Category Archives: Earth and Planetary Astrophysics

New constraints on the presence of debris disks around G 196-3 B and VHS J125601.92-125723.9 b [EPA]

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http://arxiv.org/abs/2303.12163


We obtained deep images of G 196-3 B and VHS J1256-1257 b with the NOrthern Extended Millimeter Array (NOEMA) at 1.3 mm. These data were combined with recently published Atacama Large Millimeter Array (ALMA) and Very Large Array (VLA) data of VHS J1256-1257 b at 0.87 mm and 0.9 cm, respectively. Neither G 196-3 B nor VHS J1256-1257 b were detected in the NOEMA, ALMA and VLA data. At 1.3 mm, we imposed flux upper limits of 0.108 mJy (G 196-3 B) and 0.153 mJy (VHS J1256-1257 b) with a 3-sigma confidence. Using the flux upper limits at the millimeter and radio wavelength regimes, we derived maximum values of 0.016 M${\rm Earth}$ and 0.004 M${\rm Earth}$ for the mass of any cold dust that might be surrounding G 196-3 B and VHS J1256-1257 b, respectively. We put our results in the context of other deep millimeter observations of free-floating and companion objects with substellar masses smaller than 20 M$_{\rm Jupiter}$ and ages between 1 and a few hundred million years. Only two very young objects are detected out of a few tens concluding, as other groups did before, that the disks around these very low-mass objects must have small masses and possibly reduced sizes. If debris disks around substellar objects scale down in a similar manner as protoplanetary disks do, millimeter observations of moderately young brown dwarfs and planets must be at least two orders of magnitude deeper for being able to detect and characterize their surrounding debris disks.

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O. Zakhozhay, M. Osorio, V. Bejar, et. al.
Thu, 23 Mar 23
57/67

Comments: Accepted fro publication in A&A

The Winchcombe Fireball — that Lucky Survivor [EPA]

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http://arxiv.org/abs/2303.12126


On February 28, 2021, a fireball dropped $\sim0.6$ kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball’s atmospheric trajectory, light curve, fragmentation behaviour, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive ($\sim13$ kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure ($\sim0.6$ MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km/s). A near-catastrophic fragmentation at $\sim0.07$ MPa points to the body’s fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region $\sim0.08$ Myr ago and it never had a perihelion distance smaller than $\sim0.7$ AU, while other CM2 meteorites with known orbits approached the Sun closer ($\sim0.5$ AU) and were heated to at least 100 K higher temperatures.

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S. McMullan, D. Vida, H. Devillepoix, et. al.
Thu, 23 Mar 23
62/67

Comments: Accepted for publication in MAPS

Dark Exoplanets [EPA]

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http://arxiv.org/abs/2303.12129


The prevailing assumption is that all exoplanets are made of ordinary matter. However, we propose an unconventional possibility that some exoplanets could be made of dark matter, which we name “dark exoplanets.” In this paper, we explore methods to search for dark exoplanets, including the mass-radius relation, spectroscopy, missing transit, and transit light curve. Specifically, we focus on the transit light curve method and demonstrate how to distinguish partially transparent dark exoplanets from fully opaque ordinary exoplanets using both observed exoplanet data and dark exoplanet mock data. Our analysis shows that dark exoplanets with a large radius (above around 10% of the star radius) and a small optical depth (below around one) can be identified with current telescope sensitivities.

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Y. Bai, S. Lu and N. Orlofsky
Thu, 23 Mar 23
66/67

Comments: 23 pages, 9 figures

Discovery of a massive giant planet with extreme density around a sub-giant star TOI-4603 [EPA]

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http://arxiv.org/abs/2303.11841


We present the discovery of a transiting massive giant planet around TOI-4603, a sub-giant F-type star from NASA’s Transiting Exoplanet Survey Satellite (TESS). The newly discovered planet has a radius of $1.042^{+0.038}{-0.035}$ $R{J}$, and an orbital period of $7.24599^{+0.00022}{-0.00021}$ days. Using radial velocity measurements with the PARAS {and TRES} spectrographs, we determined the planet’s mass to be $12.89^{+0.58}{-0.57}$ $M_{J}$, resulting in a bulk density of $14.1^{+1.7}{-1.6}$ g ${cm^{-3}}$. This makes it one of the few massive giant planets with extreme density and lies in the transition mass region of massive giant planets and low-mass brown dwarfs, an important addition to the population of less than five objects in this mass range. The eccentricity of $0.325\pm0.020$ and an orbital separation of $0.0888\pm0.0010$ AU from its host star suggest that the planet is likely undergoing high eccentricity tidal (HET) migration. We find a fraction of heavy elements of $0.13^{+0.05}{-0.06}$ and metal enrichment of the planet ($Z_{P}/Z_{star}$) of $4.2^{+1.6}_{-2.0}$. Detection of such systems will offer us to gain valuable insights into the governing mechanisms of massive planets and improve our understanding of their dominant formation and migration mechanisms.

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A. Khandelwal, R. Sharma, A. Chakraborty, et. al.
Wed, 22 Mar 23
4/68

Comments: accepted for publication in A&A Letters

Forming super-Mercuries: The role of stellar abundances [EPA]

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http://arxiv.org/abs/2303.11948


Super-Mercuries, rocky exoplanets with bulk iron mass fraction of more than 60 per cent, appear to be preferentially hosted by stars with higher iron mass fraction than the Earth. It is unclear whether these iron-rich planets can form in the disc, or if giant impacts are necessary. Here we investigate the formation of super-Mercuries in their natal protoplanetary discs by taking into account their host stars’ abundances (Fe, Mg, Si, S). We employ a disc evolution model which includes the growth, drift, evaporation and recondensation of pebbles to compute the pebble iron mass fraction. The recondensation of outward-drifting iron vapour near the iron evaporation front is the key mechanism that facilitates an increase in the pebble iron mass fraction. We also simulate the growth of planetary seeds around the iron evaporation front using a planet formation model which includes pebble accretion and planet migration, and compute the final composition of the planets. Our simulations are able to reproduce the observed iron compositions of the super-Mercuries provided that all the iron in the disc are locked in pure Fe grains and that the disc viscosity is low. The combined effects of slow orbital migration of planets and long retention time of iron vapour in low-viscosity discs makes it easier to form iron-rich planets. Furthermore, we find that decreasing the stellar Mg/Si ratio results in an increase in the iron mass fraction of the planet due to a reduction in the abundance of Mg2SiO4, which has a very similar condensation temperature as iron, in the disc. Our results thus imply that super-Mercuries are more likely to form around stars with low Mg/Si, in agreement with observational data.

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J. Mah and B. Bitsch
Wed, 22 Mar 23
5/68

Comments: 9 pages, 6 figures, accepted for publication in A&A

Comparing Apples with Apples: Robust Detection Limits for Exoplanet High-Contrast Imaging in the Presence of non-Gaussian Noise [EPA]

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http://arxiv.org/abs/2303.12030


Over the past decade, hundreds of nights have been spent on the worlds largest telescopes to search for and directly detect new exoplanets using high-contrast imaging (HCI). Thereby, two scientific goals are of central interest: First, to study the characteristics of the underlying planet population and distinguish between different planet formation and evolution theories. Second, to find and characterize planets in our immediate Solar neighborhood. Both goals heavily rely on the metric used to quantify planet detections and non-detections.
Current standards often rely on several explicit or implicit assumptions about the noise. For example, it is often assumed that the residual noise after data post-processing is Gaussian. While being an inseparable part of the metric, these assumptions are rarely verified. This is problematic as any violation of these assumptions can lead to systematic biases. This makes it hard, if not impossible, to compare results across datasets or instruments with different noise characteristics.
We revisit the fundamental question of how to quantify detection limits in HCI. We focus our analysis on the error budget resulting from violated assumptions. To this end, we propose a new metric based on bootstrapping that generalizes current standards to non-Gaussian noise. We apply our method to archival HCI data from the NACO-VLT instrument and derive detection limits for different types of noise. Our analysis shows that current standards tend to give detection limit that are about one magnitude too optimistic in the speckle-dominated regime. That is, HCI surveys may have excluded planets that can still exist.

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M. Bonse, E. Garvin, T. Gebhard, et. al.
Wed, 22 Mar 23
7/68

Comments: After first iteration with the referee, resubmitted to AJ. Comments welcome!

Optical spectropolarimetry of binary asteroid Didymos-Dimorphos before and after the DART impact [EPA]

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http://arxiv.org/abs/2303.11776


We have monitored the Didymos-Dimorphos binary asteroid in spectropolarimetric mode in the optical range before and after the DART impact. The ultimate goal was to obtain constraints on the characteristics of the ejected dust for modelling purposes. Before impact, Didymos exhibited a linear polarization rapidly increasing with phase angle, reaching a level of about 5% in the blue and about 4.5 in the red. The shape of the polarization spectrum was anti-correlated with that of its reflectance spectrum, which appeared typical of an S-class asteroid. After impact, the level of polarization dropped by about 1 percentage point (pp) in the blue band and about 0.5 pp in the red band, then continued to linearly increase with phase angle, with a slope similar to that measured prior to impact. The polarization spectra, once normalised by their values at an arbitrary wavelength, show very little or no change over the course of all observations, before and after impact. The lack of any remarkable change in the shape of the polarization spectrum after impact suggests that the way in which polarization varies with wavelength depends on the composition of the scattering material, rather than on its structure, be this a surface or a debris cloud.

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S. Bagnulo, Z. Gray, M. Granvik, et. al.
Wed, 22 Mar 23
31/68

Comments: ApJL, in press

A Constraint on the Amount of Hydrogen from the CO Chemistry in Debris Disks [EPA]

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http://arxiv.org/abs/2303.11544


The faint CO gases in debris disks are easily dissolved into C by UV irradiation, while CO can be reformed via reactions with hydrogen. The abundance ratio of C/CO could thus be a probe of the amount of hydrogen in the debris disks. We conduct radiative transfer calculations with chemical reactions for debris disks. For a typical dust-to-gas mass ratio of debris disks, CO formation proceeds without the involvement of H$2$ because a small amount of dust grains makes H$_2$ formation inefficient. We find that the CO to C number density ratio depends on a combination of $n\mathrm{H}Z^{0.4}\chi^{-1.1}$, where $n_\mathrm{H}$ is the hydrogen nucleus number density, $Z$ is the metallicity, and $\chi$ is the FUV flux normalized by the Habing flux. Using an analytic formula for the CO number density, we give constraints on the amount of hydrogen and metallicity for debris disks. CO formation is accelerated by excited H$_2$ either when the dust-to-gas mass ratio is increased or the energy barrier of chemisorption of hydrogen on the dust surface is decreased. This acceleration of CO formation occurs only when the shielding effects of CO are insignificant. In shielded regions, the CO fractions are almost independent of the parameters of dust grains.

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K. Iwasaki, H. Kobayashi, A. Higuchi, et. al.
Wed, 22 Mar 23
36/68

Comments: 29pages, 13figures, accepted for ApJ

Short-lived radioisotope enrichment in star-forming regions from stellar winds and supernovae [EPA]

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http://arxiv.org/abs/2303.11393


The abundance of the short-lived radioisotopes 26-Al and 60-Fe in the early Solar system is usually explained by the Sun either forming from pre-enriched material, or the Sun’s protosolar disc being polluted by a nearby supernova explosion from a massive star. Both hypotheses suffer from significant drawbacks: the former does not account for the dynamical evolution of star-forming regions, while in the latter the time for massive stars to explode as supernovae can be similar to, or even longer than, the lifetime of protoplanetary discs. In this paper, we extend the disc enrichment scenario to include the contribution of 26-Al from the winds of massive stars before they explode as supernovae. We use N-body simulations and a post-processing analysis to calculate the amount of enrichment in each disc, and we vary the stellar density of the star-forming regions. We find that stellar winds contribute to disc enrichment to such an extent that the Solar system’s 26-Al/60-Fe ratio is reproduced in up to 50 per cent of discs in dense (rho = 1000Msun pc^-3) star-forming regions. When winds are a significant contributor to the SLR enrichment, we find that Solar system levels of enrichment can occur much earlier (before 2.5 Myr) than when enrichment occurs from supernovae, which start to explode at later ages (>4 Myr). We find that Solar system levels of enrichment all but disappear in low-density star-forming regions (rho < 10Msun pc^-3), implying that the Solar system must have formed in a dense, populous star-forming region if 26-Al and 60-Fe were delivered directly to the protosolar disc from massive-star winds and supernovae.

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R. Parker, T. Lichtenberg, M. Patel, et. al.
Wed, 22 Mar 23
62/68

Comments: 16 pages, 10 figures, 1 appendix with 3 further figures, accepted for publication in MNRAS

A search for Kuiper Belt occultations using the Weizmann Fast Astronomical Survey Telescope [EPA]

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http://arxiv.org/abs/2303.12020


Measuring the size distribution of small (km-scale) KBOs can help constrain models of Solar System formation and planetary migration. Such small, distant bodies are hard to detect with current or planned telescopes, but can be identified as sub-second occultations of background stars. We present the analysis of data from the Weizmann Fast Astronomical Survey Telescope (W-FAST), consisting of fast photometry of ~10^6 star hours at a frame rate of 10-25 Hz. Our pipeline utilizes a matched-filter approach with a large template bank, including red-noise treatment, and injection of simulated events for estimating the detection efficiency. The KBO radius at which our survey is 10% (50%) efficient is 1.1 (2.0) km. The data from 2020-2021 observing seasons were analyzed and no occultations were identified. We discuss a sample of sub-second false-positive events, both occultation-like and flare-like, which are still not fully understood but could be instructive for future surveys looking for short-duration events. We use our null-detection result to set limits on the km-scale KBO number density. Our individual radius bin limits are consistent with most previous works, with N(r>1km) <=10^6 deg^-2 (95% confidence limit). Our integrated (all size) limits, assuming a power law normalized to large (~45 km) KBOs gives a power law index q<3.93 (95% confidence limit). Finally, our results are in tension with a recently reported KBO detection from the ground, at the p=4×10^-4 level.

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G. Nir, E. Ofek, D. Polishook, et. al.
Wed, 22 Mar 23
64/68

Comments: N/A

Rainy downdrafts in abyssal atmospheres [EPA]

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http://arxiv.org/abs/2303.10604


Results from Juno’s microwave radiometer indicate non-uniform mixing of ammonia vapor in Jupiter’s atmosphere down to tens of bars, far beneath the cloud level. Helioseismic observations suggest solar convection may require narrow, concentrated downdrafts called entropy rain to accommodate the Sun’s luminosity. Both observations suggest some mechanism of non-local convective transport. We seek to predict the depth that a concentrated density anomaly can reach before efficiently mixing with its environment in bottomless atmospheres. We modify classic self-similar analytical models of entraining thermals to account for the compressibility of an abyssal atmosphere. We compare these models to the output of high resolution three dimensional fluid dynamical simulations to more accurately model the chaotic influence of turbulence. We find that localized density anomalies propagate down to ~3-8 times their initial size without substantially mixing with their environment. Our analytic model accurately predicts the initial flow, but the self-similarity assumption breaks down after the flow becomes unstable at a characteristic penetration depth. In the context of Jupiter, our findings suggest that precipitation concentrated into localized downdrafts of size ~20km can coherently penetrate to on the order of a hundred kilometers (tens of bars) beneath its initial vaporization level without mixing with its environment. This finding is consistent with expected convective storm length-scales, and Juno MWR measurements of ammonia depletion. Compositional gradients of volatiles beneath their cloud levels may be common on stormy giant planets. In the context of the Sun, we find that turbulent downdrafts in abyssal atmospheres cannot maintain their coherence through the Sun’s convective layer, a potential challenge for the entropy rain hypothesis.

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S. Markham, T. Guillot and C. Li
Tue, 21 Mar 23
11/68

Comments: 20 pages, 16 figures. Accepted by A&A

Collisional evolution of dust and water ice in protoplanetary discs during and after an accretion outburst [EPA]

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http://arxiv.org/abs/2303.11318


Most protoplanetary discs are thought to undergo violent and frequent accretion outbursts, during which the accretion rate and central luminosity are elevated for several decades. This temporarily increases the disc temperature, leading to the sublimation of ice species as snowlines move outwards. In this paper, we investigate how an FUor-type accretion outburst alters the growth and appearance of dust aggregates at different locations in protoplanetary discs. We develop a model based on the Monte Carlo approach to simulate locally the coagulation and fragmentation of icy dust particles and investigate different designs for their structure and response to sublimation. Our main finding is that the evolution of dust grains located between the quiescent and outburst water snowlines is driven by significant changes in composition and porosity. The time required for the dust population to recover from the outburst and return to a coagulation/fragmentation equilibrium depends on the complex interplay of coagulation physics and outburst properties, and can take up to 4500 yr at 5 au. Pebble-sized particles, the building blocks of planetesimals, are either deprecated in water ice or completely destroyed, respectively resulting in drier planetesimals or halting their formation altogether. When accretion outbursts are frequent events, the dust can be far from collisional equilibrium for a significant fraction of time, offering opportunities to track past outbursts in discs at millimetre wavelengths. Our results highlight the importance of including accretion outbursts in models of dust coagulation and planet formation.

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A. Houge and S. Krijt
Tue, 21 Mar 23
24/68

Comments: 21 pages, 14 figures, accepted for publication in MNRAS

Giant Impacts and Debris Disk Morphology [EPA]

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http://arxiv.org/abs/2303.10189


Certain debris disks have non-axisymmetric shapes in scattered light which are unexplained. The appearance of a disk depends on how its constituent Keplerian ellipses are arranged. The more the ellipses align apsidally, the more non-axisymmetric the disk. Apsidal alignment is automatic for fragments released from a catastrophic collision between solid bodies. We synthesize scattered light images, and thermal emission images, of such giant impact debris. Depending on the viewing geometry, and if and how the initial apsidal alignment is perturbed, the remains of a giant impact can appear in scattered light as a one-sided or two-sided “fork”, a lopsided “needle”, or a set of “double wings”. Double wings are difficult to reproduce in other scenarios involving gravitational forcing or gas drag, which do not align orbits as well. We compare our images with observations and offer a scorecard assessing whether the scattered light asymmetries in HD 15115, HD 32297, HD 61005, HD 111520, HD 106906, beta Pic, and AU Mic are best explained by giant impacts, gravitational perturbations, or sculpting by the interstellar medium.

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J. Jones, E. Chiang, G. Duchene, et. al.
Tue, 21 Mar 23
57/68

Comments: Accepted to ApJ. Animations available at this https URL

Igneous Rim Accretion on Chondrules in Low-Velocity Shock Waves [EPA]

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http://arxiv.org/abs/2303.10450


Shock wave heating is a leading candidate for the mechanisms of chondrule formation. This mechanism forms chondrules when the shock velocity is in a certain range. If the shock velocity is lower than this range, dust particles smaller than chondrule precursors melt, while chondrule precursors do not. We focus on the low-velocity shock waves as the igneous rim accretion events. Using a semi-analytical treatment of the shock-wave heating model, we found that the accretion of molten dust particles occurs when they are supercooling. The accreted igneous rims have two layers, which are the layers of the accreted supercooled droplets and crystallized dust particles. We suggest that chondrules experience multiple rim-forming shock events.

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Y. Matsumoto and S. Arakawa
Tue, 21 Mar 23
66/68

Comments: accepted for publication in ApJ

A Biotic Habitable Zone: Impacts of Adaptation in Biotic Temperature Regulation [EPA]

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http://arxiv.org/abs/2303.10052


The search for biosignatures necessitates developing our understanding of life under different conditions. If life can influence the climate evolution of its planet then understanding the behaviour of life-climate feedbacks under extreme conditions is key to determine the ‘edges’ of the habitable zone. Additionally understanding the behaviour of a temperature limited biosphere will help towards formulating biosignature predictions for alien life living under conditions very different to those on Earth. Towards this aim, we extend the ‘ExoGaia Model’ – an abstract model of microbial life living on a highly simplified 0-dimensional planet. Via their metabolisms, microbes influence the atmospheric composition and therefore the temperature of the planet and emergent feedback loops allow microbes to regulate their climate and maintain long term habitability. Here, we adapt the ExoGaia model to include temperature adaptation of the microbes by allowing different species to have different temperature ‘preferences’. We find that rather than adapting towards the planet’s abiotic conditions the biosphere tends to more strongly influence the climate of its planet, suggesting that the surface temperature of an inhabited planet might be significantly different from that predicted using abiotic models. We find that the success rate for microbial establishment on planets is improved when adaptation is allowed. However, planetary abiotic context is important for determining whether overall survival prospects for life will be improved or degraded. These results indicate the necessity to develop an understanding of life living under different limiting regimes to form predictions for the boundaries of the habitable zone.

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A. Nicholson and N. Mayne
Mon, 20 Mar 23
7/51

Comments: N/A

Predicting the Yield of Small Transiting Exoplanets around Mid-M and Ultra-Cool Dwarfs in the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey [EPA]

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http://arxiv.org/abs/2303.09959


We simulate the yield of small (0.5-4.0 R$\oplus$) transiting exoplanets around single mid-M and ultra-cool dwarfs (UCDs) in the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey. We consider multiple approaches for simulating M3-T9 sources within the survey fields, including scaling local space densities and using Galactic stellar population synthesis models. These approaches independently predict $\sim$100,000 single mid-M dwarfs and UCDs brighter than a Roman F146 magnitude of 21 that are within the survey fields. Assuming planet occurrence statistics previously measured for early-to-mid M dwarfs, we predict that the survey will discover 1347$^{+208}{-124}$ small transiting planets around these sources, each to a significance of 7.1$\sigma$ or greater. Significant departures from this prediction would test whether the occurrence rates of small planets increase or decrease around mid-M dwarfs and UCDs compared to early-M dwarfs. We predict the detection of 13$^{+4}{-3}$ habitable, terrestrial planets ($R_p<$1.23 R$\oplus$) in the survey. However, atmospheric characterization of these planets will be challenging with current or near-future space telescope facilities due to the faintness of the host stars. Nevertheless, accurate statistics for the occurrence of small planets around mid-M dwarfs and UCDs will enable direct tests of predictions from planet formation theories and will determine our understanding of planet demographics around the objects at the bottom of the main sequence. This understanding is critical given the prevalence of such objects in our Galaxy, whose planets may therefore comprise the bulk of the galactic census of exoplanets.

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P. Tamburo, P. Muirhead and C. Dressing
Mon, 20 Mar 23
20/51

Comments: 19 pages, 10 figures, submitted to AJ

Global N-body simulations of circumbinary planet formation around Kepler-16 and -34 analogues I: Exploring the pebble accretion scenario [EPA]

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http://arxiv.org/abs/2303.09899


Numerous circumbinary planets have been discovered in surveys of transiting planets. Often, these planets are found to orbit near to the zone of dynamical instability, close to the central binary. The existence of these planets has been explained by hydrodynamical simulations that show that migrating circumbinary planets, embedded in circumbinary discs, halt at the central cavity that is formed by the central binary. Transit surveys are naturally most sensitive to finding circumbinary planets with the shortest orbital periods. The future promise of detecting longer period systems using radial-velocity searches, combined with the anticipated detection of numerous circumbinary planets by ESA’s PLATO mission, points to the need to model and understand the formation and evolution of circumbinary planets in a more general sense than has been considered before. With this goal in mind, we present a newly developed global model of circumbinary planet formation that is based on the mercury6 symplectic N-body integrator, combined with a model for the circumbinary disc and prescriptions for a range of processes involved in planet formation such as pebble accretion, gas envelope accretion and migration. Our results show that under reasonable assumptions, the pebble accretion scenario can produce circumbinary systems that are similar to those observed, and in particular is able to produce planets akin to Kepler-16b and Kepler-34b. Comparing our results to other systems, we find that our models also adequately reproduce such systems, including multi-planet systems. Resonances between neighbouring planets are frequently obtained, whilst ejections of planets by the central binary acts as an effective source of free floating planets.

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G. Coleman, R. Nelson and A. Triaud
Mon, 20 Mar 23
21/51

Comments: Accepted for publication in MNRAS, 23 pages, 16 figures

Atmospheres as windows into sub-Neptune interiors: coupled chemistry and structure of hydrogen-silane-water envelopes [EPA]

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http://arxiv.org/abs/2303.09653


Sub-Neptune exoplanets are commonly hypothesized to consist of a silicate-rich magma ocean topped by a hydrogen-rich atmosphere. Previous work studying the outgassing of silicate material has demonstrated that such atmosphere-interior interactions can affect the atmosphere’s overall structure and extent. But these models only considered SiO in an atmosphere of hydrogen gas, without considering chemical reactions between them. Here we couple calculations of the chemical equilibrium between H, Si, and O species with an atmospheric structure model. We find that substantial amounts of silane, SiH$4$, and water, H$_2$O, are produced by the interaction between the silicate-rich interior and hydrogen-rich atmosphere. These species extend high into the atmosphere, though their abundance is greatest at the hottest, deepest regions. For example, for a 4 $M\oplus$ planet with an equilibrium temperature of 1000 K, a base temperature of 5000 K, and a 0.1 $M_\oplus$ hydrogen envelope, silicon species and water can comprise 30 percent of the atmosphere by number at the bottom of the atmosphere. Due to this abundance enhancement, we find that convection is inhibited at temperatures $\gtrsim 2500$ K. This temperature is lower, implying that the resultant non-convective region is thicker, than was found in previous models which did not account for atmospheric chemistry. Our findings show that significant endogenous water is be produced by magma-hydrogen interactions alone, without the need to accrete ice-rich material. We discuss the observability of the signatures of atmosphere-interior interaction and directions for future work, including condensate lofting and more complex chemical networks.

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W. Misener and H. Schlichting
Mon, 20 Mar 23
47/51

Comments: 10 pages, 7 figures, under review at MNRAS

Massive Protostellar Disks as a Hot Laboratory of Silicate Grain Evolution [EPA]

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http://arxiv.org/abs/2303.09148


Typical accretion disks around massive protostars are hot enough for water ice to sublimate. We here propose to utilize the massive protostellar disks for investigating the collisional evolution of silicate grains with no ice mantle, which is an essential process for the formation of rocky planetesimals in protoplanetary disks around lower-mass stars. We for the first time develop a model of massive protostellar disks that includes the coagulation, fragmentation, and radial drift of dust. We show that the maximum grain size in the disks is limited by collisional fragmentation rather than by radial drift. We derive analytic formulas that produce the radial distribution of the maximum grain size and dust surface density in the steady state. Applying the analytic formulas to the massive protostellar disk of GGD27-MM1, where the grain size is constrained from a millimeter polarimetric observation, we infer that the silicate grains in this disk fragment at collision velocities above ~ 10 m/s. The inferred fragmentation threshold velocity is lower than the maximum grain collision velocity in typical protoplanetary disks around low-mass stars, implying that coagulation alone may not lead to the formation of rocky planetesimals in those disks. With future measurements of grain sizes in massive protostellar disks, our model will provide more robust constraints on the sticking property of silicate grains.

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R. Yamamuro, K. Tanaka and S. Okuzumi
Fri, 17 Mar 23
17/67

Comments: 17 pages, 5 figures,accepted for publication to The Astrophysical Journal

OGLE-2016-BLG-1195 AO: Lens, Companion to Lens or Source, or None of the Above? [EPA]

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http://arxiv.org/abs/2303.08876


We systematically investigate the claim by Vandorou et al. (2023) to have detected the host star of the low mass-ratio ($q<10^{-4}$) microlensing planet OGLE-2016-BLG-1195Lb, via Keck adaptive optics (AO) measurements $\Delta t=4.12\,$yr after the peak of the event ($t_0$). If correct, this measurement would contradict the microlens parallax measurement derived from Spitzer observations in solar orbit taken near $t_0$. We show that this host identification would be in $4\,\sigma$ conflict with the original ground-based lens-source relative proper-motion measurements. By contrast, Gould (2022) estimated a probability $p=10\%$ that the other star'' resolved by single-epoch late-time AO would be a companion to the host or the microlensed source, which is much more probable than a 4$\,\sigma$ statistical fluctuation. In addition, independent of this proper-motion discrepancy, the kinematics of this host-identification are substantially less probable than those of the Spitzer solution. Hence, this identification should not be accepted, pending additional observations that would either confirm or contradict it, which could be taken in 2023. Motivated by this tension, we present two additional investigations. We explore the possibility that Vandorou et al. (2023) identified the wrongstar” (or stellar asterism) on which to conduct their analysis. We find that astrometry of KMT and Keck images favors a star (or asterism) lying about 175 mas northwest of the one that they chose. We also present event parameters from a combined fit to all survey data, which yields, in particular, a more precise mass ratio, $q=(4.6\pm 0.4)\times 10^{-5}$. Finally, we discuss the broader implications of minimizing such false positives for the first measurement of the planet mass function, which will become possible when AO on next-generation telescopes are applied to microlensing planets.

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A. Gould, Y. Shvartzvald, J. Zhang, et. al.
Fri, 17 Mar 23
28/67

Comments: 31 pages, 7 figures, 3 tables, 2 appendices, submitted to AAS Journals

ExoplANNET: A deep learning algorithm to detect and identify planetary signals in radial velocity data [EPA]

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http://arxiv.org/abs/2303.09335


The detection of exoplanets with the radial velocity method consists in detecting variations of the stellar velocity caused by an unseen sub-stellar companion. Instrumental errors, irregular time sampling, and different noise sources originating in the intrinsic variability of the star can hinder the interpretation of the data, and even lead to spurious detections. In recent times, work began to emerge in the field of extrasolar planets that use Machine Learning algorithms, some with results that exceed those obtained with the traditional techniques in the field. We seek to explore the scope of the neural networks in the radial velocity method, in particular for exoplanet detection in the presence of correlated noise of stellar origin. In this work, a neural network is proposed to replace the computation of the significance of the signal detected with the radial velocity method and to classify it as of planetary origin or not. The algorithm is trained using synthetic data of systems with and without planetary companions. We injected realistic correlated noise in the simulations, based on previous studies of the behaviour of stellar activity. The performance of the network is compared to the traditional method based on null hypothesis significance testing. The network achieves 28 % fewer false positives. The improvement is observed mainly in the detection of small-amplitude signals associated with low-mass planets. In addition, its execution time is five orders of magnitude faster than the traditional method. The superior performance exhibited by the algorithm has only been tested on simulated radial velocity data so far. Although in principle it should be straightforward to adapt it for use in real time series, its performance has to be tested thoroughly. Future work should permit evaluating its potential for adoption as a valuable tool for exoplanet detection.

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L. Nieto and R. Díaz
Fri, 17 Mar 23
29/67

Comments: Paper under peer-review, comments are welcome

On the origin of the non-detection of metastable HeI in the upper atmosphere of the hot Jupiter WASP-80b [EPA]

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http://arxiv.org/abs/2303.09501


We aim to narrow down the origin of the non-detection of the metastable HeI triplet at about 10830 A obtained for the hot Jupiter WASP-80b. We measure the X-ray flux of WASP-80 from archival observations and use it as input to scaling relations accounting for the coronal [Fe/O] abundance ratio to infer the extreme-ultraviolet (EUV) flux in the 200-504 A range, which controls the formation of metastable HeI. We run three dimensional (magneto) hydrodynamic simulations of the expanding planetary upper atmosphere interacting with the stellar wind to study the impact on the HeI absorption of the stellar high-energy emission, the He/H abundance ratio, the stellar wind, and the possible presence of a planetary magnetic field up to 1 G. For a low stellar EUV emission, which is favoured by the measured logR’HK value, the HeI non-detection can be explained by a solar He/H abundance ratio in combination with a strong stellar wind, or by a sub-solar He/H abundance ratio, or by a combination of the two. For a high stellar EUV emission, the non-detection implies a sub-solar He/H abundance ratio. A planetary magnetic field is unlikely to be the cause of the non-detection. The low EUV stellar flux, driven by the low [Fe/O] coronal abundance, is the likely primary cause of the HeI non-detection. High-quality EUV spectra of nearby stars are urgently needed to improve the accuracy of high-energy emission estimates, which would then enable one to employ the observations to constrain the planetary He/H abundance ratio and the stellar wind strength. This would greatly enhance the information that can be extracted from HeI atmospheric characterisation observations.

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L. Fossati, I. Pillitteri, I. Shaikhislamov, et. al.
Fri, 17 Mar 23
39/67

Comments: Accepted for publication on A&A, 20 pages

Azimuthal C/O Variations in a Planet-Forming Disk [EPA]

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http://arxiv.org/abs/2303.08927


The elemental carbon-to-oxygen ratio (C/O) in the atmosphere of a giant planet is a promising diagnostic of that planet’s formation history in a protoplanetary disk. Alongside efforts in the exoplanet community to measure C/O in planetary atmospheres, observational and theoretical studies of disks are increasingly focused on understanding how the gas-phase C/O varies both with radial location and between disks. This is mostly tied to the icelines of major volatile carriers such as CO and H2O. Using ALMA observations of CS and SO, we have unearthed evidence for an entirely novel type of C/O variation in the protoplanetary disk around HD 100546: an azimuthal variation from a typical, oxygen-dominated ratio (C/O=0.5) to a carbon-dominated ratio (C/O>1.0). We show that the spatial distribution and peculiar line kinematics of both CS and SO molecules can be well-explained by azimuthal variations in the C/O ratio. We propose a shadowing mechanism that could lead to such a chemical dichotomy. Our results imply that tracing the formation history of giant exoplanets using their atmospheric C/O ratios will need to take into account time-dependent azimuthal C/O variations in a planet’s accretion zone.

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L. Keyte, M. Kama, A. Booth, et. al.
Fri, 17 Mar 23
59/67

Comments: Accepted in Nature Astronomy

Detection of a high-velocity sodium feature on the ultra-hot Jupiter WASP-121 b [EPA]

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http://arxiv.org/abs/2303.09376


Ultra-hot Jupiters, with their high equilibrium temperatures and resolved spectral lines, have emerged as a perfect testbed for new analysis techniques in the study of exoplanet atmospheres. In particular, the resolved sodium doublet as a resonant line has proven a powerful indicator to probe the atmospheric structure over a wide pressure range. We explore an atmospheric origin of the observed blueshifted feature next to the sodium doublet of the ultra-hot Jupiter WASP-121~b, using a partial transit obtained with the 4-UT mode of ESPRESSO. We study its atmospheric dynamics visible across the terminator by splitting the data into mid-transit and egress. We determine that the blueshifted high-velocity absorption component is generated only during the egress part of the transit when a larger fraction of the day side of the planet is visible. For the egress data, MERC retrieves the blueshifted high-velocity absorption component as an equatorial day-to-night side wind across the evening limb, with no zonal winds visible on the morning terminator with weak evidence compared to a model with only vertical winds. For the mid-transit data, the observed line broadening is attributed to a vertical, radial wind. We attribute the equatorial day-to-night side wind over the evening terminator to a localised jet and restrain its existence between the substellar point and up to $10^\circ$ to the terminator in longitude, an opening angle of the jet of at most $60^\circ$ in latitude, and a lower boundary in altitude between [1.08, 1.15] $R_p$. Due to the partial nature of the transit, we cannot make any statements on whether the jet is truly super-rotational and one-sided or part of a symmetric day-to-night side atmospheric wind from the hotspot.

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J. Seidel, F. Borsa, L. Pino, et. al.
Fri, 17 Mar 23
65/67

Comments: 15 pages, 10 figures, 2 appendixes, accepted for publication in A&A on March 10th, 2023

Biosignature Line Ratios of [P II] in Exoplanetary and Nebular Environments [EPA]

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http://arxiv.org/abs/2301.07736


Being the backbone element of DNA, phosphorus is a key component in the search for life in the Universe. To aid in its detection, we present line emissivity ratios for the five lowest-lying forbidden [P~II] transitions, namely those among the levels $3s^23p^2(^3P_0,^3P_1, ^3P_2,^1D_2,^1S_0)$. The wavelengths range between 0.44-70 \mum, and several lie within the spectroscopic domain observable with the James Webb Space Telescope (JWST). These line ratios have been calculated using a new collisional-radiative-recombination (CRR) model combining calculated collision strengths and level-specific recombination rate coefficients; with both datasets computed using the accurate Breit-Pauli R-Matrix method. The CRR model includes a new scheme for \eion recombination to emission line formation. We compare its effect to models incorporating only electron impact excitation and spontaneous radiative decay. We find that electron-ion recombination has a significant impact on all line ratios, and represents a major improvement in physical accuracy of emission line models.

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K. Hoy, S. Nahar and A. Pradhan
Fri, 20 Jan 23
1/72

Comments: 5 pages, 4 figures

TESS Unveils the Full Phase Curve of WASP-19b [EPA]

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http://arxiv.org/abs/2301.07772


We present the detection and analysis of the full-orbit phase curve and secondary eclipse of the short-period transiting hot Jupiter system WASP-19b with a single joint fit to photometric data and resolve parameter degeneracy. We analyze data taken by the Transiting Exoplanet Survey Satellite (TESS) during sectors 9 and 36.

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M. Eftekhar and P. Adibi
Fri, 20 Jan 23
3/72

Comments: published 2022 November 15 The Planetary Science Journal

Tracing the history of an unusual compound presolar grain from progenitor star to asteroid parent body host [EPA]

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http://arxiv.org/abs/2301.08228


We conducted a TEM study of an unusual oxide-silicate composite presolar grain (F2-8) from the unequilibrated ordinary chondrite Semarkona. The presolar composite grain is relatively large, has an amoeboidal shape, and contains Mg-rich olivine, Mg-Al spinel, and Ca-rich pyroxene. The shape and phase assemblage are reminiscent of amoeboid-olivine-aggregates and add to the growing number of TEM observations of presolar refractory inclusion-like (CAIs and AOAs) grains. In addition to the dominant components, F2-8 also contains multiple subgrains, including an alabandite-oldhamite composite grain within the olivine and several magnetite subgrains within the Mg-Al spinel. We argue that the olivine, Mg-Al spinel, and alabandite-oldhamite formed by equilibrium condensation, whereas the Ca-rich pyroxene formed by non-equilibrium condensation, all in an M-type AGB star envelope. On the other hand, the magnetite subgrains are likely the result of aqueous alteration on the Semarkona asteroidal parent body. Additional evidence of secondary processing includes Fe-enrichment in the Mg-Al spinel and olivine, elevated Al contents in the olivine, and beam sensitivity and a modulated structure for the olivine. Compound presolar grains record condensation conditions over a wide range of temperatures. Additionally, the presence of several different presolar phases in a composite grain can impart information on the relative rates and effects of post-condensation processing in a range of environments, including the interstellar medium, solar nebula, and the host asteroid parent body. The TEM observations of F2-8 provide insights across the lifetime of the grain from its formation by condensation in an M-type AGB star envelope, its transit through the interstellar medium, and aqueous alteration during its residence on Semarkona’s asteroidal parent body.

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S. Singerling, L. Nittler, J. Barosch, et. al.
Fri, 20 Jan 23
6/72

Comments: 36 total pages, including 6 figures, 3 supplemental figures, 4 tables, and 2 supplemental tables

A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b [EPA]

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http://arxiv.org/abs/2301.08192


Close-in giant exoplanets with temperatures greater than 2,000 K (”ultra-hot Jupiters”) have been the subject of extensive efforts to determine their atmospheric properties using thermal emission measurements from the Hubble and Spitzer Space Telescopes. However, previous studies have yielded inconsistent results because the small sizes of the spectral features and the limited information content of the data resulted in high sensitivity to the varying assumptions made in the treatment of instrument systematics and the atmospheric retrieval analysis. Here we present a dayside thermal emission spectrum of the ultra-hot Jupiter WASP-18b obtained with the NIRISS instrument on JWST. The data span 0.85 to 2.85 $\mu$m in wavelength at an average resolving power of 400 and exhibit minimal systematics. The spectrum shows three water emission features (at $>$6$\sigma$ confidence) and evidence for optical opacity, possibly due to H$^-$, TiO, and VO (combined significance of 3.8$\sigma$). Models that fit the data require a thermal inversion, molecular dissociation as predicted by chemical equilibrium, a solar heavy element abundance (”metallicity”, M/H = 1.03$_{-0.51}^{+1.11}$ $\times$ solar), and a carbon-to-oxygen (C/O) ratio less than unity. The data also yield a dayside brightness temperature map, which shows a peak in temperature near the sub-stellar point that decreases steeply and symmetrically with longitude toward the terminators.

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L. Coulombe, B. Benneke, R. Challener, et. al.
Fri, 20 Jan 23
7/72

Comments: JWST ERS bright star observations. Uploaded to inform JWST Cycle 2 proposals. Manuscript under review. 50 pages, 14 figures, 2 tables

Characterisation of chaos in meteoroid streams. Application to the Geminids [EPA]

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http://arxiv.org/abs/2301.07998


Dynamically linking a meteor shower with its parent body can be challenging. This is in part due to the limit of today’s tools (such as D-criteria) and in part due to the complex dynamics of meteoroid streams. We choose a method to study chaos in meteoroid streams and apply it to the Geminid meteoroid stream. We decide to draw chaos maps. We show that the Orthogonal Fast Lyapunov Indicator is well-suited to our problem, amongst the chaos indicator we studied. The maps are drawn for three size bins, ranging from $10^{-1}$ to $10^{-4}$ m. We show the influence of mean-motion resonances with the Earth and with Venus, which tend to trap the largest particles. The chaos maps present 3 distinct regimes in eccentricity, reflecting close encounters with the planets. We also study the effect of non-gravitational forces. We determine a first approximation of the particle size $r_{lim}$ needed to counterbalance the resonances with the diffusion due to the non-gravitational forces. We find that, for the Geminids, $r_{lim}$ lies in the range $[3;8]\times 10^{-4}$ m. However, $r_{lim}$ depends on the orbital phase space.

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A. Courtot, J. Vaubaillon and M. Fouchard
Fri, 20 Jan 23
23/72

Comments: 14 pages, 14 figures, in revision for A&A

Characterization of a set of small planets with TESS and CHEOPS and an analysis of photometric performance [EPA]

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http://arxiv.org/abs/2301.08162


The radius valley carries implications for how the atmospheres of small planets form and evolve, but this feature is only visible with highly-precise characterizations of many small planets. We present the characterization of 9 planets and one planet candidate with both NASA TESS and ESA CHEOPS observations, which adds to the overall population of planets bordering the radius valley. While five of our planets – TOI 118 b, TOI 262 b, TOI 455 b, TOI 560 b, and TOI 562 b – have already been published, we vet and validate transit signals as planetary using followup observations for four new TESS planets, including TOI 198 b, TOI 244 b, TOI 444 b, and TOI 470 b. While a three times increase in primary mirror size should mean that one CHEOPS transit yields an equivalent model uncertainty in transit depth as about nine TESS transits under ideal conditions, we find that our CHEOPS transits typically yield uncertainties equivalent to between 2 and 12 TESS transits, averaging 5.9 equivalent transits. Therefore, we find that while our fits to CHEOPS transits provide overall lower uncertainties on transit depth and better precision relative to fits to TESS transits, our uncertainties for these fits do not always match expected predictions given photon-limited noise. We find no correlations between number of equivalent transits and any physical parameters, indicating that this behavior is not strictly systematic, but rather might be due to other factors such as in-transit gaps during CHEOPS visits or non-homogeneous detrending of CHEOPS light curves.

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D. Oddo, D. Dragomir, A. Brandeker, et. al.
Fri, 20 Jan 23
29/72

Comments: Accepted for publication in AJ

Grid-Based Simulations of Polar Circumbinary Disks: Polar Alignment and Vortex Formation [EPA]

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http://arxiv.org/abs/2301.07796


We describe the first grid-based simulations of the polar alignment of a circumbinary disk. We simulate the evolution of an inclined disk around an eccentric binary using the grid-based code ATHENA++. The use of a grid-based numerical code allows us to explore lower disk viscosities than have been examined in previous studies. We find that the disk aligns to a polar orientation when the $\alpha$ viscosity is high, while disks with lower viscosity nodally precess with little alignment over 1000 binary orbital periods. The timescales for polar alignment and disk precession are compared as a function of disk viscosity, and are found to be in agreement with previous studies. At very low disk viscosities (e.g. $\alpha = 10^{-5}$), anticyclonic vortices are observed along the inner edge of the disk. These vortices can persist for thousands of binary orbits, creating azimuthally localized overdensities as well as multiple pairs of spiral arms. The vortex is formed at $\sim 3-4$ times the binary semi-major axis, close to the inner edge of the disk, and orbits at roughly the local Keplerian speed. The presence of a vortex in the disk may play an important role in the evolution of circumbinary systems, such as driving episodic accretion and accelerating the formation of polar circumbinary planets.

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I. Rabago, Z. Zhu, R. Martin, et. al.
Fri, 20 Jan 23
37/72

Comments: 10 pages, 11 figures, Accepted for publication in MNRAS. Visualizations of the simulations in this paper can be found online at this https URL

The geometric albedo of the hot Jupiter HD 187933b measured with CHEOPS [EPA]

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http://arxiv.org/abs/2301.07731


Context.Measurements of the occultation of an exoplanet at visible wavelengths allow us to determine the reflective properties of a planetary atmosphere. The observed occultation depth can be translated into a geometric albedo. This in turn aids in characterising the structure and composition of an atmosphere by providing additional information on the wavelength-dependent reflective qualities of the aerosols in the atmosphere.
Aims. Our aim is to provide a precise measurement of the geometric albedo of the gas giant HD 189733b by measuring the occultation depth in the broad optical bandpass of CHEOPS (350 – 1100 nm).
Methods. We analysed 13 observations of the occultation of HD 189733b performed by CHEOPS utilising the Python package PyCHEOPS. The resulting occultation depth is then used to infer the geometric albedo accounting for the contribution of thermal emission from the planet. We also aid the analysis by refining the transit parameters combining observations made by the TESS and CHEOPS space telescopes.
Results. We report the detection of an $24.7 \pm 4.5$ ppm occultation in the CHEOPS observations. This occultation depth corresponds to a geometric albedo of $0.076 \pm 0.016$. Our measurement is consistent with models assuming the atmosphere of the planet to be cloud-free at the scattering level and absorption in the CHEOPS band to be dominated by the resonant Na doublet. Taking into account previous optical-light occultation observations obtained with the Hubble Space Telescope, both measurements combined are consistent with a super-stellar Na elemental abundance in the dayside atmosphere of HD 189733b. We further constrain the planetary Bond albedo to between 0.013 and 0.42 at 3$\sigma$ confidence.

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A. Krenn, M. Lendl, J. Patel, et. al.
Fri, 20 Jan 23
38/72

Comments: 17 pages, 10 figures, accepted for publication in A&A

Global mapping of fragmented rocks on the Moon with a neural network: Implications for the failure mode of rocks on airless surfaces [EPA]

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http://arxiv.org/abs/2301.08151


It has been recently recognized that the surface of sub-km asteroids in contact with the space environment is not fine-grained regolith but consists of centimeter to meter-scale rocks. Here we aim to understand how the rocky morphology of minor bodies react to the well known space erosion agents on the Moon. We deploy a neural network and map a total of ~130,000 fragmented boulders scattered across the lunar surface and visually identify a dozen different desintegration morphologies corresponding to different failure modes. We find that several fragmented boulder morphologies are equivalent to morphologies observed on asteroid Bennu, suggesting that these morphologies on the Moon and on asteroids are likely not diagnostic of their formation mechanism. Our findings suggest that the boulder fragmentation process is characterized by an internal weakening period with limited morphological signs of damage at rock scale until a sudden highly efficient impact shattering event occurs. In addition, we identify new morphologies such as breccia boulders with an advection-like erosion style. We publicly release the produced fractured boulder catalog along with this paper.

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O. Ruesch and V. Bickel
Fri, 20 Jan 23
44/72

Comments: N/A

Planet Search with the Keck/NIRC2 Vortex Coronagraph in Ms-band for Vega [EPA]

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http://arxiv.org/abs/2301.07714


Gaps in circumstellar disks can signal the existence of planetary perturbers, making such systems preferred targets for direct imaging observations of exoplanets. Being one of the brightest and closest stars to the Sun, the photometric standard star Vega hosts a two-belt debris disk structure. Together with the fact that its planetary system is being viewed nearly face-on, Vega has been one of the prime targets for planet imaging efforts. Using the vector vortex coronagraph on Keck/NIRC2 in Ms-band at 4.67 $\mu$m, we report the planet detection limits from 1 au to 22 au for Vega with an on-target time of 1.8 h. We reach a 3 Jupiter mass limit exterior to 12 au, which is nearly an order of magnitude deeper than existing studies. Combining with existing radial velocity studies, we can confidently rule out the existence of companions more than ~8 Jupiter mass from 22 au down to 0.1 au for Vega. Interior and exterior to ~4 au, this combined approach reaches planet detection limits down to ~2-3 Jupiter mass using radial velocity and direct imaging, respectively. By reaching multi-Jupiter mass detection limits, our results are expected to be complemented by the planet imaging of Vega in the upcoming observations using the James Webb Space Telescope to obtain a more holistic understanding of the planetary system configuration around Vega.

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B. Ren, N. Wallack, S. Hurt, et. al.
Fri, 20 Jan 23
54/72

Comments: 6 pages, 3 figures, 1 table, A&A accepted. Contrast curve for 2018 observation available in anc folder. Happy Rabbit Year!

DREAM I. Orbital architecture orrery [EPA]

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http://arxiv.org/abs/2301.07727


The distribution of close-in exoplanets is shaped by a complex interplay between atmospheric and dynamical processes. The Desert-Rim Exoplanets Atmosphere and Migration (DREAM) program aims at disentangling those processes through the study of the hot Neptune desert, whose rim hosts planets that are undergoing, or survived, atmospheric evaporation and orbital migration. In this first paper, we use the Rossiter-McLaughlin Revolutions (RMR) technique to investigate the orbital architecture of 14 close-in planets ranging from mini-Neptune to Jupiter-size and covering a broad range of orbital distances. While no signal is detected for the two smallest planets, we were able to constrain the sky-projected spin–orbit angle of six planets for the first time, to revise its value for six others, and, thanks to constraints on the stellar inclination, to derive the 3D orbital architecture in seven systems. These results reveal a striking three-quarters of polar orbits in our sample, all being systems with a single close-in planet but of various stellar and planetary types. High-eccentricity migration is favored to explain such orbits for several evaporating warm Neptunes, supporting the role of late migration in shaping the desert and populating its rim. Putting our measurements in the wider context of the close-in planet population will be useful to investigate the various processes shaping their architectures.

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V. Bourrier, O. Attia, M. Mallonn, et. al.
Fri, 20 Jan 23
65/72

Comments: 25 pages and 12 figures (plus Appendix)

Revisiting mass-radius relationships for exoplanet populations: a machine learning insight [EPA]

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http://arxiv.org/abs/2301.07143


The growing number of exoplanet discoveries and advances in machine learning techniques allow us to find, explore, and understand characteristics of these new worlds beyond our Solar System. We analyze the dataset of 762 confirmed exoplanets and eight Solar System planets using efficient machine-learning approaches to characterize their fundamental quantities. By adopting different unsupervised clustering algorithms, the data are divided into two main classes: planets with $\log R_{p}\leq0.91R_{\oplus}$ and $\log M_{p}\leq1.72M_{\oplus}$ as class 1 and those with $\log R_{p}>0.91R_{\oplus}$ and $\log M_{p}>1.72M_{\oplus}$ as class 2. Various regression models are used to reveal correlations between physical parameters and evaluate their performance. We find that planetary mass, orbital period, and stellar mass play preponderant roles in predicting exoplanet radius. The validation metrics (RMSE, MAE, and $R^{2}$) suggest that the Support Vector Regression has, by and large, better performance than other models and is a promising model for obtaining planetary radius. Not only do we improve the prediction accuracy in logarithmic space, but also we derive parametric equations using the M5P and Markov Chain Monte Carlo methods. Planets of class 1 are shown to be consistent with a positive linear mass-radius relation, while for planets of class 2, the planetary radius represents a strong correlation with their host stars’ masses.

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M. Mousavi-Sadr, D. Jassur and G. Gozaliasl
Thu, 19 Jan 23
1/100

Comments: Submitted to MNRAS. 15 pages, 17 figures

On computing viscoelastic Love numbers for general planetary models: the \texttt{ALMA${}^3$} code [EPA]

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http://arxiv.org/abs/2301.07351


The computation of the Love numbers for a spherically symmetric self-gravitating viscoelastic Earth is a classical problem in global geodynamics. Here we revisit the problem of the numerical evaluation of loading and tidal Love numbers in the static limit for an incompressible planetary body, adopting a Laplace inversion scheme based upon the Post-Widder formula as an alternative to the {traditional viscoelastic normal modes method. We also consider, whithin the same framework, complex-valued, frequency-dependent Love numbers that describe the response to a periodic forcing, which are paramount in the study of the tidal deformation of planets. Furthermore, we numerically obtain the time-derivatives of Love numbers, suitable for modeling geodetic signals in response to surface loads variations. A number of examples are shown, in which time and frequency-dependent Love numbers are evaluated for the Earth and planets adopting realistic rheological profiles. The numerical solution scheme is implemented in ALMA${}^3$ (the plAnetary Love nuMbers cAlculator, version 3), an upgraded open-source Fortran 90 program that computes the Love numbers for radially layered planetary bodies with a wide range of rheologies, including transient laws like Andrade or Burgers.

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D. Melini, C. Saliby and G. Spada
Thu, 19 Jan 23
30/100

Comments: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Geophysical Journal International following peer review. The version of record is available online at this https URL

Some additional results of the Hilda group orbital elements approximations [EPA]

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http://arxiv.org/abs/2301.07364


The quantitative characterization of amplitudes and periods of perturbations in orbital elements can help to our understanding the minor bodies dynamics, especially in case motion in vicinity of resonances. The main goal of this study is to present the new way of the orbital elements approximation by the results of numerical integration. We develop the approximation of orbital elements of the small body by the perturbations with combinational frequencies. We use a criterion of minimum of the standard error in our approximation. In result we give the approximation of orbital elements for the selected members of the Hilda group in the 3:2 mean motion resonance with Jupiter.

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A. Rosaev
Thu, 19 Jan 23
35/100

Comments: 7 pages, 5 figures

Redox evolution of the crystallizing terrestrial magma ocean and its influence on atmosphere outgassing [EPA]

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http://arxiv.org/abs/2301.07505


Magma oceans are episodes of large-scale melting of the mantle of terrestrial planets. The energy delivered by the Moon-forming impact induced a deep magma ocean on the young Earth, corresponding to the last episode of core-mantle equilibration. The crystallization of this magma ocean led to the outgassing of volatiles initially present in the Earth’s mantle, resulting in the formation of a secondary atmosphere. During outgassing, the magma ocean acts as a chemical buffer for the atmosphere via the oxygen fugacity, set by the equilibrium between ferrous- and ferric-iron oxides in the silicate melts. By tracking the evolution of the oxygen fugacity during magma ocean solidification, we model the evolving composition of a C-O-H atmosphere. We use the atmosphere composition to calculate its thermal structure and radiative flux. This allows us to calculate the lifetime of the terrestrial magma ocean. We find that, upon crystallizing, the magma ocean evolves from a mildly reducing to a highly oxidized redox state, thereby transiting from a CO- and H2-dominated atmosphere to a CO2- and H2O-dominated one. We find the overall duration of the magma ocean crystallization to depend mostly on the bulk H content of the mantle, and to remain below 1.5 millions years for up to 9 Earth’s water oceans’ worth of H. Our model also suggests that reduced atmospheres emit lower infrared radiation than oxidized ones, despite of the lower greenhouse effect of reduced species, resulting in a longer magma ocean lifetime in the former case. Although developed for a deep magma ocean on Earth, the framework applies to all terrestrial planet and exoplanet magma oceans, depending on their volatile budgets.

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M. Maurice, R. Dasgupta and P. Hassanzadeh
Thu, 19 Jan 23
80/100

Comments: 31 pages, 9+2 figures, accepted for publication in PSJ

Hint of an exocomet transit in the CHEOPS lightcurve of HD 172555 [EPA]

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http://arxiv.org/abs/2301.07418


HD$\,$172555 is a young ($\sim$20$\,$Myr) A7V star surrounded by a 10$\,$au wide debris disk suspected to be replenished partly by collisions between large planetesimals. Small evaporating transiting bodies, exocomets, have also been detected in this system by spectroscopy. After $\beta\,$Pictoris, this is another example of a system possibly witnessing a phase of heavy bombardment of planetesimals. In such system, small bodies trace dynamical evolution processes. We aim at constraining their dust content by using transit photometry. We performed a 2-day-long photometric monitoring of HD$\,$172555 with the CHEOPS space telescope in order to detect shallow transits of exocomets with a typical expected duration of a few hours. The large oscillations in the lightcurve indicate that HD$\,$172555 is a $\delta\,$Scuti pulsating star. Once removing those dominating oscillations, we find a hint for a transient absorption. If fitted with an exocomet transit model, it corresponds to an evaporating body passing near the star at a distance of $6.8\pm1.4\,$R$_\star$ (or $0.05\pm 0.01\,$au) with a radius of 2.5 km. These properties are comparable to those of the exocomets already found in this system using spectroscopy, as well as those found in the $\beta\,$Pic system. The nuclei of solar system’s Jupiter family comets, with radii of 2-6$\,$km, are also comparable in size. This is the first evidence for an exocomet photometric transit detection in the young system of HD$\,$172555.

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F. Kiefer, V. Grootel, A. Etangs, et. al.
Thu, 19 Jan 23
99/100

Comments: 12 pages, 10 figures, 5 tables, accepted for publication in A&A

A 2022 $τ$-Herculid meteor cluster from an airborne experiment: automated detection, characterization, and consequences for meteoroids [EPA]

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http://arxiv.org/abs/2301.06851


Context. The existence of meteor clusters has long since been a subject of speculation and so far only seven events have been reported, among which two involve less than five meteors, and three were seen during the Leonid storms. Aims. The 1995 outburst of Comet 73P/Schwassmann-Wachmann was predicted to result in a meteor shower in May 2022. We detected the shower, proved this to be the result of this outburst, and detected another meteor cluster during the same observation mission. Methods. The {\tau}-Herculids meteor shower outburst on 31 May 2022 was continuously monitored for 4 hours during an airborne campaign. The video data were analyzed using a recently developed computer-vision processing chain for meteor real-time detection. Results. We report and characterize the detection of a meteor cluster involving 38 fragments, detected at 06:48 UT for a total duration of 11.3 s. The derived cumulative size frequency distribution index is relatively shallow: s = 3.1. Our open-source computer-vision processing chain (named FMDT) detects 100% of the meteors that a human eye is able to detect in the video. Classical automated motion detection assuming a static camera was not suitable for the stabilized camera setup because of residual motion. Conclusions. From all reported meteor clusters, we crudely estimate their occurrence to be less than one per million observed meteors. Low heliocentric distance enhances the probability of such meteoroid self-disruption in the interplanetary space.

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J. Vaubaillon, C. Loir, C. Ciocan, et. al.
Wed, 18 Jan 23
1/133

Comments: 6 pqges, 5 figures

Neural posterior estimation for exoplanetary atmospheric retrieval [EPA]

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http://arxiv.org/abs/2301.06575


Retrieving the physical parameters from spectroscopic observations of exoplanets is key to understanding their atmospheric properties. Exoplanetary atmospheric retrievals are usually based on approximate Bayesian inference and rely on sampling-based approaches to compute parameter posterior distributions. Accurate or repeated retrievals, however, can result in very long computation times due to the sequential nature of sampling-based algorithms. We aim to amortize exoplanetary atmospheric retrieval using neural posterior estimation (NPE), a simulation-based inference algorithm based on variational inference and normalizing flows. In this way, we aim (i) to strongly reduce inference time, (ii) to scale inference to complex simulation models with many nuisance parameters or intractable likelihood functions, and (iii) to enable the statistical validation of the inference results. We evaluate NPE on a radiative transfer model for exoplanet spectra petitRADTRANS, including the effects of scattering and clouds. We train a neural autoregressive flow to quickly estimate posteriors and compare against retrievals computed with MultiNest. NPE produces accurate posterior approximations while reducing inference time down to a few seconds. We demonstrate the computational faithfulness of our posterior approximations using inference diagnostics including posterior predictive checks and coverage, taking advantage of the quasi-instantaneous inference time of NPE. Our analysis confirms the reliability of the approximate posteriors produced by NPE. The accuracy and reliability of the inference results produced by NPE establishes it as a promising approach for atmospheric retrievals. Amortization of the posterior inference makes repeated inference on several observations computationally inexpensive since it does not require on-the-fly simulations, making the retrieval efficient, scalable, and testable.

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M. Vasist, F. Rozet, O. Absil, et. al.
Wed, 18 Jan 23
7/133

Comments: N/A

GJ 806 (TOI-4481): A bright nearby multi-planetary system with a transiting hot, low-density super-Earth [EPA]

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http://arxiv.org/abs/2301.06873


One of the main scientific goals of the TESS mission is the discovery of transiting small planets around the closest and brightest stars in the sky. Here, using data from the CARMENES, MAROON-X, and HIRES spectrographs, together with TESS, we report the discovery and mass determination of a planetary system around the M1.5 V star GJ 806 (TOI-4481). GJ 806 is a bright (V=10.8 mag, J=7.3 mag) and nearby (d=12 pc) M dwarf that hosts at least two planets. The innermost planet, GJ 806 b, is transiting and has an ultra-short orbital period of 0.93 d, a radius of 1.331+-0.023 Re, a mass of 1.90+-0.17 Me, a mean density of 4.40+-0.45 g/cm3, and an equilibrium temperature of 940+-10 K. We detect a second, non-transiting, super-Earth planet in the system, GJ 806c, with an orbital period of 6.6 d, a minimum mass of 5.80+-0.30 Me, and an equilibrium temperature of 490+-5 K. The radial velocity data also shows evidence for a third periodicity at 13.6 d, although the current dataset does not provide sufficient evidence to unambiguously distinguish between a third super-Earth mass (Msin(i)=8.50+-0.45 Me) planet or stellar activity. Additionally, we report one transit observation of GJ 806 b taken with CARMENES in search for a possible extended atmosphere of H or He, but we can only place upper limits to its existence. This is not surprising as our evolutionary models support the idea that any possible primordial H/He atmosphere that GJ 806 b might have had, would long have been lost. However, GJ 806b’s bulk density makes it likely that the planet hosts some type of volatile atmosphere. In fact, with a transmission spectroscopy metrics (TSM) of 44 and an emission spectroscopy metrics (ESM) of 24, GJ 806 b the third-ranked terrestrial planet around an M dwarf suitable for transmission spectroscopy studies, and the most promising terrestrial planet for emission spectroscopy studies.

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E. Palle, J. Orell-Miquel, M. Brady, et. al.
Wed, 18 Jan 23
21/133

Comments: Under second review in A&A. This paper is NOT yet accepted, but it is made openly available to the community due to the approaching JWST deadline

Takeout and Delivery: Erasing the Dusty Signature of Late-stage Terrestrial Planet Formation [EPA]

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http://arxiv.org/abs/2301.05719


The formation of planets like Earth is expected to conclude with a series of late-stage giant impacts that generate warm dusty debris, the most anticipated visible signpost of terrestrial planet formation in progress. While there is now evidence that Earth-sized terrestrial planets orbit a significant fraction of solar-type stars, the anticipated dusty debris signature of their formation is rarely detected. Here we discuss several ways in which our current ideas about terrestrial planet formation imply transport mechanisms capable of erasing the anticipated debris signature. A tenuous gas disk may be regenerated via “takeout” (i.e., the liberation of planetary atmospheres in giant impacts) or “delivery” (i.e., by asteroids and comets flung into the terrestrial planet region) at a level sufficient to remove the warm debris. The powerful stellar wind from a young star can also act, its delivered wind momentum producing a drag that removes warm debris. If such processes are efficient, terrestrial planets may assemble inconspicuously, with little publicity and hoopla accompanying their birth. Alternatively, the rarity of warm excesses may imply that terrestrial planets typically form very early, emerging fully formed from the nebular phase without undergoing late-stage giant impacts. In either case, the observable signposts of terrestrial planet formation appear more challenging to detect than previously assumed. We discuss observational tests of these ideas.

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J. Najita and S. Kenyon
Wed, 18 Jan 23
26/133

Comments: 20 pages, 3 figures, accepted for publication in ApJ

Dynamical tides in Jupiter and other rotationally flattened planets and stars with stable stratification [EPA]

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http://arxiv.org/abs/2301.07097


We develop a numerical method for directly computing the dissipative dynamical tidal response of rapidly rotating, oblate stars and gaseous planets with realistic internal structures. Applying these calculations to neutrally and stably stratified polytropes, we identify the most relevant resonances in models with rotation rates up to nearly the mass-shedding limit. We then compute the dynamical tidal response for Jupiter interior models including both stably stratified and convective regions. These calculations show that resonances involving waves with both gravito-inertial and purely inertial character are capable of explaining a discrepancy between observations and hydrostatic calculations of Jupiter’s response to tidal forcing by Io. This result contrasts with recent work that excluded Jupiter’s rotational flattening, and opens the door to resonances involving a wider range of internal oscillation modes than previously considered.

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J. Dewberry
Wed, 18 Jan 23
34/133

Comments: 14 pages, 10 figures, submitted to MNRAS (comments welcome)

Has the dust clump in the debris disk of Beta Pictoris moved? [EPA]

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http://arxiv.org/abs/2301.06891


The edge-on debris disk of the nearby young star Beta Pictoris shows an unusual brightness asymmetry in the form of a clump. The clump has been detected in both the mid-IR and CO and its origin has so far remained uncertain. Here we present new mid-IR observations of Beta Pic to track any motion of the dust clump. Together with previous observations, the data span a period of 12 years. We measured any projected displacement of the dust clump over the 12-yr period to be $0.2^{+1.3}_{-1.4}$ au away from the star based on the median and 1$\sigma$ uncertainty, and constrain this displacement to be <11 au at the 3$\sigma$ level. This implies that the observed motion is incompatible with Keplerian motion at the 2.8$\sigma$ level. It has been posited that a planet migrating outwards may trap planetesimals into a 2:1 resonance, resulting in the observed clump at pericentre of their orbits that trails the planet. The observed motion is also incompatible with such resonant motion at the 2.6$\sigma$ level. While Keplerian motion and resonant motion is still possible, the data suggest that the dust clump is more likely stationary. Such a stationary dust clump could originate from the collision or tidal disruption of a planet-sized body, or from secular perturbations due to a planet that create regions with enhanced densities in the disk.

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Y. Han, M. Wyatt and W. Dent
Wed, 18 Jan 23
44/133

Comments: 14 pages, 8 figures, 5 tables. Published in MNRAS

Switching integrators reversibly in the astrophysical $N$-body problem [EPA]

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http://arxiv.org/abs/2301.06253


We present a simple algorithm to switch between $N$-body time integrators in a reversible way. We apply it to planetary systems undergoing arbitrarily close encounters and highly eccentric orbits, but the potential applications are broader. Upgrading an ordinary non-reversible switching integrator to a reversible one is straightforward and introduces no appreciable computational burden in our tests. Our method checks if the integrator during the time step violates a time-symmetric selection condition and redoes the step if necessary. In our experiments a few percent of steps would have violated the condition without our corrections. By eliminating them the algorithm avoids long-term error accumulation, of several orders magnitude in some cases.

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D. Hernandez and W. Dehnen
Wed, 18 Jan 23
49/133

Comments: 10 pages, 8 figures, submitted to MNRAS, comments welcome

Polarized Signatures of a Habitable World: Comparing Models of an Exoplanet Earth with Visible and Near-infrared Earthshine Spectra [EPA]

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http://arxiv.org/abs/2301.05734


In the JWST, Extremely Large Telescopes, and LUVOIR era, we expect to characterize a number of potentially habitable Earth-like exoplanets. However, the characterization of these worlds depends crucially on the accuracy of theoretical models. Validating these models against observations of planets with known properties will be key for the future characterization of terrestrial exoplanets. Due to its sensitivity to the micro- and macro-physical properties of an atmosphere, polarimetry will be an important tool that, in tandem with traditional flux-only observations, will enhance the capabilities of characterizing Earth-like planets. In this paper we benchmark two different polarization-enabled radiative-transfer codes against each other and against unique linear spectropolarimetric observations of the earthshine that cover wavelengths from $\sim$0.4 to $\sim$2.3 $\mu$m. We find that while the results from the two codes generally agree with each other, there is a phase dependency between the compared models. Additionally, with our current assumptions, the models from both codes underestimate the level of polarization of the earthshine. We also report an interesting discrepancy between our models and the observed 1.27 $\mu$m $O_2$ feature in the earthshine, and provide an analysis of potential methods for matching this feature. Our results suggest that only having access to the 1.27 $\mu$m $O_2$ feature coupled with a lack of observations of the $O_2$ A and B bands could result in a mischaracterization of an Earth-like atmosphere. Providing these assessments is vital to aid the community in the search for life beyond the solar system.

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K. Gordon, T. Karalidi, K. Bott, et. al.
Wed, 18 Jan 23
57/133

Comments: 24 pages, 18 figures

Glycine amino acid transformation under impacts by small solar system bodies, simulated via high-pressure torsion method [EPA]

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http://arxiv.org/abs/2301.06927


Impacts by small solar system bodies (meteoroids, asteroids, comets and transitional objects) are characterized by a combination of energy dynamics and chemical modification on both terrestrial and small solar system bodies. In this context, the discovery of glycine amino acid in meteorites and comets has led to a hypothesis that impacts by astronomical bodies could contribute to delivery and polymerization of amino acids in the early Earth to generate proteins as essential molecules for life. Besides the possibility of abiotic polymerization of glycine, its decomposition by impacts could generate reactive groups to form other essential organic biomolecules. In this study, the high-pressure torsion (HPT) method, as a new platform for simulation of impacts by small solar system bodies, was applied to glycine. In comparison with high-pressure shock experiments, the HPT method simultaneously introduces high pressure and deformation strain. It was found that glycine was not polymerized in the experimental condition assayed, but partially decomposed to ethanol under pressures of 1 and 6 GPa and shear strains of <120 m/m. The detection of ethanol implies the inherent availability of remaining nitrogen-containing groups, which can incorporate to the formation of other organic molecules at the impact site. In addition, this finding highlights a possibility of the origin of ethanol previously detected in comets.

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K. Edalati, I. Taniguchi, R. Floriano, et. al.
Wed, 18 Jan 23
58/133

Comments: N/A

KMT-2022-BLG-0440Lb: A New $q < 10^{-4}$ Microlensing Planet with the Central-Resonant Caustic Degeneracy Broken [EPA]

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http://arxiv.org/abs/2301.06779


We present the observations and analysis of a high-magnification microlensing planetary event, KMT-2022-BLG-0440, for which the weak and short-lived planetary signal was covered by both the KMTNet survey and follow-up observations. The binary-lens models with a central caustic provide the best fits, with a planet/host mass ratio, $q = 0.75$–$1.00 \times 10^{-4}$ at $1\sigma$. The binary-lens models with a resonant caustic and a brown-dwarf mass ratio are both excluded by $\Delta\chi^2 > 70$. The binary-source model can fit the anomaly well but is rejected by the “color argument” on the second source. From Bayesian analyses, it is estimated that the host star is likely a K or M dwarf located in the Galactic disk, the planet probably has a Neptune-mass, and the projected planet-host separation is $1.9^{+0.6}{-0.7}$ or $4.6^{+1.4}{-1.7}$ au, subject to the close/wide degeneracy. This is the third $q < 10^{-4}$ planet from a high-magnification planetary signal ($A \gtrsim 65$). Together with another such planet, KMT-2021-BLG-0171Lb, the ongoing follow-up program for the KMTNet high-magnification events has demonstrated its ability in detecting high-magnification planetary signals for $q < 10^{-4}$ planets, which are challenging for the current microlensing surveys.

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J. Zhang, W. Zang, Y. Jung, et. al.
Wed, 18 Jan 23
59/133

Comments: to be submitted to MNRAS

Pluto's Surface Mapping using Unsupervised Learning from Near-Infrared Observations of LEISA/Ralph [EPA]

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http://arxiv.org/abs/2301.06027


We map the surface of Pluto using an unsupervised machine learning technique using the near-infrared observations of the LEISA/Ralph instrument onboard NASA’s New Horizons spacecraft. The principal component reduced Gaussian mixture model was implemented to investigate the geographic distribution of the surface units across the dwarf planet. We also present the likelihood of each surface unit at the image pixel level. Average I/F spectra of each unit were analyzed — in terms of the position and strengths of absorption bands of abundant volatiles such as N${}{2}$, CH${}{4}$, and CO and nonvolatile H${}_{2}$O — to connect the unit to surface composition, geology, and geographic location. The distribution of surface units shows a latitudinal pattern with distinct surface compositions of volatiles — consistent with the existing literature. However, previous mapping efforts were based primarily on compositional analysis using spectral indices (indicators) or implementation of complex radiative transfer models, which need (prior) expert knowledge, label data, or optical constants of representative endmembers. We prove that an application of unsupervised learning in this instance renders a satisfactory result in mapping the spatial distribution of ice compositions without any prior information or label data. Thus, such an application is specifically advantageous for a planetary surface mapping when label data are poorly constrained or completely unknown, because an understanding of surface material distribution is vital for volatile transport modeling at the planetary scale. We emphasize that the unsupervised learning used in this study has wide applicability and can be expanded to other planetary bodies of the Solar System for mapping surface material distribution.

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A. Emran, C. Ore, C. Ahrens, et. al.
Wed, 18 Jan 23
81/133

Comments: Accepted for publication in The Planetary Science Journal. 50 pages, 17 figures including appendix

Interplanetary Laser Tri-lateration Network: simulation with INPOP planetary ephemerides [EPA]

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http://arxiv.org/abs/2301.06394


This study is done in the context of the project titled Interplanetary Laser Tri-lateration Network (ILTN) proposed by \cite{2018P&SS..153..127S} and investigated more in details by \cite{2022P&SS..21405415B} and \cite{2022P&SS..21505423B}. The original idea was to propose interplanetary measurements (in this case between Venus, Mars and the earth) as a way to measure the solar system expansion. But some recent interests on the measurement of asteroid masses and more generally the study of the mass distribution in the outer solar system appear with the ILTN. In this work, we are investigating how different possible configurations of interplanetary measurements of distances can be introduced in planetary ephemeris construction and how they improve our knowledge of planet orbits and other related parameters.

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A. Fienga
Wed, 18 Jan 23
84/133

Comments: N/A

Chelyabinsk : a rock with many different (stony) faces: An infrared study [EPA]

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http://arxiv.org/abs/2301.06525


In order to provide spectral ground truth data for remote sensing applications, we have measured midinfrared spectra (2 to 18 micron) of three typical, well defined lithologies from the Chelyabinsk meteorite. These lithologies are classified as (a) moderately shocked, light lithology, (b) shock darkened lithology, and (c) impact melt lithology. Analyses were made from bulk material in four size fractions (0 to 25 micron, 25 to 63 micron, 63 to 125 micron, and 125 to 250 micron), and from additional thin sections. Characteristic infrared features in the powdered bulk material of the moderately shocked, light lithology, dominated by olivine, pyroxene and feldspathic glass, are a Christiansen feature (CF) between 8.5 and 8.8 micron; a transparency feature (TF) in the finest size fraction at about 13 micron, and strong reststrahlen bands (RB) at about 9.1 micron, 9.5 micron, 10.3 micron, 10.8 micron, 11.2 to 11.3 micron, 12 micron, and between 16 and 17 micron. The ranges of spectral features for the micro FTIR spots show a wider range than those obtained in diffuse reflectance, but are generally similar. With increasing influence of impact shock from pristine LL5 (or LL6) material (which have a low or moderate degree of shock) to the shock-darkened lithology and the impact melt lithology as endmembers, we observe the fading or disappearing of spectral features. Most prominent is the loss of a twin peak feature between 10.8 and 11.3 micron, which turns into a single peak. In addition, in the pure impact melt endmember lithology features at about 9.6 micron and about 9.1 micron are also lost. These losses are most likely correlated with decreasing amounts of crystal structure as the degree of shock melting increases.

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A. Morlok, A. Bischoff, M. Patzeck, et. al.
Wed, 18 Jan 23
92/133

Comments: N/A

Terrestrial Effects of Nearby Supernovae: Updated Modeling [EPA]

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http://arxiv.org/abs/2301.05757


We have re-evaluated recent studies of effects on Earth by cosmic rays (CRs) from nearby supernovae (SNe) at 100 pc and 50 pc, in the diffusive transport CR case, here including an early time suppression at lower CR energies neglected in the previous work. Inclusion of this suppression leads to lower overall CR flux at early times, lower atmospheric ionization, smaller resulting ozone depletion, and lower sea-level muon radiation dose. Differences in atmospheric impacts are most pronounced for the 100 pc case with less significant differences in the 50 pc case. We find a greater discrepancy in the modeled sea-level muon radiation dose, with significantly smaller dose values in the 50 pc case; our results indicate it is unlikely that muon radiation is a significant threat to the biosphere for SNe beyond at least 20 pc. We have also performed new modeling of effects by SNe at 20 pc and 10 pc. Overall, our results indicate that, considering only effects of SN CRs, the “lethal” SN distance may be closer to 20 pc rather than the typically quoted 8-10 pc.

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B. Thomas and A. Yelland
Wed, 18 Jan 23
102/133

Comments: 21 pages, 6 figures; submitted to ApJ

A Mixed Stirring Mechanism for Debris Discs with Giant and Dwarf Planetary Perturbations [EPA]

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http://arxiv.org/abs/2301.05265


Debris discs consist of belts of bodies ranging in size from dust grains to planetesimals; these belts are visible markers of planetary systems around other stars that can reveal the influence of extrasolar planets through their shape and structure. Two key stirring mechanisms — self-stirring by planetesimals and secular perturbation by an external giant planet — have been identified to explain the dynamics of planetesimal belts; their relative importance has been studied independently, but are yet to be considered in combination. In this work we perform a suite of 286 N-body simulations exploring the evolution of debris discs over 1~Gyr, combining the gravitational perturbations of both dwarf planets embedded in the discs, and an interior giant planet. Our systems were somewhat modeled after the architecture of the outer Solar system: a Solar mass star, a single massive giant planet at 30~au ($M_{\rm GP} =$ 10 to 316~$\mathrm{M}{\oplus}$), and a debris disc formed by 100 massive dwarf planets and 1000 massless particles ($M{\rm DD} =$ 3.16 to 31.6~$\mathrm{M}_{\oplus}$). We present the evolution of both the disc and the giant planet after 1~Gyr. The time evolution of the average eccentricity and inclination of the disc is strongly dependent on the giant planet mass as well as on the remaining disc mass. We also found that efficient stirring is achieved even with small disc masses. In general, we find that a mixed mechanism is more efficient in the stirring of cold debris discs than either mechanism acting in isolation.

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M. Muñoz-Gutiérrez, J. Marshall and A. Peimbert
Mon, 16 Jan 23
1/50

Comments: Accepted for publication in MNRAS. 11 pages, 6 figures (4 animated). Animated figures can be found at this https URL

Leaky Dust Traps: How Fragmentation impacts Dust Filtering by Planets [EPA]

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http://arxiv.org/abs/2301.05505


The nucleosynthetic isotope dichotomy between carbonaceous and non-carbonaceous meteorites has been interpreted as evidence for spatial separation and coexistence of two distinct planet-forming reservoirs for several million years in the solar protoplanetary disk. Rapid formation of Jupiter’s core within one million years after CAIs has been suggested as a potential mechanism for spatial and temporal separation. In this scenario, Jupiter’s core would open a gap in the disk and trap inwards-drifting dust grains in the pressure bump at the outer edge of the gap, separating the inner and outer disk materials from each other. We performed simulations of dust particles in a protoplanetary disk with a gap opened by an early formed Jupiter core, including dust growth and fragmentation as well as dust transport using the dust evolution software DustPy. Our numerical experiments indicate that particles trapped in the outer edge of the gap rapidly fragment and are transported through the gap, contaminating the inner disk with outer disk materials on a timescale that is inconsistent with the meteoritic record. This suggests that other processes must have initiated or at least contributed to the isotopic separation between the inner and outer Solar System.

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S. Stammler, T. Lichtenberg, J. Drążkowska, et. al.
Mon, 16 Jan 23
11/50

Comments: Accepted for publication in Astronomy & Astrophysics Letters

Carbon Depletion in the Early Solar System [EPA]

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http://arxiv.org/abs/2301.05706


Earth and other rocky objects in the inner Solar System are depleted in carbon compared to objects in the outer Solar System, the Sun, or the ISM. It is believed that this is a result of the selective removal of refractory carbon from primordial circumstellar material. In this work, we study the irreversible release of carbon into the gaseous environment via photolysis and pyrolysis of refractory carbonaceous material during the disk phase of the early Solar System. We analytically solve the one-dimensional advection equation and derive an explicit expression that describes the depletion of carbonaceous material in solids under the influence of radial and vertical transport. We find both depletion mechanisms individually fail to reproduce Solar System abundances under typical conditions. While radial transport only marginally restricts photodecomposition, it is the inefficient vertical transport that limits carbon depletion under these conditions. We show explicitly that an increase in the vertical mixing efficiency, and/or an increase in the directly irradiated disk volume, favors carbon depletion. Thermal decomposition requires a hot inner disk (> 500 K) beyond 3 AU to deplete the formation region of Earth and chondrites. We find FU Ori-type outbursts to produce these conditions such that moderately refractory compounds are depleted. However, such outbursts likely do not deplete the most refractory carbonaceous compounds beyond the innermost disk region. Hence, the refractory carbon abundance at 1 AU typically does not reach terrestrial levels. Nevertheless, under specific conditions, we find photolysis and pyrolysis combined to reproduce Solar System abundances.

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F. Binkert and T. Birnstiel
Mon, 16 Jan 23
20/50

Comments: Accepted for publication in MNRAS

Probing Ganymede's atmosphere with HST Ly$α$ images in transit of Jupiter [EPA]

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http://arxiv.org/abs/2301.05583


We report results from far-ultraviolet observations by the Hubble Space Telescope of Jupiter’s largest moon Ganymede transiting across the planet’s dayside hemisphere. {Within} a targeted campaign on 9 September 2021 two exposures were taken during one transit passage to probe for attenuation of Jupiter’s hydrogen Lyman-$\alpha$ dayglow above the moon limb. The background dayglow is slightly attenuated over an extended region around Ganymede, with stronger attenuation in the second exposure when Ganymede was near the planet’s center. In the first exposure when the moon was closer to Jupiter’s limb, the effects from the Ganymede corona are hardly detectable, likely because the Jovian Lyman-$\alpha$ dayglow is spectrally broader and less intense at this viewing geometry. The obtained vertical H column densities of around $(1-2)\times 10^{12}$~cm$^{-2}$ are consistent with previous results. Constraining angular variability around Ganymede’s disk, we derive an upper limit on a local H$_2$O column density of $(2-3)\times 10^{16}$~cm$^{-2}$, such as could arise from outgassing plumes in regions near the observed moon limb.

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L. Roth, G. Marchesini, T. Becker, et. al.
Mon, 16 Jan 23
21/50

Comments: N/A

Detection of HCN and diverse redox chemistry in the plume of Enceladus [EPA]

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http://arxiv.org/abs/2301.05259


The Cassini spacecraft discovered that Saturn’s moon Enceladus possesses a series of jets erupting from its South Polar Terrain. Previous studies of in situ data collected by Cassini’s Ion and Neutral Mass Spectrometer (INMS) have identified H$_2$O, CO$_2$, CH$_4$, H$_2$, and NH$_3$ within the plume of ejected material. Identification of minor species in the plume remains an ongoing challenge, owing to the large number of possible combinations that can be used to fit the INMS data. Here, we present the discovery of several new compounds of strong importance to the habitability of Enceladus, including HCN, CH$_2$O, C$_2$H$_2$, and C$_3$H$_6$. Our analyses of the low velocity INMS data coupled with our detailed statistical framework enable discriminating between previously ambiguous species in the plume by alleviating the effects of high-dimensional model fitting. Together with plausible mineralogical catalysts and redox gradients derived from surface radiolysis, these compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life.

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J. Peter, T. Nordheim and K. Hand
Mon, 16 Jan 23
22/50

Comments: 20 pages, 8 figures

Size-selective accretion of dust onto CPDs: Low CPD masses and filtration of larger grains [EPA]

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http://arxiv.org/abs/2301.05662


The major satellites of Jupiter and Saturn are believed to have formed in circumplanetary discs, which orbit forming giant protoplanets. Gas and dust in CPDs have different distributions and affect each other by drag, which varies with grain size. Yet simulations of multiple dust grain sizes with separate dynamics have not been done before. We seek to assess how much dust of each grain size there is in circumplanetary discs. We run multifluid 3D hydrodynamical simulations including gas and four discrete grain sizes of dust from 1$\mu$m to 1mm, representing a continuous distribution. We consider a 1 $M_\mathrm{Jup}$ protoplanet embedded in a protoplanetary disc around a 1 $M_{\odot}$ star. Our results show a truncated MRN distribution at smaller grain sizes, which starts to tail off by $a=100\mu$m and is near zero at 1mm. Large dust grains, which hold most of the dust mass, have very inefficient accretion to the CPD, due to dust filtration. Therefore CPDs’ dust masses must be small, with mass ratio ~ a few $\times 10^{-6}$ to the protoplanet. These masses and the corresponding millimetre opacities are in line with CPD fluxes observed to date.

Read this paper on arXiv…

S. Karlin, O. Panić and S. Loo
Mon, 16 Jan 23
24/50

Comments: 14 pages, 15 figures; accepted for publication in MNRAS

Size-selective accretion of dust onto CPDs: Low CPD masses and filtration of larger grains [EPA]

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http://arxiv.org/abs/2301.05662


The major satellites of Jupiter and Saturn are believed to have formed in circumplanetary discs, which orbit forming giant protoplanets. Gas and dust in CPDs have different distributions and affect each other by drag, which varies with grain size. Yet simulations of multiple dust grain sizes with separate dynamics have not been done before. We seek to assess how much dust of each grain size there is in circumplanetary discs. We run multifluid 3D hydrodynamical simulations including gas and four discrete grain sizes of dust from 1$\mu$m to 1mm, representing a continuous distribution. We consider a 1 $M_\mathrm{Jup}$ protoplanet embedded in a protoplanetary disc around a 1 $M_{\odot}$ star. Our results show a truncated MRN distribution at smaller grain sizes, which starts to tail off by $a=100\mu$m and is near zero at 1mm. Large dust grains, which hold most of the dust mass, have very inefficient accretion to the CPD, due to dust filtration. Therefore CPDs’ dust masses must be small, with mass ratio ~ a few $\times 10^{-6}$ to the protoplanet. These masses and the corresponding millimetre opacities are in line with CPD fluxes observed to date.

Read this paper on arXiv…

S. Karlin, O. Panić and S. Loo
Mon, 16 Jan 23
3/50

Comments: 14 pages, 15 figures; accepted for publication in MNRAS

Detection of HCN and diverse redox chemistry in the plume of Enceladus [EPA]

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http://arxiv.org/abs/2301.05259


The Cassini spacecraft discovered that Saturn’s moon Enceladus possesses a series of jets erupting from its South Polar Terrain. Previous studies of in situ data collected by Cassini’s Ion and Neutral Mass Spectrometer (INMS) have identified H$_2$O, CO$_2$, CH$_4$, H$_2$, and NH$_3$ within the plume of ejected material. Identification of minor species in the plume remains an ongoing challenge, owing to the large number of possible combinations that can be used to fit the INMS data. Here, we present the discovery of several new compounds of strong importance to the habitability of Enceladus, including HCN, CH$_2$O, C$_2$H$_2$, and C$_3$H$_6$. Our analyses of the low velocity INMS data coupled with our detailed statistical framework enable discriminating between previously ambiguous species in the plume by alleviating the effects of high-dimensional model fitting. Together with plausible mineralogical catalysts and redox gradients derived from surface radiolysis, these compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life.

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J. Peter, T. Nordheim and K. Hand
Mon, 16 Jan 23
4/50

Comments: 20 pages, 8 figures

Probing Ganymede's atmosphere with HST Ly$α$ images in transit of Jupiter [EPA]

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http://arxiv.org/abs/2301.05583


We report results from far-ultraviolet observations by the Hubble Space Telescope of Jupiter’s largest moon Ganymede transiting across the planet’s dayside hemisphere. {Within} a targeted campaign on 9 September 2021 two exposures were taken during one transit passage to probe for attenuation of Jupiter’s hydrogen Lyman-$\alpha$ dayglow above the moon limb. The background dayglow is slightly attenuated over an extended region around Ganymede, with stronger attenuation in the second exposure when Ganymede was near the planet’s center. In the first exposure when the moon was closer to Jupiter’s limb, the effects from the Ganymede corona are hardly detectable, likely because the Jovian Lyman-$\alpha$ dayglow is spectrally broader and less intense at this viewing geometry. The obtained vertical H column densities of around $(1-2)\times 10^{12}$~cm$^{-2}$ are consistent with previous results. Constraining angular variability around Ganymede’s disk, we derive an upper limit on a local H$_2$O column density of $(2-3)\times 10^{16}$~cm$^{-2}$, such as could arise from outgassing plumes in regions near the observed moon limb.

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L. Roth, G. Marchesini, T. Becker, et. al.
Mon, 16 Jan 23
9/50

Comments: N/A

Carbon Depletion in the Early Solar System [EPA]

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http://arxiv.org/abs/2301.05706


Earth and other rocky objects in the inner Solar System are depleted in carbon compared to objects in the outer Solar System, the Sun, or the ISM. It is believed that this is a result of the selective removal of refractory carbon from primordial circumstellar material. In this work, we study the irreversible release of carbon into the gaseous environment via photolysis and pyrolysis of refractory carbonaceous material during the disk phase of the early Solar System. We analytically solve the one-dimensional advection equation and derive an explicit expression that describes the depletion of carbonaceous material in solids under the influence of radial and vertical transport. We find both depletion mechanisms individually fail to reproduce Solar System abundances under typical conditions. While radial transport only marginally restricts photodecomposition, it is the inefficient vertical transport that limits carbon depletion under these conditions. We show explicitly that an increase in the vertical mixing efficiency, and/or an increase in the directly irradiated disk volume, favors carbon depletion. Thermal decomposition requires a hot inner disk (> 500 K) beyond 3 AU to deplete the formation region of Earth and chondrites. We find FU Ori-type outbursts to produce these conditions such that moderately refractory compounds are depleted. However, such outbursts likely do not deplete the most refractory carbonaceous compounds beyond the innermost disk region. Hence, the refractory carbon abundance at 1 AU typically does not reach terrestrial levels. Nevertheless, under specific conditions, we find photolysis and pyrolysis combined to reproduce Solar System abundances.

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F. Binkert and T. Birnstiel
Mon, 16 Jan 23
19/50

Comments: Accepted for publication in MNRAS

Leaky Dust Traps: How Fragmentation impacts Dust Filtering by Planets [EPA]

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http://arxiv.org/abs/2301.05505


The nucleosynthetic isotope dichotomy between carbonaceous and non-carbonaceous meteorites has been interpreted as evidence for spatial separation and coexistence of two distinct planet-forming reservoirs for several million years in the solar protoplanetary disk. Rapid formation of Jupiter’s core within one million years after CAIs has been suggested as a potential mechanism for spatial and temporal separation. In this scenario, Jupiter’s core would open a gap in the disk and trap inwards-drifting dust grains in the pressure bump at the outer edge of the gap, separating the inner and outer disk materials from each other. We performed simulations of dust particles in a protoplanetary disk with a gap opened by an early formed Jupiter core, including dust growth and fragmentation as well as dust transport using the dust evolution software DustPy. Our numerical experiments indicate that particles trapped in the outer edge of the gap rapidly fragment and are transported through the gap, contaminating the inner disk with outer disk materials on a timescale that is inconsistent with the meteoritic record. This suggests that other processes must have initiated or at least contributed to the isotopic separation between the inner and outer Solar System.

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S. Stammler, T. Lichtenberg, J. Drążkowska, et. al.
Mon, 16 Jan 23
23/50

Comments: Accepted for publication in Astronomy & Astrophysics Letters

A Mixed Stirring Mechanism for Debris Discs with Giant and Dwarf Planetary Perturbations [EPA]

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http://arxiv.org/abs/2301.05265


Debris discs consist of belts of bodies ranging in size from dust grains to planetesimals; these belts are visible markers of planetary systems around other stars that can reveal the influence of extrasolar planets through their shape and structure. Two key stirring mechanisms — self-stirring by planetesimals and secular perturbation by an external giant planet — have been identified to explain the dynamics of planetesimal belts; their relative importance has been studied independently, but are yet to be considered in combination. In this work we perform a suite of 286 N-body simulations exploring the evolution of debris discs over 1~Gyr, combining the gravitational perturbations of both dwarf planets embedded in the discs, and an interior giant planet. Our systems were somewhat modeled after the architecture of the outer Solar system: a Solar mass star, a single massive giant planet at 30~au ($M_{\rm GP} =$ 10 to 316~$\mathrm{M}{\oplus}$), and a debris disc formed by 100 massive dwarf planets and 1000 massless particles ($M{\rm DD} =$ 3.16 to 31.6~$\mathrm{M}_{\oplus}$). We present the evolution of both the disc and the giant planet after 1~Gyr. The time evolution of the average eccentricity and inclination of the disc is strongly dependent on the giant planet mass as well as on the remaining disc mass. We also found that efficient stirring is achieved even with small disc masses. In general, we find that a mixed mechanism is more efficient in the stirring of cold debris discs than either mechanism acting in isolation.

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M. Muñoz-Gutiérrez, J. Marshall and A. Peimbert
Mon, 16 Jan 23
38/50

Comments: Accepted for publication in MNRAS. 11 pages, 6 figures (4 animated). Animated figures can be found at this https URL

Distribution and dynamics of decimeter-sized dust agglomerates in the coma of 67P/Churyumov-Gerasimenko [EPA]

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http://arxiv.org/abs/2301.04895


We present a method to analyze images of the coma of 67P/Churyumov-Gerasimenko obtained using OSIRIS, the main imaging system onboard \textit{Rosetta}, where dust aggregates can be seen as bright tracks because of their relative velocity with respect to the spacecraft. We applied this method to 105 images taken in 2015 July, 2015 December and 2016 January, identifying more than 20000 individual objects. We performed a photometric analysis of them, finding their phase function. This phase function follows the same trend as the one found for the nucleus, consistent with the detected particles having a size larger than $\sim 1$ mm. Additionally, the phase function becomes shallower for increasing heliocentric distances, indicating a decrease in the mean agglomerate size. In order to characterize the agglomerates observed in the image, we developed a simplified model for their ejection and dynamics in the coma, and generated synthetic images based on it. We solved the inverse problem by finding the simulation parameters that give the best fit between synthetic and real images. In doing so, we were able to obtain a mean agglomerate size $\sim$ dm and initial speed $\simeq$ 1 m s$^{-1}$. Both show a decrease with increasing heliocentric distance, sign of the reduction in activity. Also, the sizes obtained by the comparison are not compatible with ejection caused by water activity, so other sources have to be invoked, mainly CO$_2$.

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P. Lemos, J. Agarwal and M. Schröter
Fri, 13 Jan 23
4/72

Comments: 12 pages, 13 figures. Accepted for publication in MNRAS

Space environment and magnetospheric Poynting fluxes of the exoplanet $τ$ Boötis b [EPA]

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http://arxiv.org/abs/2301.05015


Context: The first tentative detection of a magnetic field on the Hot Jupiter type exoplanet $\tau$ Bo\”otis b was recently reported by Turner et al. (2021). The magnetic field was inferred from observations of circularly-polarized radio emission obtained with the LOFAR telescopes. The radio emission is possibly a consequence of the interaction of the surrounding stellar wind with the planet’s magnetic field. Methods: We perform magnetohydrodynamic simulations of the space environment around $\tau$ Bo\”otis b and its interaction with the stellar wind using the PLUTO code. We study the magnetospheric energy fluxes and effects of different magnetic field orientations in order to understand the physical processes which cause energy fluxes leading to the observed radio emission given the proposed magnetic field strength in Turner et al. (2021). Furthermore we study the effect of stellar wind density and pressure on magnetospheric energy fluxes given the uncertainty of extrasolar stellar wind predictions. Results: We find in our simulations that the interaction is most likely super–Alfv\’enic and energy fluxes generated by the stellar wind–planet interaction are consistent with the observed radio powers. Magnetospheric Poynting fluxes are of the order of 1-8 $\times10^{18}$ W for open, semi-open and closed magnetospheres. The Poynting fluxes are energetically consistent with the radio powers in Turner et al. (2021) for a magnetospheric Poynting flux-to-radio efficiency $> 10^{-3}$ when the magnetic fields of the planet and star are aligned. In case of lower efficiency factors the magnetospheric emission scenario is according to the parameter space modeled in this study not powerful enough. In case of a magnetic polarity reversal of the host star towards an anti-aligned field configuration, expected radio powers in the magnetospheric emission scenario fall below the observable threshold.

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F. Elekes and J. Saur
Fri, 13 Jan 23
5/72

Comments: Accepted for publication in Astronomy and Astrophysics (08.01.2023)

Venus, Phosphine and the Possibility of Life [EPA]

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http://arxiv.org/abs/2301.05160


The search for life elsewhere in the universe is one of the central aims of science in the 21st century. While most of this work is aimed at planets orbiting other stars, the search for life in our own Solar System is an important part of this endeavour. Venus is often thought to have too harsh an environment for life, but it may have been a more hospitable place in the distant past. If life evolved there in the past then the cloud decks of Venus are the only remaining niche where life as we know it might survive today. The discovery of the molecule phosphine, PH$_3$, in these clouds has reinvigorated research looking into the possibility of life in the clouds. In this review we examine the background to studies of the possibility of life on Venus, discuss the discovery of phosphine, review conflicting and confirming observations and analyses, and then look forward to future observations and space missions that will hopefully provide definitive answers as to the origin of phosphine on Venus and to the question of whether life might exist there.

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D. Clements
Fri, 13 Jan 23
7/72

Comments: Invited review, accepted for publication in Contemporary Physics

Activity distribution of comet 67P/Churyumov-Gerasimenko from combined measurements of non-gravitational forces and torques [EPA]

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http://arxiv.org/abs/2301.04892


Aims. Understanding the activity is vital for deciphering the structure, formation, and evolution of comets. We investigate models of cometary activity by comparing them to the dynamics of 67P/Churyumov-Gerasimenko. Methods. We matched simple thermal models of water activity to the combined Rosetta datasets by fitting to the total outgassing rate and four components of the outgassing induced non-gravitational force and torque, with a final manual adjustment of the model parameters to additionally match the other two torque components. We parametrised the thermal model in terms of a distribution of relative activity over the surface of the comet, and attempted to link this to different terrain types. We also tested a more advanced thermal model based on a pebble structure. Results. We confirm a hemispherical dichotomy and non-linear water outgassing response to insolation. The southern hemisphere of the comet and consolidated terrain show enhanced activity relative to the northern hemisphere and dust-covered, unconsolidated terrain types, especially at perihelion. We further find that the non-gravitational torque is especially sensitive to the activity distribution, and to fit the pole-axis orientation in particular, activity must be concentrated (in excess of the already high activity in the southern hemisphere and consolidated terrain) around the south pole and on the body and neck of the comet over its head. This is the case for both the simple thermal model and the pebble-based model. Overall, our results show that water activity cannot be matched by a simple model of sublimating surface ice driven by the insolation alone, regardless of the surface distribution, and that both local spatial and temporal variations are needed to fit the data.

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N. Attree, L. Jorda, O. Groussin, et. al.
Fri, 13 Jan 23
16/72

Comments: Accepted for publication in A&A. 13 pages, 22 figures including appendix

Observability of silicates in volatile atmospheres of super-Earths and sub-Neptunes [EPA]

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http://arxiv.org/abs/2301.05190


Many of the confirmed short period super-Earths and smaller sub-Neptunes are sufficiently irradiated for the surface silicates to be sustained in a long-lasting molten state. While there is no direct evidence of magma ocean influence on exoplanets, theory suggests that due to outgassing and diverse evolution paths, a wide range of resulting atmospheric compositions should be possible. Atmospheric contamination caused by the outgassing of the underlying magma ocean is potentially detectable using low resolution spectroscopy. The James Webb Space Telescope provides the necessary spectral coverage and sensitivity to characterise smaller planets, including lava worlds. In this light, we assess observability of outgassed silicates submerged in volatile atmospheres on the edge of the evaporation valley. By placing a hypothetical 2 R${_\oplus}$ planet around a Sun-like star, we self-consistently model, in 1-D, a wide range of potential atmospheric compositions, including thermal structure and outgassing. We focus on atmospheres rich in H, C and N. We assess diverse chemistry of silicates and volatiles, and what features of outgassed species could be detected via emission spectroscopy using MIRI LRS. Results indicate that even for substantial volatile envelopes, strong in infrared opacity, the presence of silicates causes deep thermal inversions, affecting emission. Similar to pure lava worlds, SiO remains the only outgassed species with major infrared, 5 and 9 \textmu m, bands. However, even a small amount of volatiles, especially of H2O and H-, may hinder its observability. We also find that the C/O ratio plays a large role in determining the abundance of SiO. Detecting SiO on a strongly irradiated planet could indicate an atmosphere with high metallicity and a low C/O ratio, which may be a result of efficient interaction between the atmosphere and the underlying melt.

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M. Zilinskas, Y. Miguel, C. Buchem, et. al.
Fri, 13 Jan 23
19/72

Comments: Accepted for publication at Astronomy & Astrophysics

Rotation Periods, Inclinations, and Obliquities of Cool Stars Hosting Directly Imaged Substellar Companions: Spin-Orbit Misalignments are Common [EPA]

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http://arxiv.org/abs/2301.04692


The orientation between a star’s spin axis and a planet’s orbital plane provides valuable information about the system’s formation and dynamical history. For non-transiting planets at wide separations, true stellar obliquities are challenging to measure, but lower limits on spin-orbit orientations can be determined from the difference between the inclination of the star’s rotational axis and the companion’s orbital plane ($\Delta i$). We present results of a uniform analysis of rotation periods, stellar inclinations, and obliquities of cool stars (SpT $\gtrsim$ F5) hosting directly imaged planets and brown dwarf companions. As part of this effort, we have acquired new $v \sin i_*$ values for 22 host stars with the high-resolution Tull spectrograph at the Harlan J. Smith telescope. Altogether our sample contains 62 host stars with rotation periods, most of which are newly measured using light curves from the Transiting Exoplanet Survey Satellite. Among these, 53 stars have inclinations determined from projected rotational and equatorial velocities, and 21 stars predominantly hosting brown dwarfs have constraints on $\Delta i$. Eleven of these (52$^{+10}_{-11}$% of the sample) are likely misaligned, while the remaining ten host stars are consistent with spin-orbit alignment. As an ensemble, the minimum obliquity distribution between 10-250 AU is more consistent with a mixture of isotropic and aligned systems than either extreme scenario alone–pointing to direct cloud collapse, formation within disks bearing primordial alignments and misalignments, or architectures processed by dynamical evolution. This contrasts with stars hosting directly imaged planets, which show a preference for low obliquities. These results reinforce an emerging distinction between the orbits of long-period brown dwarfs and giant planets in terms of their stellar obliquities and orbital eccentricities.

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B. Bowler, Q. Tran, Z. Zhang, et. al.
Fri, 13 Jan 23
23/72

Comments: AJ, accepted

Formation of Rocky Super-Earths From A Narrow Ring of Planetesimals [EPA]

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http://arxiv.org/abs/2301.04680


The formation of super-Earths, the most abundant planets in the Galaxy, remains elusive. These planets have masses that typically exceed that of the Earth by a factor of a few; appear to be predominantly rocky, although often surrounded by H/He atmospheres; and frequently occur in multiples. Moreover, planets that encircle the same star tend to have similar masses and radii, whereas those belonging to different systems exhibit remarkable overall diversity. Here, we advance a theoretical picture for rocky planet formation that satisfies the aforementioned constraints: building upon recent work – which demonstrates that planetesimals can form rapidly at discrete locations in the disk – we propose that super-Earths originate inside rings of silicate-rich planetesimals at approximately ~1 AU. Within the context of this picture, we show that planets grow primarily through pairwise collisions among rocky planetesimals, until they achieve terminal masses that are regulated by isolation and orbital migration. We quantify our model with numerical simulations and demonstrate that our synthetic planetary systems bear a close resemblance to compact, multi-resonant progenitors of the observed population of short-period extrasolar planets. Our results thus indicate that the absence of short-period super-Earths within the solar system can simply be attributed to the comparatively low mass of the primordial planetesimal ring within the protosolar nebula.

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K. Batygin and A. Morbidelli
Fri, 13 Jan 23
25/72

Comments: 14 pages, 4 figures, accepted for publication in Nature Astronomy

Towards a population synthesis of discs and planets. II. Confronting disc models and observations at the population level [EPA]

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http://arxiv.org/abs/2301.04656


Aims. We want to find the distribution of initial conditions that best reproduces disc observations at the population level. Methods. We first ran a parameter study using a 1D model that includes the viscous evolution of a gas disc, dust, and pebbles, coupled with an emission model to compute the millimetre flux observable with ALMA. This was used to train a machine learning surrogate model that can compute the relevant quantity for comparison with observations in seconds. This surrogate model was used to perform parameter studies and synthetic disc populations. Results. Performing a parameter study, we find that internal photoevaporation leads to a lower dependency of disc lifetime on stellar mass than external photoevaporation. This dependence should be investigated in the future. Performing population synthesis, we find that under the combined losses of internal and external photoevaporation, discs are too short lived. Conclusions. To match observational constraints, future models of disc evolution need to include one or a combination of the following processes: infall of material to replenish the discs, shielding of the disc from internal photoevaporation due to magnetically driven disc winds, and extinction of external high-energy radiation. Nevertheless, disc properties in low-external-photoevaporation regions can be reproduced by having more massive and compact discs. Here, the optimum values of the $\alpha$ viscosity parameter lie between $3\times10^{-4}$ and $10^{-3}$ and with internal photoevaporation being the main mode of disc dispersal.

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A. Emsenhuber, R. Burn, J. Weder, et. al.
Fri, 13 Jan 23
28/72

Comments: Accepted for publication in A&A

Constraining the Limitations of NEATM-like Models: A Case Study with Near-Earth Asteroid (285263) 1998 QE2 [EPA]

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http://arxiv.org/abs/2301.05071


Near-Earth Asteroids (NEAs) are a key testbed for investigations into planet formation, asteroid dynamics, and planetary defense initiatives. These studies rely on understanding NEA sizes, albedo distributions, and regolith properties. Simple thermal models are a commonly used method for determining these properties, however they have inherent limitations due to the simplifying assumptions they make about asteroid shapes and properties. With the recent collapse of the Arecibo Telescope and a decrease of direct size measurements, as well as future facilities such as LSST and NEO Surveyor coming online soon, these models will play an increasingly important role in our knowledge of the NEA population. Therefore, it is key to understand the limits of these models. In this work we constrain the limitations of simple thermal models by comparing model results to more complex thermophysical models, radar data, and other existing analyses. Furthermore, we present a method for placing tighter constraints on inferred NEA properties using simple thermal models. These comparisons and constraints are explored using the NEA (285263) 1998 QE2 as a case study. We analyze QE2 with a simple thermal model and data from both the NASA IRTF SpeX instrument and NEOWISE mission. We determine an albedo between 0.05 and 0.10 and thermal inertia between 0 and 425 J m$^{-2}$ s$^{-1/2}$ K$^{-1}$. We find that overall the simple thermal model is able to well constrain the properties of QE2, however we find that model uncertainties can be influenced by topography, viewing geometry, and the wavelength range of data used.

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S. Myers, E. Howell, C. Magri, et. al.
Fri, 13 Jan 23
35/72

Comments: 17 pages, 13 figures

How the origin of stars in the Galaxy impacts the composition of planetary building blocks [EPA]

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http://arxiv.org/abs/2301.05034


Context. Our Galaxy is composed of different stellar populations with varying chemical abundances, which are thought to imprint the composition of planet building blocks (PBBs). As such, the properties of stars should affect the properties of planets and small bodies formed in their systems. In this context, high-resolution spectroscopic surveys open a window into the chemical links between and their host stars.
Aims. We aim to determine the PBB composition trends for various stellar populations across the Galaxy by comparing the two large spectroscopic surveys APOGEE and GALAH. We assess the reliability of the PBB composition as determined with these surveys with a propagation error study.
Methods. Stellar spectroscopic abundances from the large surveys GALAH-DR3 and APOGEE-DR17 were used as input with a stoichiometric condensation model. We classified stars into different Galactic components and we quantified the PBB composition trends as a function of [Fe/H]. We also analysed the distribution composition patterns in the [$\alpha$/Fe]-[Fe/H] diagram.
Results. Our propagation error study suggests that the overall trends with [Fe/H] and [$\alpha$/Fe] are robust, which is supported by the double study of both APOGEE and GALAH. We therefore confirm the existence of a bimodal PBB composition separating the thin disc stars from the thick disc stars. Furthermore, we confirm that the stoichiometric water PBB content is anti-correlated with [Fe/H].
Conclusions. Our results imply that metal-poor stars both in the thin and thick disks are suitable hosts for water-rich PBBs and for ice-rich small bodies. However, for metal-poor stars ([Fe/H]<0), the PBBs around thick disc stars should have a higher water content than that around thin disc stars because of the $\alpha$-contentdependence of the water mass fraction.

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N. Cabral, A. Guilbert-Lepoutre, B. Bitsch, et. al.
Fri, 13 Jan 23
39/72

Comments: N/A

A Two-limb Explanation for the Optical-to-infrared Transmission Spectrum of the Hot Jupiter HAT-P-32Ab [EPA]

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http://arxiv.org/abs/2301.04812


We present a new optical transmission spectrum of the hot Jupiter HAT-P-32Ab acquired with the Carnegie Observatories Spectrograph and Multiobject Imaging Camera (COSMIC) on the Palomar 200 inch Hale Telescope (P200). The P200/COSMIC transmission spectrum, covering a wavelength range of 3990–9390 \AA, is composed of 25 spectrophotometric bins with widths ranging from 200 to 400 \AA and consistent with previous transit measurements obtained in the common wavelength range. We derive a combined optical transmission spectrum based on measurements from five independent instruments, which, along with the 1.1–1.7 $\mu$m spectrum acquired by the Hubble Space Telescope and two Spitzer measurements, exhibits an enhanced scattering slope blueward of a relatively flat optical continuum, a water absorption feature at 1.4 $\mu$m, and a carbon dioxide feature at 4.4 $\mu$m. We perform Bayesian spectral retrieval analyses on the 0.3–5.1 $\mu$m transmission spectrum and find that it can be well explained by a two-limb approximation of $134^{+45}{-33}\times$ solar metallicity, with a strongly hazy morning limb of $1134^{+232}{-194}$ K and a haze-free evening limb of $1516^{+33}_{-44}$~K. This makes HAT-P-32Ab a promising target for James Webb Space Telescope to look for asymmetric signatures directly in the light curves.

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X. Li, G. Chen, H. Zhao, et. al.
Fri, 13 Jan 23
40/72

Comments: 17 pages, 10 figures. Accepted for publication in RAA

Kinematic Evidence of an Embedded Protoplanet in HD 142666 Identified by Machine Learning [EPA]

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http://arxiv.org/abs/2301.05075


Observations of protoplanetary discs have shown that forming exoplanets leave characteristic imprints on the gas and dust of the disc. In the gas, these forming exoplanets cause deviations from Keplerian motion, which can be detected through molecular line observations. Our previous work has shown that machine learning can correctly determine if a planet is present in these discs. Using our machine learning models, we identify strong, localized non-Keplerian motion within the disc HD 142666. Subsequent hydrodynamics simulations of a system with a 5 Jupiter-mass planet at 75 au recreates the kinematic structure. By currently established standards in the field, we conclude that HD 142666 hosts a planet. This work represents a first step towards using machine learning to identify previously overlooked non-Keplerian features in protoplanetary discs.

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J. Terry, C. Hall, S. Abreau, et. al.
Fri, 13 Jan 23
46/72

Comments: 7 pages, 3 figures, 1 table. Submitted to ApJ

Closed field line vortices in planetary magnetospheres [EPA]

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http://arxiv.org/abs/2301.04930


In a rotation-dominated magnetosphere, there is a region where closed field lines rotate around the planet, and also a region where the open field lines stretch away from the planet, forming the lobes of the magnetotail. This paper shows that there could be a third, significantly different region, where the closed field lines form twisted vortex structures anchored in the magnetotail. Such patterns form when there are significant plasma sources inside the magnetosphere and the time scale of the plasmoid formation process is substantially larger than the planetary rotation period. In the presence of vortices, the Dungey and Vasyliunas cycles act differently. The Dungey flow does not penetrate the central region of the polar cap. Tail reconnection events are rare, thus leaving the plasma time enough to participate in the essentially 3-dimensional vortex-forming plasma motion. The above conditions are fulfilled for Saturn. We discovered vortex-like patterns in the plasma and magnetic field data measured by the Cassini spacecraft in the nightside magnetosphere of Saturn. The plasma whirling around in these vortices never reaches the dayside, instead, it performs a retrograde motion in the high latitude regions of the magnetotail. Low-energy plasma data suggest that the observed patterns correspond to the closed field line vortices.

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Z. Nemeth
Fri, 13 Jan 23
53/72

Comments: to be published in MNRAS

Interstellar Heritage and the Birth Environment of the Solar System [EPA]

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http://arxiv.org/abs/2301.05212


In this chapter, we explore the origins of cometary material and discuss the clues cometary composition provides in the context of the origin of our solar system. The review focuses on both cometary refractory and volatile materials, which jointly provide crucial information about the processes that shaped the solar system into what it is today. Both areas have significantly advanced over the past decade. We also view comets more broadly and discuss compositions considering laboratory studies of cometary materials, including interplanetary dust particles and meteoritic material that are potential cometary samples, along with meteorites, and in situ/remote studies of cometary comae. In our review, we focus on key areas from elemental/molecular compositions, isotopic ratios, carbonaceous and silicate refractories, short-lived radionuclides, and solar system dynamics that can be used as probes of the solar birth environment. We synthesize this data that points towards the birth of our solar system in a clustered star-forming environment.

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E. Bergin, C. Alexander, M. Drozdovskaya, et. al.
Fri, 13 Jan 23
63/72

Comments: 31 pages, 7 figures, 2 tables; Chapter in press for the book Comets III, edited by K. Meech and M. Combi, University of Arizona Press

Conclusive evidence for a population of water-worlds around M-dwarfs remains elusive [EPA]

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http://arxiv.org/abs/2301.04321


The population of small, close-in exoplanets is bifurcated into super-Earths and sub-Neptunes. We calculate physically motivated mass-radius relations for sub-Neptunes, with rocky cores and H/He dominated atmospheres, accounting for their thermal evolution, irradiation and mass-loss. For planets $\lesssim 10~$M$_\oplus$, we find that sub-Neptunes retain atmospheric mass fractions that scale with planet mass and show that the resulting mass-radius relations are degenerate with results for `water-worlds’ consisting of a 1:1 silicate-to-ice composition ratio. We further demonstrate that our derived mass-radius relation is in excellent agreement with the observed exoplanet population orbiting M-dwarfs and that planet mass and radii alone are insufficient to determine the composition of some sub-Neptunes. Finally, we highlight that current exoplanet demographics show an increase in the ratio of super-Earths to sub-Neptunes with both stellar mass (and therefore luminosity) and age, which are both indicative of thermally driven atmospheric escape processes. Therefore, such processes should not be ignored when making compositional inferences in the mass-radius diagram.

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J. Rogers, H. Schlichting and J. Owen
Thu, 12 Jan 23
1/68

Comments: 15 pages, 2 figures. Submitted to ApJL

The Similar Seven: A set of very-alike exoplanets to test correlations between system parameters and atmospheric properties [EPA]

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http://arxiv.org/abs/2301.04174


Studies of exoplanetary atmospheres have found no definite correlations between observed high altitude aerosols and other system parameters. This could be, in part, because of the lack of homogeneous exoplanet samples for which specific parameters can be isolated and inspected. Here we present a set of seven exoplanets with very similar system parameters. We analyze existing photometric timeseries, Gaia parallax, and high-resolution spectroscopic data to produce a new set of homogeneous stellar, planetary, and orbital parameters for these systems. With this we confirm that most measured parameters for all systems are very similar, except for the host stars’ metallicities and possibly high energy irradiation levels, which require UV and X-ray observations to constrain. From the sample, WASP-6b, WASP-96b and WASP-110b, have observed transmission spectra that we use to estimate their aerosol coverage levels using the Na I doublet 5892.9{\AA}. We find a tentative correlation between the metallicity of the host stars and the planetary aerosol levels. The trend we find with stellar metallicity can be tested by observing transmission spectra of the remaining planets in the sample. Based on our prediction, WASP-25b and WASP-55b should have higher levels of aerosols than WASP-124b and HATS-29b. Finally, we highlight how targeted surveys of alike planets like the ones presented here might prove key for identifying driving factors for atmospheric properties of exoplanets in the future and could be used as a sample selection criterium for future observations with e.g. JWST, ARIEL, and the next generation of ground-based telescopes.

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C. McGruder, M. López-Morales, R. Brahm, et. al.
Thu, 12 Jan 23
22/68

Comments: ACCEPT by ApJL Jan 9th 2023

The smallest planetary drivers of white dwarf pollution [EPA]

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http://arxiv.org/abs/2301.04160


Many potential mechanisms for delivering planetary debris to within a few Roche radii of white dwarfs rely on gravitational scattering events that feature perturbers which are giant planets or terrestrial planets. However, the population of these planets orbiting white dwarfs is still unknown, and for a substantial fraction of white dwarfs the largest planetary survivors of stellar evolution may be sub-terrestrial mass minor planets. Here, we attempt to identify the smallest mass perturbers that could pollute white dwarfs. Through computationally expensive numerical simulations of both unstable and stable configurations of minor planets, we find that this critical lower bound equals approximately one Luna mass. Further, we find that as this mass limit is approached from above, the typical cooling age at which white dwarf pollution occurs increases. Consequently, there is a two order-of-magnitude range of perturber masses between Earth and its moon that has remained largely unexplored in white dwarf pollution studies, despite the potential formation of thousands of such Luna-sized objects in these systems.

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D. Veras and A. Rosengren
Thu, 12 Jan 23
24/68

Comments: Accepted for publication in MNRAS

The CARMENES search for exoplanets around M dwarfs. A long-period planet around GJ 1151 measured with CARMENES and HARPS-N data [EPA]

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http://arxiv.org/abs/2301.04442


Detecting a planetary companion in a short-period orbit through radio emission from the interaction with its host star is a new prospect in exoplanet science. Recently, a tantalising signal was found close to the low-mass stellar system GJ 1151 using LOFAR observations. We studied spectroscopic time-series data of GJ 1151 in order to search for planetary companions, investigate possible signatures of stellar magnetic activity, and to find possible explanations for the radio signal. We used the combined radial velocities measured from spectra acquired with the CARMENES, HARPS-N, and HPF instruments, extracted activity indices from those spectra in order to mitigate the impact of stellar magnetic activity on the data, and performed a detailed analysis of Gaia astrometry and all available photometric time series coming from the MEarth and ASAS-SN surveys. We found a M$>$10.6 M${\oplus}$ companion to GJ 1151 in a 390d orbit at a separation of 0.57 au. Evidence for a second modulation is also present; this could be due to long-term magnetic variability or a second (substellar) companion. The star shows episodes of elevated magnetic activity, one of which could be linked to the observed LOFAR radio emission. We show that it is highly unlikely that the detected GJ 1151 b, or any additional outer companion is the source of the detected signal. We cannot firmly rule out the suggested explanation of an undetected short-period planet that could be related to the radio emission, as we establish an upper limit of 1.2 M${\oplus}$ for the minimum mass.

Read this paper on arXiv…

J. Blanco-Pozo, M. Perger, M. Damasso, et. al.
Thu, 12 Jan 23
29/68

Comments: 18 pages, 11 figures. Accepted version, A&A (2023)

The CARMENES search for exoplanets around M dwarfs. A long-period planet around GJ 1151 measured with CARMENES and HARPS-N data [EPA]

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http://arxiv.org/abs/2301.04442


Detecting a planetary companion in a short-period orbit through radio emission from the interaction with its host star is a new prospect in exoplanet science. Recently, a tantalising signal was found close to the low-mass stellar system GJ 1151 using LOFAR observations. We studied spectroscopic time-series data of GJ 1151 in order to search for planetary companions, investigate possible signatures of stellar magnetic activity, and to find possible explanations for the radio signal. We used the combined radial velocities measured from spectra acquired with the CARMENES, HARPS-N, and HPF instruments, extracted activity indices from those spectra in order to mitigate the impact of stellar magnetic activity on the data, and performed a detailed analysis of Gaia astrometry and all available photometric time series coming from the MEarth and ASAS-SN surveys. We found a M$>$10.6 M${\oplus}$ companion to GJ 1151 in a 390d orbit at a separation of 0.57 au. Evidence for a second modulation is also present; this could be due to long-term magnetic variability or a second (substellar) companion. The star shows episodes of elevated magnetic activity, one of which could be linked to the observed LOFAR radio emission. We show that it is highly unlikely that the detected GJ 1151 b, or any additional outer companion is the source of the detected signal. We cannot firmly rule out the suggested explanation of an undetected short-period planet that could be related to the radio emission, as we establish an upper limit of 1.2 M${\oplus}$ for the minimum mass.

Read this paper on arXiv…

J. Blanco-Pozo, M. Perger, M. Damasso, et. al.
Thu, 12 Jan 23
29/68

Comments: 18 pages, 11 figures. Accepted version, A&A (2023)

A JWST transmission spectrum of a nearby Earth-sized exoplanet [EPA]

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http://arxiv.org/abs/2301.04191


The critical first step in the search for life on exoplanets over the next decade is to determine whether rocky planets transiting small M-dwarf stars possess atmospheres and, if so, what processes sculpt them over time. Because of its broad wavelength coverage and improved resolution compared to previous methods, spectroscopy with JWST offers a new capability to detect and characterize the atmospheres of Earth-sized, M-dwarf planets. Here we use JWST to independently validate the discovery of LHS 475b, a warm (586 K), 0.99 Earth-radius exoplanet, interior to the habitable zone, and report a precise 2.9-5.3 um transmission spectrum. With two transit observations, we rule out primordial hydrogen-dominated and cloudless pure methane atmospheres. Thus far, the featureless transmission spectrum remains consistent with a planet that has a high-altitude cloud deck (similar to Venus), a tenuous atmosphere (similar to Mars), or no appreciable atmosphere at all (akin to Mercury). There are no signs of stellar contamination due to spots or faculae. Our observations demonstrate that JWST has the requisite sensitivity to constrain the secondary atmospheres of terrestrial exoplanets with absorption features <50 ppm, and that our current atmospheric constraints speak to the nature of the planet itself, rather than instrumental limits.

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J. Lustig-Yaeger, G. Fu, E. May, et. al.
Thu, 12 Jan 23
39/68

Comments: A co-first author paper Lustig-Yaeger and Fu et al., Under review in Nature Astronomy, Comments welcome

Detecting exomoons from radial velocity measurements of self-luminous planets: application to observations of HR 7672 B and future prospects [EPA]

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http://arxiv.org/abs/2301.04206


The detection of satellites around extrasolar planets, so called exomoons, remains a largely unexplored territory. In this work, we study the potential of detecting these elusive objects from radial velocity monitoring of self-luminous directly imaged planets. This technique is now possible thanks to the development of dedicated instruments combining the power of high-resolution spectroscopy and high-contrast imaging. First, we demonstrate a sensitivity to satellites with a mass ratio of 1-4% at separations similar to the Galilean moons from observations of a brown-dwarf companion (HR 7672 B; Kmag=13; 0.7″ separation) with the Keck Planet Imager and Characterizer (KPIC; R~35,000 in K band) at the W. M. Keck Observatory. Current instrumentation is therefore already sensitive to large unresolved satellites that could be forming from gravitational instability akin to binary star formation. Using end-to-end simulations, we then estimate that future instruments such as MODHIS, planned for the Thirty Meter Telescope, should be sensitive to satellites with mass ratios of ~1e-4. Such small moons would likely form in a circumplanetary disk similar to the Jovian satellites in the solar system. Looking for the Rossiter-McLaughlin effect could also be an interesting pathway to detecting the smallest moons on short orbital periods. Future exomoon discoveries will allow precise mass measurements of the substellar companions that they orbit and provide key insight into the formation of exoplanets. They would also help constrain the population of habitable Earth-sized moons orbiting gas giants in the habitable zone of their stars.

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J. Ruffio, K. Horstman, D. Mawet, et. al.
Thu, 12 Jan 23
46/68

Comments: Accepted to AJ (Jan 10, 2023)

A Possible Converter to Denoise the Images of Exoplanet Candidates through Machine Learning Techniques [EPA]

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http://arxiv.org/abs/2301.04292


The method of direct imaging has detected many exoplanets and made important contribution to the field of planet formation. The standard method employs angular differential imaging (ADI) technique, and more ADI image frames could lead to the results with larger signal-to-noise-ratio (SNR). However, it would need precious observational time from large telescopes, which are always over-subscribed. We thus explore the possibility to generate a converter which can increase the SNR derived from a smaller number of ADI frames. The machine learning technique with two-dimension convolutional neural network (2D-CNN) is tested here. Several 2D-CNN models are trained and their performances of denoising are presented and compared. It is found that our proposed Modified five-layer Wide Inference Network with the Residual learning technique and Batch normalization (MWIN5-RB) can give the best result. We conclude that this MWIN5-RB can be employed as a converter for future observational data.

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P. Chintarungruangchai, I. Jiang, J. Hashimoto, et. al.
Thu, 12 Jan 23
47/68

Comments: 30 pages, 12 figures, 1 table, published by New Astronomy

Observed polarized scattered light phase functions of planet-forming disks [EPA]

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http://arxiv.org/abs/2301.04617


Dust particles are the building blocks from which planetary bodies are made. A major goal of the studies of planet-forming disks is to constrain the properties of dust particles and aggregates in order to trace their origin, structure, and the associated growth and mixing processes in the disk. Observations of scattering and/or emission of dust in a location of the disk often lead to degenerate information about the kind of particles, such as size, porosity, or fractal dimension of aggregates. Progress can be made by deriving the full (polarizing) scattering phase function of such particles at multiple wavelengths. This has now become possible by careful extraction from scattered light images. Such an extraction requires knowledge about the shape of the scattering surface in the disk and we discuss how to obtain such knowledge as well as the associated uncertainties. We use a sample of disk images from observations with VLT/SPHERE to, for the first time, extract the phase functions of a whole sample of disks with broad phase angle coverage. We find that polarized phase functions come in two categories. Comparing the extracted functions with theoretical predictions from rigorous T-Matrix computations of aggregates, we show that one category can be linked back to fractal, porous aggregates, while the other is consistent with more compact, less porous aggregates. We speculate that the more compact particles become visible in disks where embedded planets trigger enhanced vertical mixing.

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C. Ginski, R. Tazaki, C. Dominik, et. al.
Thu, 12 Jan 23
53/68

Comments: Submitted to ApJ with parallel submission to arxiv for logistical reasons; We will update the arxiv submission with the final version once the manuscript was refereed and accepted by ApJ. Data files for all phase functions will be made available once refereeing is concluded. We welcome comments from the community

Mid-infrared bi-directional reflectance spectroscopy of impact melt glasses and tektites [EPA]

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http://arxiv.org/abs/2301.04476


We have analyzed 14 impact melt glass samples, covering the compositional range from highly felsic to mafic/basaltic, as part of our effort to provide mid-infrared spectra (7-14 micron) for MERTIS (Mercury Radiometer and Thermal Infrared Spectrometer), an instrument onboard of the ESA/JAXA BepiColombo mission.
Since Mercury was exposed to many impacts in its history, and impact glasses are also common on other bodies, powders of tektites (Irghizite, Libyan Desert Glass, Moldavite, Muong Nong, Thailandite) and impact glasses (from the Dellen, El’gygytgyn, Lonar, Mien, Mistastin, and Popigai impact structures) were analyzed in four size fractions of (0-25, 25-63, 93-125 and 125-250 micron) from 2.5 to 19 micron in bi-directional reflectance. The characteristic Christiansen Feature (CF) is identified between 7.3 micron (Libyan Desert Glass) and 8.2 micron (Dellen). Most samples show mid-infrared spectra typical of highly amorphous material, dominated by a strong Reststrahlen Band (RB) between 8.9 micron (Libyan Desert Glass) and 10.3 micron (Dellen). Even substantial amounts of mineral fragments hardly affect this general band shape. Comparisons of the SiO2 content representing the felsic/mafic composition of the samples with the CF shows felsic/intermediate glass and tektites forming a big group, and comparatively mafic samples a second one. An additional sign of a highly amorphous state is the lack of features at wavelengths longer than about 15 micron. The tektites and two impact glasses, Irghizite and El’gygytgyn respectively, have much weaker water features than most of the other impact glasses.

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A. Morlok, A. Stojic, I. Weber, et. al.
Thu, 12 Jan 23
57/68

Comments: N/A

Ejecta cloud distributions for the statistical analysis of impact cratering events onto asteroids' surfaces: a sensitivity analysis [EPA]

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http://arxiv.org/abs/2301.04284


This work presents the model of an ejecta cloud distribution to characterise the plume generated by the impact of a projectile onto asteroids surfaces. A continuum distribution based on the combination of probability density functions is developed to describe the size, ejection speed, and ejection angles of the fragments. The ejecta distribution is used to statistically analyse the fate of the ejecta. By combining the ejecta distribution with a space-filling sampling technique, we draw samples from the distribution and assigned them a number of \emph{representative fragments} so that the evolution in time of a single sample is representative of an ensemble of fragments. Using this methodology, we analyse the fate of the ejecta as a function of different modelling techniques and assumptions. We evaluate the effect of different types of distributions, ejection speed models, coefficients, etc. The results show that some modelling assumptions are more influential than others and, in some cases, they influence different aspects of the ejecta evolution such as the share of impacting and escaping fragments or the distribution of impacting fragments on the asteroid surface.

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M. Trisolini, C. Colombo and Y. Tsuda
Thu, 12 Jan 23
60/68

Comments: N/A

A deep radius valley revealed by Kepler short cadence observations [EPA]

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http://arxiv.org/abs/2301.04062


The characteristics of the radius valley, i.e., an observed lack of planets between 1.5-2 Earth radii at periods shorter than about 100 days, provide insights into the formation and evolution of close-in planets. We present a novel view of the radius valley by refitting the transits of 431 planets using Kepler 1-minute short cadence observations, the vast majority of which have not been previously analysed in this way. In some cases, the updated planetary parameters differ significantly from previous studies, resulting in a deeper radius valley than previously observed. This suggests that planets are likely to have a more homogeneous core composition at formation. Furthermore, using support-vector machines, we find that the radius valley location strongly depends on orbital period and stellar mass and weakly depends on stellar age, with $\partial \log {\left(R_{p, \text{valley}} \right)}/ \partial \log{P} = -0.096_{-0.027}^{+0.023}$, $\partial \log {\left(R_{p, \text{valley}} \right)}/ \partial \log{M_{\star}} = 0.231_{-0.064}^{+0.053}$, and $\partial \log {\left(R_{p, \text{valley}} \right)}/ \partial \log{\left( \text{age} \right)} = 0.033_{-0.025}^{+0.017}$. These findings favour thermally-driven mass loss models such as photoevaporation and core-powered mass loss, with a slight preference for the latter scenario. Finally, this work highlights the value of transit observations with short photometric cadence to precisely determine planet radii, and we provide an updated list of precisely and homogeneously determined parameters for the planets in our sample.

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C. Ho and V. Eylen
Wed, 11 Jan 23
2/80

Comments: 19 pages, 17 figures, accepted in MNRAS

Photosynthetic Fluorescence from Earth-Like Planets around Sun-Like and Cool Stars [EPA]

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http://arxiv.org/abs/2301.03824


Remote sensing of the Earth has demonstrated that photosynthesis is traceable as the vegetation red edge (VRE), which is the steep rise in the reflection spectrum of vegetation, and as solar-induced fluorescence. This study examined the detectability of biological fluorescence from two types of photosynthetic pigments, chlorophylls (Chls) and bacteriochlorophylls (BChls), on Earth-like planets with oxygen-rich/poor and anoxic atmospheres around the Sun and M dwarfs. Atmospheric absorption, such as H2O, CH4, O2, and O3, and the VRE obscure the fluorescence emissions from Chls and BChls. We found that BChl-based fluorescence for wavelengths of 1000-1100 nm, assuming the spectrum of BChl b-bearing purple bacteria, could provide a suitable biosignature but only in the absence of the water cloud coverage or other strong absorbers near 1000 nm. The Chl fluorescence is weaker for several reasons, e.g., spectral blending with the VRE. The apparent reflectance excess is greatly increased in both Chl and BChl cases around TRAPPIST-1 due to fluorescence and stellar absorption lines. This could be a promising feature for detecting the fluorescence around ultracool red dwarfs by follow-up ground-based observations with high spectral resolution; however, it requires a long time around Sun-like stars, even for a LUVOIR-like space mission. Moreover, the simultaneous detection of fluorescence and VRE is key to identifying traces of photosynthesis because absorption, reflectance, and fluorescence are physically connected. For further validation of fluorescence detection, the nonlinear response of biological fluorescence as a function of light intensity could be considered.

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Y. Komatsu, Y. Hori, M. Kuzuhara, et. al.
Wed, 11 Jan 23
6/80

Comments: N/A

An Analytical Theory for the Growth from Planetesimals to Planets by Polydisperse Pebble Accretion [EPA]

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http://arxiv.org/abs/2301.03825


Pebble accretion is recognized as a significant accelerator of planet formation. Yet, only formulae for single-sized (monodisperse) distribution have been derived in the literature. These can lead to significant underestimates for Bondi accretion, for which the best accreted pebble size may not be the one that dominates the mass distribution. We derive in this paper the polydisperse theory of pebble accretion. We consider a power-law distribution in pebble radius, and we find the resulting surface and volume number density distribution functions. We derive also the exact monodisperse analytical pebble accretion rate for which 3D and 2D accretion are limits. In addition, we find analytical solutions to the polydisperse 2D Hill and 3D Bondi limits. We integrate the polydisperse pebble accretion numerically for the MRN distribution, finding a slight decrease (by an exact factor 3/7) in the Hill regime compared to the monodisperse case. In contrast, in the Bondi regime, we find 1-2 orders of magnitude higher accretion rates compared to monodisperse, also extending the onset of pebble accretion to 1-2 order of magnitude lower in mass. We find Myr-timescales, within the disk lifetime, for Bondi accretion on top of planetary seeds of masses $10^{-6}-10^{-4} M_\oplus$, over a significant range of the parameter space. This mass range overlaps with the high mass end of the planetesimal initial mass function, and thus pebble accretion is possible directly following formation by streaming instability. This alleviates the need for mutual planetesimal collisions as a major contribution to planetary growth.

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W. Lyra, A. Johansen, M. Cañas, et. al.
Wed, 11 Jan 23
10/80

Comments: 17 pages, 12 figures. Accepted to ApJ

Meteorite Parent Body Aqueous Alteration Simulations of Interstellar Residue Analogs [EPA]

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http://arxiv.org/abs/2301.04103


Some families of carbonaceous chondrites are rich in prebiotic organics that may have contributed to the origin of life on Earth and elsewhere. However, the formation and chemical evolution of complex soluble organic molecules from interstellar precursors under relevant parent body conditions has not been thoroughly investigated. In this study, we approach this topic by simulating meteorite parent body aqueous alteration of interstellar residue analogs. The distributions of amines and amino acids are qualitatively and quantitatively investigated and linked to closing the gap between interstellar and meteoritic prebiotic organic abundances. We find that the abundance trend of methylamine > ethylamine> glycine > serine > alanine > \b{eta}-alanine does not change from pre- to post-aqueous alteration, suggesting that certain cloud conditions have an influential role on the distributions of interstellar-inherited meteoritic organics. However, the abundances for most of the amines and amino acids studied here varied by about 2-fold when aqueously processed for 7 days at 125 {\deg}C, and the changes in the {\alpha}- to \b{eta}-alanine ratio were consistent with those of aqueously altered carbonaceous chondrites, pointing to an influential role of meteorite parent body processing on the distributions of interstellar-inherited meteoritic organics. We detected higher abundances of {\alpha}- over \b{eta}-alanine, which is opposite to what is typically observed in aqueously altered carbonaceous chondrites; these results may be explained by at least the lack of minerals and insoluble organic matter-relevant materials in the experiments. The high abundance of volatile amines in the non-aqueously altered samples suggests that these types of interstellar volatiles can be efficiently transferred to asteroids and comets, supporting the idea of the presence of interstellar organics in solar system objects.

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D. Qasim, H. McLain, J. Aponte, et. al.
Wed, 11 Jan 23
11/80

Comments: Published in ACS Earth and Space Chemistry; Supporting Info available at this https URL

Emergent Spectral Fluxes of Hot Jupiters: an Abrupt Rise in Day Side Brightness Temperature Under Strong Irradiation [EPA]

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http://arxiv.org/abs/2301.03639


We study the emergent spectral fluxes of transiting hot Jupiters, using secondary eclipses from Spitzer. To achieve a large and uniform sample, we have re-analyzed all secondary eclipses for all hot Jupiters observed by Spitzer at 3.6- and/or 4.5 microns. Our sample comprises 457 eclipses of 122 planets, including eclipses of 13 planets not previously published. We use these eclipse depths to calculate the spectral fluxes emergent from the exoplanetary atmospheres, and thereby infer temperature and spectral properties of hot Jupiters. We find that an abrupt rise in brightness temperature, similar to a phase change, occurs on the day side atmospheres of the population at an equilibrium temperature between 1714K and 1818K (99-percent confidence limits). The amplitude of the rise is 291 +/-49 Kelvins, and two viable causes are the onset of magnetic drag that inhibits longitudinal heat redistribution, and/or the rapid dissipation of day side clouds. We also study hot Jupiter spectral properties with respect to metallicity and temperature inversions. Models exhibiting 4.5 micron emission from temperature inversions reproduce our fluxes statistically for the hottest planets, but the transition to emission is gradual, not abrupt. The Spitzer fluxes are sensitive to metallicity for planets cooler than approximately 1200 Kelvins, and most of the hot Jupiter population falls between model tracks having solar to 30X-solar metallicity.

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D. Deming, M. Line, H. Knutson, et. al.
Wed, 11 Jan 23
12/80

Comments: 29 pages, 12 figures, 4 tables (3 are MR), accepted for the Astronomical Journal

Moist convection is most vigorous at intermediate atmospheric humidity [EPA]

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http://arxiv.org/abs/2301.03669


In Earth’s current climate, moist convective updraft speeds increase with surface warming. This trend suggests that very vigorous convection might be the norm in extremely hot and humid atmospheres, such as those undergoing a runaway greenhouse transition. However, theoretical and numerical evidence suggests that convection is actually gentle in water vapor-dominated atmospheres, implying that convective vigor may peak at some intermediate humidity level. Here, we perform small-domain convection-resolving simulations of an Earth-like atmosphere over a wide range of surface temperatures and confirm that there is indeed a peak in convective vigor, which we show occurs near T_s ~ 330 K. We show that a similar peak in convective vigor exists when the relative abundance of water vapor is changed by varying the amount of background (non-condensing) gas at fixed T_s, which may have implications for Earth’s climate and atmospheric chemistry during the Hadean and Archean. We also show that Titan-like thermodynamics (i.e., a thick nitrogen atmosphere with condensing methane and low gravity) produce a peak in convective vigor at T_s ~ 95 K, which is curiously close to the current surface temperature of Titan. Plotted as functions of the saturation specific humidity at cloud base, metrics of convective vigor from both Earth-like and Titan-like experiments all peak when cloud-base air contains roughly 10% of the condensible gas by mass. Our results point to a potentially common phenomenon in terrestrial atmospheres: that moist convection is most vigorous when the condensible component is between dilute and non-dilute abundance.

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J. Seeley and R. Wordsworth
Wed, 11 Jan 23
15/80

Comments: N/A

Solar System Abundances and Condensation Temperatures of the Halogens Fluorine, Chlorine, Bromine, and Iodine [EPA]

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http://arxiv.org/abs/2301.03674


We review a large body of literature for concentrations of halogens in chondrites and stellar halogen data used for solar system abundances (i.e., representative abundances of the solar system at the time of its formation) and associated analytical problems. Claims of lower solar system chlorine, bromine and iodine abundances from recent analyses of CI-chondrites are untenable because of incompatibility of such low values with nuclear abundance systematics and measurements of halogens in the sun and other stars. We suspect analytical problems associated with these peculiar rock types caused lower analytical results in several studies. Mass concentrations in CI-chondrites are F=92+-20 ppm, Cl=717+-110 ppm, Br=3.77+-0.90 ppm, and I=0.77+-0.31 ppm, and abundances normalized to N(Si) =10^6 atoms are N(F)=1270+-270, N(Cl)=5290+-810, N(Br)=12.3+-2.9, and N(I)=1.59+-0.64. Meteoritic values scaled to present-day photospheric abundances with log N(H)=12 are A(F)=4.61+-0.09, A(Cl)=5.23+-0.06, A(Br)=2.60+-0.09, and A(I)=1.71+-0.15. These recommended present-day solar system abundances compare to the sunspot values of N(F)=776+-260, A(F)=4.40+-0.25, and N(Cl)=5500+-810, A(Cl)=5.25+-0.12 and are consistent with F and Cl abundance ratios in other stars and other astronomical environments. The chlorine abundance of 776+-21 ppm by Yokoyama et al. (2022) for the CI-chondrite-like asteroid Ryugu is consistent with the chlorine abundance evaluated for CI-chondrites here. Updated equilibrium 50% condensation temperatures from our previous work (Lodders 2003, Fegley & Schaefer 2010, Fegley & Lodders 2018) considering solid-solution and kinetic inhibition effects are 713K (F), 427K (Cl), 392K (Br) and 312K (I) at 10^-4 bar total pressure. Condensation temperatures computed with lower halogen abundances do not represent the correct condensation temperatures from a solar composition gas. (abridged)

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K. Lodders and B. Jr
Wed, 11 Jan 23
22/80

Comments: 59 pages, 5 figures, 18 tables

A Second Earth-Sized Planet in the Habitable Zone of the M Dwarf, TOI-700 [EPA]

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http://arxiv.org/abs/2301.03617


We report the discovery of TOI-700 e, a 0.95 R$\oplus$ planet residing in the Optimistic Habitable Zone (HZ) of its host star. This discovery was enabled by multiple years of monitoring from NASA’s Transiting Exoplanet Survey Satellite (TESS) mission. The host star, TOI-700 (TIC 150428135), is a nearby (31.1 pc), inactive, M2.5 dwarf ($V{mag} = 13.15$). TOI-700 is already known to host three planets, including the small, HZ planet, TOI-700 d. The new planet has an orbital period of 27.8 days and, based on its radius (0.95 R$_\oplus$), it is likely rocky. TOI-700 was observed for 21 sectors over Years 1 and 3 of the TESS mission, including 10 sectors at 20-second cadence in Year 3. Using this full set of TESS data and additional follow-up observations, we identify, validate, and characterize TOI-700 e. This discovery adds another world to the short list of small, HZ planets transiting nearby and bright host stars. Such systems, where the stars are bright enough that follow-up observations are possible to constrain planet masses and atmospheres using current and future facilities, are incredibly valuable. The presence of multiple small, HZ planets makes this system even more enticing for follow-up observations.

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E. Gilbert, A. Vanderburg, J. Rodriguez, et. al.
Wed, 11 Jan 23
58/80

Comments: 16 pages, 4 figures, 2 tables, accepted for publication in ApJL

Constraints on the lunar core viscosity from tidal deformation [EPA]

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http://arxiv.org/abs/2301.04035


We use the tidal deformations of the Moon induced by the Earth and the Sun as a tool for studying the inner structure of our satellite. Based on measurements of the degree-two tidal Love numbers k2 and h2 and dissipation coefficients from the GRAIL mission, Lunar Laser Ranging and Laser Altimetry on board of the LRO spacecraft, we perform Monte Carlo samplings for 120,000 possible combinations of thicknesses and viscosities for two classes of the lunar models. The first one includes a uniform core, a low viscosity zone (LVZ) at the core-mantle boundary, a mantle and a crust. The second one has an additional inner core. All models are consistent with the lunar total mass as well as its moment of inertia. By comparing predicted and observed parameters for the tidal deformations we find that the existence of an inner core cannot be ruled out. Furthermore, by deducing temperature profiles for the LVZ and an Earth-like mantle, we obtain stringent constraints on the radius (500 +- 1) km, viscosity,21 (4.5 +- 0.8) x 10^16 Pa.s and the density (3400 +- 10) kg/m^3 of the LVZ. We also infer the first estimation for the outer core viscosity, (2.07 +- 1.03) x 10^17 Pa.s, for two different possible structures: a Moon with a 70 km thick outer core and a large inner core (290 km radius with a density of 6000 kg/m3), and a Moon with a thicker outer core (169 km thick) but a denser and smaller inner core (219 km radius for 8000 kg/m^3).

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A. Briaud, A. Fienga, D. Melini, et. al.
Wed, 11 Jan 23
72/80

Comments: N/A