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Physics Astrophysics Earth and Planetary Astrophysics

astro-ph.EP Watch Earth and Planetary Astrophysics

Wednesday 26 August

Earth and Planetary Astrophysics

STXM-XANES and TEM analysis of UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs)

B. Guérin, C. Engrand, C. Le Guillou et al. (+7 more)

The Concordia micrometeorite collection contains UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) of probable cometary origin. Eight FIB sections of UCAMMs were studied by Scanning Transmission X-ray Microscopy - X-ray Absorption Near Edge Structure and (Scanning)Transmission Electronic Microscopy. Three different phases of organic matter (OM) exist in UCAMMs and small mineral aggregates are distributed in the OM. Two OMs share spectral features with those of insoluble organic matter (IOM) of carbonaceous chondrites and of cometary grains returned by the Stardust mission. The third OM is N-rich (N/C at. ratios up to 0.22) and has only a few equivalents in extraterrestrial OM analyzed so far, such as in cometary particles collected during the Stardust mission, Interplanetary Dust Particles (IDPs) and UCAMMs collected near the Dome Fuji Station. This N-rich OM could have formed by irradiation of N-rich ices in the outer regions of the protoplanetary disk. UCAMMs contain variable amounts of minerals, consisting of crystalline Mg-rich silicates, Fe(Ni) sulfides and Fe oxides, which can be cemented in a Si-rich groundmass. Hypocrystalline mineral assemblages are also observed. Glassy phases showing morphological resemblance to GEMS are also found in some UCAMMs. This mineralogy is mainly consistent with that of previous UCAMM analyses, and is close to what is observed in Chondritic Porous IDPs, which are also considered as cometary dust particles. A mineral exhibiting a phyllosilicate texture has been observed in this work, and raises the question of the possibility of aqueous alteration on comets. Overall, UCAMMs' mineralogical and organic characterization implies a complex formation history of UCAMMs, and the presence of large-scale radial mixing in the early solar system, to transport their mineral components to the outer parts of the protoplanetary disk.
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All authors B. Guérin, C. Engrand, C. Le Guillou, H. Leroux, E. Dartois, J. Duprat, S. Bernard, K. Benzerara, L. Delauche, D. Troadec

Earth and Planetary Astrophysics

A calibrated dust-trail model of the Leonid meteoroid stream and forecasts of the 2031-2035 encounters

Shinsuke Abe

We combine N-body dust-trail generation with a fast nodal-encounter forecast and apply the model to the Leonid returns of 2031-2035. The dominant error is neither the ejection physics nor the encounter machinery but the parent trajectory at the moment of ejection: a back-integration of 55P/Tempel-Tuttle places the pre-1700 ejection sites more than 1 au from the fitted apparition solutions. We therefore anchor the ejection sites, not the dust, to the JPL Horizons ephemeris. Anchoring removes an age-proportional bias in the modelled nodes and, for the first time in this model, reproduces the classical attribution of the 2001 and 2002 storms to the 1767 trail, with peak times accurate to 1 and 40 min. A second systematic is not a property of the parent: a forecast read from a stored dataset holds each node where the snapshot left it, while the real node moves a median 1.2e-2 au in 0.12 revolutions. Two frozen snapshots of the same trail disagree by as much, so each year uses its own epoch-matched dataset. A completeness audit – every encounter the model predicts, not only the nominated ones – over-predicts the 1932 trail eighteenfold. We predict two comparable maxima on 2034 November 18, zenithal hourly rate ~1.4e3 at 03:30 UT from the 1932 trail and ~1.2e3 at 23:45 UT from the 1733 trail, with ~1.4e3 in 2033 and ~650 in 2035. Which dominates is a direct observational test of the trail-density term.
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Earth and Planetary Astrophysics

Assessing the Climate and Habitability of Tidally Locked Rocky Exoplanets

Erica Bisesi, Giuseppe Murante, Jost von Hardenberg et al. (+5 more)

Tidally locked exoplanets orbiting M dwarf stars are prime targets in the search for habitable worlds, yet their complex climate dynamics challenge conventional models of habitability. We homogeneously estimated the liquid-water habitability of exoplanets with the highest up-to-date Earth-similarity index. We modified the climate model PLASIM to apply it to tidally locked exoplanets across a range of parameters. We systematically classified and compared potentially habitable exoplanets and selected among the ones featuring the highest Earth-similarity index in the conservative sample of the Habitable Wolds Catalog, both relative to each other and as a function of atmospheric pressure. Our analysis revealed three main climate regimes: Snowball, Hot, and Eyeball planets-the latter having a warm and habitable substellar region with T > 273 K and a localized hydrological cycle. Although surface temperature generally increases with pressure, Eyeball planet climates remain stable in a wide pressure range. Complex atmospheric dynamics govern the behavior of the climate, highlighting the need for detailed climate simulations to guide future observations.
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All authors Erica Bisesi, Giuseppe Murante, Jost von Hardenberg, José A. Caballero, Michele Maris, Daniela Billi, Nicoletta La Rocca, Laura Silva

Earth and Planetary Astrophysics · Cross-listed from astro-ph.GA

Laplace surface of eccentric orbits around Kerr black hole and black-hole effects on Lidov-Kozai cycles

Haonan Quan and Xing Wei

We study the Laplace surface of eccentric orbits around a Kerr black hole with a companion star. The two relativistic effects (periapsis apsidal precession and Lense-Thirring precession) balance companion's tidal effect. By solving the secular equations, we find that the two branches of equilibrium solutions exist only in a narrow range of orbital inclinations of test particle, and that the stability exists when companion's obliquity approaches 90 degree. We then study the black-hole effects on Lidov-Kozai cycles. In addition to the black-hole suppression on cycle amplitude, we find that the cycle frequency is non-monotonic about distance from black hole and reaches its minimum in the transition between GR apsidal precession and companions's tidal precession. Finally we use this mechanism to well interpret the nearly isotropic orientation of S-cluster in the Galactic center.
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Earth and Planetary Astrophysics

Centimeter-wave OH observations of comets 12P/Pons-Brooks and C/2023 A3 (Tsuchinshan-ATLAS) with FAST

Long-Fei Chen, Juncen Li, Zhen Wang et al. (+5 more)

We present centimeter-wave spectroscopic observations of the OH 18-cm lines in two bright comets, 12P/Pons-Brooks and C/2023 A3 (Tsuchinshan-ATLAS), conducted with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) during their 2024 apparitions. For the Halley-type comet 12P/Pons-Brooks, five epochs of OH observations were obtained. The main OH lines at 1665 and 1667 MHz were robustly detected in absorption during one pre-perihelion epoch, while upper limits were derived for two post-perihelion epochs. For the dynamically new Oort Cloud comet C/2023 A3 (Tsuchinshan-ATLAS), six epochs of OH observations were obtained. The 1665 and 1667 MHz lines were robustly detected in absorption during two epochs immediately following the comet's closest approach to Earth. We also reported a tentative detection of the 1721 MHz satellite line in one of these two epochs. The low OH detection rates for these two bright comets are primarily attributable to their unfavorable heliocentric radial velocity during the observations, which resulted in the anti-maser negative inversion mode of the OH excitation. We calculated the OH production rates for both comets and found that, after considering the small beam size of FAST and the collisional quenching effect, production rates are consistent with the data from literature. Specifically, this matches the power-law fit of the OH production rates for comet 12P/Pons-Brooks, as well as the production rates at comparable heliocentric distances among comet C/2023 A3 (Tsuchinshan-ATLAS) and four other dynamically new Oort Cloud comets.
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All authors Long-Fei Chen, Juncen Li, Zhen Wang, Jian-Yang Li, Wing-Huen Ip, Zhong-Yi Lin, Bin Yang, Chao-Wei Tsai

Tuesday 25 August

Earth and Planetary Astrophysics

Discovery and Characterization of the TOI-4468 Planetary System: A Transiting Hot Jupiter With a Lone Nearby Outer Companion

Joseph R. Livesey, Benjamin J. Hord, Juliette Becker et al. (+28 more)

We report the discovery of two planets, a hot Jupiter and a nearby outer sub-Neptune, orbiting the star TOI-4468. This system is unique among the current exoplanet census in that it features a close outer companion to a hot Jupiter without an accompanying inner companion. By jointly fitting radial velocity measurements taken with the NEID spectrograph and transit photometry from TESS and several ground-based observatories, we constrain the orbital periods, masses, and radii of these two planets. We confirm the planetary nature of the hot Jupiter TOI-4468 b ($R = 1.01 R_J$, $m = 0.54 M_J$, $P = 2.77$ days). We also validate the outer planet TOI-4468 c ($R = 0.28 R_J$, $P = 7.01$ days) statistically, incorporating constraints from ground-based observations. We also identify, but cannot confirm, an additional radial velocity signal which may be due to an outer giant in this system with an orbital period of 624 days. From the observed geometry of this system, we argue that it must never have encountered an early secular resonance that is thought to excite the mutual inclination of other hot Jupiter/outer companion systems. We discuss the possibility of an undetected inner companion, as well as potential implications for hot Jupiter formation.
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All authors Joseph R. Livesey, Benjamin J. Hord, Juliette Becker, Andrew Vanderburg, Joseph E. Rodriguez, Elise Koo, Chelsea X. Huang, Gudmundur Stefánsson, Karen A. Collins, Ivan A. Strakhov, Zijun He, Maxwell A. Kroft, Robert Aloisi, Khalid Barkaoui, Fabian Rodriguez Frustaglia, Alyssa Jankowski, Kinga Kasprzyk, Judith Korth, Coleman Nelson, Hannu Parviainen, Adam Popowicz, Manfred Raetz, Richard P. Schwarz, Eva Stafne, Keivan G. Stassun, Thomas G. Beatty, Paul Foster, Thomas MacLean, Devansh Mathur, Lizhou Sha, Melinda Soares-Furtado

Earth and Planetary Astrophysics · Cross-listed from astro-ph.IM

Spatially Scanned STIS Spectra of the Exoplanet Host Star 55 Cnc

D. E. Welty, J. D. Lothringer, D. K. Sing et al. (+3 more)

We discuss the analysis of two sets of optical/near-IR spectra of the exoplanet host star 55 Cnc, obtained with the Space Telescope Imaging Spectrograph (STIS) and grating G750L in spatial scanning mode, in order to assess the performance of that relatively new observing mode for studies of transiting exoplanets. Standard pipeline reductions of the CCD spectral images were augmented by custom procedures for removing both cosmic rays and the strong fringing seen at wavelengths longer than 7000 A. Both total ("white-light") fluxes and the fluxes for narrower wavelength intervals were extracted from the processed spectral images. Apart from slight ($\sim$400 ppm) orbit-to-orbit offsets between the relative fluxes in each set, the patterns exhibited by the flux values within each orbit are very similar. The systematic differences in the fluxes are somewhat smaller than those seen in STIS spectra of 55 Cnc obtained in "stare mode", where the CCD is deliberately saturated at a fixed pointing. A parameterized detrending method similar to those commonly used to remove instrumental effects from time series observations of exoplanet host stars was then applied to the extracted fluxes. For the total fluxes, the scatter about the detrending models is $\sim$30-40 ppm – comparable to the best precision previously obtained for time series photometry with HST – but is somewhat larger for narrower wavelength bins. The depth of the transit of the super-Earth 55 Cnc e ($\sim$450 ppm for the total flux) is consistent with previous values. Both the scan-mode and the stare-mode observations of 55 Cnc e appear to indicate an unexpected (and variable?) increase in the transit radius Rp/Rs between 0.55 and 1.0 $\mu$m. While these data are somewhat limited, they do suggest that spatial scanning with the STIS CCD can provide high-quality optical/near-IR spectra of the brighter exoplanet hosts. (edited)
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All authors D. E. Welty, J. D. Lothringer, D. K. Sing, A. M. Jones, A. Riley, C. R. Proffitt

Earth and Planetary Astrophysics

Tidal Demise: The Evolution and Fate of a Hypothetical Venus Moon

Stephen R. Kane, Franck Selsis, Jeremy Leconte et al. (+1 more)

Venus possesses no natural satellite, raising the question whether a formed moon could have survived. We explore the tidal evolution of a Venus-moon system, coupling Venus's spin to the satellite's orbit under tides from the moon and Sun. We survey spin period ($P_0 = 5$–100~hr), moon mass ($M_m = 0.01$–$10~M_{\rm Moon}$), eccentricity, quality factor, and initial semi-major axis under both constant-$Q$ and constant time lag models. Survival depends on competition between outward migration ($\propto M_m$) and synchronous radius expansion ($\propto M_m^2$): for circular orbits around rapidly spinning Venus ($P_0 \lesssim 12$~hr), a lunar-mass satellite survives the age of the Solar System in both models. For $P_0 \lesssim 10$~hr, eccentricity pumping can destabilize low-mass satellites, while for $P_0 \gtrsim 15$~hr or $M_m \gtrsim 2~M_{\rm Moon}$ the synchronous radius overtakes the orbit and drives Roche destruction within $\sim$0.03–1.7~Gyr in the constant-$Q$ model. The constant time lag model instead permits quasi-synchronous survival for massive moons at fast spin. Explaining Venus's present state requires satisfying two constraints simultaneously: loss of the satellite and despinning of an initially rapid rotator. Both are met only within a restricted region of parameter space, favoring moderate post-impact spin periods and lunar-to-super-lunar masses. Giant impact simulations predict spin periods $\gtrsim$12~hr for Venus's present rotation, placing a lunar-mass satellite at the survival boundary. For last-impact conditions within this region, the present absence of a Venusian satellite arises through tidal evolution alone; a subsequent catastrophic stripping event, while capable of removing a moon, is not required.
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All authors Stephen R. Kane, Franck Selsis, Jeremy Leconte, Sean N. Raymond

Earth and Planetary Astrophysics

Kepler-50: Two Planets in Close Resonance Perturbed by a Non-transiting Planet

Daniel Jontof-Hutter, Jason F. Rowe, Jack J. Lissauer et al. (+1 more)

Kepler-50 has two transiting planets close to the 6:5 commensurability. We analyze transit times measured from Kepler data with dynamical fits. We attribute the residual signal to a near-resonance non-transiting third planet in the system. The parameters of the third planet are degenerate. We identified 55 (15) regions of interest for an exterior (interior) perturber, and characterize system parameters in each region of interest with posterior sampling. We find that removing samples that are not long-term stable provides few additional constraints on posteriors, and that the transit times do not confirm the likely 2-body resonant state of the transiting planets as $\approx$ 68% of posterior samples that are likely stable are also likely in libration. We identify a small fraction of samples that are in 3-body libration. Despite the degeneracies, we recover robust, tightly constrained masses for Kepler-50 b and c ($2.35^{+0.48}_{-0.43}$ $M_{\oplus}$ and $4.43^{+0.45}_{-0.49}$ $M_{\oplus}$, respectively) and strongly detected non-zero relative eccentricity for Kepler-50 b and c with ($e_c\cos\varpi_c$ - $e_b\cos\varpi_b$) = -0.045 $\pm 0.003$, and ($e_c\sin\varpi_c$ - $e_b\sin\varpi_b$) = -0.030 $\pm 0.004$. These close neighbors are in the radius valley and sub-Neptune by size, respectively ($1.750 \pm 0.038$ $R_{\oplus}$ and $2.079 \pm 0.060$ $R_{\oplus}$). With one of the closest planet pairs known and one of the closest to first-order commensurability, the Kepler-50 system is an especially valuable benchmark for planet formation theory.
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All authors Daniel Jontof-Hutter, Jason F. Rowe, Jack J. Lissauer, Daniel C. Fabrycky

Earth and Planetary Astrophysics

Flyby-induced high-eccentricity migration and the prevalence of hot Jupiters in M67

Mika V. Kontiainen, Cathie J. Clarke and Andrew J. Winter

Few planetary systems form in isolation. Rather, interactions in their birth environments may sculpt their architectures or drive them into unstable configurations. Here we study the role of environmental perturbations in triggering dynamical instabilities leading to hot Jupiter formation in dense clusters, focusing on whether the elevated occurrence rate of hot Jupiters in the open cluster M67 can be explained through flyby-induced high-eccentricity migration. We develop a hybrid method for modelling the secular and tidal evolution of planetary systems under external perturbations by passing stars using a combination of analytic and numerical approaches. We evolve 10,000 realizations each of systems with either a single planet, two planets, or a planet and a stellar companion for $\sim$4 Gyr in an M67-like cluster, comparing outcome statistics against a control sample without flybys. In single- and two-planet systems, the rate of flyby-induced hot Jupiter formation is negligible. However, in systems with an initially isotropically oriented stellar companion, the cluster environment boosts hot Jupiter formation by a factor of $\sim$2, accompanied by a factor of $\sim$3 increase in the rate of planets undergoing tidal disruption. Based on observationally motivated estimates of primordial populations, our hot Jupiter yields are consistent with both field and M67 occurrence rates, provided the primordial wide binary fraction among solar-type stars is close to $\sim$50 per cent, binary-driven high-eccentricity migration is the dominant formation pathway, and a substantial fraction of tidally disrupted systems survive as hot Jupiters through partial mass loss.
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Earth and Planetary Astrophysics

Magnesium silicate condensation in sub-Neptune envelopes: the fundamental link between chemistry, structure, and observables

William Misener, Peter Gao, Nicole L. Wallack et al. (+2 more)

Chemical interactions between the hydrogen-dominated envelopes and silicate-rich interiors of sub-Neptunes likely play a key role in shaping their atmospheric structure, mass-radius relations, and upper atmosphere composition. While atmospheric abundances and structure deeply influence each other, many existing models have either considered the effects of chemical interactions without the structural implications or have modeled the envelope structure using oversimplified chemical networks. In this work, we introduce Rocky Raccoon, a coupled chemical equilibrium-atmospheric structure model. This model incorporates Mg, Si, O, C, and H species and produces self-consistent atmospheric chemical and thermal profiles for sub-Neptune envelopes, treating multi-species condensation for the first time. We find that the condensation sequence of magnesium silicates above a magma ocean is determined by the basal magma composition. We show that these condensation sequences drive the upper atmospheric composition to two endmembers: high oxygen abundances in the underlying melt produce compositions rich in oxygen-bearing volatiles (sub-solar C/O) and higher mean molecular weight atmospheres with $\mu \sim 4$ amu, while oxygen-poor melts produce lower mean molecular weight atmospheres dominated by methane and silane (super-solar C/O). The transition between the two regimes is abrupt and depends on melt properties like Mg/Si ratios and oxygen abundances. The different condensation sequences also lead to different thermal profiles, as deep convection is inhibited over different regions due to varying molecular weight gradients. Further experiments and simulations are key to resolving critical uncertainties in the condensation sequences and the corresponding significant impacts on sub-Neptune composition and thermal structure.
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All authors William Misener, Peter Gao, Nicole L. Wallack, Maggie A. Thompson, Anat Shahar

Earth and Planetary Astrophysics

Atmospheric Retrieval of Combined JWST, HST, and Ground-Based Observations Reveals a Featureless Transmission Spectrum for GJ 1132 b

Mohammad Senobar and Sareh Ataiee

We present a panchromatic transmission spectrum of GJ1132b spanning $0.71$–$5.16~\mu$m, combining published transit observations from Magellan/LDSS3C, HST/WFC3 G141, and JWST/NIRSpec (G395H and G395M). Using petitRADTRANS and PyMultiNest, we perform Bayesian atmospheric retrievals, comparing a flat-line, Gaussian-feature models, and clear and cloudy atmospheric scenarios, including tests with and without the first JWST visit flagged as a potential outlier in a previous study. The inclusion of shorter-wavelength spectra shifts the marginal molecular preference from H$_2$O (JWST-only) to NH$_3$ (panchromatic). Of the seven molecules tested (NH$_3$, CO$_2$, CO, CH$_4$, H$_2$O, HCN, and N$_2$O), only NH$_3$ shows a marginal preference, which is weakened when the JWST first visit is excluded. Cloudy atmospheres yield higher Bayesian evidence than high-mean-molecular-weight clear models, but none provides compelling evidence over the flat-line scenario. A thin ($P_{\rm ref} \sim 10^{-3}$~bar), N$_2$-dominated atmosphere ($\mu \sim 16$~amu) with traces of NH$_3$, H$_2$O, and CH$_4$, combined with a grey, optically thin power-law cloud (opacity at 350~nm $\le 10^{-3}~{\rm cm^2\,g^{-1}}$), remains indistinguishable from the flat-line model when the first JWST visit is included and is further disfavoured when it is excluded, strengthening a bare-rock interpretation. We conclude that current spectra show no evidence for an atmosphere on GJ1132b. The observations are best explained by a bare rocky planet with $R_{\rm p} = 1.129 \pm 0.002\,R_\oplus$, though a tenuous, obscured atmosphere cannot be excluded when the JWST first visit is included.
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Earth and Planetary Astrophysics

Potential survivable niches for microbial life on the lunar south pole

Prabal Saxena, Stefano Bertone, Heather V. Graham et al. (+5 more)

Most lunar surface conditions are incredibly harsh for microbial survival. High ultraviolet radiation, temperatures, and energetic particle radiation limit survival over most unprotected lunar surfaces, particularly in equatorial regions where all previous crewed exploration occurred. However, whether these harsh conditions are widespread at lunar poles has not been examined considering topographical effects. Here, we show that recent microorganism survivability data and lunar surface remote sensing reveal likely survivable niches in lunar polar regions. Analysis of topography and latitude-driven surface conditions using remote sensing data and high-resolution illumination models indicates the lunar south pole possesses significant regions with persistent low temperatures and ultraviolet flux. Comparing these conditions to survivability data of specific microorganisms, we find significant lunar polar areas likely possess surface conditions amenable to microbial survival. Our findings suggest lunar polar regions may be less hostile to microbial survival than previously assumed. This does not encompass growth likelihood, but survival in a cryptobiotic state where growth would be possible if habitable conditions were present. Potential microbial survivability at lunar poles is particularly significant given many examined microbes will likely be transported to the Moon during crewed lunar south pole exploration planned in numerous near-term missions. Thoughtfully planning exploration and tracking its impact is key to limiting and understanding potential unintended life transfer to the Moon.
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All authors Prabal Saxena, Stefano Bertone, Heather V. Graham, Natalie M. Curran, Aaron B. Regberg, Andrew Needham, D.E. Pugel, Noah E. Petro

Earth and Planetary Astrophysics · Cross-listed from astro-ph.IM

NIRC2-Pol: First Light of Near-Infrared Polarimetry on Keck II

Briley L. Lewis, Manxuan Zhang, Maxwell A. Millar-Blanchaer et al. (+21 more)

NIRC2, the Near Infrared Camera 2 on the Keck II telescope, was recently upgraded with a new suite of polarimetric observing modes. The new polarimetry modes (referred to as NIRC2-Pol) open up a wide range of new studies, including investigations of exoplanets, the Galactic center, active galactic nuclei, and solar system objects. The new modes enabled by the upgrade span the 1.1 to 4.1 micron range (i.e. J through L' bands) and include imaging polarimetry, coronagraphic imaging polarimetry, and spectropolarimetry. NIRC2-Pol is unique, as Keck II is the largest telescope (10 m) on which AO-fed infrared polarimetry capabilities are available, one of few with L' polarimetric imaging, and the only one where there is both a polarimetric mode and a vortex coronagraph. Here, we introduce the design of NIRC2-Pol, its capabilities, and its current operational status. We also present its first on-sky results: the first L' polarimetric images of the AB Aurigae circumstellar disk. These images more clearly reveal the disk's iconic spiral arms than previous L' total intensity imaging.
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All authors Briley L. Lewis, Manxuan Zhang, Maxwell A. Millar-Blanchaer, Eduardo Marin, Jayke S. Nguyen, Carlos Alvarez, Jaren N. Ashcraft, Mahawa Cisse, Charles-Antoine Claveau, Greg Doppmann, Michael P. Fitzgerald, Matthew Freeman, Trisha Hammen, Ryan Hersey, Nemanja Jovanovic, Scott Lilley, Jessica Lu, James E. Lyke, Keith Matthews, Dimitri Mawet, William Melby, Thomas McIntosh, Max Service, Jacob Taylor

Earth and Planetary Astrophysics

Volatile depletion in rocky planets as a chemical fingerprint of hybrid accretion

Haiyang S. Wang, Anders Johansen, Ziyan Xu et al. (+7 more)

Volatile depletion in rocky planets relative to their host stars is commonplace in both the Solar System and exoplanetary systems, yet the connections between planet formation and composition remain elusive. Here we model devolatilization during pebble accretion in combination with collisional growth from volatile-depleted planetesimals to explore the formation pathways of Earth and Mars. Using Bayesian inference, we find that bulk silicate Earth is best reproduced by ${\gtrsim}$75% contribution from two protoplanets formed via pebble accretion, supplemented by up to $\sim$25% material from planetesimals that are compositionally akin to the asteroid Vesta. Using instead a planetesimal volatile-depletion curve that is not observed among known meteorite parent bodies would allow the planetesimal contribution to reach 40$^{+15}_{-14}$%. In comparison, bulk silicate Mars reflects 27$\pm$5% pebble-accreted material and 73${\pm}$5% Vesta-like planetesimals. We identify volatile depletion as a chemical fingerprint of hybrid accretion, in which both pebble accretion and collisional assembly contribute to terrestrial planet growth. By quantitatively linking formation pathways to volatile budgets, our findings demonstrate how planetary accretion histories can be inferred from elemental signatures, with broad implications for interpreting the chemical diversity of rocky exoplanets.
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All authors Haiyang S. Wang, Anders Johansen, Ziyan Xu, Marie-Luise Steinmeyer, Michiel Lambrechts, Elishevah van Kooten, Chao-Chin Yang, Zhaohuan Zhu, Dante S. Lauretta, Martin Bizzarro

Earth and Planetary Astrophysics · Cross-listed from astro-ph.IM

Sub-diffraction-limited coronagraphic imaging with nano-printed PIAACMC phase masks

Elena Tonucci, Sebastiaan Y. Haffert, Warren B. Foster et al. (+22 more)

Imaging Earth-like exoplanets in the habitable zone of their host star is among the main science objectives of future ground-based and space-based observatories. However, the extreme contrast and small separations needed to image such planets cannot be reached with current technology. The Phase-Induced Amplitude Apodization Complex Mask Coronagraph (PIAACMC) is a promising coronagraph to reach this goal. The PIAACMC uses a set of aspheric lenses to apodize the entrance pupil without throughput losses and a phase-shifting focal plane mask for starlight suppression. These allow us to maintain high throughput and achieve a small inner-working angle (IWA), unlocking the capability to observe exoplanets at the diffraction limit. The masks are manufactured in-house at Leiden University with Nanoscribe, a micro-3D-printer that uses two-photon polymerization to achieve sub-micron precision in height. We present the first scientific results with a focal plane mask for the PIAACMC on the Magellan Adaptive Optics eXtreme (MagAO-X) instrument for the 6.5-meter Magellan Clay telescope at Las Campanas Observatory, Chile. We show laboratory and on-sky contrast curves with a broadband z' filter centered at 908 nm with a 14% bandwidth. We use the PIAACMC to detect binary companions at separations ~0.8-5 lambda/D (~23-144 mas). This demonstrates the PIAACMC's capability to observe at the diffraction limit and below, with a sub-lambda/D IWA. Future work includes exploring new mask designs to improve the contrast in broadband light and performing active focal plane wavefront sensing and control.
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All authors Elena Tonucci, Sebastiaan Y. Haffert, Warren B. Foster, Jared R. Males, Olivier Guyon, Laird M. Close, Kyle van Gorkom, Alexander D. Hedglen, Parker T. Johnson, Maggie Y. Kautz, Jay K. Kueny, Rico Landman, Jialin Li, Joshua Liberman, Joseph D. Long, Miles Lucas, Jennifer Lumbres, Matthijs Mars, Eden A. McEwen, Avalon McLeod, Tiffany Nguyen, Logan A. Pearce, María Eugenia Redondo González, Lauren Schatz, Katie Twitchell

Earth and Planetary Astrophysics

The Hot Neptune Initiative (HONEI) III. An ultra-hot super Neptune orbiting the metal-rich subgiant star TOI-5646: the largest host for a desert dweller

L. Mancini, F. Manni, D. Kubyshkina et al. (+25 more)

We report the confirmation of the TESS transiting-planet candidate orbiting the metal-rich F8\,IV-V subgiant star TOI-5646 (V=11.38 mag; T=6136 K). The planetary nature of TOI-5646b was confirmed by means of HARPS-N follow-up radial velocity measurements. We determined that the planet has an orbital period of 2.4277 days and an orbital eccentricity compatible with zero. With a mass of 45.9 Earth masses, a radius of 6.6 Earth radii, and an equilibrium temperature of 1935 K, it is one of the hottest super-Neptune exoplanets ever discovered in the Neptune desert. Its density, 0.87 g cm^-3, is lower than that of most other desert dwellers, but still appears to follow the trend that the desert is populated by dense planets than those in the ridge and savanna. The metallicity of the parent star ([Fe/H]=0.32) follows the trend whereby the host stars of Neptune-sized exoplanets in the desert and the ridge are generally richer in metal than those in the savanna. The log{g} of the parent star (4.09) suggests that the host is an evolved star, making this a peculiar system: TOI-5646 is the largest star (1.8 Solar radii) ever discovered to host a Neptune-sized planet in the desert. Internal structure modelling revealed that TOI-5646b is highly enriched in metals, with an inferred bulk metallicity between 0.7 and 0.95. Atmospheric evolution simulations indicate that the planet has undergone significant mass loss (6-16%) through intense XUV irradiation from its host star. These results indicate a peculiar formation history (potentially involving early protoplanetary disk dispersal), a planetary collision, or a late tidal destruction event, to explain its current state as a low-density survivor in the Neptune desert.
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All authors L. Mancini, F. Manni, D. Kubyshkina, E. A. van Dijk, L. Naponiello, M. Damasso, V. D'Orazi, K. Biazzo, A. V. Bonomo, L. Fossati, Y. Miguel, J. de Leon, M. E. Everett, W. Fong, A. Fukui, D. Gandolfi, S. B. Howell, D. W. Latham, M. Lopez-Morales, P. MacQueen, F. Murgas, N. Narita, E. Palle, M. Pinamonti, T. Pugh, A. Sozzetti, S. Vissapragada, S. W. Yee

Earth and Planetary Astrophysics

Nitrogen- and nitrogen-oxygen-bearing organic molecules in comet 67P/Churyumov-Gerasimenko: An untargeted investigation

N. Hänni, K. Altwegg, D. Baklouti et al. (+6 more)

Comets provide a unique window into the history of the Solar System as they carry some of the best-preserved material and make it available to in situ exploration. A milestone in comet studies was the European Space Agency's Rosetta mission, which, for the first time, rendezvoused with a comet, namely 67P/Churyumov-Gerasimenko (67P), and studied it from a close range for two years. Amongst other unexpected insights, data from this mission show that comets contain a surprisingly large portion of organics, both in the refractory and the icy phases. For this work, we evaluated high-resolution mass spectra collected in comet 67P's inner coma by Rosetta's ROSINA-Double Focusing Mass Spectrometer (DFMS). In unprecedented detail, we investigated the N- and NO-bearing cometary complex organic molecules (COMs) of the general sum formula CnHmN and CnHmNO, where n and m are the stoichiometric coefficients of carbon and hydrogen. Our discussion-driven approach combines the empirical concept of Occam's razor with knowledge from studies of relevant astrophysical environments and constraints expected from naive bottom-up assembly of molecules. We present an exemplary minimal and non-unique set of molecules needed to explain the DFMS observations. While this set might not capture the full organic diversity, but rather its lower limit, it identifies many N- and NO-bearing COMs with reasonable certainty, while excluding others, potentially informing future observational campaigns, and hence contributes to the exploration of the origin and evolution of organic complexity in space. Among the key results is strong evidence for an abundant presence of heterocycles as well as substantial alkylation of both cyclic and acyclic species. These findings align well with reports on soluble organic matter in meteorites and asteroids and ...
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All authors N. Hänni, K. Altwegg, D. Baklouti, M. Combi, S. A. Fuselier, J. De Keyser, D. R. Müller, M. Rubin, S. F. Wampfler

Earth and Planetary Astrophysics

Occultation of microlensed images by circum-lens disks: Implications for surveys

Elizabeth Bailey

Microlensing surveys typically apply automated criteria to exclude lightcurves that depart from time-symmetric and achromatic Paczyński curves. In surveys using such automated detection pipelines, occultation of microlensed images by circum-lens material could lead to underdetection or misclassification of ring- or disk-bearing compact object populations. This work characterizes the family of lightcurve morphologies by which uniform thin circum-lens disks of varying size and orientation, and low mass relative to their host lens, can intersect the ray paths produced during microlensing events. These morphology classes are paired with squared residuals relative to an unocculted lightcurve. We find that substantial deviations from an unocculted microlensing curve can occur across a wide range of parameter space. This effect holds relevance for free-floating planets and brown dwarfs where disks or ring systems can be present. Another potential consideration is that disk-shaped accretion flows onto primordial black holes (PBHs) during the cosmic dark ages could have resulted in remnant quiescent disks of baryonic material. Pipelines should be designed to account for disk-bearing lens populations, opening previously underutilized avenues to potentially observe disks and rings in these contexts and ensuring populations are accurately characterized.
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Earth and Planetary Astrophysics

Linear Continuum Modelling to Explain The Majority of Bulk Features of Kuiper Belt Object Spectra

Wesley C. Fraser, Laura E. Buchanan, Ian Wong et al. (+2 more)

The first analyses of the James Webb Space Telescope spectra of trans-Neptunian Objects (TNOs) revealed three discrete types of surfaces. This seems to contradict ground-based spectro-photometric datasets, which suggest a continuum of colors with only two surface types. Here we present linear spectral modelling that reconciles these two results. In our model, the sole parameter is the object's optical slope, and the reflectance spectrum at all wavelengths is linearly proportional to that color, with the slope of that function evaluated from the spectra themselves. When applied to small (H>5 for H2O-types and H>4 for the merged sample of organic-rich and CO2-types) and distant (q>18 au) objects, we find that this model does a reasonable job of reproducing the overall spectral behavior of both samples. Bootstrapping simulations show that if the optical slope were not a good predictor of an object's spectrum, then finding an explained variance of the model that is better than observed occurred in 2.3% of realizations for the H2O-types and 0% of realizations for the organics sample. In a chi^2 sense, the optical color is a better predictor of most spectra as compared to the mean spectrum of a class. The trends of optical color and spectra band-areas exhibited for many key compositional materials are well reproduced, and demonstrate that those materials govern the overall spectral shape within a class. Importantly, these results require that within a given class, the band-areas of those key materials are predictable given only its optical color and its surface type. Unsurprisingly, our simple one-parameter model does not account for the full spectral diversity of TNOs. We speculate that albedo encapsulates much of the remaining diversity.
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All authors Wesley C. Fraser, Laura E. Buchanan, Ian Wong, Bryan Holler, Michael E. Brown

Monday 24 August

Earth and Planetary Astrophysics

An Evolving Cosmic Shoreline and Sandbar Bounding the Rocky Airless Valley

Barron K. Nguyen, Laura K. Schaefer, Xuan Ji et al. (+7 more)

Recent JWST observations challenge the traditional 'cosmic shoreline' from both sides, revealing thick volatile atmospheres on the hottest close-in 'lava worlds,' where irradiation should drive the most extreme escape, and bare rocky surfaces on cooler terrestrial planets around M dwarfs, where atmospheres would be expected to survive. Using a coupled atmosphere-interior evolution model, we show that atmosphere retention is governed not by a single escape boundary but by two: a hot, outgassing-regulated 'cosmic sandbar' and a cooler, escape-regulated 'cosmic shoreline,' separated by an 'airless valley' that may mark a graveyard of stripped sub-Neptune cores. The sandbar arises because long-lived magma oceans, sustained further by tidal heating from secular eccentricity excitation in multi-planet systems, keep most volatiles dissolved and expose only a small atmospheric reservoir to escape, whereas cooler planets solidify, sequestering volatiles in the deep solid mantle while overexposing the rest to loss. This two-regime structure recasts the single cosmic shoreline as two boundaries set by distinct physics: outgassing and escape. We provide time-evolving fits for both boundaries across G, K, and M stellar types as a function of volatile inventory, planetary mass, age, and tidal heating. Lava worlds with thick atmospheres are unlikely around stars cooler than K-type unless sustained by extreme tidal and/or other interior heating. This framework links atmosphere survival from USP lava worlds to habitable zone planets, informing target selection and interpretation for TRAPPIST-1 and JWST DDT characterization.
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All authors Barron K. Nguyen, Laura K. Schaefer, Xuan Ji, Christopher A. Theissen, Fei Dai, Bo Peng, Yao Tang, Andrea Zorzi, Michelle Hill, Megan Weiner Mansfield

Earth and Planetary Astrophysics

An analysis of the Herbig star population and their protoplanetary disks within 1 kpc

L. M. Stapper, M. Vioque, A. J. Winter et al. (+6 more)

Herbig stars are intermediate mass pre-main sequence stars of 1.5 to $\sim15$~M$_\odot$ and are in between low and high-mass star formation. This work provides a catalog of all 243 known bona-fide Herbig stars with clear infrared excess and in many cases accretion signatures within 1~kpc. It contains archival, recalibrated, and newly derived stellar parameters, accretion rate properties, and disk dust mass measurements. We derive the latter by using newly obtained millimeter photometry and literature values. We find that 50% of Herbig dust disks are more massive than 10~M$_\oplus$, while this is only true for 20% and 5% of the T~Tauri disks in Lupus and Upper~Scorpius respectively. Furthermore, the Herbig disk dust mass distribution is bimodal, it consists of a high and low disk mass population with a mean dust mass of 21~M$_\oplus$ and 0.45~M$_\oplus$ respectively. We find that the catalog is near complete for within 300~pc, however, this decreases to 24% out to 1~kpc. We observe a flat relation for Herbig disks due to objects with short disk lifetimes, caused by a combination of low disk masses and high accretion rates. Furthermore, we find the peak of the occurrence rate of massive (>10~M$_\oplus$) disks to occur at $\sim$1-2~M$_\odot$ stars, coinciding with the peak in occurrence rate of giant exoplanets. The small number of Herbig stars with low accretion rates ($<10^{-8}$~M$_\odot$~yr$^{-1}$) or low disk dust masses ($\lesssim1$~M$_\oplus$), combined with the lack of an age dependence in the disk dust mass distribution, suggests that the observed Herbig star population represents the surviving disk-hosting phase in the optically visible late stages of intermediate-mass star formation. We argue that this is either due to the formation of deep dust traps in these disks or replenishment by late-infall, or a combination of the two.
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All authors L. M. Stapper, M. Vioque, A. J. Winter, D. J. Wilner, J. P. Williams, M. Benisty, A. S. Booth, S. L. Grant, M. R. Hogerheijde

Earth and Planetary Astrophysics

GravDyn: A Python Framework for Gravitational Modeling of Irregular Celestial Bodies Using Polyhedral, mascon, and Series Expansion Methods

Safwan Aljbaae, valerio Carruba, Allan K. de Almeida Jr et al. (+4 more)

GravDyn is an open-source Python package for computing gravitational potentials and accelerations around irregular celestial bodies. It implements three approaches within the same workflow: the constant-density polyhedral method, a layered mascon approximation based on tetrahedral decomposition, and the Potential Series Expansion Method (PSEM). The package handles shape-model preprocessing, builds the selected gravity representation, and evaluates potentials and accelerations efficiently. The three implemented methods serve different regimes: the polyhedral model provides a reference solution near the surface, the mascon model supports layered internal density structures, and PSEM offers fast evaluation outside the Brillouin sphere once the polynomial coefficients have been generated. Validation tests against the polyhedral solution show that the mascon and PSEM models reproduce the reference potential with small relative errors while reducing evaluation costs. GravDyn is intended for mission design and studies of spacecraft motion, orbital stability, and gravitational modeling around asteroids and other small bodies.
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All authors Safwan Aljbaae, valerio Carruba, Allan K. de Almeida Jr, Gabriel Antonio Caritá, Antonio F. B. A. Prado, Marcelo L. Mota, Carlos E. Ferreira Lopes

Earth and Planetary Astrophysics

The Highly Unusual Behavior and Chemical Composition of Interstellar Comet 2I/Borisov

Allison N. Bair, David G. Schleicher, Theodore Kareta et al. (+2 more)

We report on imaging, spectroscopy, and narrowband photometry of interstellar comet 2I/Borisov obtained at Lowell Observatory from 2019 September 13 to December 16. We measured chemical composition on four nights before perihelion, from October 4 to November 25 (2.466 to 2.028 au), with CN detections on all nights. Our measurements from October 27 represent the earliest reported detections of C$_2$ and C$_3$, where C$_2$-to-CN and C$_3$-to-CN log production rate ratios were $-$0.7 and $-$1.3, respectively. Both ratios increased by nearly 4$\times$ to $-$0.3 and $-$0.9 by November 25, an extremely large increase with heliocentric distance that is unprecedented in the Lowell Observatory comet database. We additionally observed OH and NH on November 25, with a derived H$_2$O production rate of 4.5$\times $10$^{26}$ mol s$^{-1}$ and very high log production rate ratios for CN-to-OH ($-$2.0) and NH-to-OH ($-$1.7). Monitoring from broadband $R$ images from September 13 to December 16 suggests dust ($A(0^{\circ})f\rho$) production peaked around October 19, 50 days before its December 8 perihelion passage. Narrowband images from October 4 and 27 reveal a nearly symmetric CN distribution in Borisov's coma, suggesting activity over its entire sunward hemisphere and possibly its entire nucleus. Our results, combined with those from others, reveal a chemical composition and behavior with heliocentric distance unlike any other comet we have observed.
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All authors Allison N. Bair, David G. Schleicher, Theodore Kareta, Matthew M. Knight, Michael S.P. Kelley

Earth and Planetary Astrophysics

Quantitative Links between Formation and Atmospheric Composition for Giant Planets

Yayaati Chachan, Ruth Murray-Clay and Jonathan J. Fortney

Precise atmospheric abundances of giant exoplanets are becoming increasingly prevalent and there is a need to systematically convert these measurements into metrics that inform us about the planets' accretion history. We present a quantitative framework for relating atmospheric composition to the accretion of metals and primordial gas. This includes i) new relations that simplify and generalize the connection between atmospheric metallicity and metal mass fraction, ii) methods for inferring the source of the metals and quantifying the quantity of metals accreted via different sources, and iii) relating the derived quantities to expectations from formation models. We also derive a new estimate of the minimum disk mass needed to form a planetary system based on the amount of excess metals accreted by a planet, assuming that this excess originates from the drift and evaporation of pebbles at condensation fronts. This paper is accompanied by an open-source code that implements the methods presented herein.
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Earth and Planetary Astrophysics

WASP-12b Exhibits Persistent In-Transit H$\alpha$ Absorption

Shreyas Vissapragada, Fabienne Nail, Morgan MacLeod et al. (+6 more)

High-resolution H$\alpha$ and He 10830 Å transit spectroscopy can trace the extended upper atmospheres of exoplanets, typically revealing excess in-transit absorption that occurs in the planet's rest frame. However, hydrodynamical simulations predict that absorption should not strictly follow the planet's orbital motion if gas quickly escapes the planetary Roche lobe and shears into tidal tails. The ultra-hot Jupiter WASP-12b fills an exceptionally large fraction of its Roche lobe ($R_p/R_\mathrm{Roche} = 0.55$), and in this paper we present evidence for tidally-modulated outflow kinematics on this unique planet. We observed a transit of WASP-12b with MMT/Hectochelle and found an excess H$\alpha$ absorption of $3.29^{+0.35}_{-0.36}\%$ (9.3$\sigma$) during the transit and extending at least 30~min post-egress. The signal does not follow the planet's orbital motion and instead appears largely in the stellar rest frame, similar to the extended helium outflows in HAT-P-32b and HAT-P-67b, and is slightly redshifted ($+5.4_{-1.7}^{+1.5}$ km s$^{-1}$). We demonstrate that a similar signal appears across previous high-sensitivity observations dating back to 2012 once the atypical signal kinematics and baseline self-subtraction are taken into account. Finally, we present a three-dimensional Athena++ model of WASP-12b's outflowing atmosphere that simultaneously exhibits the observed extended morphology and lack of planet-aligned velocity gradient. Our study highlights the necessity of three-dimensional simulations for interpreting absorption lines formed in strong outflows, where gas may not simply follow the planet's Doppler signature.
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All authors Shreyas Vissapragada, Fabienne Nail, Morgan MacLeod, Adam Jensen, Stefan Czesla, Mercedes Lopez-Morales, Jea Adams Redai, Kevin N. Ortiz Ceballos, Jaehyon Rhee

Earth and Planetary Astrophysics

CHIANTE I: Obliquity Measurements of Four High-Priority Ariel Targets in Binaries

Alex S. Polanski, Malena Rice, Catherine A. Clark et al. (+10 more)

We present the first results from CHIANTE: a program using the EXtreme PREcision Spectrograph (EXPRES) at the Lowell Discovery Telescope to characterize potential targets of the Ariel mission, anticipated to launch in 2031. We report Rossiter-McLaughlin measurements of four Ariel tier 3 hot-Jupiters which reside in binary star systems: KELT-2 Ab, KELT-3 Ab, TOI-1333 Ab, and TOI-1789 Ab. Joint modeling of EXPRES and archival radial velocities with photometry from TESS finds all four planets to be aligned their host stars, despite the host stars spanning the $T_{\text{eff}}$ realignment break, which has been found to divide the planets in multi-star systems into two subsets: those around cool stars that are preferentially aligned, and those around hot stars that exhibit stellar obliquities consistent with isotropy. We revise the $T_{\text{eff}}$ realignment break to be $=6193\pm103$ K, consistent with, but hotter than, previous work. We compare the observed stellar obliquity distribution for all multi-star, hot-Jupiter hosts above this boundary to an expected distribution produced via stellar von-Zeipel-Kozai-Lidov (ZKL) oscillations, a mechanism often invoked to explain misaligned planets in multi-star systems. A simple population synthesis model finds that a pure ZKL population is unable to replicate the observed obliquities. In particular, both the number of aligned and near-polar systems we see today are underestimated. However, adding contributions from aligned and planet-planet scattering populations alongside ZKL oscillations better describes the observed distribution. Nonetheless, more obliquity measurements for planets in multi-star systems are needed to better discern the contributions of each mechanism the observed stellar obliquity distribution.
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All authors Alex S. Polanski, Malena Rice, Catherine A. Clark, Rachael M. Roettenbacher, Lily L. Zhao, John M. Brewer, Momo Ellwarth, Emily A. Gilbert, Joe Llama, Andrew W. Mayo, Andrew E. Szymkowiak, Gerard T. van Belle, Olivia Weiss

Earth and Planetary Astrophysics

Preparing for the Early eVolution Explorer: The Impact of Flare Temperature on Ozone Column Depth in Earth-Like Atmospheres

Jaime S. Crouse, Nicholas F. Wogan, Ward S. Howard et al. (+4 more)

Atmospheric photochemical models incorporating the impacts of stellar flares often assume a $\sim$9,000 K spectrum at ultraviolet-optical wavelengths. Recent multiwavelength observations, however, reveal a more complex picture with temperature measurements spanning 4,000-40,000 K, although the occurrence rates for flares with different temperatures remain unknown. Here, we model the evolution of a Proterozoic Earth-like world with 0.01 bar of O$_2$ under repeated flaring to identify the impact of flare effective temperatures. We explore four scenarios - two host star types (K2V and M2.5V) and two flare temperatures (9,000 K and 19,000 K) - selected to bound the potential parameter space. The hotter flares have a larger impact on O$_3$ photochemistry for both stellar types. M-star planetary atmospheres are more volatile and exhibit rapid changes in their O$_3$ production and destruction rates. Meanwhile, K-star planetary atmospheres are more stable and are only impacted by the hottest flares, proving advantageous for biosignature searches. We simulate 0.2-1.0 $\mu$m reflected light spectra for all four scenarios, and find that 19,000 K flares can result in either production or destruction of O$_3$ depending on the host star spectral type increasing the 0.2 $\mu$m feature by $\sim$2$\times$ for the K2V star but decreasing it by 50% for the M2.5V star. Future missions such as the EVE SMEX mission concept will provide robust flare temperature constraints for young FGKM stars, which will serve as inputs to improve photochemical models to inform future HWO observations.
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All authors Jaime S. Crouse, Nicholas F. Wogan, Ward S. Howard, Meredith A. MacGregor, Guadalupe Tovar Mendoza, Jacob Lustig-Yaeger, Evgenya L. Shkolnik

Earth and Planetary Astrophysics

Dust trapping, collisional velocity and velocity dispersion in gravito-turbulent discs

Cristiano Longarini, Cathie J. Clarke, Richard A. Booth et al. (+1 more)

High-resolution ALMA observations indicate that planet formation is already well underway in the earliest stages of disc evolution, when discs are typically massive enough to be regulated by gravitational instability (GI). In this regime, the interplay between dust dynamics and GI may enable rapid core formation, but the conditions under which this process operates remain poorly constrained. In this work, we use three-dimensional global SPH simulations to investigate the dynamics of dust particles in gravitationally unstable discs over a wide range of Stokes numbers. We focus on three key quantities that regulate early planet formation: dust trapping in spiral arms, collisional velocities between dust grains, and the dust velocity dispersion. We find that particles with Stokes numbers in the range St ~ 0.1-1 undergo the strongest concentration within spiral arms while simultaneously exhibiting low velocity dispersion. This combination makes this aerodynamic regime the most favourable for the onset of dust-driven gravitational instability and direct dust collapse. Where direct comparisons of collision velocities are possible, our three-dimensional results are in excellent agreement with previous two-dimensional studies and are consistent with a picture in which grains are partially coupled to a Kolmogorov-like turbulent velocity field in the gas. Our results indicate that, in young self-gravitating discs, dust particles in this intermediate coupling regime provide a natural pathway to the formation of planetary cores.
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All authors Cristiano Longarini, Cathie J. Clarke, Richard A. Booth, Cat Leedham

Earth and Planetary Astrophysics

Exploring Long-period Architectures: Four New Planet Candidates from Kepler with Periods >342 days

Matthew T. Hansen and Jason A. Dittmann

The Kepler detection pipeline, as well as the transit method, has a bias towards shorter periods, leaving a dearth of detections at longer orbital periods. This relative lack of detections has left an incomplete picture of the architectures of exoplanet systems within the long-period regime. We have built a single transit detection pipeline, utilizing a classification convolutional neural network and the onboard spacecraft diagnostics of the Kepler spacecraft, to detect long-period planets. We apply our pipeline to all currently known planetary systems in the Kepler field hosting at least one planet with an orbital period longer than 6 days. We manually vet all new signals from our pipeline, and identify four new planetary candidates, all of which are in systems where the inner planets exhibit transit timing variations (TTVs). Two of these candidates, Kepler 1752.02 and Kepler 199.03, cause two transit events that are consistent with periods of $777.78^{+0.01}_{-0.02}$ and $505.495^{+0.004}_{-0.004}$ days, and radii of $3.55^{+0.15}_{-0.15}$ and $2.74^{+0.05}_{-0.05}$ $R_{\oplus}$, respectively. Our remaining two candidates, Kepler 1897.02 and Kepler 1811.02, are single transit candidates with radii $4.81^{+0.20}_{-0.19}$ and $3.25^{+0.28}_{-0.30}$ $R_{\oplus}$, respectively. The shortest orbital periods for these candidates, consistent with the Kepler dataset (gaps and coverage), are 342 days for Kepler 1897.02 and 544 days for Kepler 1811.02. The new planetary candidates, on their own, are incapable of reproducing the observed TTV signals in the inner system. Although difficult to schedule, follow-up observations are needed to further constrain the new candidates and potentially discover the planets causing the perturbations.
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