http://arxiv.org/abs/2305.13489

Enceladus’ plume consists mainly of a mixture of water vapor and solid ice particles that may originate from a subsurface ocean. The physical processes underlying Enceladus’ plume particle dynamics are still being debated, and quantifying the particles’ size distribution and launch velocities can help constrain these processes. Cassini’s Visual and Infrared Mapping Spectrometer (VIMS) observed the Enceladus plume over a wavelength range of 0.9 micron to 5.0 microns for a significant fraction of Enceladus’ orbital period on three dates in the summer of 2017. We find that the relative brightness of the plume on these different dates varies with wavelength, implying that the particle size distribution in the plume changes over time. These observations also enable us to study how the particles’ launch velocities vary with time and observed wavelength. We find that the typical launch velocity of particles remains between 140 m/s and 148 m/s at wavelengths between 1.2 microns and 3.7 microns. This may not be consistent with prior models where particles are only accelerated by interactions with the vent walls and gas, and could imply that mutual particle collisions close to the vent are more important than previously recognized.

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H. Sharma, M. Hedman and S. Vahidinia
Wed, 24 May 23
81/81

Comments: 13 pages, 8 figures, accepted for publication in PSJ

http://arxiv.org/abs/2305.13234

In this work we present, for the first time, infrared spectra of Titan from the Spitzer Space Telescope ($2004-2009$). The data are from both the short wavelength-low resolution (SL, $5.13-14.29\mathrm{\mu m}, R\sim60-127$) and short wavelength-high resolution channels (SH, $9.89 – 19.51\mathrm{\mu m}, R\sim600$) showing the emissions of CH${4}$, C${2}$H${2}$, C${2}$H${4}$, C${2}$H${6}$, C${3}$H${4}$, C${3}$H${6}$, C${3}$H${8}$, C${4}$H${2}$, HCN, HC${3}$N, and CO${2}$. We compare the results obtained for Titan from Spitzer to those of the Cassini Composite Infrared Spectrometer (CIRS) for the same time period, focusing on the $16.35-19.35\mathrm{\mu m}$ wavelength range observed by the SH channel but impacted by higher noise levels in CIRS observations. We use the SH data to provide estimated haze extinction cross-sections for the $16.67-17.54\mathrm{\mu m}$ range that are missing in previous studies. We conclude by identifying spectral features in the $16.35-19.35\mathrm{\mu m}$ wavelength range, including two prominent emission features at 16.39 and $17.35\mathrm{\mu m}$, that could be analyzed further through upcoming James Webb Space Telescope Cycle 1 observations with the Mid-Infrared Instrument ($5.0-28.3\mathrm{\mu m}, R\sim1500-3500$). We also highlight gaps in current spectroscopic knowledge of molecular bands, including candidate trace species such as C${60}$ and detected trace species such as C${3}$H${6}$, that could be addressed by theoretical and laboratory study.

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B. Coy, C. Nixon, N. Rowe-Gurney, et. al.
Tue, 23 May 23
77/77

Comments: Accepted to Planetary Science Journal April 28, 2023

http://arxiv.org/abs/2305.11297

Kilometre-sized planetesimals form from pebbles of a range of sizes. We present the first simulations of the streaming instability that begin with a realistic, peaked size distribution, as expected from grain growth predictions. Our 3D numerical simulations directly form planetesimals via the gravitational collapse of pebble clouds. Models with multiple grain sizes show spatially distinct dust populations. The smallest grains in the size distribution do not participate in the formation of filaments or the planetesimals that are formed by the remaining ~80% of the dust mass. This implies a size cutoff for pebbles incorporated into asteroids and comets. Observations cannot resolve this dust clumping. However, we show that clumping, combined with optical depth effects, can cause significant underestimates of the dust mass, with 20%-80% more dust being present even at moderate optical depths if the streaming instability is active.

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J. Rucska and J. Wadsley
Mon, 22 May 23
13/60

Comments: Submitted to MNRAS, 16 pages, 10 figures

http://arxiv.org/abs/2305.11359

While various indirect methods are used to detect exoplanets, one of the most effective and accurate methods is the transit method, which measures the brightness of a given star for periodic dips when an exoplanet is passing in front of the parent star. For systems with multiple transiting planets, the gravitational perturbations between planets affect their transit times. The difference in transit times allows a measurement of the planet masses and orbital eccentricities. These parameters help speculating on the formation, evolution and stability of the system. Using Transit Timing Variations (TTVs), we measure the masses and eccentricities of two planets orbiting K2-21, a relatively bright K7 dwarf star. These two planets exhibit measurable TTVs, have orbital periods of about 9.32 days and 15.50 days, respectively, and a period ratio of about 1.66, which is relatively near to the 5:3 mean motion resonance. We report that the inner and outer planets in the K2-21 system have properties consistent with the presence of a hydrogen and helium dominated atmospheres, as we estimate their masses to be 1.59^{+0.52}{-0.44} M_E and 3.88^{+1.22}{-1.07} M_E and densities of 0.22^{+0.05}{-0.04} rho_E and 0.34^{+0.08}{-0.06} rho_E, respectively (M_E and rho_E are the mass and density of Earth, respectively). Our results show that the inner planet is less dense than the outer planet; one more counter-intuitive exoplanetary system such as Kepler-105, LTT 1445, TOI-175 and Kepler-279 systems.

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M. Moutamid, K. Stevenson, B. Quarles, et. al.
Mon, 22 May 23
19/60

Comments: N/A

http://arxiv.org/abs/2305.11336

Circumstellar discs likely have a short window when they are self-gravitating and prone to the effects of disc instability, but during this time the seeds of planet formation can be sown. It has long been argued that disc fragmentation can form large gas giant planets at wide orbital separations, but its place in the planet formation paradigm is hindered by a tendency to form especially large gas giants or brown dwarfs. We instead suggest that planet formation can occur early in massive discs, through the gravitational collapse of dust which can form the seeds of giant planets. This is different from the usual picture of self-gravitating discs, in which planet formation is considered through the gravitational collapse of the gas disc into a gas giant precursor. It is familiar in the sense that the core is formed first, and gas is accreted thereafter, as is the case in the core accretion scenario. However, by forming a $\sim 1 M_{\oplus}$ seed from the gravitational collapse of dust within a self-gravitating disc there exists the potential to overcome traditional growth barriers and form a planet within a few times $10^5$ years. The accretion of pebbles is most efficient with centimetre-sized dust, but the accretion of millimetre sizes can also result in formation within a Myr. Thus, if dust can grow to these sizes, planetary seeds formed within very young, massive discs could drastically reduce the timescale of planet formation and potentially explain the observed ring and gap structures in young discs.

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H. Baehr
Mon, 22 May 23
46/60

Comments: MNRAS accepted. 15 pages, 12 figures

http://arxiv.org/abs/2305.11412

We calculate the upper bounds of the population of theoretically stable Centaur orbits between Uranus and Neptune. These small bodies are on low-eccentricity, low-inclination orbits in two specific bands of semi-major axis, centred at $\sim$24.6 au and $\sim$25.6 au. They exhibit unusually long Gyr-stable lifetimes in previously published numerical integrations, orders of magnitude longer than that of a typical Centaur. Despite the increased breadth and depth of recent solar system surveys, no such objects have been found. Using the Outer Solar System Origins Survey (OSSOS) survey simulator to calculate the detection efficiency for these objects in an ensemble of fully characterised surveys, we determine that a population of 72 stable Centaurs with absolute magnitude $H_{r}\leq10$ ($95\%$ confidence upper limit) could remain undetected. The upcoming Legacy Survey of Space and Time (LSST) will be able to detect this entire intrinsic population due to its complete coverage of the ecliptic plane. If detected, these objects will be interesting dynamically-accessible mission targets — especially as comparison of the stable Centaur orbital phase space to the outcomes of several modern planetary migration simulations suggests that these objects could be close to primordial in nature.

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R. Dorsey, M. Bannister, S. Lawler, et. al.
Mon, 22 May 23
48/60

Comments: Accepted to PSJ. 8 pages, 3 figures. Comments welcome

http://arxiv.org/abs/2305.11698

The term $\alpha$-meteoroid' was introduced to describe a group of micrometeoroids with certain dynamical properties, which -- alongside the group of the $\beta$-meteoroids -- had been identified by the first generation of reliable in-situ dust detectors in interplanetary space. In recent years, use of the term $\alpha$-meteoroid has become more frequent again, under a subtly but crucially altered definition. This work shall bring attention to the discrepancy between the term's original and newly established meaning, and spotlight the now-overlooked group of particles that the term used to describe. We review past and present pertinent literature around the term $\alpha$-meteoroid, and assess the dynamics of the originally referred-to particles with respect to possible sources, showing that their formation is the expected consequence of collisional grinding of the zodiacal cloud at short heliocentric distances. The abundance of the original $\alpha$-meteoroids, which are essentiallybound $\beta$-meteoroids’, makes them relevant to all in-situ dust experiments in the inner solar system. Due to the change of the term’s meaning, however, they are not considered by contemporary studies. The characterization of this particle population could elucidate the processing of the innermost zodiacal cloud, and should thus be objective of upcoming in-situ dust experiments. The attained ambiguity of the term $\alpha$-meteoroid is not easily resolved, warranting great care and clarity going forward.

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M. Sommer
Mon, 22 May 23
59/60

Comments: N/A

http://arxiv.org/abs/2305.11071

Individual vibrational band spectroscopy presents an opportunity to examine exoplanet atmospheres in detail by distinguishing where the vibrational state populations of molecules differ from the current assumption of a Boltzmann distribution. Here, retrieving vibrational bands of OH in exoplanet atmospheres is explored using the hot Jupiter WASP-33b as an example. We simulate low-resolution spectroscopic data for observations with the JWST’s NIRSpec instrument and use high resolution observational data obtained from the Subaru InfraRed Doppler instrument (IRD). Vibrational band-specific OH cross section sets are constructed and used in retrievals on the (simulated) low and (real) high resolution data. Low resolution observations are simulated for two WASP-33b emission scenarios: under the assumption of local thermal equilibrium (LTE) and a toy non-LTE model for vibrational excitation of selected bands. We show that mixing ratios for individual bands can be retrieved with sufficient precision to allow the vibrational population distributions of the forward models to be reconstructed. A simple fit for the Boltzmann distribution in the LTE case shows that the vibrational temperature is recoverable in this manner. For high resolution, cross-correlation applications, we apply the individual vibrational band analysis to an IRD spectrum of WASP-33b, applying an ‘un-peeling’ technique. Individual detection significances for the two strongest bands are shown to be in line with Boltzmann distributed vibrational state populations consistent with the effective temperature of the WASP-33b atmosphere reported previously. We show the viability of this approach for analysing the individual vibrational state populations behind observed and simulated spectra including reconstructing state population distributions.

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S. Wright, S. Nugroho, M. Brogi, et. al.
Fri, 19 May 23
14/46

Comments: Submitted for publication in AJ

http://arxiv.org/abs/2305.10414

Recently, the first JWST measurement of thermal emission from a rocky exoplanet was reported. The inferred dayside brightness temperature of TRAPPIST-1 b at 15 $\mu$m is consistent with the planet having no atmosphere and therefore no mechanism by which to circulate heat to its nightside. In this Letter, we compare the measured secondary eclipse depth of TRAPPIST-1 b to predictions from a suite of self-consistent radiative-convective equilibrium models in order to quantify the maximum atmospheric thickness consistent with the observation. We find that plausible atmospheres (i.e., those that contain at least 100 ppm CO$_2$) with surface pressures greater than 0.01 bar (0.1 bar) are ruled out at 1$\sigma$ (3$\sigma$), regardless of the choice of background atmosphere. Thicker atmospheres of up to 10 bar (100 bar) at 1$\sigma$ (3$\sigma$) are only allowed if the atmosphere lacks any strong absorbers across the mid-IR wavelength range, a scenario that we deem unlikely. We additionally model the emission spectra for bare-rock planets of various compositions. We find that a variety of silicate surfaces match the measured eclipse depth to within 1$\sigma$, and the best-fit grey albedo is $0.02 \pm 0.11$. We conclude that planned secondary eclipse observations at 12.8 $\mu$m will serve to validate the high observed brightness temperature of TRAPPIST-1 b, but are unlikely to further distinguish among the consistent atmospheric and bare-rock scenarios.

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J. Ih, E. Kempton, E. Whittaker, et. al.
Thu, 18 May 23
48/67

Comments: 8 pages, 4 figures, submitted to ApJL

http://arxiv.org/abs/2305.09177

Hot Jupiters have been perceived as loners devoid of planetary companions in close orbital proximity. However, recent discoveries based on space-borne precise photometry have revealed that at least some fraction of giant planets coexists with low-mass planets in compact orbital architectures. We report detecting a 1.446-day transit-like signal in the photometric time series acquired with the Transiting Exoplanet Survey Satellite (TESS) for the WASP-84 system, which is known to contain a hot Jupiter on a circular 8.5-day orbit. The planet was validated based on TESS photometry, and its signal was distilled in radial velocity measurements. The joint analysis of photometric and Doppler data resulted in a multi-planetary model of the system. With a mass of $15\, M_{\oplus}$, radius of $2\, R_{\oplus}$, and orbital distance of 0.024 au, the new planet WASP-84 c was classified as a hot super-Earth with the equilibrium temperature of 1300 K. A growing number of companions to hot Jupiters indicates that a non-negligible part of them must have formed under a quiescent scenario such as disc migration or in-situ formation.

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G. Maciejewski, J. Golonka, W. Łoboda, et. al.
Wed, 17 May 23
2/67

Comments: submitted to MNRAS Letters on 2023 Apr 05

http://arxiv.org/abs/2305.09093

A planetary embryo embedded in a gaseous disc can grow by pebble accretion while subjected to a gravitational force from the disc that changes its orbital elements. Usually, that force is considered to arise from the Lindblad and corotation resonances with the embryo. However, more important contributions exist for low-mass planets. Radiative thermal diffusion in the vicinity of embryos yields an additional contribution to the disc’s force that damps the eccentricity and inclination much more vigorously than the resonant interaction with the disc, and that in general induces fast inward migration. In addition, the irradiation of the disc by a hot embryo gives rise to an additional contribution that excites eccentricity and inclination, and induces outward migration. Which of the two contributions dominates depends on the embryo’s luminosity. We assess the importance of these contributions (termed thermal forces) on the dynamics and growth of a set of pebble-accreting embryos initially of Martian mass, by means of N-body simulations that include analytic expressions for the disc’s force. We find very different outcomes for the embryos subjected to thermal forces and those subjected only to resonant forces. Importantly, we find that the median final mass of the embryos subjected to thermal forces is nearly independent of the metallicity, whereas this mass roughly scales with the metallicity when they are subjected only to resonant forces. These results can be explained by the strong damping of eccentricity and inclination at low metallicity, which enhances the embryos’ accretion efficiency.

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S. Cornejo, F. Masset and F. Sánchez-Salcedo
Wed, 17 May 23
34/67

Comments: Accepted for publication in MNRAS

http://arxiv.org/abs/2305.09654

Photochemical hazes are expected to form in hot Jupiter atmospheres and may explain the strong scattering slopes and muted spectral features observed in the transmission spectra of many hot Jupiters. Absorption and scattering by photochemical hazes have the potential to drastically alter temperature structure and atmospheric circulation of these planets but have previously been neglected in general circulation models (GCMs). We present GCM simulations of hot Jupiter HD 189733b that include photochemical hazes as a radiatively active tracer fully coupled to atmospheric dynamics. The influence of haze radiative feedback strongly depends on the assumed haze optical properties. For soot hazes, two distinct thermal inversions form, separated by a local temperature minimum around 10$^{-5}$ bar caused by upwelling on the dayside mixing air with low haze abundance upwards. The equatorial jet broadens and slows down. The horizontal distribution of hazes remains relatively similar to simulations with radiatively passive tracers. For Titan-type hazes, the equatorial jet accelerates and extends to much lower pressures, resulting in a dramatically different 3D distribution of hazes compared to radiatively passive or soot hazes. Further experimental and observational studies to constrain the optical properties of photochemical hazes will therefore be crucial for understanding the role of hazes in exoplanet atmospheres. In the dayside emission spectrum, for both types of hazes the amplitude of near-infrared features is reduced, while the emitted flux at longer wavelengths ($>$4 $\mu$m) increases. Haze radiative feedback leads to increased phase curve amplitudes in many infrared wavelength regions, mostly due to stronger dayside emission.

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M. Steinrueck, T. Koskinen, P. Lavvas, et. al.
Wed, 17 May 23
48/67

Comments: 31 pages, 18 figures, accepted for publication in ApJ

http://arxiv.org/abs/2305.07864

We study a Jupiter-mass planet formation for the first time in radiative magneto-hydrodynamics (MHD) simulations and compare it with pure hydrodynamical simulations, as well as to different isothermal configurations. We found that the meridional circulation is the same in every setup. The planetary spiral wakes drive a vertical stirring inside the protoplanetary disc and the encounter with these shock fronts also helps in delivering gas vertically onto the Hill-sphere. The accretion dynamics are unchanged: the planet accretes vertically, and there is outflow in the midplane regions inside the Hill-sphere. We determined the effective $\alpha$-viscosity generated in the disc by the various angular momentum loss mechanisms, which showed that magnetic fields produce high turbulence in the ideal MHD limit, that grows from $\alpha \sim 10^{-2.5}$ up to $\sim 10^{-1.5}$ after the planet spirals develop. In the HD simulations, the planetary spirals contribute to $\alpha \sim 10^{-3}$, making this a very important angular momentum transport mechanism. Due to the various $\alpha$ values in the different setups, the gap opening is different in each case. In the radiative MHD setups, the high turbulent viscosity prevents gap opening, leading to a higher Hill mass, and no clear dust trapping regions. While the Hill accretion rate is $10^{-6} \rm{M_{Jup}/yr}$ in all setups, the accretion variability is orders of magnitude higher in radiative runs than in isothermal ones. Finally, with higher-resolution runs, the magneto-rotational instability started to be resolved, changing the effective viscosity and increasing the heating in the disc.

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M. Cilibrasi, M. Flock and J. Szulágyi
Tue, 16 May 23
1/83

Comments: N/A

http://arxiv.org/abs/2305.08610

Transmission spectroscopy is one of the most successful methods of learning about exoplanet atmospheres. The process of retrievals using transmission spectroscopy consists of creating numerous forward models and comparing them to observations to solve the inverse problem of constraining the atmospheric properties of exoplanets. We explore the impact of one simplifying assumption commonly employed by forward models of transiting exoplanets: namely that the planet can be treated as an isolated, non-rotating spherical body. The centrifugal acceleration due to a planet’s rotation opposes the gravitational pull on a planet’s atmosphere and increases its scale height. Conventional forward models used for retrievals generally do not include this effect. We find that atmospheric retrievals produce significantly different results for close-in planets with low gravity when this assumption is removed, e.g., differences between true and retrieved values of gas abundances greater than 1$\sigma$ for a simulated planet analogous to WASP-19 b. We recommend that the correction to the atmospheric scale height due to this effect be taken into account for the analysis of high precision transmission spectra of exoplanets in the future, most immediately JWST Cycle 1 targets WASP-19 b and WASP-121 b.

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A. Banerjee, J. Barstow, C. Haswell, et. al.
Tue, 16 May 23
3/83

Comments: 5 pages, 4 figures, accepted for publication in MNRAS Letters

http://arxiv.org/abs/2305.07753

We present the dayside thermal emission spectrum of WASP-77Ab from 2.8 — 5.2 $\mu$m as observed with the NIRSpec instrument on the James Webb Space Telescope (JWST). WASP-77Ab was previously found to have a sub-solar metallicity and a solar carbon-to-oxygen (C/O) ratio from H$2$O and CO absorption lines detected using high-resolution spectroscopy. By performing atmospheric retrievals on the JWST spectrum assuming chemical equilibrium, we find a sub-solar metallicity [M/H]=$-0.91^{+0.24}{-0.16}$ and C/O ratio $0.36^{+0.10}_{-0.09}$. We identify H$_2$O and CO and constrain their abundances, and we find no CO$_2$ in the spectrum. The JWST and high-resolution spectroscopy results agree within $\sim1\sigma$ for the metallicity and within 1.8$\sigma$ for the C/O ratio. However, our results fit less well in the picture painted by the shorter wavelength spectrum measured by HST WFC3. Comparing the JWST thermal emission spectra of WASP-77Ab and HD 149026b shows that both hot Jupiters have nearly identical brightness temperatures in the near-infrared, but distinctly different atmospheric compositions. Our results reaffirm high-resolution spectroscopy as a powerful and reliable method to measure molecular abundances. Our results also highlight the incredible diversity of hot Jupiter atmospheric compositions.

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P. August, J. Bean, M. Zhang, et. al.
Tue, 16 May 23
57/83

Comments: Submitted to ApJL

http://arxiv.org/abs/2305.08792

In the context of a recently proposed contact-binary model of the Kreutz system, all its members are products of the process of cascading fragmentation of the two lobes of the parent, Aristotle’s comet of 372 BC. This process presumably began with the lobes’ separation from each other near aphelion. However, not every object in a Kreutz-like orbit is a Kreutz sungrazer. Any surviving sungrazer that had split off from the progenitor before the lobes separated, as well as its surviving fragments born in any subsequent tidal or nontidal event, are by definition not members of the Kreutz system. Yet, as parts of the same progenitor, they belong — as do all Kreutz sungrazers — to a broader assemblage of related objects, which I refer to as a super-Kreutz system. After estimating the ratio of the number of super-Kreutz members to nonmembers among potential historical sungrazers, I generate representative extended pedigree charts for both the Kreutz system and super-Kreutz system. While the fragmentation paths and relationships among the individual sungrazers or potential sungrazers in the two charts are (with at most a few exceptions) arbitrary, the purpose of the exercise is to suggest that the Kreutz system proper could in effect represent an ultimate deagglomeration stage of the super-Kreutz system.

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Z. Sekanina
Tue, 16 May 23
65/83

Comments: 15 pages, 3 figures, 4 tables

http://arxiv.org/abs/2305.08253

The traditional paradigm of viscosity-dominated evolution of protoplanetary discs has been recently challenged by magnetized disc winds. However, distinguishing wind-driven and turbulence-driven accretion through observations has been difficult. In this study, we present a novel approach to identifying their separate contribution to angular momentum transport by studying the gap and ring morphology of planet-forming discs in the ALMA continuum. We model the gap-opening process of planets in discs with both viscous evolution and wind-driven accretion by 2D multi-fluid hydrodynamical simulations. Our results show that gap-opening planets in wind-driven accreting discs generate characteristic substructures that differ from those in purely viscous discs. Specifically, we demonstrate that discs, where wind-driven accretion dominates the production of substructures, exhibit significant asymmetries. Based on the diverse outputs of mock images in the ALMA continuum, we roughly divide the planet-induced features into four regimes (moderate-viscosity dominated, moderate-wind dominated, strong-viscosity dominated, inviscid). The classification of these regimes sets up a potential method to constrain the strength of magnetized disc wind and viscosity based on the observed gap and ring morphology. We discuss the asymmetry feature in our mock images and its potential manifestation in ALMA observations.

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Y. Wu, Y. Chen, H. Jiang, et. al.
Tue, 16 May 23
67/83

Comments: 11 pages, 6 figures, resubmitted to MNRAS, version addressing referee’s comments. Welcome any comments and suggestions!

http://arxiv.org/abs/2305.07190

The zeta ring is the innermost component of the Uranian ring system. It is of scientific interest because its morphology changed significantly between the Voyager 2 encounter in 1986 and subsequent Earth-based observations around 2007. It is also of practical interest because some Uranus mission concepts have the spacecraft pass through the inner flank of this ring. Recent re-examinations of the Voyager 2 images have revealed additional information about this ring that provide a more complete picture of the ring’s radial brightness profile and phase function. These data reveal that this ring’s brightness varies with phase angle in a manner similar to other tenuous rings, consistent with it being composed primarily of sub-millimeter-sized particles. The total cross section of particles within this ring can also be estimated from these data, but translating that number into the actual risk to a spacecraft flying through this region depends on a number of model-dependent parameters. Fortunately, comparisons with Saturn’s G and D rings allows the zeta-ring’s particle number density to be compared with regions previously encountered by the Voyager and Cassini spacecraft. Finally, these data indicate that the observed changes in the zeta-ring’s structure between 1986 and 2007 are primarily due to a substantial increase in the amount of dust at distances between 38,000 km and 40,000 km from Uranus’ center.

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M. Hedman, I. Regan, T. Becker, et. al.
Mon, 15 May 23
23/53

Comments: 28 Pages, 12 Figures, Accepted for publication in PSJ

http://arxiv.org/abs/2305.06950

We present the discovery and confirmation of a transiting hot, bloated Super-Neptune using photometry from TESS and LCOGT and radial velocity measurements from HARPS. The host star TOI-2498 is a V = 11.2, G-type (T${eff}$ = 5905 $\pm$ 12K) solar-like star with a mass of 1.12 $\pm$ 0.02 M${\odot}$ and a radius of 1.26 $\pm$ 0.04 R${\odot}$. The planet, TOI-2498 b, orbits the star with a period of 3.7 days, has a radius of 6.1 $\pm$ 0.3 R${\oplus}$, and a mass of 35 $\pm$ 4 M$_{\oplus}$. This results in a density of 0.86 $\pm$ 0.25 g cm$^{-3}$. TOI-2498 b resides on the edge of the Neptune desert; a region of mass-period parameter space in which there appears to be a dearth of planets. Therefore TOI-2498 b is an interesting case to study to further understand the origins and boundaries of the Neptune desert. Through modelling the evaporation history, we determine that over its $\sim$3.6 Gyr lifespan, TOI-2498 b has likely reduced from a Saturn sized planet to its current radius through photoevaporation. Moreover, TOI-2498 b is a potential candidate for future atmospheric studies searching for species like water or sodium in the optical using high-resolution, and for carbon based molecules in the infra-red using JWST.

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G. Frame, D. Armstrong, H. Cegla, et. al.
Fri, 12 May 23
1/53

Comments: 13 pages, 11 figures, accepted for publication in MNRAS

http://arxiv.org/abs/2305.06787

Neptune’s tropospheric winds are among the most intense in the Solar System, but the dynamical mechanisms that produce them remain uncertain. Measuring wind speeds at different pressure levels may help understand the atmospheric dynamics of the planet. The goal of this work is to directly measure winds in Neptune’s stratosphere with ALMA Doppler spectroscopy. We derived the Doppler lineshift maps of Neptune at the CO(3-2) and HCN(4-3) lines at 345.8 GHz ($\lambda$~0.87 mm) and 354.5 GHz (0.85 mm), respectively. For that, we used spectra obtained with ALMA in 2016 and recorded with a spatial resolution of ~0.37″ on Neptune’s 2.24″ disk. After subtracting the planet solid rotation, we inferred the contribution of zonal winds to the measured Doppler lineshifts at the CO and HCN lines. We developed an MCMC-based retrieval methodology to constrain the latitudinal distribution of wind speeds. We find that CO(3-2) and HCN(4-3) lines probe the stratosphere of Neptune at pressures of $2^{+12}{-1.8}$ mbar and $0.4^{+0.5}{-0.3}$ mbar, respectively. The zonal winds at these altitudes are less intense than the tropospheric winds based on cloud tracking from Voyager observations. We find equatorial retrograde (westward) winds of $-180^{+70}{-60}$ m/s for CO, and $-190^{+90}{-70}$ m/s for HCN. Wind intensity decreases towards mid-latitudes, and wind speeds at 40$^\circ$S are $-90^{+50}{-60}$ m/s for CO, and $-40^{+60}{-80}$ m/s for HCN. Wind speeds become 0 m/s at about 50$^\circ$S, and we find that the circulation reverses to a prograde jet southwards of 60$^\circ$S. Overall, our direct stratospheric wind measurements match previous estimates from stellar occultation profiles and expectations based on thermal wind equilibrium. These are the first direct Doppler wind measurements performed on the Icy Giants, opening a new method to study and monitor their stratospheric dynamics.

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&. Carrión-González, R. Moreno, E. Lellouch, et. al.
Fri, 12 May 23
43/53

Comments: Accepted for publication in A&A Letters on 10/05/2023. 8 pages, 1 Table, 5 Figures

http://arxiv.org/abs/2305.05697

The near-infrared transmission spectrum of the warm sub-Neptune exoplanet GJ 1214 b has been observed to be flat and featureless, implying a high metallicity atmosphere with abundant aerosols. Recent JWST MIRI LRS observations of a phase curve of GJ 1214 b showed that its transmission spectrum is flat out into the mid-infrared. In this paper, we use the combined near- and mid-infrared transmission spectrum of GJ 1214 b to constrain its atmospheric composition and aerosol properties. We generate a grid of photochemical haze models using an aerosol microphysics code for a number of background atmospheres spanning metallicities from 100 to 1000 $\times$ solar, as well as a steam atmosphere scenario. The flatness of the combined data set largely rules out atmospheric metallicities $\leq$300 $\times$ solar due to their large corresponding molecular feature amplitudes, preferring values $\geq$1000 $\times$ solar and column haze production rates $\geq$10$^{-10}$ g cm$^{-2}$ s$^{-1}$. The steam atmosphere scenario with similarly high haze production rates also exhibit sufficiently small molecular features to be consistent with the transmission spectrum. These compositions imply that atmospheric mean molecular weights $\geq$15 g mol$^{-1}$ are needed to fit the data. Our results suggest that haze production is highly efficient on GJ 1214 b and could involve non-hydrocarbon, non-nitrogen haze precursors. Further characterization of GJ 1214 b’s atmosphere would likely require multiple transits and eclipses using JWST across the near and mid-infrared, potentially complemented by groundbased high resolution transmission spectroscopy.

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P. Gao, A. Piette, M. Steinrueck, et. al.
Thu, 11 May 23
15/55

Comments: 21 pages, 10 figures, 4 tables. Accepted for publication by ApJ

http://arxiv.org/abs/2305.05700

Context. Upcoming space missions will provide us with surface-resolved NEA reflectance spectra. Neural networks are useful tools for analysing reflectance spectra and determining material composition with high precision and low processing time. Aims. We applied neural-network models on disk-resolved spectra of the Eros and Itokawa asteroids observed by the NEAR Shoemaker and Hayabusa spacecraft. With this approach, the mineral variations or intensity of space weathering can be mapped. Methods. We tested two types of convolutional neural networks. The first one was trained using asteroid reflectance spectra with known taxonomy classes. The other one used silicate reflectance spectra with assigned mineral abundances and compositions. Results. The reliability of the classification model depends on the resolution of reflectance spectra. Typical F1 score and Cohen’s ${\kappa}_C$ values decrease from about 0.90 for high-resolution spectra to about 0.70 for low-resolution spectra. The predicted silicate composition does not strongly depend on spectrum resolution and coverage of the 2${\mu}$m band of pyroxene. The typical root mean square error is between 6 and 10 percentage points. For the Eros and Itokawa asteroids, the predicted taxonomy classes favour the S-type and the predicted surface compositions are homogeneous and correspond to the composition of L/LL and LL ordinary chondrites, respectively. On the Itokawa surface, the model identified fresh spots that were connected with craters or coarse-grain areas. Conclusions. The neural network models trained with measured spectra of asteroids and silicate samples are suitable for deriving surface silicate mineralogy with a reasonable level of accuracy. The predicted surface mineralogy is comparable to the mineralogy of returned samples measured in the laboratory. Moreover, the taxonomical predictions can point out locations of fresher areas.

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D. Korda, T. Kohout, K. Flanderová, et. al.
Thu, 11 May 23
37/55

Comments: 14 pages, 12 figures, 4 tables; plus appendices

http://arxiv.org/abs/2305.06240

There are no planets intermediate in size between Earth and Neptune in our Solar System, yet these objects are found around a substantial fraction of other stars. Population statistics show that close-in planets in this size range bifurcate into two classes based on their radii. It is hypothesized that the group with larger radii (referred to as “sub-Neptunes”) is distinguished by having hydrogen-dominated atmospheres that are a few percent of the total mass of the planets. GJ 1214b is an archetype sub-Neptune that has been observed extensively using transmission spectroscopy to test this hypothesis. However, the measured spectra are featureless, and thus inconclusive, due to the presence of high-altitude aerosols in the planet’s atmosphere. Here we report a spectroscopic thermal phase curve of GJ 1214b obtained with JWST in the mid-infrared. The dayside and nightside spectra (average brightness temperatures of 553 $\pm$ 9 and 437 $\pm$ 19 K, respectively) each show >3$\sigma$ evidence of absorption features, with H$_2$O as the most likely cause in both. The measured global thermal emission implies that GJ 1214b’s Bond albedo is 0.51 $\pm$ 0.06. Comparison between the spectroscopic phase curve data and three-dimensional models of GJ 1214b reveal a planet with a high metallicity atmosphere blanketed by a thick and highly reflective layer of clouds or haze.

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E. Kempton, M. Zhang, J. Bean, et. al.
Thu, 11 May 23
50/55

Comments: Published online in Nature on May 10, 2023

http://arxiv.org/abs/2305.06206

A new generation of observatories is enabling detailed study of exoplanetary atmospheres and the diversity of alien climates, allowing us to seek evidence for extraterrestrial biological and geological processes. Now is therefore the time to identify the most unique planets to be characterised with these instruments. In this context, we report on the discovery and validation of TOI-715 b, a $R_{\rm b}=1.55\pm 0.06\rm R_{\oplus}$ planet orbiting its nearby ($42$ pc) M4 host (TOI-715/TIC 271971130) with a period $P_{\rm b} = 19.288004_{-0.000024}^{+0.000027}$ days. TOI-715 b was first identified by TESS and validated using ground-based photometry, high-resolution imaging and statistical validation. The planet’s orbital period combined with the stellar effective temperature $T_{\rm eff}=3075\pm75~\rm K$ give this planet an instellation $S_{\rm b} = 0.67_{-0.20}^{+0.15}~\rm S_\oplus$, placing it within the most conservative definitions of the habitable zone for rocky planets. TOI-715 b’s radius falls exactly between two measured locations of the M-dwarf radius valley; characterising its mass and composition will help understand the true nature of the radius valley for low-mass stars. We demonstrate TOI-715 b is amenable for characterisation using precise radial velocities and transmission spectroscopy. Additionally, we reveal a second candidate planet in the system, TIC 271971130.02, with a potential orbital period of $P_{02} = 25.60712_{-0.00036}^{+0.00031}$ days and a radius of $R_{02} = 1.066\pm0.092\,\rm R_{\oplus}$, just inside the outer boundary of the habitable zone, and near a 4:3 orbital period commensurability. Should this second planet be confirmed, it would represent the smallest habitable zone planet discovered by TESS to date.

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G. Dransfield, M. Timmermans, A. Triaud, et. al.
Thu, 11 May 23
53/55

Comments: Accepted for publication in MNRAS

http://arxiv.org/abs/2305.05056

We explore terrestrial planet formation with a focus on the supply of solid-state organics as the main source of volatile carbon. For the water-poor Earth, the water ice line, or ice sublimation front, within the planet-forming disk has long been a key focal point. We posit that the soot line, the location where solid-state organics are irreversibly destroyed, is also a key location within the disk. The soot line is closer to the host star than the water snowline and overlaps with the location of the majority of detected exoplanets. In this work, we explore the ultimate atmospheric composition of a body that receives a major portion of its materials from the zone between the soot line and water ice line. We model a silicate-rich world with 0.1% and 1% carbon by mass with variable water content. We show that as a result of geochemical equilibrium, the mantle of these planets would be rich in reduced carbon but have relatively low water (hydrogen) content. Outgassing would naturally yield the ingredients for haze production when exposed to stellar UV photons in the upper atmosphere. Obscuring atmospheric hazes appear common in the exoplanetary inventory based on the presence of often featureless transmission spectra (Kreidberg et al. 2014, Knutson et al. 2014, Libby-Roberts et al. 2020). Such hazes may be powered by the high volatile content of the underlying silicate-dominated mantle. Although this type of planet has no solar system counterpart, it should be common in the galaxy with potential impact on habitability.

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E. Bergin, E. Kempton, M. Hirschmann, et. al.
Wed, 10 May 23
10/65

Comments: 15 pages, 6 figures, accepted by Astrophysical Journal Letters. ApJL version has 5 figures. We include an extra figure (Figure 6) in this submission which is an artist rendering of a young disk including the soot and water ice lines. Image Credit for Fig. 6: Ari Gea/SayoStudio

http://arxiv.org/abs/2305.05217

In this study, we carried out photometric, spectroscopic, and for the first time, polarimetric observations of the Amor-type near-Earth asteroid (2059) Baboquivari. Our findings represent the first reliable determination of Baboquivari’s physical properties. We used data from a 1m-class telescope (T100) along with ALCDEF data for photometric analyses and a 1.5-m-class telescope (RTT150) for polarimetric, spectroscopic, and additional photometric observations. We obtained the synodic rotation period of Baboquivari as 129.93 +/- 2.31 hours and the standard phase function parameters H and G as 16.05 +/- 0.05, 0.22 +/- 0.02, respectively. Our colour index (V-R) measurement of 0.45 +/- 0.02 is consistent with spectroscopic observations, indicating an S (or sub-S) spectral type. Using the polarimetric and spectroscopic data, we found that the geometric albedo is 0.15 +/- 0.03, and the spectral type is Sq. Based on the estimated albedo and absolute magnitude, Baboquivari has an effective diameter of 2.12 +/- 0.21 km. Due to the scattered data in the light curve, its slow rotation and location among the NEAs suggest that Baboquivari may be a non-principal axis (NPA) rotator.

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O. Erece, I. Khamitov, M. Kaplan, et. al.
Wed, 10 May 23
52/65

Comments: 17 pages, 9 figures, accepted to publish in Planetary and Space Science (2023)

http://arxiv.org/abs/2305.03789

Planetary debris disks around other stars are analogous to the Asteroid and Kuiper belts in the Solar System. Their structure reveals the configuration of small bodies and provides hints for the presence of planets. The nearby star Fomalhaut hosts one of the most prominent debris disks, resolved by HST, Spitzer, Herschel, and ALMA. Images of this system at mid-infrared wavelengths using JWST/MIRI not only show the narrow Kuiper-Belt-analog outer ring, but also that (1) what was thought from indirect evidence to be an asteroid-analog structure is instead broad, extending outward into the outer system; (2) there is an intermediate belt, probably shepherded by an unseen planet. The newly discovered belt is demarcated by an inner gap, located at ~ 78 au, and it is misaligned relative to the outer belt. The previously known collisionally generated dust cloud, Fomalhaut b, could have originated from this belt, suggesting increased dynamical stirring and collision rates there. We also discovered a large dust cloud within the outer ring, possible evidence of another dust-creating collision. Taken together with previous observations, Fomalhaut appears to be the site of a complex and possibly dynamically active planetary system.

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A. Gaspar, S. Wolff, G. Rieke, et. al.
Tue, 9 May 23
36/88

Comments: 17 Figures, 3 tables; includes Supplementary Information package; Published in Nature Astronomy

http://arxiv.org/abs/2305.04922

Small planets located at the lower mode of the bimodal radius distribution are generally assumed to be composed of iron and silicates in a proportion similar to that of the Earth. However, recent discoveries are revealing a new group of low-density planets that are inconsistent with that description. We intend to confirm and characterize the TESS planet candidate TOI-244.01, which orbits the bright ($K$ = 7.97 mag), nearby ($d$ = 22 pc), and early-type (M2.5 V) M-dwarf star GJ 1018 with an orbital period of 7.4 days. We used Markov Chain Monte Carlo methods to model 57 precise radial velocity measurements acquired by the ESPRESSO spectrograph together with TESS photometry and complementary HARPS data. We find TOI-244 b to be a super-Earth with a radius of $R_{\rm p}$ = 1.52 $\pm$ 0.12 $\rm R_{\oplus}$ and a mass of $M_{\rm p}$ = 2.68 $\pm$ 0.30 $\rm M_{\oplus}$. These values correspond to a density of $\rho$ = 4.2 $\pm$ 1.1 $\rm g \cdot cm^{-3}$, which is below what would be expected for an Earth-like composition. We find that atmospheric loss processes may have been efficient to remove a potential primordial hydrogen envelope, but high mean molecular weight volatiles such as water could have been retained. Our internal structure modeling suggests that TOI-244 b has a $479^{+128}{-96}$ km thick hydrosphere over a 1.17 $\pm$ 0.09 $\rm R{\oplus}$ solid structure composed of a Fe-rich core and a silicate-dominated mantle compatible with that of the Earth. On a population level, we find two tentative trends in the density-metallicity and density-insolation parameter space for the low-density super-Earths, which may hint at their composition. With a 8$\%$ precision in radius and 12$\%$ precision in mass, TOI-244 b is among the most precisely characterized super-Earths, which, together with the likely presence of an extended hydrosphere, makes it a key target for atmospheric observations.

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A. Castro-González, O. Demangeon, J. Lillo-Box, et. al.
Tue, 9 May 23
42/88

Comments: Accepted for publication in A&A

http://arxiv.org/abs/2305.04896

The catalog of km-sized near-Earth objects (NEOs) is nearly complete. Typical impact monitoring analyses search for possible impacts over the next 100 years and none of the km-sized objects represent an impact threat over that time interval. Assessing the impact risk over longer time scales is a challenge since orbital uncertainties grow. To overcome this limitation we analyze the evolution of the Minimum Orbit Intersection Distance (MOID), which bounds the closest possible encounters between the asteroid and the Earth. The evolution of the MOID highlights NEOs that are in the vicinity of the Earth for longer periods of time, and we propose a method to estimate the probability of a deep Earth encounter during these periods. This metric is used to rank the km-sized catalog in terms of their long-term impact hazard to identify targets of potential interest for additional observation and exploration.

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O. Fuentes-Muñoz, D. Scheeres, D. Farnocchia, et. al.
Tue, 9 May 23
63/88

Comments: 20 pages, 17 figures, Accepted for Publication in The Astronomical Journal

http://arxiv.org/abs/2305.04880

Polarization phase-curve measurements provide a unique constraint on the surface properties of asteroids that are complementary to those from photometry and spectroscopy, and have led to the identification of the “Barbarian” asteroids as a class of objects with highly unusual surfaces. We present new near-infrared polarimetric observations of six Barbarian asteroids obtained with the WIRC+Pol instrument on the Palomar Hale telescope. We find a dramatic change in polarimetric behavior from visible to near-infrared for these objects, including a change in the polarimetric inversion angle that is tied to the index of refraction of the surface material. Our observations support a two-phase surface composition consisting of high albedo, high index of refraction inclusions with a small optical size scale embedded in a dark matrix material more closely related to C-complex asteroids. These results are consistent with the interpretation that the Barbarians are remnants of a population of primitive bodies that formed shortly after CAIs. Near-infrared polarimetry provides a direct test of the constituent grains of asteroid surfaces.

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J. Masiero, M. Devogele, I. Macias, et. al.
Tue, 9 May 23
70/88

Comments: 13 pages, 3 figures, accepted for publication in PSJ

http://arxiv.org/abs/2305.04911

I show that exoplanets can be used to test origins scenarios. Origins scenarios start with certain initial conditions, proceed via a network of chemical reactions and, if successful, result in a chemistry that is closer to a living system than the initial conditions. Exoplanet environments can be applied to test each of these three aspects of origins scenarios. I show what tests can be applied to the UV-driven cyanosulfidic scenario and how the application of some of these tests has already falsified certain versions of this scenario. Testing initial conditions has replaced certain reactants with others and has affected the overall chemical network underlying the cyanosulfidic scenario. The sequence of reactions the scenario invokes provide a predicted upper limit on the ubiquity of life in the universe that has ample room for improvement. The outcome of the experiments in different environments is part of a predicted distribution of biosignature detections that can be compared to future observed distributions.

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P. Rimmer
Tue, 9 May 23
74/88

Comments: Early uncorrected draft of: Rimmer, P.B., 2023. Origins of Life on Exoplanets. Conflicting Models for the Origin of Life, (Editors: Smoukov, S.K., Seckbach, J. and Gordon, R.) John Wiley & Sons. pp.407-424

http://arxiv.org/abs/2305.04549

The motion of solid particles embedded in gaseous protoplanetary disks is influenced by turbulent fluctuations. Consequently, the dynamics of moderately to weakly coupled solids can be distinctly different from the dynamics of the gas. Additionally, gravitational perturbations from an embedded planet can further impact the dynamics of solids. In this work, we investigate the combined effects of turbulent fluctuations and planetary dust stirring in a protoplanetary disk on three-dimensional dust morphology and on synthetic ALMA continuum observations. We carry out 3D radiative two-fluid (gas+1-mm-dust) hydrodynamic simulations in which we explicitly model the gravitational perturbation of a Jupiter-mass planet. We derived a new momentum-conserving turbulent diffusion model that introduces a turbulent pressure to the pressureless dust fluid to capture the turbulent transport of dust. The model implicitly captures the effects of orbital oscillations and reproduces the theoretically predicted vertical settling-diffusion equilibrium. We find a Jupiter-mass planet to produce distinct and large-scale three-dimensional flow structures in the mm-size dust, which vary strongly in space. We quantify these effects by locally measuring an effective vertical diffusivity (equivalent alpha) and find azimuthally averaged values in a range $\delta_\mathrm{eff}\sim5\cdot 10^{-3} – 2\cdot 10^{-2}$ and local peaks at values of up to $\delta_\mathrm{eff}\sim3\cdot 10^{-1}$. In synthetic ALMA continuum observations of inclined disks, we find effects of turbulent diffusion to be observable, especially at disk edges, and effects of planetary dust stirring in edge-on observations.

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F. Binkert, J. Szulágyi and T. Birnstiel
Tue, 9 May 23
76/88

Comments: Accepted for publication in MNRAS

http://arxiv.org/abs/2305.03104

Short and ultra-short planets are a peculiar type of exoplanets with periods as short as a few days or less. Although it is challenging to detect them, already several are observed with many additional candidates. If these planets have formation pathways to their longer period counterparts, they are predicted to reside in multi-planet systems. Thus, gravitational perturbation from potential planetary neighbors may affect their orbital configuration. However, due to their close proximity to their host star, they are also subjects to general relativity precession and torques from the stellar spin quadrupole moment ($J_2$). Here we show that an evolving $J_2$ due to magnetic braking, affects the magnitude and location of secular resonances of the short period planet in a multi-planet system. Thus, driving the short period planet into and out of a secular resonance, exciting the planet’s eccentricity and inclination. The high inclination can hinder transit observation, and, in some cases, the high eccentricity may result in an unstable configuration. We propose that evolving $J_2$ in a multi-planet system can be critical in understanding the detectability and stability of short-period planets.

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T. Faridani, S. Naoz, G. Li, et. al.
Mon, 8 May 23
9/63

Comments: 15 pages, 7 figures

http://arxiv.org/abs/2305.03417

Cometary dust particles are best preserved remnants of the matter present at the onset of the formation of the Solar System. Space missions, telescopic observations and laboratory analyses advanced the knowledge on the properties of cometary dust. Cometary samples were returned from comet 81P/Wild2 by the Stardust mission. The chondritic (porous) anhydrous interplanetary dust particles and chondritic porous micrometeorites, and the ultracarbonaceous Antarctic micrometeorites (UCAMMs) also show strong evidence for a cometary origin. The composition of cometary dust is generally chondritic, but with high C and N compared with CI. The cometary organic matter is mixed with minor amounts of crystalline and amorphous minerals. The most abundant crystalline minerals are ferromagnesian silicates, refractory minerals and low Ni Fe sulfides are also present. The presence of carbonates in cometary dust is still debated, but a phyllosilicate-like phase was observed in a UCAMM. GEMS phases are usually abundant. Some of the organic matter present in cometary dust particle resembles the insoluble organic matter present in primitive meteorites, but amorphous carbon and exotic (e.g. N-rich) organic phases are also present. The H isotopic composition of the organic matter traces a formation at very low temperatures, in the protosolar cloud or in the outer regions of the protoplanetary disk. The presolar dust concentration in cometary dust can reach about 1%, which is the most elevated value observed in extraterrestrial samples. The differential size distribution of cometary dust in comet trails is well represented by a power-law distribution with a mean power index N typically ranging from -3 to -4. Polarimetric and light scattering studies suggest mixtures of porous agglomerates of sub-micrometer minerals with organic matter. Cometary dust particles have low tensile strength, and low density.

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C. Engrand, J. Lasue, D. Wooden, et. al.
Mon, 8 May 23
18/63

Comments: N/A