ph_EP" }, { "text": "Characterization of the KOI-94 System with Transit Timing Variation\n Analysis: Implication for the Planet-Planet Eclipse: The KOI-94 system is a closely-packed, multi-transiting planetary system\ndiscovered by the Kepler space telescope. It is known as the first system that\nexhibited a rare event called a \"planet-planet eclipse (PPE),\" in which two\nplanets partially overlap with each other in their double-transit phase. In\nthis paper, we constrain the parameters of the KOI-94 system with an analysis\nof the transit timing variations (TTVs). Such constraints are independent of\nthe radial velocity (RV) analysis recently performed by Weiss and coworkers,\nand valuable in examining the reliability of the parameter estimate using TTVs.\nWe numerically fit the observed TTVs of KOI-94c, KOI-94d, and KOI-94e for their\nmasses, eccentricities, and longitudes of periastrons, and obtain the best-fit\nparameters including $m_{\\rm c} = 9.4_{-2.1}^{+2.4} M_{\\oplus}$, $m_{\\rm d} =\n52.1_{-7.1}^{+6.9} M_{\\oplus}$, $m_{\\rm e} = 13.0_{-2.1}^{+2.5} M_{\\oplus}$,\nand $e \\lesssim 0.1$ for all the three planets. While these values are mostly\nin agreement with the RV result, the mass of KOI-94d estimated from the TTV is\nsignificantly smaller than the RV value $m_{\\rm d} = 106 \\pm 11 M_{\\oplus}$. In\naddition, we find that the TTV of the outermost planet KOI-94e is not well\nreproduced in the current modeling. We also present analytic modeling of the\nPPE and derive a simple formula to reconstruct the mutual inclination of the\ntwo planets from the observed height, central time, and duration of the\nbrightening caused by the PPE. Based on this model, the implication of the\nresults of TTV analysis for the time of the next PPE is discussed.", "category": "astro-ph_EP" }, { "text": "Toroidal vortices as a solution to the dust migration problem: In an earlier letter, we reported that dust settling in protoplanetary discs\nmay lead to a dynamical dust-gas instability that produces global toroidal\nvortices. In this letter, we investigate the evolution of a dusty\nprotoplanetary disc with two different dust species (1 mm and 50 cm dust\ngrains), under the presence of the instability. We show how toroidal vortices,\ntriggered by the interaction of mm grains with the gas, stop the radial\nmigration of metre-sized dust, potentially offering a natural and efficient\nsolution to the dust migration problem.", "category": "astro-ph_EP" }, { "text": "Failure modes and conditions of a cohesive, spherical body due to YORP\n spin-up: This paper presents transition of the failure mode of a cohesive, spherical\nbody due to YORP spin-up. On the assumption that the distribution of materials\nin the body is homogeneous, failed regions first appearing in the body at\ndifferent spin rates are predicted by comparing the yield condition of an\nelastic stress in the body. It is found that as the spin rate increases, the\nlocations of the failed regions move from the equatorial surface to the central\nregion. To avoid such failure modes, the body should have higher cohesive\nstrength. The results by this model are consistent with those by a plastic\nfinite element model. Then, this model and a two-layered-cohesive model first\nproposed by Hirabayashi et al. are used to classify possible evolution and\ndisruption of a spherical body. There are three possible pathways to\ndisruption. First, because of a strong structure, failure of the central region\nis dominant and eventually leads to a breakup into multiple components. Second,\na weak surface and a weak interior make the body oblate. Third, a strong\ninternal core prevents the body from failing and only allows surface shedding.\nThis implies that observed failure modes may highly depend on the internal\nstructure of an asteroid, which could provide crucial information for giving\nconstraints on the physical properties.", "category": "astro-ph_EP" }, { "text": "DART Mission Determination of Momentum Transfer: Model of Ejecta Plume\n Observations: The NASA Double Asteroid Redirection Test (DART) spacecraft will impact the\nsecondary member of the [65803] Didymos binary in order to perform the first\ndemonstration of asteroid deflection by kinetic impact. Determination of the\nmomentum transfer to the target body from the kinetic impact is a primary\nplanetary defense objective, using ground-based telescopic observations of the\norbital period change of Didymos and imaging of the DART impact ejecta plume by\nthe LICIACube cubesat, along with modeling and simulation of the DART impact.\nLICIACube, contributed by the Italian Space Agency, will perform a flyby of\nDidymos a few minutes after the DART impact, to resolve the ejecta plume\nspatial structure and to study the temporal evolution. LICIACube ejecta plume\nimages will help determine the vector momentum transfer from the DART impact,\nby determining or constraining the direction and the magnitude of the momentum\ncarried by ejecta. A model is developed for the impact ejecta plume optical\ndepth, using a point source scaling model of the DART impact. The model is\napplied to expected LICIACube plume images and shows how plume images enable\ncharacterization of the ejecta mass versus velocity distribution. The ejecta\nplume structure, as it evolves over time, is determined by the amount of ejecta\nthat has reached a given altitude at a given time. The evolution of the plume\noptical depth profiles determined from LICIACube images can distinguish between\nstrength-controlled and gravity-controlled impacts, by distinguishing the\nrespective mass versus velocity distributions. LICIACube plume images\ndiscriminate the differences in plume structure and evolution that result from\ndifferent target physical properties, mainly strength and porosity, thereby\nallowing inference of these properties to improve the determination of momentum\ntransfer.", "category": "astro-ph_EP" }, { "text": "Evidence for a lost population of close-in exoplanets: We investigate the evaporation history of known transiting exoplanets in\norder to consider the origin of observed correlations between mass, surface\ngravity and orbital period. We show that the survival of the known planets at\ntheir current separations is consistent with a simple model of evaporation, but\nthat many of the same planets would not have survived closer to their host\nstars. These putative closer-in systems represent a lost population that could\naccount for the observed correlations. We conclude that the relation underlying\nthe correlations noted by Mazeh et al. (2005) and Southworth et al. (2007) is\nmost likely a linear cut-off in the M^2/R^3 vs a^-2 plane, and we show that the\ndistribution of exoplanets in this plane is in close agreement with the\nevaporation model.", "category": "astro-ph_EP" }, { "text": "The Effect of the Approach to Gas Disk Gravitational Instability on the\n Rapid Formation of Gas Giant Planets: Observational evidence suggests that gas disk instability may be responsible\nfor the formation of at least some gas giant exoplanets, particularly massive\nor distant gas giants. With regard to close-in gas giants, Boss (2017) used the\n$\\beta$ cooling approximation to calculate hydrodynamical models of inner gas\ndisk instability, finding that provided disks with low values of the initial\nminimum Toomre stability parameter (i.e., $Q_i < 2$ inside 20 au) form,\nfragmentation into self-gravitating clumps could occur even for $\\beta$ as high\nas 100 (i.e., extremely slow cooling). Those results implied that the evolution\nof disks toward low $Q_i$ must be taken into account. This paper presents such\nmodels: initial disk masses of 0.091 $M_\\odot$ extending from 4 to 20 au around\na 1 $M_\\odot$ protostar, with a range (1 to 100) of $\\beta$ cooling parameters,\nthe same as in Boss (2017), but with all the disks starting with $Q_i = 2.7$,\ni.e., gravitationally stable, and allowed to cool from their initial outer disk\ntemperature of 180 K to as low as 40 K. All the disks eventually fragment into\nat least one dense clump. The clumps were again replaced by virtual\nprotoplanets (VPs) and the masses and orbits of the resulting ensemble of VPs\ncompare favorably with those of Boss (2017), supporting the claim that disk\ninstability can form gas giants rapidly inside 20 au, provided that\nsufficiently massive protoplanetary disks exist.", "category": "astro-ph_EP" }, { "text": "Emergence of vortices at the edges of planet-driven gaps in\n protoplanetary discs: Young planets embedded in protoplanetary discs (PPDs) excite spiral density\nwaves, which propagate, shock and deposit angular momentum in the disc. This\nresults in gap opening around the planetary orbit, even for low (sub-thermal)\nmass planets, provided that the effective viscosity in the disc is low. The\nedges of these planet-induced gaps are known to be prone to emergence of\nobservable vortices via the Rossby Wave Instability (RWI). We study timescales\nfor the development of vortices driven by low mass planets in inviscid discs.\nWe employ a recently developed semi-analytical theory of vortensity production\nby the planet-driven shock to predict vortensity evolution near the planet,\nfrom which we derive the radial profile of the planet-induced gap as a function\nof time (this procedure can have multiple other uses, e.g. to study dust\ntrapping, suppression of pebble accretion, etc.). We then analyze the linear\nstability of the gap edges against the RWI, obtaining the timescales for the\nfirst appearance of unstable modes and (later) fully developed vortices at gap\nedges. We present useful formulae for these timescales as functions of\nplanetary and disc parameters and provide their physical justification. We also\nthoroughly test our semi-analytical framework against high resolution 2D\nhydrodynamic simulations, confirming the accuracy of our theoretical\npredictions. We discuss ways in which our semi-analytical framework can be\nextended to incorporate additional physics, e.g. planetary accretion,\nmigration, and non-zero disc viscosity. Our results can be used to interpret\nobservations of PPDs and to predict emergence of vortices in simulations.", "category": "astro-ph_EP" }, { "text": "Heating of the Atmospheres of Short-orbit Exoplanets by Their Rapid\n Orbital Motion Through an Extreme Space Environment: Exoplanets with short orbit period reside very close to their host stars.\nThey transition very rapidly between different sectors of the circumstellar\nspace environment along their orbit, leading to large variations of the\nmagnetic field in the vicinity of the planet on short timescales. This rapid\nchange of the magnetic flux through the conducting and resistive layer of the\nplanetary upper atmosphere may drive currents that dissipate in the form of\nJoule Heating. Here, we estimate the amount of Joule Heating dissipation in the\nupper atmosphere of Trappist-1e, and two hypothetical planets orbiting the Sun\nin close-in orbits. We find that the rapid orbital motion could drive a\nsignificant amount of atmospheric heating and could significantly affect the\nplanetary atmosphere escape rate. Thus, the process should be accounted for\nwhen studying the long-term evolution of exoplanetary atmospheres.", "category": "astro-ph_EP" }, { "text": "Binary Survival in the Outer Solar System: As indicated by their special characteristics, the cold classical Kuiper belt\nobjects (KBOs) formed and survived at 42-47 au. Notably, they show a large\nfraction of equal-size binaries whose formation is probably related to the\naccretion of KBOs themselves. These binaries are uncommon in other --hot,\nresonant, scattered-- populations, which are thought to have been implanted\nfrom the massive disk below 30 au to >30 au during Neptune's migration. Here we\nhighlight the possibility that equal-size binaries formed in the disk but were\nsubsequently removed by impacts and/or dynamical effects (e.g., scattering\nencounters with Neptune). We determine the dependence of these processes on the\nsize and separation of binary components. Our results indicate that tighter\nbinaries, if they formed in the massive disk, have relatively good chances of\nsurvival (unless the disk was long-lived). In contrast, the widest binaries in\nthe hot population, such as 2002 VF130, have a very low survival probability\n(<1%) even if the massive disk was short-lived. They may represent a trace of\nlucky survivors of a much larger population of the original disk binaries, or\nthey formed at ~30-40~au and dodged the impact- and encounter-related\nperturbations that we studied here. We find that all known satellites of the\nlargest KBOs would survive during the dynamical implantation of these bodies in\nthe Kuiper belt. The low orbital eccentricities of Pluto's small moons may have\nbeen excited by impacts and/or encounters of the Pluto system to Neptune.", "category": "astro-ph_EP" }, { "text": "The Hubble Wide Field Camera 3 Test of Surfaces in the Outer Solar\n System: The Compositional Classes of the Kuiper Belt: We present the first results of the Hubble Wide Field Camera 3 Test of\nSurfaces in the Outer Solar System (H/WTSOSS). The purpose of this survey was\nto measure the surface properties of a large number of Kuiper belt objects and\nattempt to infer compositional and dynamical correlations. We find that the\nCentaurs and the low-perihelion scattered disk and resonant objects exhibit\nvirtually identical bifurcated optical colour distributions and make up two\nwell defined groups of object. Both groups have highly correlated optical and\nNIR colours which are well described by a pair of two component mixture models\nthat have different red components, but share a common neutral component. The\nsmall, $H_{606}\\gtrsim5.6$ high-perihelion excited objects are entirely\nconsistent with being drawn from the two branches of the mixing model\nsuggesting that the colour bifurcation of the Centaurs is apparent in all small\nexcited objects. On the other hand, objects larger than $H_{606}\\sim5.6$ are\nnot consistent with the mixing model, suggesting some evolutionary process\navoided by the smaller objects. The existence of a bifurcation amongst all\nexcited populations argues that the two separate classes of object existed in\nthe primordial disk before the excited Kuiper belt was populated. The cold\nclassical objects exhibit a different type of surface which has colours that\nare consistent with being drawn from the red branch of the mixing model, but\nwith much higher albedos.", "category": "astro-ph_EP" }, { "text": "Searching for Saturn's Dust Swarm: Limits on the size distribution of\n Irregular Satellites from km to micron sizes: We describe a search for dust created in collisions between the Saturnian\nirregular satellites using archival \\emph{Spitzer} MIPS observations. Although\nwe detected a degree scale Saturn-centric excess that might be attributed to an\nirregular satellite dust cloud, we attribute it to the far-field wings of the\nPSF due to nearby Saturn. The Spitzer PSF is poorly characterised at such\nradial distances, and we expect PSF characterisation to be the main issue for\nfuture observations that aim to detect such dust. The observations place an\nupper limit on the level of dust in the outer reaches of the Saturnian system,\nand constrain how the size distribution extrapolates from the smallest known\n(few km) size irregulars down to micron-size dust. Because the size\ndistribution is indicative of the strength properties of irregulars, we show\nhow our derived upper limit implies irregular satellite strengths more akin to\ncomets than asteroids. This conclusion is consistent with their presumed\ncapture from the outer regions of the Solar System.", "category": "astro-ph_EP" }, { "text": "KMT-2021-BLG-0912Lb: A microlensing super Earth around a K-type star: The light curve of the microlensing event KMT-2021-BLG-0912 exhibits a very\nshort anomaly relative to a single-lens single-source form. We investigate the\nlight curve for the purpose of identifying the origin of the anomaly. We model\nthe light curve under various interpretations. From this, we find four\nsolutions, in which three solutions are found under the assumption that the\nlens is composed of two masses (2L1S models), and the other solution is found\nunder the assumption that the source is comprised of a binary-star system (1L2S\nmodel). The 1L2S model is ruled out based on the contradiction that the faint\nsource companion is bigger than its primary, and one of the 2L1S solutions is\nexcluded from the combination of the relatively worse fit, blending constraint,\nand lower overall probability, leaving two surviving solutions with the\nplanet/host mass ratios of $q\\sim 2.8\\times 10^{-5}$ and $\\sim 1.1\\times\n10^{-5}$. A subtle central deviation supports the possibility of a tertiary\nlens component, either a binary companion to the host with a very large or\nsmall separation or a second planet lying near the Einstein ring, but it is\ndifficult to claim a secure detection due to the marginal fit improvement, lack\nof consistency among different data sets, and difficulty in uniquely specifying\nthe nature of the tertiary component. With the observables of the event, it is\nestimated that the masses of the planet and host are $\\sim (6.9~M_\\oplus,\n0.75~M_\\odot)$ according to one solution and $\\sim (2.8~M_\\oplus,\n0.80~M_\\odot)$ according to the other solution, indicating that the planet is a\nsuper Earth around a K-type star, regardless of the solution.", "category": "astro-ph_EP" }, { "text": "Terrestrial planet formation in low-mass disks: dependence with initial\n conditions: In general, most of the studies of terrestrial-type planet formation\ntypically use ad hoc initial conditions. In this work we improved the initial\nconditions described in Ronco & de El\\'ia (2014) starting with a\nsemi-analytical model wich simulates the evolution of the protoplanetary disk\nduring the gas phase. The results of the semi-analytical model are then used as\ninitial conditions for the N-body simulations. We show that the planetary\nsystems considered are not sensitive to the particular initial distribution of\nembryos and planetesimals and thus, the results are globally similar to those\nfound in the previous work.", "category": "astro-ph_EP" }, { "text": "The PLATO 2.0 Mission: PLATO 2.0 has recently been selected for ESA's M3 launch opportunity\n(2022/24). Providing accurate key planet parameters (radius, mass, density and\nage) in statistical numbers, it addresses fundamental questions such as: How do\nplanetary systems form and evolve? Are there other systems with planets like\nours, including potentially habitable planets? The PLATO 2.0 instrument\nconsists of 34 small aperture telescopes (32 with 25 sec readout cadence and 2\nwith 2.5 sec candence) providing a wide field-of-view (2232 deg2) and a large\nphotometric magnitude range (4-16 mag). It focusses on bright (4-11 mag) stars\nin wide fields to detect and characterize planets down to Earth-size by\nphotometric transits, whose masses can then be determined by ground-based\nradial-velocity follow-up measurements. Asteroseismology will be performed for\nthese bright stars to obtain highly accurate stellar parameters, including\nmasses and ages. The combination of bright targets and asteroseismology results\nin high accuracy for the bulk planet parameters: 2%, 4-10% and 10% for planet\nradii, masses and ages, respectively. The planned baseline observing strategy\nincludes two long pointings (2-3 years) to detect and bulk characterize planets\nreaching into the habitable zone (HZ) of solar-like stars and an additional\nstep-and-stare phase to cover in total about 50% of the sky. PLATO 2.0 will\nobserve up to 1,000,000 stars and detect and characterize hundreds of small\nplanets, and thousands of planets in the Neptune to gas giant regime out to the\nHZ. It will therefore provide the first large-scale catalogue of bulk\ncharacterized planets with accurate radii, masses, mean densities and ages.\nThis catalogue will include terrestrial planets at intermediate orbital\ndistances, where surface temperatures are moderate. Coverage of this parameter\nrange with statistical numbers of bulk characterized planets is unique to PLATO\n2.0.", "category": "astro-ph_EP" }, { "text": "Asteroid Models from Multiple Data Sources: In the past decade, hundreds of asteroid shape models have been derived using\nthe lightcurve inversion method. At the same time, a new framework of 3-D shape\nmodeling based on the combined analysis of widely different data sources such\nas optical lightcurves, disk-resolved images, stellar occultation timings,\nmid-infrared thermal radiometry, optical interferometry, and radar\ndelay-Doppler data, has been developed. This multi-data approach allows the\ndetermination of most of the physical and surface properties of asteroids in a\nsingle, coherent inversion, with spectacular results. We review the main\nresults of asteroid lightcurve inversion and also recent advances in multi-data\nmodeling. We show that models based on remote sensing data were confirmed by\nspacecraft encounters with asteroids, and we discuss how the multiplication of\nhighly detailed 3-D models will help to refine our general knowledge of the\nasteroid population. The physical and surface properties of asteroids, i.e.,\ntheir spin, 3-D shape, density, thermal inertia, surface roughness, are among\nthe least known of all asteroid properties. Apart for the albedo and diameter,\nwe have access to the whole picture for only a few hundreds of asteroids. These\nquantities are nevertheless very important to understand as they affect the\nnon-gravitational Yarkovsky effect responsible for meteorite delivery to Earth,\nor the bulk composition and internal structure of asteroids.", "category": "astro-ph_EP" }, { "text": "K2-288Bb: A Small Temperate Planet in a Low-mass Binary System\n Discovered by Citizen Scientists: Observations from the Kepler and K2 missions have provided the astronomical\ncommunity with unprecedented amounts of data to search for transiting\nexoplanets and other astrophysical phenomena. Here, we present K2-288, a\nlow-mass binary system (M2.0 +/- 1.0; M3.0 +/- 1.0) hosting a small (Rp = 1.9\nREarth), temperate (Teq = 226 K) planet observed in K2 Campaign 4. The\ncandidate was first identified by citizen scientists using Exoplanet Explorers\nhosted on the Zooniverse platform. Follow-up observations and detailed analyses\nvalidate the planet and indicate that it likely orbits the secondary star on a\n31.39-day period. This orbit places K2-288Bb in or near the habitable zone of\nits low-mass host star. K2-288Bb resides in a system with a unique\narchitecture, as it orbits at >0.1 au from one component in a moderate\nseparation binary (aproj approximately 55 au), and further follow-up may\nprovide insight into its formation and evolution. Additionally, its estimated\nsize straddles the observed gap in the planet radius distribution. Planets of\nthis size occur less frequently and may be in a transient phase of radius\nevolution. K2-288 is the third transiting planet system identified by the\nExoplanet Explorers program and its discovery exemplifies the value of citizen\nscience in the era of Kepler, K2, and the Transiting Exoplanet Survey\nSatellite.", "category": "astro-ph_EP" }, { "text": "Initial mass function of planetesimals formed by the streaming\n instability: The streaming instability is a mechanism to concentrate solid particles into\noverdense filaments that undergo gravitational collapse and form planetesimals.\nHowever, it remains unclear how the initial mass function of these\nplanetesimals depends on the box dimensions of numerical simulations. To\nresolve this, we perform simulations of planetesimal formation with the largest\nbox dimensions to date, allowing planetesimals to form simultaneously in\nmultiple filaments that can only emerge within such large simulation boxes. In\nour simulations, planetesimals with sizes between 80 km and several hundred\nkilometers form. We find that a power law with a rather shallow exponential\ncutoff at the high-mass end represents the cumulative birth mass function\nbetter than an integrated power law. The steepness of the exponential cutoff is\nlargely independent of box dimensions and resolution, while the exponent of the\npower law is not constrained at the resolutions we employ. Moreover, we find\nthat the characteristic mass scale of the exponential cutoff correlates with\nthe mass budget in each filament. Together with previous studies of\nhigh-resolution simulations with small box domains, our results therefore imply\nthat the cumulative birth mass function of planetesimals is consistent with an\nexponentially tapered power law with a power-law exponent of approximately -1.6\nand a steepness of the exponential cutoff in the range of 0.3-0.4.", "category": "astro-ph_EP" }, { "text": "RVSPY -- Radial Velocity Survey for Planets around Young Stars. Target\n characterization and high-cadence survey: We introduce our Radial Velocity Survey for Planets around Young stars\n(RVSPY), characterise our target stars, and search for substellar companions at\norbital separations smaller than a few au from the host star. We use the FEROS\nspectrograph to obtain high signal-to-noise spectra and time series of precise\nradial velocities (RVs) of 111 stars most of which are surrounded by debris\ndiscs. Our target stars have spectral types between early F and late K, a\nmedian age of 400 Myr, and a median distance of 45 pc. We determine for all\ntarget stars their basic stellar parameters and present the results of the\nhigh-cadence RV survey and activity characterization. We achieve a median\nsingle-measurement RV precision of 6 m/s and derive the short-term intrinsic RV\nscatter of our targets (median 22 m/s), which is mostly caused by stellar\nactivity and decays with age from >100 m/s at <20 Myr to <20 m/s at >500 Myr.\nWe discover six previously unknown close companions with orbital periods\nbetween 10 and 100 days, three of which are low-mass stars, and three are in\nthe brown dwarf mass regime. We detect no hot companion with an orbital period\n<10 days down to a median mass limit of ~1 M_Jup for stars younger than 500\nMyr, which is still compatible with the established occurrence rate of such\ncompanions around main-sequence stars. We find significant RV periodicities\nbetween 1.3 and 4.5 days for 14 stars, which are, however, all caused by\nrotational modulation due to starspots. We also analyse the TESS photometric\ntime series data and find significant periodicities for most of the stars. For\n11 stars, the photometric periods are also clearly detected in the RV data. We\nalso derive stellar rotation periods ranging from 1 to 10 days for 91 stars,\nmostly from TESS data. From the intrinsic activity-related short-term RV\njitter, we derive the expected mass-detection thresholds for longer-period\ncompanions.", "category": "astro-ph_EP" }, { "text": "Global simulations of protoplanetary disks with net magnetic flux: I.\n Non-ideal MHD case: The planet-forming region of protoplanetary disks is cold, dense, and\ntherefore weakly ionized. For this reason, magnetohydrodynamic (MHD) turbulence\nis thought to be mostly absent, and another mechanism has to be found to\nexplain gas accretion. It has been proposed that magnetized winds, launched\nfrom the ionized disk surface, could drive accretion in the presence of a\nlarge-scale magnetic field. The efficiency and the impact of these surface\nwinds on the disk structure is still highly uncertain. We present the first\nglobal simulations of a weakly ionized disk that exhibits large-scale\nmagnetized winds. We also study the impact of self-organization, which was\npreviously demonstrated only in non-stratified models. We perform numerical\nsimulations of stratified disks with the PLUTO code. We compute the ionization\nfraction dynamically, and account for all three non-ideal MHD effects: ohmic\nand ambipolar diffusions, and the Hall drift. Simplified heating and cooling\ndue to non-thermal radiation is also taken into account in the disk atmosphere.\nWe find that disks can be accreting or not, depending on the configuration of\nthe large-scale magnetic field. Magnetothermal winds, driven both by magnetic\nacceleration and heating of the atmosphere, are obtained in the accreting case.\nIn some cases, these winds are asymmetric, ejecting predominantly on one side\nof the disk. The wind mass loss rate depends primarily on the average ratio of\nmagnetic to thermal pressure in the disk midplane. The non-accreting case is\ncharacterized by a meridional circulation, with accretion layers at the disk\nsurface and decretion in the midplane. Finally, we observe self-organization,\nresulting in axisymmetric rings of density and associated pressure \"bumps\". The\nunderlying mechanism and its impact on observable structures are discussed.", "category": "astro-ph_EP" }, { "text": "Breaking the Ice: Planetesimal Formation at the Snowline: Recently Saito & Sirono (2011) proposed that large ice aggregates which drift\nin- wards in protoplanetary disks break up during sublimation, ejecting\nembedded silicate particles. This would lead to a concentration of small solid\nparticles close to the snow- line. In view of this model we carried out\nlaboratory experiments where we observed freely levitating ice aggregates\nsublimating. We find that frequent break up is indeed very common. Scaled to a\n10 cm aggregate about 2x10^4 small silicate aggregates might result. This\nsupports the idea that sublimation of drifting ice aggregates might locally\nincrease the density of small dust (silicate) particles which might more easily\nbe swept up by larger dust aggregates or trigger gravitational instability.\nEither way this might locally boost the formation of planetesimals at the\nsnowline.", "category": "astro-ph_EP" }, { "text": "FU Orionis outbursts, preferential recondensation of water ice, and the\n formation of giant planets: Ices, including water ice, prefer to recondense onto pre-existing nuclei\nrather than spontaneously forming grains from a cloud of vapor. Interestingly,\ndifferent potential recondensation nuclei have very different propensities to\nactually nucleate water ice at the temperatures associated with freeze-out in\nprotoplanetary discs. Therefore, if a region in a disc is warmed and then\nrecooled, water vapor should not be expected to refreeze evenly onto all\navailable grains. Instead it will preferentially recondense onto the most\nfavorable grains. When the recooling is slow enough, only the most favorable\ngrains will nucleate ice, allowing them to recondense thick ice mantles. We\nquantify the conditions for preferential recondensation to rapidly create\npebble-sized grains in protoplanetary discs and show that FU Orionis type\noutbursts have the appropriate cooling rates to drive pebble creation in a band\nabout 5 astronomical units wide outside of the quiescent frost line from\napproximately Jupiter's orbit to Saturn's (about 4 to 10 au). Those pebbles\ncould be of the appropriate size to proceed to planetesimal formation via the\nStreaming Instability, or to contribute to the growth of planetesimals through\npebble accretion. We suggest that this phenomenon contributed to the formation\nof the gas giants in our own Solar System.", "category": "astro-ph_EP" }, { "text": "Revisiting parameters for the WASP-1 planetary system: We present thirteen new transit light curves for the WASP-1 b exoplanet.\nObservations were acquired with 0.5 - 1.2-m telescopes between 2007 and 2013.\nOur homogeneous analysis, which also includes the literature data, results in\ndetermining precise system parameters. New values are in agreement with those\nreported in previous studies. Transit times follow a linear ephemeris with no\nsign of any transit time variations. This finding is in line with the paradigm\nthat Jupiter-like planets on tight orbits are devoid of close planetary\ncompanions.", "category": "astro-ph_EP" }, { "text": "Mapping out the parameter space for photoevaporation and core-powered\n mass-loss: Understanding atmospheric escape in close-in exoplanets is critical to\ninterpreting their evolution. We map out the parameter space over which\nphotoevaporation and core-powered mass loss dominate atmospheric escape.\nGenerally, the transition between the two regimes is determined by the location\nof the Bondi radius (i.e. the sonic point of core-powered outflow) relative to\nthe penetration depth of XUV photons. Photoevaporation dominates the loss when\nthe XUV penetration depth lies inside the Bondi radius ($R_{XUV}1 AU away from their parent stars have atmospheric\nenvironments cold enough for water and/or ammonia clouds. We have developed a\nnew equilibrium cloud and reflected light spectrum model, ExoREL, for widely\nseparated giant exoplanets. The model includes the dissolution of ammonia in\nliquid water cloud droplets, an effect studied for the first time for\nexoplanets. While preserving the causal relationship between temperature and\ncloud condensation, ExoREL is simple and fast to enable efficient exploration\nof parameter space. Using the model, we find that the mixing ratio of methane\nand the cloud top pressure of a giant exoplanet can be uniquely determined from\na single observation of its reflected light spectrum at wavelengths less than 1\nmicron if it has a cloud deck deeper than ~0.3 bars. This measurement is\nenabled by the weak and strong bands of methane and requires a signal-to-noise\nratio of 20. The cloud pressure once derived, provides information about the\ninternal heat flux of the planet. Importantly, we find that for a low,\nUranus-like internal heat flux, the planet can have a deep liquid water cloud,\nwhich will sequester ammonia and prevent the formation of the ammonia cloud\nthat would otherwise be the uppermost cloud layer. This newly identified\nphenomenon causes a strong sensitivity of the cloud top pressure on the\ninternal heat flux. Reflected light spectroscopy from future direct-imaging\nmissions therefore not only measure the atmospheric abundances but also\ncharacterize the thermal evolution of giant exoplanets.", "category": "astro-ph_EP" }, { "text": "Large grains can grow in circumstellar discs: We perform coagulation & fragmentation simulations to understand grain growth\nin T Tauri & brown dwarf discs. We present a physically-motivated approach\nusing a probability distribution function for the collision velocities and\nseparating the deterministic & stochastic velocities. We find growth to larger\nsizes compared to other models. Furthermore, if brown dwarf discs are\nscaled-down versions of T Tauri discs (in terms of stellar & disc mass, and\ndisc radius), growth at the same location with respect to the outer edge occurs\nto similar sizes in both discs.", "category": "astro-ph_EP" }, { "text": "Observation of metre-scale impactors by the Desert Fireball Network: The Earth is impacted by 35-40 metre-scale objects every year. These\nmeteoroids are the low mass end of impactors that can do damage on the ground.\nDespite this they are very poorly surveyed and characterised, too infrequent\nfor ground based fireball bservation efforts, and too small to be efficiently\ndetected by NEO telescopic surveys whilst still in interplanetary space. We\nwant to evaluate the suitability of different instruments for characterising\nmetre-scale impactors and where they come from. We use data collected over the\nfirst 3 years of operation of the continent-scale Desert Fireball Network, and\ncompare results with other published results as well as orbital sensors. We\nfind that although the orbital sensors have the advantage of using the entire\nplanet as collecting area, there are several serious problems with the accuracy\nof the data, notably the reported velocity vector, which is key to getting an\naccurate pre-impact orbit and calculating meteorite fall positions. We also\noutline dynamic range issues that fireball networks face when observing large\nmeteoroid entries.", "category": "astro-ph_EP" }, { "text": "Rotation acceleration of asteroids (10115) 1992 SK, (1685) Toro, and\n (1620) Geographos due to the YORP effect: The rotation state of small asteroids is affected by the\nYarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect, which is a net torque\ncaused by solar radiation directly reflected and thermally reemitted from the\nsurface. Due to this effect, the rotation period slowly changes, which can be\nmost easily measured in light curves because the shift in the rotation phase\naccumulates over time quadratically. We collected archived light curves and\ncarried out new photometric observations for asteroids (10115) 1992 SK, (1620)\nGeographos, and (1685) Toro. We applied the method of light curve inversion to\nfit observations with a convex shape model. The YORP effect was modeled as a\nlinear change of the rotation frequency $\\upsilon \\equiv \\mathrm{d}\\omega /\n\\mathrm{d}t$ and optimized together with other spin and shape parameters. We\ndetected the acceleration $\\upsilon = (8.3 \\pm 0.6) \\times\n10^{-8}\\,\\mathrm{rad}\\,\\mathrm{d}^{-2}$ of the rotation for asteroid (10115)\n1992 SK. This observed value agrees well with the theoretical value of\nYORP-induced spin-up computed for our shape and spin model. For (1685) Toro, we\nobtained $\\upsilon = (3.3 \\pm 0.3) \\times\n10^{-9}\\,\\mathrm{rad}\\,\\mathrm{d}^{-2}$, which confirms an earlier tentative\nYORP detection. For (1620) Geographos, we confirmed the previously detected\nYORP acceleration and derived an updated value of $\\upsilon$ with a smaller\nuncertainty. We also included the effect of solar precession into our inversion\nalgorithm, and we show that there are hints of this effect in Geographos' data.\nThe detected change of the spin rate of (10115) 1992 SK has increased the total\nnumber of asteroids with YORP detection to ten. In all ten cases, the\n$\\mathrm{d}\\omega / \\mathrm{d}t$ value is positive, so the rotation of these\nasteroids is accelerated. It is unlikely to be just a statistical fluke, but it\nis probably a real feature that needs to be explained.", "category": "astro-ph_EP" }, { "text": "Setting the stage for the search for life with the Habitable Worlds\n Observatory: Properties of 164 promising planet survey targets: The Decadal Survey on Astronomy and Astrophysics 2020 (Astro2020) has\nrecommended that NASA realize a large IR/O/UV space telescope optimized for\nhigh-contrast imaging and spectroscopy of ~25 exo-Earths and transformative\ngeneral astrophysics. The NASA Exoplanet Exploration Program (ExEP) has\nsubsequently released a list of 164 nearby (d<25 pc) targets deemed the most\naccessible to survey for potentially habitable exoplanets with the Habitable\nWorlds Observatory (HWO). We present a catalog of system properties for the 164\nExEP targets, including 1744 abundance measurements for 14 elements from the\nHypatia Catalog and 924 photometry measurements spanning from 151.6 nm to 22\n{\\mu}m in the GALEX, Str\\\"omgren, Tycho, Gaia, 2MASS, and WISE bandpasses. We\nindependently derive stellar properties for these systems by modeling their\nspectral energy distributions with Bayesian model averaging. Additionally, by\nconsulting the literature, we identify TESS flare rates for 46 stars, optical\nvariability for 78 stars, and X-ray emission for 46 stars in our sample. We\ndiscuss our catalog in the context of planet habitability and draw attention to\nkey gaps in our knowledge where precursor science can help to inform HWO\nmission design trade studies in the near future. Notably, only 33 of the 164\nstars in our sample have reliable space-based UV measurements, and only 40 have\na mid-IR measurement. We also find that phosphorus, a bio-essential element,\nhas only been measured in 11 of these stars, motivating future abundance\nsurveys. Our catalog is publicly available and we advocate for its use in\nfuture studies of promising HWO targets.", "category": "astro-ph_EP" }, { "text": "First detection of gas-phase methanol in a protoplanetary disk: The first detection of gas-phase methanol in a protoplanetary disk (TW Hya)\nis presented. In addition to being one of the largest molecules detected in\ndisks to date, methanol is also the first disk organic molecule with an\nunambiguous ice chemistry origin. The stacked methanol emission, as observed\nwith ALMA, is spectrally resolved and detected across six velocity channels\n($>3 \\sigma$), reaching a peak signal-to-noise of $5.5\\sigma$, with the\nkinematic pattern expected for TW~Hya. Using an appropriate disk model, a\nfractional abundance of $3\\times 10^{-12} - 4 \\times 10^{-11}$ (with respect to\nH$_2$) reproduces the stacked line profile and channel maps, with the favoured\nabundance dependent upon the assumed vertical location (midplane versus\nmolecular layer). The peak emission is offset from the source position\nsuggesting that the methanol emission has a ring-like morphology: the analysis\nhere suggests it peaks at $\\approx 30$~AU reaching a column density $\\approx\n3-6\\times10^{12}$~cm$^{-2}$. In the case of TW Hya, the larger (up to mm-sized)\ngrains, residing in the inner 50~AU, may thus host the bulk of the disk ice\nreservoir. The successful detection of cold gas-phase methanol in a\nprotoplanetary disk implies that the products of ice chemistry can be explored\nin disks, opening a window to studying complex organic chemistry during\nplanetary system formation.", "category": "astro-ph_EP" }, { "text": "Direct Imaging of Exoplanets at the Era of the Extremely Large\n Telescopes: Within ten years, the era of large-scale systematics surveys will decay\nthanks to a complete census of exoplanetary systems within 200 pc from the Sun.\nWith the first Lights foreseen between 2024 and 2028, the new generation of\nextremely large telescopes and planet imagers will arrive at a propitious time\nto exploit this manna of discoveries to characterize the formation, the\nevolution, and the physics of giant and telluric planets with the ultimate goal\nto search and discover bio-signatures. In that perspective, I will briefly\nsummarize the main characteristics of the direct imaging instruments of the\nELTs dedicated to the study of exoplanets, and I will review the key science\ncases (from the initial conditions of planetary formation, the architecture of\nplanetary systems and the physics and atmospheres of giant and telluric\nplanets) that they will address given their predicted performances.", "category": "astro-ph_EP" }, { "text": "Sulfuric acid as a cryofluid and oxygen isotope reservoir of\n planetesimals: The Sun exhibits a depletion in $^{17,18}$O relative to $^{16}$O by 6 %\ncompared to the Earth and Moon$^{1}$. The origin of such a non-mass-dependent\nisotope fractionation has been extensively debated since the\nthree-isotope-analysis$^{2}$ became available in 1970's. Self-shielding$^{3,4}$\nof CO molecules against UV photons in the solar system's parent molecular cloud\nhas been suggested as a source of the non-mass-dependent effect, in which a\n$^{17,18}$O-enriched oxygen was trapped by ice and selectively incorporated as\nwater into planet-forming materials$^{5}$. The truth is that the Earth-Moon and\nother planetary objects deviate positively from the Sun by ~6 % in their\nisotopic compositions. A stunning exception is the magnetite/sulfide\nsymplectite found in Acfer 094 meteorite, which shows 24 % enrichment in\n$^{17,18}$O relative to the Sun$^{6}$. Water does not explain the enrichment\nthis high. Here we show that the SO and SO$_2$ molecules in the molecular\ncloud, ~106 % enriched in $^{17,18}$O relative to the Sun, evolved through the\nprotoplanetary disk and planetesimal stages to become a sulfuric acid, 24 %\nenriched in $^{17,18}$O. The sulfuric acid provided a cryofluid environment in\nthe planetesimal and by itself reacted with ferric iron to form an amorphous\nferric-hydroxysulfate-hydrate, which eventually decomposed into the symplectite\nby shock. We indicate that the Acfer-094 symplectite and its progenitor,\nsulfuric acid, is strongly coupled with the material evolution in the solar\nsystem since the days of our molecular cloud.", "category": "astro-ph_EP" }, { "text": "The Migration of Gap-Opening Planets is not Locked to Viscous Disk\n Evolution: Most standard descriptions of Type II migration state that massive,\ngap-opening planets must migrate at the viscous drift rate. This is based on\nthe idea that the disk is separated into an inner and outer region and gas is\nconsidered unable to cross the gap. In fact, gas easily crosses the gap on\nhorseshoe orbits, nullifying this necessary premise which would set the\nmigration rate. In this work, it is demonstrated using highly accurate\nnumerical calculations that the actual migration rate is dependent on disk and\nplanet parameters, and can be significantly larger or smaller than the viscous\ndrift rate. In the limiting case of a disk much more massive than the\nsecondary, the migration rate saturates to a constant which is sensitive to\ndisk parameters and is not necessarily of order viscous rate. In the opposite\nlimit of a low-mass disk, the migration rate decreases linearly with disk mass.\nSteady-state solutions in the low disk mass limit show no pile-up outside the\nsecondary's orbit, and no corresponding drainage of the inner disk.", "category": "astro-ph_EP" }, { "text": "Stellar wind-magnetosphere interaction at exoplanets: computations of\n auroral radio powers: We present calculations of the auroral radio powers expected from exoplanets\nwith magnetospheres driven by an Earth-like magnetospheric interaction with the\nsolar wind. Specifically, we compute the twin cell-vortical ionospheric flows,\ncurrents, and resulting radio powers resulting from a Dungey cycle process\ndriven by dayside and nightside magnetic reconnection, as a function of\nplanetary orbital distance and magnetic field strength. We include saturation\nof the magnetospheric convection, as observed at the terrestrial magnetosphere,\nand we present power law approximations for the convection potentials, radio\npowers and spectral flux densities. We specifically consider a solar-age system\nand a young (1 Gyr) system. We show that the radio power increases with\nmagnetic field strength for magnetospheres with saturated convection potential,\nand broadly decreases with increasing orbital distance. We show that the\nmagnetospheric convection at hot Jupiters will be saturated, and thus unable to\ndissipate the full available incident Poynting flux, such that the magnetic\nRadiometric Bode's Law (RBL) presents a substantial overestimation of the radio\npowers for hot Jupiters. Our radio powers for hot Jupiters are $\\sim$5-1300 TW\nfor hot Jupiters with field strengths of 0.1-10 $B_J$ orbiting a Sun-like star,\nwhile we find that competing effects yield essentially identical powers for hot\nJupiters orbiting a young Sun-like star. However, in particular for planets\nwith weaker magnetic fields our powers are higher at larger orbital distances\nthan given by the RBL, and there are many configurations of planet that are\nexpected to be detectable using SKA.", "category": "astro-ph_EP" }, { "text": "Line Ratios Reveal N2H+ Emission Originates Above the Midplane in TW\n Hydrae: Line ratios for different transitions of the same molecule have long been\nused as a probe of gas temperature. Here we use ALMA observations of the N2H+\nJ~=~1-0 and J~=~4-3 lines in the protoplanetary disk around TW Hya to derive\nthe temperature at which these lines emit. We find an averaged temperature of\n39~K with a one sigma uncertainty of 2~K for the radial range 0.8-2'',\nsignificantly warmer than the expected midplane temperature beyond 0.5'' in\nthis disk. We conclude that the N2H+ emission in TW Hya is not emitting from\nnear the midplane, but rather from higher in the disk, in a region likely\nbounded by processes such as photodissociation or chemical reprocessing of CO\nand N2 rather than freeze out.", "category": "astro-ph_EP" }, { "text": "Imaging diagnostics for transitional discs: Transitional discs are a special type of protoplanetary discs where planet\nformation is thought to be taking place. These objects feature characteristic\ninner cavities and/or gaps of a few tens of AUs in the sub-millimitre images of\nthe disc. This signature suggests a localised depletion of matter in the disc\nthat could be caused by planet formation processes. However, recent\nobservations have revealed differences in the structures imaged at different\nwavelengths in some of these discs. In this paper, we aim to explain these\nobservational differences using self-consistent physical 2-D hydrodynamical and\ndust evolution models of such objects, assuming their morphology is indeed\ngenerated by the presence of a planet. We use these models to derive the\ndistribution of gas and dust in a theoretical planet-hosting disc, for various\nplanet masses and orbital separations. We then simulate observations of the\nemitted and scattered light from these models with VLT/SPHERE ZIMPOL,\nSubaru/HiCIAO, VLT/VISIR and ALMA. We do this by first computing the full\nresolution images of the models at different wavelengths, and then simulating\nthe observations accounting for the characteristics of each particular\ninstrument. The presence of the planet generates pressure bumps in the gas\ndistribution of the disc whose characteristics strongly depend on the planet\nmass and position. These bumps cause large grains to accumulate while small\ngrains are allowed into inner regions. This spatial differentiation of the\ngrain sizes explains the differences in the observations since different\nwavelengths and observing techniques trace different parts of the dust size\ndistribution. Based on this effect, we conclude that the combination of\nvisible/near-infrared polarimetric and sub-mm images is the best strategy to\nconstrain the properties of the unseen planet responsible for the disc\nstructure.", "category": "astro-ph_EP" }, { "text": "A new pattern in Saturn's D ring created in late 2011: Images obtained by the Cassini spacecraft between 2012 and 2015 reveal a\nperiodic brightness variation in a region of Saturn's D ring that previously\nappeared to be rather featureless. Furthermore, the intensity and radial\nwavenumber of this pattern have decreased steadily with time since it was first\nobserved. Based on analogies with similar structures elsewhere in the D ring,\nwe propose that this structure was created by some event that disturbed the\norbital motions of the ring particles, giving them finite orbital\neccentricities and initially aligned pericenters. Differential orbital\nprecession then transformed this structure into a spiral pattern in the ring's\noptical depth that became increasingly tightly wound over time. The observed\ntrends in the pattern's radial wavenumber are roughly consistent with this\nbasic model, and also indicate that the ring-disturbing event occurred in early\nDecember 2011. Similar events in 1979 may have generated the periodic patterns\nseen in this same region by the Voyager spacecraft. The 2011 event could have\nbeen caused by debris striking the rings, or by a disturbance in the planet's\nelectromagnetic environment. The rapid reduction in the intensity of the\nbrightness variations over the course of just a few years indicates that some\nprocess is either damping orbital eccentricities in this region or causing the\norbital pericenters of particles with the same semi-major axis to become\nmisaligned.", "category": "astro-ph_EP" }, { "text": "An optimised survey strategy for the ERIS/NIX imager: searching for\n young giant exoplanets and very low mass brown dwarfs using the K-peak custom\n photometric filter: We present optimal survey strategies for the upcoming NIX imager, part of the\nERIS instrument to be installed on the Very Large Telescope (VLT). We will use\na custom 2.2 micron K-peak filter to optimise the efficiency of a future\nlarge-scale direct imaging survey, aiming to detect brown dwarfs and giant\nplanets around nearby stars. We use the results of previous large scale imaging\nsurveys (primarily SPHERE SHINE and Gemini GPIES) to inform our choice of\ntargets, as well as improved planet population distributions. We present four\npossible approaches to optimise survey target lists for the highest yield of\ndetections: i) targeting objects with anomalous proper motion trends, ii) a\nfollow-up survey of dense fields from SPHERE SHINE and Gemini GPIES iii)\nsurveying nearby star-forming regions and iv) targeting newly discovered\nmembers of nearby young moving groups. We also compare the predicted\nperformance of NIX to other state-of-the-art direct imaging instruments.", "category": "astro-ph_EP" }, { "text": "Eleven Multi-planet Systems from K2 Campaigns 1 & 2 and the Masses of\n Two Hot Super-Earths: We present a catalog of 11 multi-planet systems from Campaigns 1 and 2 of the\nK2 mission. We report the sizes and orbits of 26 planets split between seven\n2-planet systems and four 3-planet systems. These planets stem from a\nsystematic search of the K2 photometry for all dwarf stars observed by K2 in\nthese fields. We precisely characterized the host stars with adaptive optics\nimaging and analysis of high-resolution optical spectra from Keck/HIRES and\nmedium-resolution spectra from IRTF/SpeX. We confirm two planet candidates by\nmass detection and validate the remaining 24 candidates to $>99\\%$ confidence.\nThirteen planets were previously validated or confirmed by other studies and 24\nwere previously identified as planet candidates. The planets are mostly smaller\nthan Neptune (21/26 planets) as in the Kepler mission and all have short\nperiods ($P < 50$ d) due to the duration of the K2 photometry. The host stars\nare relatively bright (most have $Kp < 12.5$ mag) and are amenable to follow-up\ncharacterization. For K2-38, we measured precise radial velocities using\nKeck/HIRES and provide initial estimates of the planet masses. K2-38b is a\nshort-period super-Earth with a radius of $1.55 \\pm 0.16~R_\\oplus$, a mass of\n$12.0 \\pm 2.9~M_\\oplus$, and a high density consistent with an iron-rich\ncomposition. The outer planet K2-38c is a lower density sub-Neptune-size planet\nwith a radius of $2.42 \\pm 0.29~R_\\oplus$ and a mass of $9.9 \\pm 4.6~M_\\oplus$\nthat likely has a substantial envelope. This new planet sample demonstrates the\ncapability of K2 to discover numerous planetary systems around bright stars.", "category": "astro-ph_EP" }, { "text": "Photometry of 10 Million Stars from the First Two Years of TESS Full\n Frame Images: The Transiting Exoplanet Survey Satellite (TESS) is the first high-precision\nfull-sky photometry survey in space. We present light curves from a magnitude\nlimited set of stars and other stationary luminous objects from the TESS Full\nFrame Images, as reduced by the MIT Quick Look Pipeline (QLP). Our light curves\ncover the full two-year TESS Primary Mission and include $\\sim$ 14,770,000 and\n$\\sim$ 9,600,000 individual light curve segments in the Southern and Northern\necliptic hemispheres, respectively. We describe the photometry and detrending\ntechniques we used to create the light curves, and compare the noise properties\nwith theoretical expectations. All of the QLP light curves are available at\nMAST as a High Level Science Product via doi.org/10.17909/t9-r086-e880\n(https://archive.stsci.edu/hlsp/qlp). This is the largest collection of TESS\nphotometry available to the public to date.", "category": "astro-ph_EP" }, { "text": "Outwards migration for planets in stellar irradiated 3D discs: For the very first time we present 3D simulations of planets embedded in\nstellar irradiated discs. It is well known that thermal effects could reverse\nthe direction of planetary migration from inwards to outwards, potentially\nsaving planets in the inner, optically thick parts of the protoplanetary disc.\nWhen considering stellar irradiation in addition to viscous friction as a\nsource of heating, the outer disc changes from a shadowed to a flared\nstructure. Using a suited analytical formula it has been shown that in the\nflared part of the disc the migration is inwards; planets can migrate outwards\nonly in shadowed regions of the disc, { because the radial gradient of entropy\nis stronger there}. In order to confirm this result numerically, we have\ncomputed the total torque acting on planets held on fixed orbits embedded in\nstellar irradiated 3D discs using the hydrodynamical code FARGOCA. We find\nqualitatively good agreement between the total torque obtained with numerical\nsimulations and the one predicted by the analytical formula. For large masses\n(>20 Earth masses) we find quantitative agreement, and we obtain outwards\nmigration regions for planets up to 60 Earth masses in the early stages of\naccretional discs. We find nevertheless that the agreement with the analytic\nformula is quite fortuitous because the formula underestimates the size of the\nhorseshoe region; this error is compensated by imperfect estimates of other\nterms, most likely the cooling rate and saturation.", "category": "astro-ph_EP" }, { "text": "Mineral dust increases the habitability of terrestrial planets but\n confounds biomarker detection: Identification of habitable planets beyond our solar system is a key goal of\ncurrent and future space missions. Yet habitability depends not only on the\nstellar irradiance, but equally on constituent parts of the planetary\natmosphere. Here we show, for the first time, that radiatively active mineral\ndust will have a significant impact on the habitability of Earth-like\nexoplanets. On tidally-locked planets, dust cools the day-side and warms the\nnight-side, significantly widening the habitable zone. Independent of orbital\nconfiguration, we suggest that airborne dust can postpone planetary water loss\nat the inner edge of the habitable zone, through a feedback involving\ndecreasing ocean coverage and increased dust loading. The inclusion of dust\nsignificantly obscures key biomarker gases (e.g. ozone, methane) in simulated\ntransmission spectra, implying an important influence on the interpretation of\nobservations. We demonstrate that future observational and theoretical studies\nof terrestrial exoplanets must consider the effect of dust.", "category": "astro-ph_EP" }, { "text": "Stellar Winds and Dust Avalanches in the AU Mic Debris Disk: We explain the fast-moving, ripple-like features in the edge-on debris disk\norbiting the young M dwarf AU Mic. The bright features are clouds of sub-micron\ndust repelled by the host star's wind. The clouds are produced by avalanches:\nradial outflows of dust that gain exponentially more mass as they shatter\nbackground disk particles in collisional chain reactions. The avalanches are\ntriggered from a region a few AU across -- the \"avalanche zone\" -- located on\nAU Mic's primary \"birth\" ring, at a true distance of $\\sim$35 AU from the star\nbut at a projected distance more than a factor of 10 smaller: the avalanche\nzone sits directly along the line of sight to the star, on the side of the ring\nnearest Earth, launching clouds that disk rotation sends wholly to the\nsoutheast, as observed. The avalanche zone marks where the primary ring\nintersects a secondary ring of debris left by the catastrophic disruption of a\nprogenitor up to Varuna in size, less than tens of thousands of years ago. Only\nwhere the rings intersect are particle collisions sufficiently violent to spawn\nthe sub-micron dust needed to seed the avalanches. We show that this picture\nworks quantitatively, reproducing the masses, sizes, and velocities of the\nobserved escaping clouds. The Lorentz force exerted by the wind's magnetic\nfield, whose polarity reverses periodically according to the stellar magnetic\ncycle, promises to explain the observed vertical undulations. The timescale\nbetween avalanches, about 10 yr, might be set by time variability of the wind\nmass-loss rate or, more speculatively, by some self-regulating limit cycle.", "category": "astro-ph_EP" }, { "text": "Thermal and orbital evolution of low-mass exoplanets: Thermal, orbital, and rotational dynamics of tidally loaded exoplanets are\ninterconnected by intricate feedback. The rheological structure of the planet\ndetermines its susceptibility to tidal deformation and, as a consequence,\nparticipates in shaping its orbit. The orbital parameters and the spin state,\nconversely, control the rate of tidal dissipation and may lead to substantial\nchanges of the interior. We investigate the coupled thermal-orbital evolution\nof differentiated rocky exoplanets governed by the Andrade viscoelastic\nrheology. The coupled evolution is treated by a semi-analytical model, 1d\nparametrized heat transfer and self-consistently calculated tidal dissipation.\nFirst, we conduct several parametric studies, exploring the effect of the\nrheological properties, the planet's size, and the orbital eccentricity on the\ntidal locking and dissipation. These tests show that the role of tidal locking\ninto high spin-orbit resonances is most prominent on low eccentric orbits,\nwhere it results in substantially higher tidal heating than the synchronous\nrotation. Second, we calculate the long-term evolution of three currently known\nlow-mass exoplanets with nonzero orbital eccentricity and absent or yet unknown\neccentricity forcing (namely GJ 625 b, GJ 411 b, and Proxima Centauri b). The\ntidal model incorporates the formation of a stable magma ocean and a\nconsistently evolving spin rate. We find that the thermal state is strongly\naffected by the evolution of eccentricity and spin state and proceeds as a\nsequence of thermal equilibria. Final despinning into synchronous rotation\nslows down the orbital evolution and helps to maintain long-term stable orbital\neccentricity.", "category": "astro-ph_EP" }, { "text": "The Effect of Multiple Heat Sources on Exomoon Habitable Zones: With dozens of Jovian and super-Jovian exoplanets known to orbit their host\nstars in or near the stellar habitable zones, it has recently been suggested\nthat moons the size of Mars could offer abundant surface habitats beyond the\nsolar system. Several searches for such exomoons are now underway, and the\nexquisite astronomical data quality of upcoming space missions and ground-based\nextremely large telescopes could make the detection and characterization of\nexomoons possible in the near future. Here we explore the effects of tidal\nheating on the potential of Mars- to Earth-sized satellites to host liquid\nsurface water, and we compare the tidal heating rates predicted by tidal\nequilibrium model and a viscoelastic model. In addition to tidal heating, we\nconsider stellar radiation, planetary illumination and thermal heat from the\nplanet. However, the effects of a possible moon atmosphere are neglected. We\nmap the circumplanetary habitable zone for different stellar distances in\nspecific star-planet-satellite configurations, and determine those regions\nwhere tidal heating dominates over stellar radiation. We find that the\n`thermostat effect' of the viscoelastic model is significant not just at large\ndistances from the star, but also in the stellar habitable zone, where stellar\nradiation is prevalent. We also find that tidal heating of Mars-sized moons\nwith eccentricities between 0.001 and 0.01 is the dominant energy source beyond\n3--5 AU from a Sun-like star and beyond 0.4--0.6 AU from an M3 dwarf star. The\nlatter would be easier to detect (if they exist), but their orbital stability\nmight be under jeopardy due to the gravitational perturbations from the star.", "category": "astro-ph_EP" }, { "text": "Stellar orbit evolution in close circumstellar disc encounters: The formation and early evolution of circumstellar discs often occurs within\ndense, newborn stellar clusters. For the first time, we apply the moving-mesh\ncode AREPO, to circumstellar discs in 3-D, focusing on disc-disc interactions\nthat result from stellar fly-bys. Although a small fraction of stars are\nexpected to undergo close approaches, the outcomes of the most violent\nencounters might leave an imprint on the discs and host stars that will\ninfluence both their orbits and their ability to form planets. We first\nconstruct well-behaved 3-D models of self-gravitating discs, and then create a\nsuite of numerical experiments of parabolic encounters, exploring the effects\nof pericenter separation r_p, disc orientation and disc-star mass ratio\n(M_d/M_*) on the orbital evolution of the host stars. Close encounters (2r_p<~\ndisc radius) can truncate discs on very short time scales. If discs are\nmassive, close encounters facilitate enough orbital angular momentum extraction\nto induce stellar capture. We find that for realistic primordial disc masses\nM_d<~0.1M_*, non-colliding encounters induce minor orbital changes, which is\nconsistent with analytic calculations of encounters in the linear regime. The\nsame disc masses produce entirely different results for grazing/colliding\nencounters. In the latter case, rapidly cooling discs lose orbital energy by\nradiating away the energy excess of the shock-heated gas, thus causing capture\nof the host stars into a bound orbit. In rare cases, a tight binary with a\ncircumbinary disc forms as a result of this encounter.", "category": "astro-ph_EP" }, { "text": "True Polar Wander on Dynamic Planets: Approximative Methods vs. Full\n Solution: Almost three decades ago, the problem of long term polar wander on a dynamic\nplanet was formulated and simplified within the framework of normal mode\ntheory. The underlying simplifications have been debated ever since, recently\nin a series of papers by Hu et al. 2017a, 2017b, and 2019, who clarify the role\nof neglecting short-term relaxation modes of the body. However, the authors\nstill do not solve the governing equations in full, because they make\napproximations to the Liouville equation (LE). In this paper I use a time\ndomain approach and for previously studied test loads I solve both the\nrelaxation of the body and the LE in full. I also compute the energy balance of\ntrue polar wander (TPW) in order to analyze the existing LE approximations. For\nfast rotating bodies such as the Earth, I show that the rotation axis is always\naligned with the maximum principal axis of inertia (w||MMOI) once free\noscillations are damped. The w||MMOI assumption is also re-derived\ntheoretically. Contrary to previous beliefs, I demonstrate that it is not\nnecessarily linked to the quasi-fluid simplification of the body's viscoelastic\nresponse to loading and rotation, but that it is an expression of neglecting\nthe Coriolis and Euler forces in the equation of motion. For slowly rotating\nbodies such as Venus, the full LE together with energy analysis indicate that\nprevious estimates of TPW in the normal direction need to be revisited. The\nnumerical code LIOUSHELL is made freely available.", "category": "astro-ph_EP" }, { "text": "The Rossiter-McLaughlin effect and exoplanet transits: A delicate\n association at medium and low spectral resolution: The characterization of exoplanetary atmospheres via transit spectroscopy is\nbased on the comparison between the stellar spectrum filtered through the\natmosphere and the unadulterated spectrum from the occulted stellar region. The\ndisk-integrated spectrum is often used as a proxy for the occulted spectrum,\nyet they differ along the transit chord depending on stellar type and\nrotational velocity. This is refereed to as the Rossiter-McLaughlin (RM)\neffect, which is known to bias transmission spectra at high spectral resolution\nwhen calculated with the disk-integrated stellar spectrum. Recently, it was\nshown that the first claimed atmospheric signal from an exoplanet cannot arise\nfrom absorption in the core of the sodium doublet, because the features\nobserved at high resolution are well reproduced by the RM effect. However, it\nremains unclear as to whether the detection made at medium spectral resolution\nwith the HST arises from the smoothed RM signature or from the wings of the\nplanetary absorption line. More generally, the impact of the RM effect at\nmedium and low spectral resolution remains poorly explored. To address this\nquestion, we simulated realistic transmission spectra in a variety of systems\nusing the EVaporating Exoplanets code. We find that the RM effect should not\nbias broadband atmospheric features, such as hazes or molecular absorption,\nmeasured with the JWST/NIRSPEC (prism mode) at low resolution. However,\nabsorption signatures from metastable helium or sodium measured at medium\nresolution with the JWST/NIRSPEC (G140H mode) or HST/STIS can be biased,\nespecially for planets on misaligned orbits across fast rotators. In contrast,\nwe show that the Na signature originally reported in HD209458b, an aligned\nsystem, cannot be explained by the RM effect, supporting a planetary origin.", "category": "astro-ph_EP" }, { "text": "From exo-Earths to exo-Venuses -- Flux and Polarization Signatures of\n Reflected Light: Terrestrial exoplanets in habitable zones are ubiquitous. It is, however,\nunknown which have Earth-like or Venus-like climates. Distinguishing different\nplanet-types is crucial for determining whether a planet could be habitable. We\ninvestigate the potential of polarimetry for distinguishing exo-Earths from\nexo-Venuses. We present computed fluxes and polarisation of starlight that is\nreflected by exoplanets with atmospheres in evolutionary states from current\nEarth to current Venus, with cloud compositions ranging from pure water to 0.75\nsulfuric acid solution, for wavelengths between 0.3 and 2.5 microns. The\npolarisation of the reflected light shows larger variations with the planetary\nphase angle than the total flux. Across the visible, the largest polarisation\nis reached for an Earth-like atmosphere with water clouds, due to Rayleigh\nscattering above the clouds and the rainbow near 40 deg phase angle. In the\nnear-infrared, the planet with a Venus-like CO2 atmosphere and thin water\nclouds shows the most prominent polarisation features due to scattering by the\nsmall cloud droplets. A planet around Alpha Centauri A would leave temporal\nvariations on the order of 10E-13 W/m3 in the reflected flux and 10E-11 in the\ndegree of polarisation along the planet's orbit for a spatially unresolved\nstar-planet system. Star-planet contrasts are on the order of 10E-10. Current\npolarimeters cannot distinguish between the possible evolutionary phases of\nspatially unresolved terrestrial exoplanets, as a sensitivity near 10E-10 is\nrequired to discern the planet signal on the background of unpolarised\nstarlight. Telescopes capable of reaching planet-star contrasts lower than\n10E-9 should be able to observe the variation of the planet's resolved degree\nof polarisation as a function of its phase angle and thus to discern an\nexo-Earth from an exo-Venus based on its clouds' unique polarisation\nsignatures.", "category": "astro-ph_EP" }, { "text": "HELIOS: An Open-source, GPU-accelerated Radiative Transfer Code For\n Self-consistent Exoplanetary Atmospheres: We present the open-source radiative transfer code named HELIOS, which is\nconstructed for studying exoplanetary atmospheres. In its initial version, the\nmodel atmospheres of HELIOS are one-dimensional and plane-parallel, and the\nequation of radiative transfer is solved in the two-stream approximation with\nnon-isotropic scattering. A small set of the main infrared absorbers is\nemployed, computed with the opacity calculator HELIOS-K and combined using a\ncorrelated-$k$ approximation. The molecular abundances originate from validated\nanalytical formulae for equilibrium chemistry. We compare HELIOS with the work\nof Miller-Ricci & Fortney using a model of GJ 1214b, and perform several tests,\nwhere we find: model atmospheres with single-temperature layers struggle to\nconverge to radiative equilibrium; $k$-distribution tables constructed with\n$\\gtrsim 0.01$ cm$^{-1}$ resolution in the opacity function ($ \\lesssim 10^3$\npoints per wavenumber bin) may result in errors $\\gtrsim 1$-10 % in the\nsynthetic spectra; and a diffusivity factor of 2 approximates well the exact\nradiative transfer solution in the limit of pure absorption. We construct\n\"null-hypothesis\" models (chemical equilibrium, radiative equilibrium and solar\nelement abundances) for 6 hot Jupiters. We find that the dayside emission\nspectra of HD 189733b and WASP-43b are consistent with the null hypothesis,\nwhile it consistently under-predicts the observed fluxes of WASP-8b, WASP-12b,\nWASP-14b and WASP-33b. We demonstrate that our results are somewhat insensitive\nto the choice of stellar models (blackbody, Kurucz or PHOENIX) and metallicity,\nbut are strongly affected by higher carbon-to-oxygen ratios. The code is\npublicly available as part of the Exoclimes Simulation Platform (ESP;\nexoclime.net).", "category": "astro-ph_EP" }, { "text": "Photodissociation and induced chemical asymmetries on ultra-hot gas\n giants. A case study of HCN on WASP-76 b: Recent observations have resulted in the detection of chemical gradients on\nultra-hot gas giants. Notwithstanding their high temperature, chemical\nreactions in ultra-hot atmospheres may occur in disequilibrium, due to vigorous\nday-night circulation and intense UV radiation from their stellar hosts. The\ngoal of this work is to explore whether photochemistry is affecting the\ncomposition of ultra-hot giant planets, and if it can introduce horizontal\nchemical gradients. In particular, we focus on hydrogen cyanide (HCN) on\nWASP-76 b, as it is a photochemically active molecule with a reported detection\non only one side of this planet. We use a pseudo-2D chemical kinetics code to\nmodel the chemical composition of WASP-76 b along its equator. Our approach\nimproves on chemical equilibrium models by computing vertical mixing,\nhorizontal advection, and photochemistry. We find that production of HCN is\ninitiated through thermal and photochemical dissociation of CO and N$_2$ on the\nday side of WASP-76 b. The resulting radicals are subsequently transported to\nthe night side via the equatorial jet stream, where they recombine into\ndifferent molecules. This process results in an HCN gradient with a maximal\nabundance on the planet's morning limb. We verified that photochemical\ndissociation is a necessary condition for this mechanism, as thermal\ndissociation alone proves insufficient. Other species produced via night-side\ndisequilibrium chemistry are SO$_2$ and S$_2$. Our model acts as a proof of\nconcept for chemical gradients on ultra-hot exoplanets. We demonstrate that\neven ultra-hot planets can exhibit disequilibrium chemistry and recommend that\nfuture studies do not neglect photochemistry in their analyses of ultra-hot\nplanets.", "category": "astro-ph_EP" }, { "text": "The Beam Balance -- Measuring Binary Systems via Relativistic Beaming\n Signals from Stars and their Companions: In this paper I show that the concept of relativistic beaming -- the process\nby which light emitted by a fast moving sources is lensed towards the direction\nof motion -- can be easily extended to model the signal from both the star and\nany secondary companions. Most companions will be cooler and less massive than\ntheir host star. Their lower mass leads to faster orbital velocities, and thus\na potentially larger beaming effect. The lower temperature will mean that most\nof their light is emitted at longer wavelengths, where the relative photometric\ndominance of the primary is reduced. Thus for some systems, the secondary\ncompanion can be the main contributor to observed relativistic beaming signals\nat long wavelengths. Furthermore, if the system is observed over a range of\nwavelengths we can independently constrain the temperature of the companion,\nand the mass and radius ratio of the binary. To conclude I discuss the current\nand future observational prospects of this signal, using the properties of\nknown exoplanets to show that such a signal may be observable by upcoming\nsurveys.", "category": "astro-ph_EP" }, { "text": "The Role of Early Giant Planet Instability in the Terrestrial Planet\n Formation: The terrestrial planets are believed to have formed by violent collisions of\ntens of lunar- to Mars-size protoplanets at time t<200 Myr after the\nprotoplanetary gas disk dispersal (t_0). The solar system giant planets rapidly\nformed during the protoplanetary disk stage and, after t_0, radially migrated\nby interacting with outer disk planetesimals. An early (t<100 Myr) dynamical\ninstability is thought to have occurred with Jupiter having gravitational\nencounters with a planetary-size body, jumping inward by ~0.2-0.5 au, and\nlanding on its current, mildly eccentric orbit. Here we investigate how the\ngiant planet instability affected formation of the terrestrial planets. We\nstudy several instability cases that were previously shown to match many solar\nsystem constraints. We find that resonances with the giant planets help to\nremove solids available for accretion near ~1.5 au, thus stalling the growth of\nMars. It does not matter, however, whether the giant planets are placed on\ntheir current orbits at t_0 or whether they realistically evolve in one of our\ninstability models; the results are practically the same. The tight orbital\nspacing of Venus and Earth is difficult to reproduce in our simulations,\nincluding cases where bodies grow from a narrow annulus at 0.7-1 au, because\nprotoplanets tend to radially spread during accretion. The best results are\nobtained in the narrow-annulus model when protoplanets emerging from the\ndispersing gas nebula are assumed to have (at least) the Mars mass. This\nsuggests efficient accretion of the terrestrial protoplanets during the first\n~10 Myr of the solar system.", "category": "astro-ph_EP" }, { "text": "Oscillations in the Habitable Zone around Alpha Centauri B: The Alpha Centauri AB system is an attractive one for radial velocity\nobservations to detect potential exoplanets. The high metallicity of both Alpha\nCentauri A and B suggest that they could have possessed circumstellar discs\ncapable of forming planets. As the closest star system to the Sun, with well\nover a century of accurate astrometric measurements (and Alpha Centauri B\nexhibiting low chromospheric activity) high precision surveys of Alpha Centauri\nB's potential exoplanetary system are possible with relatively cheap\ninstrumentation. Authors studying habitability in this system typically adopt\nhabitable zones (HZs) based on global radiative balance models that neglect the\nradiative perturbations of Alpha Centauri A.\n We investigate the habitability of planets around Alpha Centauri B using 1D\nlatitudinal energy balance models (LEBMs), which fully incorporate the presence\nof Alpha Centauri A as a means of astronomically forcing terrestrial planet\nclimates. We find that the extent of the HZ is relatively unchanged by the\npresence of Alpha Centauri A, but there are variations in fractional\nhabitability for planets orbiting at the boundaries of the zone due to Alpha\nCentauri A, even in the case of zero eccentricity. Temperature oscillations of\na few K can be observed at all planetary orbits, the strength of which varies\nwith the planet's ocean fraction and obliquity.", "category": "astro-ph_EP" }, { "text": "Identification of asteroids using the Virtual Observatory: the WFCAM\n Transit Survey: The nature and physical properties of asteroids, in particular those orbiting\nin the near-Earth space, are of scientific interest and practical importance.\nExoplanet surveys can be excellent resources to detect asteroids, both already\nknown and new objects. This is due their similar observing requirements: large\nfields of view, long sequences, and short cadence. If the targeted fields are\nnot located far from the ecliptic, many asteroids will cross occasionally the\nfield of view. We present two complementary methodologies to identify asteroids\nserendipitously observed in large-area astronomical surveys. One methodology\nfocuses on detecting already known asteroids using the Virtual Observatory tool\nSkyBoT, which predicts their positions and motions in the sky at a specific\nepoch. The other methodology applies the ssos pipeline, which is able to\nidentify known and new asteroids based on their apparent motion. The\napplication of these methods to the 6.4 deg 2 of the sky covered by the\nWide-Field CAMera Transit Survey in the J-band is described. We identified 15\n661 positions of 1 821 different asteroids. Of them, 182 are potential new\ndiscoveries. A publicly accessible online, Virtual Observatory compliant\ncatalogue was created. We obtained the shapes and periods for five of our\nasteroids from their light-curves built with additional photometry taken from\nexternal archives. We demonstrated that our methodologies are robust and\nreliable approaches to find, at zero cost of observing time, asteroids observed\nby chance in astronomical surveys. Our future goal is to apply them to other\nsurveys with adequate temporal coverage.", "category": "astro-ph_EP" }, { "text": "Mercury's geochronology revised by applying Model Production Functions\n to Mariner 10 data: geological implications: Model Production Function chronology uses dynamic models of the Main Belt\nAsteroids (MBAs) and Near Earth Objects (NEOs) to derive the impactor flux to a\ntarget body. This is converted into the crater size-frequency-distribution for\na specific planetary surface, and calibrated using the radiometric ages of\ndifferent regions of the Moon's surface. This new approach has been applied to\nthe crater counts on Mariner 10 images of the highlands and of several large\nimpact basins on Mercury. MPF estimates for the plains show younger ages than\nthose of previous chronologies. Assuming a variable uppermost layering of the\nHermean crust, the age of the Caloris interior plains may be as young as 3.59\nGa, in agreement with MESSENGER results that imply that long-term volcanism\novercame contractional tectonics. The MPF chronology also suggests a variable\nprojectile flux through time, coherent with the MBAs for ancient periods and\nthen gradually comparable also to the NEOs.", "category": "astro-ph_EP" }, { "text": "The Carbon-Deficient Evolution of TRAPPIST-1c: Transiting planets orbiting M dwarfs provide the best opportunity to study\nthe atmospheres of rocky planets with current facilities. As JWST enters its\nsecond year of science operations, an important initial endeavor is to\ndetermine whether these rocky planets have atmospheres at all. M dwarf host\nstars are thought to pose a major threat to planetary atmospheres due to their\nhigh magnetic activity over several billion-year timescales, and might\ncompletely strip atmospheres. Several Cycle 1 and 2 GO and GTO programs are\ntesting this hypothesis, observing a series of rocky planets to determine\nwhether they retained their atmospheres. A key case-study is TRAPPIST-1c, which\nreceives almost the same bolometric flux as Venus. We might, therefore, expect\nTRAPPIST-1c to possess a thick, $\\mathrm{CO}_2$-dominated atmosphere. Instead,\nZieba et al. (2023) show that TRAPPIST-1c has little to no CO$_2$ in its\natmosphere. To interpret these results, we run coupled time-dependent\nsimulations of planetary outgassing and atmospheric escape to model the\nevolution of TRAPPIST-1c's atmosphere. We find that the stellar wind stripping\nthat is expected to occur on TRAPPIST-1c over its lifetime can only remove up\nto $\\sim 16$ bar of $\\mathrm{CO}_2$, less than the modern $\\mathrm{CO}_2$\ninventory of either Earth or Venus. Therefore, we infer that TRAPPIST-1c either\nformed volatile-poor, as compared to Earth and Venus, or lost a substantial\namount of $\\mathrm{CO}_2$ during an early phase of hydrodynamic hydrogen\nescape. Finally, we scale our results for the other TRAPPIST-1 planets, finding\nthat the more distant TRAPPIST-1 planets may readily retain atmospheres.", "category": "astro-ph_EP" }, { "text": "On the Outer Edges of Protoplanetary Dust Disks: The expectation that aerodynamic drag will force the solids in a gas-rich\nprotoplanetary disk to spiral in toward the host star on short timescales is\none of the fundamental problems in planet formation theory. The nominal\nefficiency of this radial drift process is in conflict with observations,\nsuggesting that an empirical calibration of solid transport mechanisms in a\ndisk is highly desirable. However, the fact that both radial drift and grain\ngrowth produce a similar particle size segregation in a disk (such that larger\nparticles are preferentially concentrated closer to the star) makes it\ndifficult to disentangle a clear signature of drift alone. We highlight a new\napproach, by showing that radial drift leaves a distinctive \"fingerprint\" in\nthe dust surface density profile that is directly accessible to current\nobservational facilities. Using an analytical framework for dust evolution, we\ndemonstrate that the combined effects of drift and (viscous) gas drag naturally\nproduce a sharp outer edge in the dust distribution (or, equivalently, a sharp\ndecrease in the dust-to-gas mass ratio). This edge feature forms during the\nearliest phase in the evolution of disk solids, before grain growth in the\nouter disk has made much progress, and is preserved over longer timescales when\nboth growth and transport effects are more substantial. The key features of\nthese analytical models are reproduced in detailed numerical simulations, and\nare qualitatively consistent with recent millimeter-wave observations that find\ngas/dust size discrepancies and steep declines in dust continuum emission in\nthe outer regions of protoplanetary disks.", "category": "astro-ph_EP" }, { "text": "TESS Photometric Mapping of a Terrestrial Planet in the Habitable Zone:\n Detection of Clouds, Oceans, and Continents: To date, a handful of exoplanets have been photometrically mapped using\nphase-modulated reflection or emission from their surfaces, but the small\namplitudes of such signals have limited previous maps almost exclusively to\ncoarse dipolar features on hot giant planets. In this work, we uncover a signal\nusing recently released data from the Transiting Exoplanet Survey Satellite\n(TESS), which we show corresponds to time-variable reflection from a\nterrestrial planet with a rotation period of 0.9972696 days. Using a spherical\nharmonic-based reflection model developed as an extension of the STARRY\npackage, we are able to reconstruct the surface features of this rocky world.\nWe recover a time-variable albedo map of the planet including persistent\nregions which we interpret as oceans and cloud banks indicative of continental\nfeatures. We argue that this planet represents the most promising detection of\na habitable world to date, although the potential intelligence of any life on\nit is yet to be determined.", "category": "astro-ph_EP" }, { "text": "Is the hot, dense sub-Neptune TOI-824b an exposed Neptune mantle?\n Spitzer detection of the hot day side and reanalysis of the interior\n composition: The Kepler and TESS missions revealed a remarkable abundance of sub-Neptune\nexoplanets. Despite this abundance, our understanding of the nature and\ncompositional diversity of sub-Neptunes remains limited, to a large part\nbecause atmospheric studies via transmission spectroscopy almost exclusively\naimed for low-density sub-Neptunes and even those were often affected by\nhigh-altitude clouds. The recent TESS discovery of the hot, dense TOI-824b\n($2.93\\,R_\\oplus$ and $18.47\\,M_\\oplus$) opens a new window into sub-Neptune\nscience by enabling the study of a dense sub-Neptune via secondary eclipses.\nHere, we present the detection of TOI-824b's hot day side via Spitzer secondary\neclipse observations in the $3.6$ and $4.5\\,\\mathrm{\\mu m}$ channels, combined\nwith a reanalysis of its interior composition. The measured eclipse depths\n(142$^{+57}_{-52}$ and 245$^{+75}_{-77}$ ppm) and brightness temperatures\n(1463$^{+183}_{-196}$ and 1484$^{+180}_{-202}$ K) indicate a poor heat\nredistribution ($f>$ 0.49) and a low Bond albedo (A$_{B}<$ 0.26). We conclude\nthat TOI-824b could be an \"exposed Neptune mantle\": a planet with a\nNeptune-like water-rich interior that never accreted a hydrogen envelope or\nthat subsequently lost it. The hot day-side temperature is then naturally\nexplained by a high-metallicity envelope re-emitting the bulk of the incoming\nradiation from the day side. TOI-824b's density is also consistent with a\nmassive rocky core that accreted up to 1% of hydrogen, but the observed eclipse\ndepths favor our high-metallicity GCM simulation to a solar-metallicity GCM\nsimulation with a likelihood ratio of 7:1. The new insights into TOI-824b's\nnature suggest that the sub-Neptune population may be more diverse than\npreviously thought, with some of the dense hot sub-Neptunes potentially not\nhosting a hydrogen-rich envelope as generally assumed for sub-Neptunes.", "category": "astro-ph_EP" }, { "text": "Transformation of Trojans into Quasi-Satellites During Planetary\n Migration and Their Subsequent Close-Encounters with the Host Planet: We use numerical integrations to investigate the dynamical evolution of\nresonant Trojan and quasi-satellite companions during the late stages of\nmigration of the giant planets Jupiter, Saturn, Uranus, and Neptune. Our\nmigration simulations begin with Jupiter and Saturn on orbits already well\nseparated from their mutual 2:1 mean-motion resonance. Neptune and Uranus are\ndecoupled from each other and have orbital eccentricities damped to near their\ncurrent values. From this point we adopt a planet migration model in which the\nmigration speed decreases exponentially with a characteristic timescale tau\n(the e-folding time). We perform a series of numerical simulations, each\ninvolving the migrating giant planets plus test particle Trojans and\nquasi-satellites. We find that the libration frequencies of Trojans are similar\nto those of quasi-satellites. This similarity enables a dynamical exchange of\nobjects back and forth between the Trojan and quasi-satellite resonances during\nplanetary migration. Furthermore, under the influence of these secondary\nresonances quasi-satellites can have their libration amplitudes enlarged until\nthey undergo a close-encounter with their host planet and escape from the\nresonance. High-resolution simulations of this escape process reveal that ~80%\nof Jovian quasi-satellites experience one or more close-encounters within\nJupiter's Hill radius (R_H) as they are forced out of the quasi-satellite\nresonance. As many as ~20% come within R_H/4 and ~2.5% come within R_H/10.\nClose-encounters of escaping quasi-satellites occur near or even below the\n2-body escape velocity from the host planet.", "category": "astro-ph_EP" }, { "text": "Explosion of Comet 17P/Holmes as revealed by the Spitzer Space Telescope: An explosion on comet 17P/Holmes occurred on 2007 Oct 23, projecting\nparticulate debris of a wide range of sizes into the interplanetary medium. We\nobserved the comet using the Spitzer spectrograph on 2007 Nov 10 and 2008 Feb\n27, and the photometer, on 2008 Mar 13. The fresh ejecta have detailed\nmineralogical features from small crystalline silicate grains. The 2008 Feb 27\nspectra, and the central core of the 2007 Nov 10 spectral map, reveal nearly\nfeatureless spectra, due to much larger grains that were ejected from the\nnucleus more slowly. We break the infrared image into three components (size,\nspeed) that also explain the temporal evolution of the mm-wave flux. Optical\nimages were obtained on multiple dates spanning 2007 Oct 27 to 2008 Mar 10 at\nthe Holloway Comet Observatory and 1.5-m telescope at Palomar Observatory. The\norientation of the leading edge of the ejecta shell and the ejecta blob,\nrelative to the nucleus, do not change as the orientation of the Sun changes;\ninstead, the configuration was imprinted by the orientation of the initial\nexplosion. The kinetic energy of the ejecta >1e21 erg is greater than the\ngravitational binding energy of the nucleus. We model the explosion as being\ndue to crystallization and release of volatiles from interior amorphous ice\nwithin a subsurface cavity; once the pressure in the cavity exceeded the\nsurface strength, the material above the cavity was propelled from the comet.\nThe size of the cavity and the tensile strength of the upper layer of the\nnucleus are constrained by the observed properties of the ejecta; tensile\nstrengths on >10 m scale must be greater than 10 kPa. The appearance of the\n2007 outburst is similar to that witnessed in 1892, but the 1892 explosion was\nless energetic by a factor of about 20.", "category": "astro-ph_EP" }, { "text": "Collisions of small ice particles under microgravity conditions (II):\n Does the chemical composition of the ice change the collisional properties?: Context: Understanding the collisional properties of ice is important for\nunderstanding both the early stages of planet formation and the evolution of\nplanetary ring systems. Simple chemicals such as methanol and formic acid are\nknown to be present in cold protostellar regions alongside the dominant water\nice; they are also likely to be incorporated into planets which form in\nprotoplanetary disks, and planetary ring systems. However, the effect of the\nchemical composition of the ice on its collisional properties has not yet been\nstudied. Aims: Collisions of 1.5 cm ice spheres composed of pure crystalline\nwater ice, water with 5% methanol, and water with 5% formic acid were\ninvestigated to determine the effect of the ice composition on the collisional\noutcomes. Methods: The collisions were conducted in a dedicated experimental\ninstrument, operated under microgravity conditions, at relative particle impact\nvelocities between 0.01 and 0.19 m s^-1, temperatures between 131 and 160 K and\na pressure of around 10^-5 mbar. Results: A range of coefficients of\nrestitution were found, with no correlation between this and the chemical\ncomposition, relative impact velocity, or temperature. Conclusions: We conclude\nthat the chemical composition of the ice (at the level of 95% water ice and 5%\nmethanol or formic acid) does not affect the collisional properties at these\ntemperatures and pressures due to the inability of surface wetting to take\nplace. At a level of 5% methanol or formic acid, the structure is likely to be\ndominated by crystalline water ice, leading to no change in collisional\nproperties. The surface roughness of the particles is the dominant factor in\nexplaining the range of coefficients of restitution.", "category": "astro-ph_EP" }, { "text": "Long lived dust rings around HD169142: Recent ALMA observations of the protoplanetary disc around HD~169142 reveal a\npeculiar structure made of concentric dusty rings: a main ring at $\\sim$20 au,\na triple system of rings at $\\sim 55-75$ au in millimetric continuum emission\nand a perturbed gas surface density from the $^{12}$CO,$^{13}$CO and\nC$^{18}$O$(J=2-1)$ surface brightness profile. In this Letter, we perform\nthree-dimensional numerical simulations and radiative transfer modeling\nexploring the possibility that two giant planets interacting with the disc and\norbiting in resonant locking can be responsible for the origin of the observed\ndust inner rings structure. We find that in this configuration the dust\nstructure is actually long lived while the gas mass of the disc is accreted\nonto the star and the giant planets, emptying the inner region. In addition, we\nalso find that the innermost planet is located at the inner edge of the dust\nring, and can accrete mass from the disc, generating a signature in the dust\nring shape that can be observed in mm ALMA observations.", "category": "astro-ph_EP" }, { "text": "Aggregate dust particles at comet 67P/Churyumov-Gerasimenko: Comets are thought to preserve almost pristine dust particles, thus providing\na unique sample of the properties of the early solar nebula. The microscopic\nproperties of this dust played a key part in particle aggregation during the\nformation of the Solar System. Cometary dust was previously considered to\ncomprise irregular, fluffy agglomerates on the basis of interpretations of\nremote observations in the visible and infrared and the study of chondritic\nporous interplanetary dust particles that were thought, but not proved, to\noriginate in comets. Although the dust returned by an earlier mission has\nprovided detailed mineralogy of particles from comet 81P/Wild, the fine-grained\naggregate component was strongly modified during collection. Here we report in\nsitu measurements of dust particles at comet 67P/Churyumov-Gerasimenko. The\nparticles are aggregates of smaller, elongated grains, with structures at\ndistinct sizes indicating hierarchical aggregation. Topographic images of\nselected dust particles with sizes of one micrometre to a few tens of\nmicrometres show a variety of morphologies, including compact single grains and\nlarge porous aggregate particles, similar to chondritic porous interplanetary\ndust particles. The measured grain elongations are similar to the value\ninferred for interstellar dust and support the idea that such grains could\nrepresent a fraction of the building blocks of comets. In the subsequent growth\nphase, hierarchical agglomeration could be a dominant process and would produce\naggregates that stick more easily at higher masses and velocities than\nhomogeneous dust particles. The presence of hierarchical dust aggregates in the\nnear-surface of the nucleus of comet 67P also provides a mechanism for lowering\nthe tensile strength of the dust layer and aiding dust release.", "category": "astro-ph_EP" }, { "text": "Revisiting the distributions of Jupiter's irregular moons: II. orbital\n characteristics: This paper statistically describes the orbital distribution laws of Jupiter's\nirregular moons, most of which are members of the Ananke, Carme and Pasiphae\ngroups. By comparing 19 known continuous distributions, it is verified that\nsuitable distribution functions exist to describe the orbital distributions of\nthese natural satellites. For each distribution type, interval estimation is\nused to estimate the corresponding parameter values. At a given significance\nlevel, a one-sample Kolmogorov-Smirnov non-parametric test is applied to verify\nthe specified distribution, and we often select the one with the largest\n$p$-value. The results show that the semi-major axis, mean inclination and\norbital period of the moons in the Ananke group and Carme group obey Stable\ndistributions. In addition, according to Kepler's third law of planetary motion\nand by comparing the theoretically calculated best-fitting cumulative\ndistribution function (CDF) with the observed CDF, we demonstrate that the\ntheoretical distribution is in good agreement with the empirical distribution.\nTherefore, these characteristics of Jupiter's irregular moons are indeed very\nlikely to follow some specific distribution laws, and it will be possible to\nuse these laws to help study certain features of poorly investigated moons or\neven predict undiscovered ones.", "category": "astro-ph_EP" }, { "text": "Dynamical Evolution of the Earth-Moon Progenitors - Whence Theia?: We present integrations of a model Solar System with five terrestrial planets\n(beginning ~30-50 Myr after the formation of primitive Solar System bodies) in\norder to determine the preferred regions of parameter space leading to a giant\nimpact that resulted in the formation of the Moon. Our results indicate which\nchoices of semimajor axes and eccentricities for Theia (the proto-Moon) at this\nepoch can produce a late Giant Impact, assuming that Mercury, Venus, and Mars\nare near the current orbits. We find that the likely semimajor axis of Theia,\nat the epoch when our simulations begin, depends on the assumed mass ratio of\nEarth-Moon progenitors (8/1, 4/1, or 1/1). The low eccentricities of the\nterrestrial planets are most commonly produced when the progenitors have\nsimilar semimajor axes at the epoch when our integrations commence.\nAdditionally, we show that mean motion resonances among the terrestrial planets\nand perturbations from the giant planets can affect the dynamical evolution of\nthe system leading to a late Giant Impact.", "category": "astro-ph_EP" }, { "text": "WASP-131 b with ESPRESSO I: A bloated sub-Saturn on a polar orbit around\n a differentially rotating solar-type star: In this paper, we present observations of two high-resolution transit\ndatasets obtained with ESPRESSO of the bloated sub-Saturn planet WASP-131~b. We\nhave simultaneous photometric observations with NGTS and EulerCam. In addition,\nwe utilised photometric lightcurves from {\\tess}, WASP, EulerCam and TRAPPIST\nof multiple transits to fit for the planetary parameters and update the\nephemeris. We spatially resolve the stellar surface of WASP-131 utilising the\nReloaded Rossiter McLaughlin technique to search for centre-to-limb convective\nvariations, stellar differential rotation, and to determine the star-planet\nobliquity for the first time. We find WASP-131 is misaligned on a nearly\nretrograde orbit with a projected obliquity of $\\lambda = 162.4\\substack{+1.3\n\\\\ -1.2}^{\\circ}$. In addition, we determined a stellar differential rotation\nshear of $\\alpha = 0.61 \\pm 0.06$ and disentangled the stellar inclination\n($i_* = 40.9\\substack{+13.3 \\\\ -8.5}^{\\circ}$) from the projected rotational\nvelocity, resulting in an equatorial velocity of $v_{\\rm{eq}} =\n7.7\\substack{+1.5 \\\\ -1.3}$~km s$^{-1}$. In turn, we determined the true 3D\nobliquity of $\\psi = 123.7\\substack{+12.8 \\\\ -8.0}^{\\circ}$, meaning the planet\nis on a perpendicular/polar orbit. Therefore, we explored possible mechanisms\nfor the planetary system's formation and evolution. Finally, we searched for\ncentre-to-limb convective variations where there was a null detection,\nindicating that centre-to-limb convective variations are not prominent in this\nstar or are hidden within red noise.", "category": "astro-ph_EP" }, { "text": "Physical Characterisation of Interstellar Comet 2I/2019 Q4 (Borisov): We present a study of interstellar comet 2I/2019 Q4 (Borisov) using both\npreperihelion and postperihelion observations spanning late September 2019\nthrough late January 2020. The intrinsic brightness of the comet was observed\nto continuously decline throughout the timespan, likely due to the decreasing\neffective scattering cross-section as a result of volatile sublimation with a\nslope of $-0.43 \\pm 0.02$ km$^{2}$ d$^{-1}$. We witnessed no significant change\nin the slightly reddish colour of the comet, with mean values of $\\left \\langle\ng - r \\right \\rangle = 0.68 \\pm 0.04$, $\\left \\langle r - i \\right \\rangle =\n0.23 \\pm 0.03$, and the normalised reflectivity gradient across the $g$ and $i$\nbands $\\overline{S'} \\left(g,i\\right) = \\left(10.6 \\pm 1.4\\right)$ % per $10^3$\n\\AA, all unremarkable in the context of solar system comets. Using the\navailable astrometric observations, we confidently detect the nongravitational\nacceleration of the comet following a shallow heliocentric distance dependency\nof $r_{\\rm H}^{-1 \\pm 1}$. Accordingly, we estimate that the nucleus is most\nlikely $\\lesssim$0.4 km in radius, and that a fraction of $\\gtrsim$0.2% of the\ntotal nucleus in mass has been eroded due to the sublimation activity since the\nearliest observation of the comet in 2018 December by the time of perihelion.\nOur morphology simulation suggests that the dust ejection speed increased from\n$\\sim$4 m s$^{-1}$ in September 2019 to $\\sim$7 m s$^{-1}$ around perihelion\nfor the optically dominant dust grains of $\\beta \\sim 0.01$, and that the\nobservable dust grains are no smaller than micron size.", "category": "astro-ph_EP" }, { "text": "CCD polarimetry of distant comets C/2010 S1 (LINEAR) and C/2010 R1\n (LINEAR) at the 6-m telescope of the SAO RAS: We present first measurements of the degree of linear polarization of distant\ncomets C/2010 S1 (LINEAR) and C/2010 R1 (LINEAR) at heliocentric distances r=\n5.9 - 7.0 AU. Observations were carried out with the SCORPIO-2 focal reducer at\nthe 6-m telescope of the SAO RAS. Both comets showed considerable level of\nactivity beyond a zone where water ice sublimation is negligible (up to 5 AU).\nSignificant spatial variations both in the intensity and polarization are found\nin both comets. The slope of radial profiles of intensity changes gradually\nwith the distance from the photocenter: from - 0.7 near the nucleus up to about\n- 1.3 for larger distances (up to 100000 km). The variation in polarization\nprofiles indicates the non uniformity in the polarization distribution over the\ncoma. The polarization degree over the coma gradually increases (in absolute\nvalue) with increasing the photocentric distance from of about - 1.9% up to -\n3% for comet C/2010 S1 (LINEAR), and from of about - 2.5% up to - 3.5% for\ncomet C/2010 R1 (LINEAR). These polarization values are significantly higher\nthan typical value of the whole coma polarization (-1.5%) for comets at\nheliocentric distances less than 5 AU. The obtained photometric and\npolarimetric data are compared with those derived early for other comets at\nsmaller heliocentric distances. Numerical modeling of light scattering\ncharacteristics was performed for media composed of particles with different\nrefractive index, shape, and size. The computations were made by using the\nsuperposition T-matrix method. We obtained that for comet C/2010 S1 (LINEAR),\nthe dust in the form of aggregates of overall radius R ~ 1.3 {\\mu}m composed of\nN = 1000 spherical monomers with radius a = 0.1 {\\mu}m, refractive index m =\n1.65 + i 0.05, allows to obtain a satisfactory agreement between the results of\npolarimetric observations of comet C/2010 S1 and computations.", "category": "astro-ph_EP" }, { "text": "The impact of faculae on the radius determination of exoplanets: The\n case of the M-star GJ1214: Precise measurements of exoplanets radii are of key importance for our\nunderstanding of the origin and nature of these objects. Measurement of the\nplanet radii using the transit method have reached a precision that the effects\nof stellar surface features have to be taken into account. While the effects\nfrom spots have already been studied in detail, our knowledge of the effects\ncaused by faculae is still limited. This is particularly the case for M-stars.\nFaculae can pose a problem if they are inhomogeneously distributed on the\nstellar surface. Using the eclipse mapping method, we study the distribution of\nthe faculae on the surface of GJ1214 using the CaIIH&K lines as tracers. In\norder to assess the homogeneity of the distribution in a quantitative way, we\nintroduce the inhomogeneity factor IHF. IHF is 0% if the distribution is\nhomogeneous, positive, if the plage regions are preferentially located along\nthe path of the planet, and negative, if they are preferentially located\noutside the path of the planet. For GJ1214, we derive a rather small value of\nIHF=7.7-7.7+12.0%. We discuss the relevance of this result in the context of\nthe PLATO and ARIEL missions.", "category": "astro-ph_EP" }, { "text": "Disentangling Atmospheric Compositions of K2-18 b with Next Generation\n Facilities: Recent analysis of the planet K2-18b has shown the presence of water vapour\nin its atmosphere. While the H2O detection is significant, the Hubble Space\nTelescope (HST) WFC3 spectrum suggests three possible solutions of very\ndifferent nature which can equally match the data. The three solutions are a\nprimary cloudy atmosphere with traces of water vapour (cloudy sub-Neptune), a\nsecondary atmosphere with a substantial amount (up to 50% Volume Mixing Ratio)\nof H2O (icy/water world) and/or an undetectable gas such as N2 (super-Earth).\nAdditionally, the atmospheric pressure and the possible presence of a\nliquid/solid surface cannot be investigated with currently available\nobservations.\n In this paper we used the best fit parameters from Tsiaras et al. (2019) to\nbuild James Webb Space Telescope (JWST) and Ariel simulations of the three\nscenarios. We have investigated 18 retrieval cases, which encompass the three\nscenarios and different observational strategies with the two observatories.\nRetrieval results show that twenty combined transits should be enough for the\nAriel mission to disentangle the three scenarios, while JWST would require only\ntwo transits if combining NIRISS and NIRSpec data. This makes K2-18b an ideal\ntarget for atmospheric follow-ups by both facilities and highlights the\ncapabilities of the next generation of space-based infrared observatories to\nprovide a complete picture of low mass planets.", "category": "astro-ph_EP" }, { "text": "The HARPS search for southern extrasolar planets. XXIII. 8 planetary\n companions to low-activity solar-type stars: In this paper, we present our HARPS radial-velocity data for eight\nlow-activity solar-type stars belonging to the HARPS volume-limited sample:\nHD6718, HD8535, HD28254, HD290327, HD43197, HD44219, HD148156, and HD156411.\nKeplerian fits to these data reveal the presence of low-mass companions around\nthese targets. With minimum masses ranging from 0.58 to 2.54 MJup, these\ncompanions are in the planetary mass domain. The orbital periods of these\nplanets range from slightly less than one to almost seven years. The eight\norbits presented in this paper exhibit a wide variety of eccentricities: from\n0.08 to above 0.8.", "category": "astro-ph_EP" }, { "text": "Effect of Finite Larmor Radius on the Cosmic Ray Penetration into an\n Interplanetary Magnetic Flux Rope: We discuss a mechanism for cosmic ray penetration into an interplanetary\nmagnetic flux rope, particularly the effect of the finite Larmor radius and\nmagnetic field irregularities. First, we derive analytical solutions for cosmic\nray behavior inside a magnetic flux rope, on the basis of the Newton-Lorentz\nequation of a particle, to investigate how cosmic rays penetrate magnetic flux\nropes under an assumption of there being no scattering by small-scale magnetic\nfield irregularities. Next, we perform a numerical simulation of a cosmic ray\npenetration into an interplanetary magnetic flux rope by adding small-scale\nmagnetic field irregularities. This simulation shows that a cosmic ray density\ndistribution is greatly different from that deduced from a guiding center\napproximation because of the effect of the finite Larmor radius and magnetic\nfield irregularities for the case of a moderate to large Larmor radius compared\nto the flux rope radius.", "category": "astro-ph_EP" }, { "text": "Rotation periods of late-type dwarf stars from time-series\n high-resolution spectroscopy of chromospheric indicators: We determine rotation periods of a sample of 48 late F-type to mid-M dwarf\nstars using time-series high-resolution spectroscopy of the Ca II H&K and\nH-alpha chromospheric activity indicators. We find good agreement between the\nrotation periods obtained from each of these two indicators. An empirical\nrelationship between the level of chromospheric emission measured by log (R'HK)\nand the spectroscopic rotation periods is reported. This relation is largely\nindependent of the spectral type and the metallicity of the stars and can be\nused to make a reliable prediction of rotation periods for late K to mid-M\ndwarfs with low levels of activity. For some stars in the sample, the measured\nspectroscopic rotation periods coincide, or are very close, to the orbital\nperiods of postulated planets. In such cases, further studies are needed to\nclarify whether the associated periodic radial velocity signals reveal the\nexistence of planets or are due to magnetic activity.", "category": "astro-ph_EP" }, { "text": "Is Extraterrestrial Life Suppressed on Subsurface Ocean Worlds due to\n the Paucity of Bioessential Elements?: The availability of bioessential elements for \"life as we know it\", such as\nphosphorus (P) or possibly molybdenum (Mo), is expected to restrict the\nbiological productivity of extraterrestrial biospheres. Here, we consider\nworlds with subsurface oceans and model the dissolved concentrations of\nbioessential elements. In particular, we focus on the sources and sinks of P\n(available as phosphates), and find that the average steady-state oceanic\nconcentration of P is likely to be lower than the corresponding value on Earth\nby a few orders of magnitude, provided that the oceans are alkaline and possess\nhydrothermal activity. While our result does not eliminate the prospects of\nlife on subsurface worlds like Enceladus, it suggests that the putative\nbiospheres might be oligotrophic, and perhaps harder to detect. Along these\nlines, potential biospheres in the clouds of Venus may end up being limited by\nthe availability of Mo. We also point out the possibility that stellar\nspectroscopy can be used to deduce potential constraints on the availability of\nbioessential elements on planets and moons.", "category": "astro-ph_EP" }, { "text": "The Next Generation Transit Survey (NGTS): We describe the Next Generation Transit Survey (NGTS), which is a\nground-based project searching for transiting exoplanets orbiting bright stars.\nNGTS builds on the legacy of previous surveys, most notably WASP, and is\ndesigned to achieve higher photometric precision and hence find smaller planets\nthan have previously been detected from the ground. It also operates in red\nlight, maximising sensitivity to late K and early M dwarf stars. The survey\nspecifications call for photometric precision of 0.1 per cent in red light over\nan instantaneous field of view of 100 square degrees, enabling the detection of\nNeptune-sized exoplanets around Sun-like stars and super-Earths around M\ndwarfs. The survey is carried out with a purpose-built facility at Cerro\nParanal, Chile, which is the premier site of the European Southern Observatory\n(ESO). An array of twelve 20cm f/2.8 telescopes fitted with back-illuminated\ndeep-depletion CCD cameras are used to survey fields intensively at\nintermediate Galactic latitudes. The instrument is also ideally suited to\nground-based photometric follow-up of exoplanet candidates from space\ntelescopes such as TESS, Gaia and PLATO. We present observations that combine\nprecise autoguiding and the superb observing conditions at Paranal to provide\nroutine photometric precision of 0.1 per cent in 1 hour for stars with I-band\nmagnitudes brighter than 13. We describe the instrument and data analysis\nmethods as well as the status of the survey, which achieved first light in 2015\nand began full survey operations in 2016. NGTS data will be made publicly\navailable through the ESO archive.", "category": "astro-ph_EP" }, { "text": "Potential Backup Targets for Comet Interceptor: Comet Interceptor is an ESA F-class mission expected to launch in 2028 on the\nsame launcher as ESA's ARIEL mission. Comet Interceptor's science payload\nconsists of three spacecraft, a primary spacecraft that will carry two smaller\nprobes to be released at the target. The three spacecraft will fly-by the\ntarget along different chords, providing multiple simultaneous perspectives of\nthe comet nucleus and its environment. Each of the spacecraft will be equipped\nwith different but complementary instrument suites designed to study the far\nand near coma environment and surface of a comet or interstellar object (ISO).\nThe primary spacecraft will perform a fly-by at ~1000 km from the target. The\ntwo smaller probes will travel deeper into the coma, closer to the nucleus. The\nmission is being designed and launched without a specific comet designated as\nits main target. Comet Interceptor will travel to the Sun-Earth L2 Lagrangian\npoint with ARIEL and wait in hibernation until a suitable long-period comet\n(LPC) is found that will come close enough to the Sun for the spacecraft to\nmaneuver to an encounter trajectory. To prepare for all eventualities, the\nscience team has assembled a preliminary set of backup targets from the known\nJupiter family comets, where a suitable fly-by trajectory can be achieved\nduring the nominal mission timeline (including the possibility of some launch\ndelay). To better prioritize this list, we are releasing our potential backup\ntargets in order to solicit the planetary community's help with observations of\nthese objects over future apparitions and to encourage publication of archival\ndata on these objects.", "category": "astro-ph_EP" }, { "text": "An Analytic Method to determine Habitable Zones for S-Type Planetary\n Orbits in Binary Star Systems: With more and more extrasolar planets discovered in and around binary star\nsystems, questions concerning the determination of the classical Habitable Zone\narise. Do the radiative and gravitational perturbations of the second star\ninfluence the extent of the Habitable Zone significantly, or is it sufficient\nto consider the host-star only? In this article we investigate the implications\nof stellar companions with different spectral types on the insolation a\nterrestrial planet receives orbiting a Sun-like primary. We present time\nindependent analytical estimates and compare these to insolation statistics\ngained via high precision numerical orbit calculations. Results suggest a\nstrong dependence of permanent habitability on the binary's eccentricity, as\nwell as a possible extension of Habitable Zones towards the secondary in close\nbinary systems.", "category": "astro-ph_EP" } ]