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Physics Astrophysics Earth and Planetary Astrophysics

astro-ph.EP Watch Earth and Planetary Astrophysics

Friday 18 September

Earth and Planetary Astrophysics

Rotational Mapping and Regional Atmospheric Retrievals of Variable Brown Dwarfs: Application to Luhman 16B and SIMP 0136

Ruizhe Wang, Heather A. Knuton, Julie Inglis et al. (+1 more)

We present a Bayesian framework for converting time-resolved spectroscopy into rotation-inferred regional spectra and atmospheric constraints for variable brown dwarfs. We derive an analytic mapping framework with evidence-optimized regularization and uncertainty propagation by marginalizing over physical parameters and model complexities. We provide methods for selecting characteristic spectral end-members from the inferred surface maps, and highlight the advantage of analyzing these rotation-inferred regional spectra over the disk-integrated time-resolved observations, while explicitly accounting for the geometric degeneracies inherent to rotational mapping. We apply this framework to published JWST/NIRSpec rotational monitoring of Luhman 16B and SIMP 0136. For both objects, we identify dominant spectral regions and retrieve regional variations in cloud structure, thermal gradients, and chemistry that are consistent with cloud radiative feedback. In addition, we demonstrate the importance of limb darkening in deriving surface maps. These results establish a statistically controlled method for linking rotational spectral variability to atmospheric heterogeneity and enable future rotational mapping and regional atmospheric studies of giant planet atmospheres.
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All authors Ruizhe Wang, Heather A. Knuton, Julie Inglis, Xianyu Tan

Earth and Planetary Astrophysics

Multiband Color Monitoring of 3I/ATLAS through Ground-Based Relay Observations

Ariel Graykowski, Bryce Bolin, Laura-May Abron et al. (+140 more)

We present multiband, long-baseline photometric observations of interstellar comet 3I throughout its 2025–2026 apparition using coordinated ground-based global relay observations. Our dataset combines measurements from professional observatories and citizen-operated Unistellar eVscopes distributed worldwide, providing dense temporal coverage from 2025 July 2 through 2026 April 1 and spanning the comet's pre- and post-perihelion trajectory. Broadband photometry was obtained in bandpasses equivalent to the Johnson–Cousins $B$ (436 nm), $V$ (545 nm), and $R$ (641 nm) filters and the Sloan $g$ (477 nm), $r$ (623 nm), and $i$ (763 nm) filters. The photometry was measured using projected aperture radii of approximately 10{,}000~km to provide a consistent probe of the inner coma across the heterogeneous dataset. We measure representative mean colors of $B-V=0.86\pm0.06$, $V-R=0.50\pm0.03$, $B-R=1.36\pm0.08$, and $g-r=0.58\pm0.08$, demonstrating a persistently red optical coma. Constant-color models provide an adequate description of the data, with little evidence for long-term color evolution with time or heliocentric distance despite substantial changes in the coma's brightness, gas production, and volatile composition. This suggests that the ensemble-averaged optical scattering properties of the coma remained relatively stable over the period sampled by our observations, even as other properties of the coma evolved. These observations provide the first densely sampled, apparition-long characterization of the broadband optical colors of an interstellar comet and establish a benchmark for comparison with future interstellar objects.
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All authors Ariel Graykowski, Bryce Bolin, Laura-May Abron, Franck Marchis, Martin Mašek, Filipp D. Romanov, Ahmed M. Abdelaziz, Dimitrios Athanasopoulos, Matthew Belyakov, Luca Buzzi, Michael W. Coughlin, Ergün Ege, Nicolas Erasmus, Thomas M. Esposito, Christoffer Fremling, Josep M. L. Garcia, Marek Husárik, Oleksandra Ivanova, Tarek M. Kamel, Sergey Karpov, Myung-Jin Kim, Tomasz Kwiatkowski, H.-J. Lee, Sofiia Mykhailova, Alessandro Nastasi, Dagmara Oszkiewicz, John W. Pickering, Alexey Sergeyev, Roman Telesnikov, Josep M. Trigo-Rodríguez, Al Alicea, Jin Beniyama, Otabek A. Burkhonov, Kamoliddin E. Ergashev, Y.H.M. Hendy, Jeong-Han Kim, Cheng-Han Hsieh, M. Emir Kenger, Thomas Lehmann, Igor Luk'yanyk, Ali Takey, Dušan Tomko, Murat Tekkesinoglu, Shane Winter, Joel Alonzo, Michael Beddo, Axel Bienefeld, Mario Billiani, John K. Bradley, Olivier Clerget, Sabine Cremer, Nicolas Delaunoy, José Donas, John Dunn, Jiří Dvořáček, Michael Edwards, Taj Entabi, Raffaele Esposito, Karen Fischer, Robert Foster, Edward Friday, Keiichi Fukui, Francois Gagnon, Matthieu Garisson, George Ghreichi, Patrice Girard, Tateki Goto, Michael Grant, Chris Greenfield, Bruno Guillet, Josef Hanus, John Harrison, David Havell, Kevin Heider, Kirt Hufstedler, Kachi Iwai, Maxime Johnson, Christian Joisten, Scott Kardel, Suzanne Kavic, Vamshi Kesireddy, Rachel Knight, David Koster, Jericho Kuehl, Ryuichi Kukita, Jan Kunc, Petri Kuossari, Alain Lambert, Scott Lancelle, Jean-Marie Laugier, Stephen Lawrence, Pedro Lemos, Jeffrey Linn, Joseph Llanes, Steeve Loisel, Gaël Lombart, Margaret A. Loose, Yohann Lorand, Chris Mahar, Scott Manley, Vincent Marcouiller, Sevastos Mastrogiorgis, Nicola Meneghelli, Mike Mitchell, Iaroslav Mokroguz, Jacques Molne, Fabrice Mortecrette, Ioannis Mytakos, Anouchka Nardi, Wataru Ono, James Owen, Larry Parchman, Bruce Parker, Michael Primm, Darren Rivett, Facundo Robles, Van Ruckman, Matthew Ryno, Nikolaj Schraufl, Jean-Pierre Schulz, Christoph Seidler, Lauren A. Sgro, Masao Shimizu, Francois Simard, Georges Simard, Bran Solo, Grant Sorenson, Marcelo Souza, David Swalander, Akimitsu Takahashi, Lydia Tamez, Petri Tikkanen, Bryan Tobias, Ian Transom, William Turnipseed, Charles Urban, Claudio Vantaggiato, Aad Verveen, Andrew Wendelborn, Stefan Will, Mark Wilson, Neil Yoblonsky, Wai-Chun Yue

Earth and Planetary Astrophysics

Comparative analysis of Neural Networks approaches for Initial Orbit Determination of Near-Earth Objects

Francesco Geroni, Roberto Paoli, Riccardo Massidda et al. (+1 more)

Initial Orbit Determination (IOD) from Very Short Arcs (VSAs) remains one of the most challenging open problems in asteroid surveillance and celestial mechanics. Classical methods require angular observations spanning a sufficient fraction of the orbit, and become ill-conditioned or fail outright when only a single observing night is available, as is the case for most newly discovered Near-Earth Objects (NEOs). We present a comparative analysis of two Neural Network (NN) models that attack the ranging problem directly: both ingest a triplet of time-tagged angular measurements $(t_i,\alpha_i,\delta_i)$, $i=1,2,3$, from a single VSA and predict the geocentric range and range-rate $(\rho,\dot\rho)$, thus completing the orbital state vector. The first is a Multi-Layer Perceptron trained on a purely data-driven objective; the second augments it with a physics-informed loss. Both are trained, under an object-disjoint partition, on a sample of the $568\,127$ VSAs of $39\,031$ real NEOs available in the NEODyS-2 catalogue. Each model returns an estimate on every arc by construction, so we assess instead whether that estimate is dynamically admissible: on a held-out test set of $56\,773$ arcs the physics-informed model places $85.1\%$ of its predictions inside the admissible region, against $76.5\%$ for the data-driven baseline, whereas Gauss's and Laplace's methods return a solution on only $45.0\%$ and $47.3\%$ of the same arcs and collapse onto the degenerate root in about nine of those cases out of ten. A stratified analysis over proper motion and true range shows that the physics-informed objective is not uniformly superior to the baseline: it trades a longer error tail for admissibility and for a marked advantage on the fast, nearby arcs that are operationally the most relevant.
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All authors Francesco Geroni, Roberto Paoli, Riccardo Massidda, Giacomo Tommei

Earth and Planetary Astrophysics

Time-resolved JWST Retrieval Analysis of the Coldest Brown Dwarf: Temperature and Chemical Variations in WISE 0855-07

Harshil Kothari, Caroline V. Morley, Brittany E. Miles et al. (+12 more)

WISE J0855-07 is the coldest known brown dwarf (estimated Teff~250 K), offering a rare opportunity to probe atmospheric physics in the temperature and mass regime that overlaps directly with exoplanets. At these temperatures, modest perturbations to the thermal structure and chemical abundances can produce measurable changes in the emergent mid-infrared spectrum, making time-resolved spectroscopy a powerful way to test whether the atmosphere is longitudinally and temporally homogeneous. Using James Webb Space Telescope NIRSpec/G395M time-series spectra spanning ~3 to 5.2 {\mu}m over 11 hr, we analyze every third spectrum from the dataset with a series of time-resolved atmospheric retrievals using the Brewster retrieval framework. Using this approach, we model epoch-to-epoch changes in the atmospheric state that drive the observed variability, including the thermal structure and key molecular abundances. From the time-series retrievals, we find that the primary source of the observed spectral variability is driven by the variations in the thermal structure, which range from ~1 to <100 K from epoch to epoch, particularly between the pressures of ~0.4 and 10 bar. In addition, changes in the abundances of CO, and possibly PH3 and CO2, further modulate the spectrum within specific molecular features. These measurements provide a retrieval-based view of atmospheric variability in an ultracold, planet-like object, directly constraining how thermal and chemical structure evolve on observable timescales.
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All authors Harshil Kothari, Caroline V. Morley, Brittany E. Miles, Melanie J. Rowland, Natasha Batalha, Michael C. Cushing, Andrew J. Skemer, James Mang, Brianna Lacy, Johanna M. Vos, Channon Visscher, Adam C. Schneider, Genaro Suarez, Mikayla J. Wilson, Allison M. McCarthy

Earth and Planetary Astrophysics

JWST MEP - A World Under Spotty Starlight: Detection of CO2 and H2O in the Hot Saturn WASP-52b with JWST NIRSpec G395H

JWST GO 3969 Team: Yanbo Pan, Ryan J. MacDonald, Néstor Espinoza et al. (+20 more)

Exoplanets orbiting active stars offer distinct challenges for atmospheric characterization with the JWST. Among such worlds, the hot Saturn WASP-52b (Teq $\sim$ 1300 K) orbits an active K-dwarf that complicates transmission spectroscopy via stellar contamination. Here, we present the first JWST NIRSpec G395H (2.8-5.2 $\mu$m) limb-averaged transmission spectrum of WASP-52b obtained through the JWST Morning/Evening Program (GO-3969), which aims to measure limb asymmetries across a sample of hot giant exoplanets. Our spectrum reveals the first detection of CO2 in WASP-52b's atmosphere (ln B = 54 / >10$\sigma$), with a retrieved abundance of log CO2 = -5.09 (+1.09/-1.14), and confirmation of H2O (ln B = 5.9 / $\sim$3-4$\sigma$), with an abundance of log H2O = -3.41 (+1.04/-1.04). We find a steep near-infrared slope that cannot be explained solely by H2O absorption, necessitating unocculted starspots (ln B = 5.7 / $\sim$3-4$\sigma$), though with properties that vary across our data reductions. The shape and amplitude of the molecular bands additionally suggest high-altitude (<10 mbar) inhomogeneous clouds covering $\approx$40 $\pm$ 20% of the terminator (ln B = 1.9 / $\sim$2.5$\sigma$), which provides evidence for the morning-evening terminator differences that are consensus predictions of general circulation models. WASP-52b's atmospheric metallicity can be sub-solar, solar, or super-solar, due to order-of-magnitude uncertainties in the molecular abundances caused by degeneracies between compositions, clouds, and starspots. However, chemical equilibrium retrievals provide a similar statistical fit while favoring a tighter constraint with a super-solar metallicity (M/H = 14.8 (+12.1/-5.9) $\times$ solar). These results highlight that chemical detections and aerosol properties may still be recovered for planets orbiting active stars via transmission spectroscopy.
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All authors JWST GO 3969 Team: Yanbo Pan, Ryan J. MacDonald, Néstor Espinoza, Bibiana Prinoth, Zafar Rustamkulov, Luis Welbanks, Daniel Kitzmann, Nicolas Crouzet, Anna Walde, Diana Powell, Eva-Maria Ahrer, Adam J. Burgasser, Duncan A. Christie, Wolf Cukier, Carlos Gascón, Måns Holmberg, Thomas Kennedy, Mercedes López-Morales, N. J. Mayne, Dominic Samra, Arjun B. Savel, Maria E. Steinrueck, Christopher P. Wirth

Earth and Planetary Astrophysics

Some challenges for the long-term survival of Naiad, Neptune's innermost moon

Harrison Agrusa, Matija Ćuk, David Nesvorný et al. (+1 more)

The Naiad-Thalassa 73:69 mean-motion resonance implies these moons have co-existed for $\gtrsim$1 Gyr, raising the question of how they survived to the present day. We examine three challenges to Naiad's long-term survival: tidal disruption, heliocentric bombardment, and runaway collisional erosion by planetocentric debris. We constrain Naiad's internal strength requirements from its nominal density and shape, compute present-day impact rates on Neptune's inner moons from heliocentric bombardment, and use $N$-body simulations to model the fate of ejecta produced by non-disruptive impacts. First, Naiad's nominal density of ${\sim}0.8\text{ g cm}^{-3}$ and elongated shape suggest it cannot be held together by self-gravity alone, implying a cohesive strength of $\gtrsim10$ kPa to avoid tidal disruption, although this constraint is relaxed if Naiad has a higher density of ${\gtrsim}1.3\text{ g cm}^{-3}$. Second, we show that Naiad may have been disrupted in the last 1 Gyr by heliocentric bombardment, although this depends sensitively on the size-frequency distribution of Kuiper Belt objects at small sizes and on Naiad's catastrophic disruption threshold, both of which are poorly constrained. Third, and most notably, we find that even small, non-disruptive impacts can trigger runaway collisional erosion by planetocentric debris on extremely short timescales. Avoiding this “sesquinary catastrophe” requires that Naiad has a collisional strength of at least several MPa, which is difficult to reconcile with being a reaccumulated “rubble pile”, leftover from the capture of Triton and the subsequent cataclysm of Neptune's primordial satellite system. Together, these results suggest that Naiad may be a physically unusual object among small ring-moons – possibly a largely coherent, monolithic fragment – and that our understanding of Neptune's inner satellite system leaves much to be explained.
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All authors Harrison Agrusa, Matija Ćuk, David Nesvorný, David Minton

Earth and Planetary Astrophysics

Faithful Neural Embeddings for 3D Exoplanet Climate Modeling

Amit Reza, Ludmila Carone and Christiane Helling

With the rapid advancement of telescopes like JWST and Ariel, there is an urgent need for efficient 3D climate models to interpret observations of exoplanet atmospheres. Traditional 3D general circulation models (GCMs) are computationally intensive, prompting the development of machine learning (ML) emulators to accelerate simulations. Recent work, such as that by Plaschzug et al. 2026 \cite{plaschzug2026accelerating}, uses a dense neural network (DNN) to predict local gas temperatures and winds from input parameters, including local gas pressure, spatial coordinates (longitude and latitude), and global temperature. However, this model relies on predicting individual temperature values (points) at specific grid points, which can be limited by the resolution and constraints of the training grid. In this work, we investigate a couple of alternative frameworks based on latent-space representations of local gas temperature ($\text{T}_{\text{gas}}$) to obtain a faithful, low-dimensional representation of these profiles. This represents the first step toward developing a latent space regression model, offering a structurally cohesive alternative to the existing point-wise prediction method \cite{plaschzug2026accelerating}. By capturing the optimal embedding space of atmospheric data, our proposed framework can produce simulated profiles while maintaining computational efficiency, making it suitable for large-scale exoplanet ensemble studies.
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Thursday 17 September

Earth and Planetary Astrophysics

The Birth of Minor-Body Populations in the $\beta$ Pictoris System I: The First 25 Myr

S. Torres, J.L. Gragera-Más, A.J. Mustill et al. (+1 more)

The discovery of the third known giant planet, $\beta$ Pic d, offers a new opportunity to investigate how planet-disk interactions build the minor-body architecture of the young Beta Pictoris system. We study the formation and redistribution of scattered-disk objects, falling evaporating bodies, a proto-Oort-cloud population, transitional interstellar objects, and interstellar objects. Using $N$-body simulations, we evolve a primordial planetesimal disk extending from 0.5 to 1000 au for 25 Myr under the perturbations of $\beta$ Pic b, c, and d, together with reconstructed stellar encounters from Gaia DR3. The resulting evolution is strongly radius-dependent. The planets efficiently restructure the inner disk, while the outermost primordial population remains largely unchanged beyond $325$ au. $\beta$ Pic c remains the main driver of the star-grazing population, showing that the falling-evaporating-body pathway persists after the inclusion of $\beta$ Pic d. At larger radii, $\beta$ Pic b and d dominate planetary scattering and produce a surviving disk edge near 50 au, consistent with the observed debris-disk truncation. Over 25 Myr, $8.74\%$ of the initial disk enters the scattered-disk population, $2.04\%$ reaches the proto-Oort-cloud region, and $6.44\%$ becomes unbound. Planetary stirring also generates a transient one-armed spiral among particles originating at $\sim60$-150 au, overlapping part of the observed "Cat's Tail" and the radial location of the prominent CO clump near 85 au. The reconstructed stellar encounters included here produce only weak perturbations, although the encounter catalog is complete only over the first ~2.5 Myr of the present epoch. The early evolution of the Beta Pictoris minor-body system is therefore dominated by its planetary architecture, offering a view of distinct minor-body populations while they are still being formed and redistributed.
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All authors S. Torres, J.L. Gragera-Más, A.J. Mustill, E. Villaver

Earth and Planetary Astrophysics

The Galactic Dynamics of Free-Floating Planets: From Ejection Kicks to Microlensing

Zara Sayed, Stefano Profumo and Nolan Smyth

Free-floating planets (FFPs) may retain dynamical signatures of the mechanisms that eject them from their host systems. We integrate $10^6$ collisionless FFP test particles for $10^8$~yr in a static, phenomenological Galactic potential, comparing a mass-independent kick model with a mass-coupled prescription ($\sigma_{\rm CB}\propto M^{-0.15}$, $v_{\rm PL}\propto M^{-0.5}$) against a matched no-kick control. The imposed mass dependence is recovered at injection, with the combined-channel median coupled kick decreasing from $10.716$ to $0.708~{\rm km\,s^{-1}}$ across five mass bins—a factor of $\sim15.1$. A mass-dependent trend remains visible after $100$~Myr of Galactic propagation in the matched kicked-versus-control displacement, whose median decreases from $0.7001$ to $0.0539$~kpc across the same bins. The remaining numerical distinction is concentrated in this mass-resolved differential displacement rather than in the bulk phase-space moments: the final velocity dispersions of the null and coupled kicked populations are nearly identical, only a few percent of particles leave the adopted disk region, and the fraction of particles satisfying the formal Galactic-unbound criterion ($E_i>0$) remains negligible in every diagnostic we report. Comparing each kicked population against its matched no-kick control shows that much of the overall kinematic heating arises from the evolution of the initially warm, nonequilibrium disk rather than from the ejection kick itself, isolating the kick's smaller contribution.
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Earth and Planetary Astrophysics

A fifth companion in the HR 8799 system revealed by Gaia

A.-M. Lagrange, K. Gozdziewski, F. Kiefer et al. (+5 more)

HR 8799 is the benchmark young multi-planet system, hosting four directly imaged giant planets orbiting between a warm inner belt and a cold outer debris ring. However, the few-au region has remained observationally inaccessible, lying beyond the reach of conventional high-contrast imaging and challenging for radial-velocity techniques due to stellar pulsations. Here we combine Gaia absolute astrometry and Hipparcos-Gaia proper-motion anomalies with radial velocities and high-contrast imaging to reveal an additional close-in substellar companion. The allowed solutions span approx. 0.3-6 au, with posteriors peaking at approx. 2-3 au and with masses around 10-14 Jupiter masses. Dynamical modelling shows that such a companion with a low eccentricity can coexist with the long-lived resonant chain of the four outer planets, and sculpt the inner edge of the warm debris belt, linking the planet architecture to the debris-disk morphology. Our results close a long-standing detection gap in HR 8799 and demonstrate the power of Gaia astrometry to uncover massive planets at intermediate separations that may remain undetectable with radial velocities or direct imaging alone.
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All authors A.-M. Lagrange, K. Gozdziewski, F. Kiefer, H. Beust, P. Rubini, A. Zurlo, P. Thebault, A. Boccaletti

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

White Dwarf Natal Kicks as Velocity-Space Random Walks. I. Fokker-Planck Theory

Stephen Majeski, Dang Pham, Taeho Ryu et al. (+2 more)

White dwarfs are the most common end state of stellar evolution, including that of our own Sun, making their formation critical to completing a more comprehensive understanding of stellar evolution and even determining the eventual fate of the solar system. Wide binaries containing white dwarfs offer a powerful probe: their components evolve largely independently, yet stellar mass loss and velocity impulses (natal kicks) on the white dwarf progenitor leave measurable imprints on orbital properties. Previous population studies typically assume that each white dwarf receives only a single natal kick as it forms. While convenient, this simplification conflicts with simulations finding the formation process to be episodic. Therefore, a more realistic picture is that white-dwarf progenitors experience multiple stochastic kicks over their evolution. Here, we present a Fokker-Planck model for the evolution of binary orbital parameter distributions subject to many, randomly-oriented mass-loss-driven kicks. This model recovers key features of white-dwarf binary observations, including a -2 power law tail in the probability distribution of separations, and the thermalization of binary eccentricities beyond separations of 1000 au. We additionally investigate how white-dwarf kicks impact a myriad of other processes, such as binary dissolution, planetary system evolution, and even the production of interstellar objects.
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All authors Stephen Majeski, Dang Pham, Taeho Ryu, Gabriel Tomassini, Andrea Chiavassa

Earth and Planetary Astrophysics

Recovering the Morning and Evening Limbs of WASP-94Ab from Its Limb-Averaged JWST Transmission Spectrum

Tyler R. Fairnington, Michael Radica, Michael Zhang et al. (+5 more)

Recent JWST observations have revealed that the morning and evening limbs of the hot Jupiter WASP-94Ab have very different transmission spectra. An analysis of these resolved limb spectra yielded a metallicity more than an order of magnitude below that obtained from the limb-averaged spectrum, which calls into question the accuracy of traditional retrievals for heterogenous planets. Here we analyze the limb-averaged JWST NIRISS and NIRSpec transmission spectra of WASP-94Ab using both a standard one-temperature-profile (1-TP) retrieval with patchy clouds, and a new two-temperature-profile (2-TP) retrieval. The 2-TP retrieval assumes a linear combination of two atmospheric components that share the same bulk elemental composition but have independent thermal structures, chemistries, and aerosol properties. This model is implemented in PLATON 7.0, a JAX-accelerated code that is over 100 times faster than its predecessor, which is key to making the retrieval computationally tractable. The limb-averaged spectrum of WASP-94Ab favors the 2-TP model by a Bayes factor K=1.8x10^{5} and shifts the metallicity downward to Zatm/Zsun = 11^{+9}_{-4} from 170^{+30}_{-24} obtained with the 1-TP model. The 2-TP retrieval predicts two, equally weighted components that reproduce the limb-resolved spectra across both instruments without prior knowledge of them. This work demonstrates that compositional information survives limb averaging for WASP-94Ab, suggesting that 2-TP retrievals can be used to identify limb-asymmetry and extend metallicity studies beyond the small set of planets amenable to limb-resolved spectroscopy.
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All authors Tyler R. Fairnington, Michael Radica, Michael Zhang, Eliza M.-R. Kempton, Jacob L. Bean, Eva-Maria Ahrer, Arjun B. Savel, Pascal S. D'Andrea

Earth and Planetary Astrophysics

Fragmentation Dynamics of Pristine Interstellar Comets: An Exploratory Multi-Physics Simulation Study

Behrooz Karamiqucham

We present an exploratory numerical model for the thermal evolution and fragmentation of pristine interstellar comets on a first passage through the inner Solar System, applied over a grid of perihelion distances ($q=0.25$–$1.5$~AU) and tensile strengths ($\sigma_t=50$–$500$~Pa). A single nucleus ($M_0=2\times10^{12}$~kg, $R_0\approx1.06$~km, dust/ice $=1$, ices 35% CO, 30% CO$_2$, 15% CH$_4$, 20% H$_2$O) follows a hyperbolic trajectory from an initially 30~K state, with heat conduction, energy-balanced multi-species sublimation, dust lifting and lag-mantle growth, and a subsurface gas-pressure failure criterion, so that fragmentation is emergent rather than prescribed. In the primary case ($q=1$~AU, $\sigma_t=100$~Pa) splitting begins at the 3~AU starting distance, once a sub-millimeter lag deposit partially confines the warming CO front; 63 binary splittings follow, with a self-limited plateau at 53 bodies before perihelion and the 64-body tracking cap reached near perihelion. Sublimation is energy-limited: total mass loss is 1.3%, volatile depletions are at most a few per cent, and most of the mass survives as a fragment swarm; the mass budget closes to machine precision. Across the grid, mass loss (0.8–1.7%) depends weakly on $q$ and $\sigma_t$ but strongly on composition, falling to 0.1% for depleted, 67P-like ices. Yet every case, including the depleted class, disaggregates, whereas Jupiter-family comets of similar composition survive repeated perihelia, so the sealing prescription over-fragments. We regard the composition ranking, the insensitivity to $\sigma_t$, percent-level mass loss, and an onset beyond 3~AU as robust, and defer absolute survival predictions to calibration against well-observed comets. Mantle insulation suppresses outbound activity, producing an inbound–outbound asymmetry.
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Earth and Planetary Astrophysics

The JWST Sub-Jupiters Survey: Direct Imaging Discovery of a Giant Planet and a Debris Disk Around the Young M-dwarf RX J0534.0-0221

Rodrigo Ferrer-Chavez, Jason J. Wang, Kevin Wagner et al. (+47 more)

We present the discovery of RX J0534.0-0221 b, a giant planet orbiting an M-dwarf star in the $\beta$ Pictoris moving group. RX J0534 was originally observed with JWST/NIRCam in the F444W and F200W filters. Observations in F444W reveal a point source at signal-to-noise ratio $\sim17.5$ at $\sim0.41$ arcsec ($\sim14$ au) from the host star, with no detection of the source in F200W. A follow-up observation with LBTI/LMIRCam in $L'$ band re-detects the source 16 months after the JWST epoch, providing evidence for common proper motion over a chance alignment with a background interloper at the $6-7\sigma$ level. Atmospheric grid model fits to the available photometry yield bolometric luminosity log$_{10}(L/L_\odot) = -5.48^{+0.10}_{-0.19}$ dex. At an age of $18-26$ Myr, hot-start evolutionary models predict $M=2.8^{+0.5}_{-0.5}$ M$_{\text{Jup}}$ and $T_{\text{eff}}=674^{+57}_{-49}$ K. From the $L'-F444W$ color and magnitudes we find evidence for disequilibrium chemistry or enhanced metallicity in the planet atmosphere. Additionally, an extended structure is detected in the JWST F200W observation, consistent with a resolved debris disk with peak density radius of $79^{+3}_{-3}$ au and an inclination of $56.5^{+1.5}_{-1.5}$ deg. RX J0534 b is one of the lowest-mass planets imaged to date. After TWA 7 b, it is the second imaged planet around an M-dwarf orbiting at Solar System scales (the first within 50 au), and the first to be confirmed via common proper motion. Future orbital monitoring and atmospheric characterization will shed light on its formation history, a particularly interesting question given the challenging nature of giant planet formation around M-dwarfs.
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All authors Rodrigo Ferrer-Chavez, Jason J. Wang, Kevin Wagner, Kellen Lawson, Aarynn L. Carter, Beth Biller, Raphael Bendahan-West, Patrick McCreery, Patricia Luppe, Steve Ertel, Andrew D. James, Ellis Bogat, Rohan Kane, Ben J. Sutlieff, Giovanni M. Strampelli, William O. Balmer, Rachel Bowens-Rubin, Evelyn L. Bruinsma, Andy Skemer, Julien H. Girard, Mark Booth, Klaus Subbotina Stephenson, Katie A. Crotts, Sebastian Marino, Aniket Sanghi, Michael Liu, Nour Skaf, Emily Rickman, Marshall D. Perrin, Laurent Pueyo, Brendan P. Bowler, James Mang, Isabel Rebollido, Michael Meyer, Tim Pearce, Markus Bonse, Clémence Fontanive, Jared Carlson, Jon Rees, Justin Rupert, Gabriel Weible, Jacob Isbell, Juan Carlos Guerra, Xueqing Chen, Mia Belle Parkinson, Vito Squicciarini, Gael Chauvin, Elisabeth Matthews, Kyle Franson, Maxwell A. Millar-Blanchaer

Earth and Planetary Astrophysics

Water Cloud and Chemical Modulations in the Coldest Brown Dwarf

Brittany E. Miles, James Mang, Caroline V. Morley et al. (+24 more)

We present high signal-to-noise, medium resolution (R ~ 1000), time-series JWST/NIRSpec spectra of WISE 0855 (265K), the coldest known brown dwarf. Medium resolution, time-series spectroscopy gives us the power to disentangle the effects of chemistry, temperature, and condensates on this cool world. Our observations span 11 hours with a 15 minute cadence covering 2.87 - 5.27 $\mu$m. The strongest time variable spectroscopic feature is carbon monoxide gas absorption producing modulations with a peak-to-peak amplitude up to 10% at some wavelengths. Using principal component analysis, we show that the variations in carbon monoxide and phosphine correlate with one another. By comparing our data to atmospheric and structure models we present evidence of patchy water clouds within the atmosphere of WISE 0855. We find that variations in CO and PH$_{3}$ abundances must originate from quenched atmospheric pressures while variations in water cloud thickness occurs at lower pressures.
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All authors Brittany E. Miles, James Mang, Caroline V. Morley, Andrew J. I. Skemer, Melanie Rowland, Brianna Lacy, Genaro Suarez, Channon Visscher, Dániel Apai, Gordon Bjoraker, Aarynn L. Carter, Jacqueline K. Faherty, Jonathan J. Fortney, Nguyen Fuda, Thomas Geballe, Harshil Kothari, Mary Anne Limbach, Mark Marley, Allison M. McCarthy, Adam Schneider, Johanna Vos, Michael Cushing, Richard Freedman, Michael Line, Roxana Lupu, Emily Martin, Mikayla J. Wilson

Earth and Planetary Astrophysics

Coupled Orbital and Interior Evolution of Sub-Neptunes

Ritika Sethi, Sarah Millholland and Tim Hallatt

Recent observations have yielded the first measurements of young exoplanet demographics. Close-in sub-Neptune occurrence rates appear to rise from young ($10-100$ Myr) to intermediate (100 Myr $-$ 1 Gyr) ages and then decline sharply in the old ($\gtrsim 1$ Gyr) Kepler field population. In this paper, we test whether these observations can be explained by the effects of planetary cooling, atmospheric mass loss, and tidal orbital migration, which we model through a fully coupled evolution framework. The orbital evolution is assumed to operate exclusively through high-eccentricity migration, in effort to estimate the maximum possible contribution from this migration channel. In reality, only a subset of planetary systems are expected to undergo HEM. We find that high-eccentricity migration rapidly populates the close-in sub-Neptune bin, producing a sharp rise in occurrence within the first $\sim 15$ Myr. After this early phase, the occurrence evolves only weakly. While the modeled young to intermediate-age evolution is broadly consistent with the observed trend within the uncertainty limits, it does not support the idea of a sustained young-to-intermediate rise driven by tidal migration. It also fails to reproduce the sharp decline in occurrence seen from intermediate to old ages, motivating additional physics or formation channels to be included in future models.
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Earth and Planetary Astrophysics

Formation of Ryugu's parent planetesimal beyond the CO$_{2}$ snow line from small pebbles: insights from thermal evolution modeling

Sota Arakawa, Hidenori Genda, Noriyuki Kawasaki et al. (+3 more)

Astronomical observations of planet-forming circumstellar disks indicate that planetesimals form from 0.1-mm- to 1-cm-sized dust aggregates, commonly called “pebbles.” When such pebbles accrete beyond the water snow line, the resulting icy planetesimals undergo water–rock differentiation and develop porous pebble-pile cores whose voids are saturated with liquid water. Circulation of this water enhances heat transport in the core, suppressing the temperature rise caused by the decay of radionuclides. In this study, we constrain the accretion age and constituent pebble size of Ryugu's parent planetesimal by modeling the thermal evolution of icy planetesimals and comparing the results with the precipitation ages and temperatures of aqueously formed minerals identified in samples returned from asteroid Ryugu. Our numerical results suggest that Ryugu's parent planetesimal accreted within 2.0 Myr of the formation of calcium–aluminum-rich inclusions. The inferred early accretion age supports the hypothesis that Ryugu's parent planetesimal formed earlier than most chondrule-bearing carbonaceous chondrite parent planetesimals, potentially explaining the absence of chondrules in Ryugu samples. We also found that the core of the parent planetesimal was composed of pebbles no larger than a few millimeters. Such small pebble sizes are consistent with theoretical predictions for planetesimals formed beyond the CO$_{2}$ snow line.
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All authors Sota Arakawa, Hidenori Genda, Noriyuki Kawasaki, Wataru Fujiya, Yosei Iwasaki, Shigeru Wakita

Earth and Planetary Astrophysics

Daytime seeing variations in Paranal through a SHABAR system. Description of the method and first measurements from the PoET solar telescope

A. M. Silva, B. Wehbe, A. Oliveira et al. (+8 more)

Aims. In this paper we present the software and first seeing measurements from a SHAdow Band Ranger (SHABAR) system that is coupled with the recently comissioned PoET solar telescope, installed at ESO's VLT platform in the Paranal Observatory. The seeing measurements that are collected by this system play a pivotal role in the observational strategy of PoET, as it employs apertures ranging between 1 and 55 arcseconds to observe resolved solar regions. As such, the usage of the smaller apertures hinges upon good observational conditions, which are assessed through real-time measurements from the instrument. Methods. We employ a SHABAR system, consisting of a series of scintillometers that are non-uniformly spaced in a bar, measuring the scintillation of the incoming light. The scintillation is measured in individual detectors, which are then used to characterize the atmospheric turbulence at a given range of heights. We use previously derived formulations, following Kolmogorov turbulence models, to model the collected data and transform it into a seeing measurement. Results. We find that the Paranal daytime seeing can reach values close to 1 arcsecond in the early morning, before the ground temperature increases and creates turbulence in the lower layers of the atmosphere. Over the day, the seeing gradually worsens, with the median seeing reaching values larger than 4 arcseconds in the afternoon. We also find that these variations appears to be stable over the first weeks of observations, yielding compatible results when comparing 37 independent days of operations, with a median seeing of 2.37 arcseconds.
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All authors A. M. Silva, B. Wehbe, A. Oliveira, M. Abreu, C. Cardenas-Conde, A. Cabral, P. Moreno, J. H. C. Martins, M. A. Monteiro, N. C. Santos, R. Gafeira

Earth and Planetary Astrophysics

Prospects for Mercury Observations with the BepiColombo Laser Altimeter (BELA): Implications for Estimating Surface Roughness from Laser Altimetry

Gaku Nishiyama, Alexander Stark, Christian Hüttig et al. (+12 more)

Surface reflectance and roughness are key to understanding Mercury's geologic evolution. The BepiColombo Laser Altimeter (BELA) will measure these properties alongside topography, but predicting its performance requires realistic modeling of laser return pulse shapes, unlike a simplified Gaussian approximation in earlier models. We develop a comprehensive return-pulse simulation framework for BELA that includes non-Gaussian transmitted pulses, analog filtering in the receiver chain, and pulse-shape modification by footprint-scale topography. Using high-resolution lunar digital terrain models and synthesized fractal topography as Mercury analogs, we develop calibration and correction methods and estimate measurement errors expected in future BELA observations. Range errors average 1.5 m or less below 1000 km altitude, and energy errors are small enough to distinguish dark deposits, regolith, and exposed ice below 900 km. Pulse width proves unreliable as a roughness proxy under realistic conditions; we instead constrain roughness from digitized pulse shapes, underscoring the value of time-resolved data for future planetary altimeters.
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All authors Gaku Nishiyama, Alexander Stark, Christian Hüttig, Kai Wickhusen, Christian Althaus, Thomas Behnke, Ernst Hauber, Klaus Gwinner, Konrad Willner, Noriyuki Namiki, Frederic Schmidt, Jean Barron, Hugo Lancery, Azar Arghavanian, Hauke Hussmann

Earth and Planetary Astrophysics

Exoplanet detection through photometric orbital phase modulations

J. Lillo-Box and O. Balsalobre-Ruza

Since the detection of the first extrasolar planets thirty-five years ago, the dawn in detected signals has been driven primarily by radial velocity and transit techniques. However, other methodologies have gained significant interest due to their ability to explore specific niches that are challenging to access with traditional approaches. In this article, we focus on the photometric orbital phase modulations induced by planets, describe the methodologies and equations and highlight their developments and prospects for the future.
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Earth and Planetary Astrophysics

Thermal Evolution of Lava Planets Across System Ages: Predictions for Hell of a Survey

Mariana Sastre, Tim Lichtenberg, Lisa Dang et al. (+22 more)

Ultra-short-period (USP) rocky exoplanets can have dayside temperatures high enough to maintain permanent magma oceans, sitting at the intersection of interior geophysics and atmospheric chemistry. Coupled feedbacks between the molten surface and outgassed atmosphere can sustain or enhance a volatile envelope, while stellar interactions can erode it. Understanding which outcome prevails, and its observable imprint, requires a multi-target approach across planets at different stages of thermal evolution. We present predictions for the five targets of JWST Cycle 4 program 8864: TOI-1807 b, TOI-2260 b, TOI-431 b, TOI-6255 b, and TOI-2431 b. Using the PROTEUS coupled interior-atmosphere framework, we construct a simulation grid and classify outcomes into six categories, defined by the final interior melt state and by whether the planet retains a detectable atmosphere thick enough to redistribute heat to the nightside. For targets retaining a non-negligible volatile envelope, our models predict higher partial pressures for most species when the surface is molten, except for S$_{2}$, whose enhancement in the solid regime suggests it may serve as a tracer of interior melt state. Despite some targets showing outcomes across multiple scenarios, most tend toward a bare-rock end-member, with global melt fraction $\leq$ 20% and atmospheric retention sensitive to escape efficiency. Our analysis reveals a minimum escape efficiency threshold below which volatile envelopes survive under energy-limited escape, constraining the conditions required for atmosphere survival on irradiated rocky planets. These predictions will guide interpretation of MIRI-LRS phase curve observations and identify which targets and features best discriminate between competing geophysical states.
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All authors Mariana Sastre, Tim Lichtenberg, Lisa Dang, Anjali Piette, Haiyang S. Wang, Mercedes López-Morales, Thomas Wilson, Charles-Édouard Boukaré, Mahesh Herath, Nicolas Cowan, Md Abdullah Al Zaman, Madyson G. Barber, Casey Brinkman-Traverse, Nicholas Connors, Ian Crossfield, Lina D'Aoust, Oliver Herbort, Leoni Janssen, Mathilde Kervazo, Owen Lammert, Yamila Miguel, Raymond Pierrehumbert, Allona Vazan, Joost P. Wardenier, Sebastian Zieba

Earth and Planetary Astrophysics

Reliability of Zodiacal Background Models at Small Solar Elongations

Csaba Kiss, Thomas G. Müller, Javier Licandro et al. (+6 more)

Present models of the zodiacal light (scattered sunlight from interplanetary dust in the visible) and zodiacal emission (thermal emission in the mid-infrared) are primarily constrained by surface-brightness measurements obtained at relatively large solar elongations (e >~ 60 deg). As a result, their predictive accuracy at smaller elongations remains uncertain. This is particularly relevant for solar elongations of e ~ 30-60 deg, where next-generation near-Earth-object discovery missions such as NEO Surveyor and NEOMIR are designed to operate. To evaluate the reliability of these models at small solar elongations, we compile and reanalyze the available small-elongation zodiacal-light and zodiacal-emission measurements and provide the first systematic validation of modern zodiacal-light models in a regime where they have never been independently tested. We compare two models derived from the COBE/DIRBE survey: one constrained primarily by the spatial and temporal variation of the monochromatic sky brightness, and another that additionally uses interband color information and fixes the absolute normalization by requiring the minimum high-latitude residual at 25um to vanish. We find that the former reproduces the observations significantly better. At wavelengths most relevant to infrared near-Earth-object surveys (8-10 um), it typically agrees with measurements to within ~10% at e ~ 40-60 deg. Although it also performs better at e ~ 30 deg, significant discrepancies remain. These results show that zodiacal emission at small solar elongations is still only weakly constrained and that its absolute brightness remains uncertain. New mid-infrared observations are required to improve background estimates for future infrared survey missions.
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All authors Csaba Kiss, Thomas G. Müller, Javier Licandro, Luca Conversi, Marco Delbo, Karri Muinonen, Marcel Popescu, Paolo Tanga, Róbert Szakáts

Earth and Planetary Astrophysics

Widespread plasma jets in the Martian magnetosheath revealed by dual-spacecraft observations

Abigail Tadlock, Chuanfei Dong, Chi Zhang et al. (+4 more)

Plasma jets in planetary magnetosheaths are transient, high dynamic pressure structures capable of strongly perturbing downstream magnetospheres and modulating solar wind energy transfer. Although recently identified at Mars, their formation mechanisms and global occurrence remain poorly constrained. Using dual-spacecraft observations from Mars Atmosphere and Volatile EvolutioN (MAVEN) and Tianwen-1, we show that magnetosheath jets occur throughout the Martian magnetosheath, in striking contrast to Earth where jet occurrence is strongly controlled by interplanetary magnetic field orientation and largely confined to quasi-parallel shock regions. We propose that this widespread distribution is linked to Mars' extended hydrogen corona, which generates pickup ions that drive proton-cyclotron waves upstream of the bow shock. Because this mechanism is generic to any body with an extended corona (or exosphere) embedded in a stellar wind, this finding bears on solar-wind interactions at comets and other small bodies, and on the space environments of unmagnetized terrestrial exoplanets. These results indicate that magnetosheath jet formation can be governed not only by external solar wind forcing but also by intrinsic planetary properties, pointing to a previously unrecognized pathway for solar wind-planet coupling at unmagnetized worlds.
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All authors Abigail Tadlock, Chuanfei Dong, Chi Zhang, Savvas Raptis, Hongyang Zhou, Xinmin Li, Jiawei Gao

Earth and Planetary Astrophysics

Delayed Methane Detection in 3I/ATLAS: GCR-Driven Subsurface Stratification and Interstellar Exposure Age Constraints

Akshat Rawat and Kinsuk Acharyya

Interstellar comet 3I/ATLAS shows unusual volatile activity, including strong H$_2$O, CO, and CO$_2$ production and a delayed post-perihelion detection of CH$_4$. In this work, we investigate the delayed CH$_4$ detection in an H$_2$O, CO$_2$, and CO ice matrix using a shape model coupled with a thermophysical nucleus model that incorporates interstellar processing by Galactic Cosmic Rays. We track the sublimation, trapping, depletion, and release of these volatiles as a function of heliocentric distance and explore the relevant parameter space through 12000 model runs to identify viable combinations of primordial volatile inventory and effective GCR exposure age that reproduce the observed production rates of these volatiles. The viable models favour a volatile-rich primordial inventory consistent with formation in an ultra-cold ($T < 20$ K) region beyond the CO snowline, followed by an effective GCR processing exposure of 0.87–3.1 Gyr during interstellar passage. GCR processing produces a continuous compositional gradient and converts part of the CO reservoir into secondary CO$_2$ and depletes near-surface CH$_4$ through radiolytic conversion. The delayed CH$_4$ detection can be explained by the survival of CH$_4$ trapped within the deeper H$_2$O matrix and its subsequent release as subsurface heating progresses after perihelion. The timing of CH$_4$ sublimation can be used to estimate the effective GCR processing age of 3I/ATLAS. The posterior distributions also reveal a degeneracy between primordial dust content and GCR exposure, where dust-rich, weakly processed and ice-rich, strongly irradiated evolutionary pathways produce processed subsurface layers with similar thermophysical properties.
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Wednesday 16 September

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

Reinforcement learning for post-coronagraphic wavefront control

Manuela Castañeda-Medina, Yann Gutierrez, Johan Mazoyer et al. (+3 more)

Direct imaging of exoplanets is limited by the extreme contrast between the star and the planets, which is mitigated using a coronagraph. However, optical aberrations cause starlight leakage through the coronagraph, producing speckles that obscure the planetary signal. Achieving the required contrast levels demands wavefront control with subnanometric precision. Deep reinforcement learning offers a promising alternative to traditional focal-plane wavefront control techniques by enabling adaptive correction strategies learned directly from interaction with the system. In this work, we present a fully data-driven method for post-coronagraphic aberration correction in a simulated high-contrast imaging testbed. The agent controls a deformable mirror using observations consisting of focal-plane measurements (images) and physics-informed wavefront sensing information derived from these images. We evaluate different observation representations and control strategies, and the method is validated on simplified simulations of a high-contrast imaging testbed, where it successfully creates dark holes, i.e., regions of the focal plane in which residual starlight is strongly suppressed, while approaching the performance of conventional wavefront control methods.
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All authors Manuela Castañeda-Medina, Yann Gutierrez, Johan Mazoyer, Baptiste Abeloos, Laurent Mugnier, Olivier Herscovici-Schiller

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

A Grid of Contribution Functions to Help the Interpretation of Time-resolved Observations of Brown Dwarfs

Myrla Phillippe, Theodora Karalidi, Elena Manjavacas et al. (+4 more)

We present a grid of thermal emission contribution functions and their corresponding atmospheric spectra model for cloudy and cloud-free brown dwarfs, spanning effective temperatures $T_{\rm eff} \in [500, 2000]$ K, surface gravities $\log g = [3.5, 5.5]$ [cgs], sedimentation efficiencies $f_{\rm sed} = 1, 2, 3, 4$ and 8, and eddy diffusion coefficients $\log K_{\rm zz} = [6, 11]$. We use temperature-pressure profiles from the Sonora Diamondback models in conjunction with the picaso radiative transfer code and the cloud modeling code virga, to explore how different atmospheric parameters influence the vertical distribution of emitted radiation for atmospheres in chemical equilibrium. We confirm that cloud opacity significantly impacts atmospheric emission depth in prominent molecular features such as CH$_4$, H$_2$O, CO, NH$_3$, CO$_2$, and atomic features Na and K. The atmospheric emission depth varies most notably in the $J$-band, and at mid-resolution spectra in the Na and K doublets. Our analysis highlights pressure-wavelength differences between cloudy and cloud-free atmospheres for characterizing L, L/T transition, and T-type brown dwarfs and demonstrates how contribution functions can guide targeted spectroscopic investigations. To facilitate observational planning, we provide an accessible database and web-based application that enable the community to compare observational data with our model grid of spectra and contribution functions with a wavelength range of 0.5 - 30 $\mu$m.
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All authors Myrla Phillippe, Theodora Karalidi, Elena Manjavacas, Natalia Oliveros-Gomez, Daniel Apai, Jonathan Fernandez, Kieran M. Manjrawala

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

Mapping Molecular Ion Distributions in a Diverse Sample of Protoplanetary Disks

Deryl E. Long, L. Ilsedore Cleeves, Charles J. Law et al. (+10 more)

Observations of ionization-tracing molecules in protoplanetary disks suggest that their ionization environments are diverse due to varying degrees of cosmic ray modulation, stellar activity, and environmental differences that alter the impact of ionizing radiation. To better understand ionization chemistry in disks, we present the largest survey of resolved observations of molecular ions to date. Using new and archival ALMA observations we detect HCO+, H13CO+, N2H+, and DCO+ toward seven protoplanetary disks (AS 209, DM Tau, GM Aur, HD 163296, LkCa 15, MWC 480, and V4046 Sgr). We compare distributions of ions to continuum features and find no robust relationships between the two. The observations do, however, reveal distinctions between Herbigs and T-Tauris and hint at a dichotomy between two types of T-Tauri ionization environments. The Herbig sources exhibit unique centrally-peaked N2H+ J = 4-3 emission, which we speculate could be tracing either a highly ionized surface layer or a zone of CO destruction, possibly due to their strong UV fields. Three T-Tauri sources in our sample exhibit bright, radially coincident rings in all optically thin molecular ion lines. We speculate that these radially coincident ion rings are evidence of a global change in ionization, possibly at the edge of a T-Tauriosphere. While it is not yet clear what factors most strongly influence the distribution of ion emission, this survey more than doubles the number of resolved ion observations in disks and points to potential distinctions in ion emission morphology related to the central star and environment.
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All authors Deryl E. Long, L. Ilsedore Cleeves, Charles J. Law, Fred C. Adams, Dana E. Anderson, Sean M. Andrews, Edwin A. Bergin, Jane Huang, A. Meredith Hughes, Chunhua Qi, Kamber R. Schwarz, Jacob B. Simon, David Wilner

Earth and Planetary Astrophysics

JWST Reveals Refractory-Rich Water Ice in Interstellar Comet 3I/ATLAS: Evidence for a Continuum of Grain Properties across Protoplanetary Disks

Silvia Protopapa, Michael S. P. Kelley, Martin A. Cordiner et al. (+12 more)

We present JWST/NIRSpec PRISM observations of the interstellar comet 3I/ATLAS obtained on 2025 August 6 (Epoch 1), 2025 December 22 (Epoch 2), and 2026 April 1 (Epoch 3), spanning eight months around perihelion at heliocentric distances of 3.3, 2.4, and 5.7 au, respectively. The spectra reveal a broad 3 $\mu$m absorption band together with H$_2$O, CO$_2$, and CO gas emission. Unlike previously reported water-ice-rich Solar System comae, the strong 3 $\mu$m absorption is accompanied by weak or absent 1.5 and 2.0 $\mu$m water-ice bands. Spectral modeling indicates that the observations are best reproduced by submicron- to micron-sized water-ice-bearing aggregates containing refractory material. Compared with Epoch 1, the Epoch 3 spectrum favors the presence of a second population of larger, micron-sized, ice-rich aggregates and exhibits a subtle Fresnel-like structure near 3.1 $\mu$m, consistent with crystalline water ice. The observations can be explained by either crystalline water ice at both epochs, with the spectral evolution arising primarily from changes in grain size and refractory mixing, or an evolution from an amorphous-like to crystalline state. The spectral properties of 3I bridge those of water-ice-bearing Solar System comae and several spectral classes of mid-sized trans-Neptunian objects, suggesting that the icy building blocks of planetesimals formed in different protoplanetary disks may span a continuum in the physical state of water ice, ranging from pure ice grains to water-ice-bearing aggregates with varying refractory content at submicron-to-micron scales, with 3I extending toward the refractory-rich end of this continuum.
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All authors Silvia Protopapa, Michael S. P. Kelley, Martin A. Cordiner, Stefanie N. Milam, Dennis Bodewits, Steven B. Charnley, Maria N. Drozdovskaya, Sara Faggi, Davide Farnocchia, Aurélie Guilbert-Lepoutre, Marco Micheli, Nathan X. Roth, Megan E. Schwamb, Darryl Z. Seligman, Geronimo L. Villanueva

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

Coronal Mass Ejections from Young Suns: An Observational View through the Solar-Stellar Connection

Kosuke Namekata

Kepler and TESS have revealed that magnetically active stars frequently produce flares and superflares, raising the possibility that frequent, fast, and massive coronal mass ejections (CMEs) may affect planetary space weather environments. However, observational constraints on stellar CMEs remain extremely limited. Several diagnostics, including Doppler-shifted spectral lines, coronal dimming, and radio bursts, have been explored mainly for cool dwarfs, while recent observations have begun to extend these searches to young solar-type stars, which serve as important benchmarks for the solar-stellar connection. The goal of this review is to summarize the current understanding and recent observational progress on CME signatures from young solar-type stars, with a primary focus on Doppler-shift methods. It examines how these signatures resemble solar observations and models, what the inferred physical properties can tell us about the occurrence of stellar CMEs and their contribution to stellar mass loss, and how Doppler-shift signatures can be connected with multi-wavelength diagnostics. Comparisons with CME candidates from cool dwarfs and close binaries further place these signatures in the broader context of stellar CMEs in different stellar environments. These results have important implications for the space weather environments of young planets, while also pointing to key directions for future observations and modeling.
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Earth and Planetary Astrophysics

Does HD 3167 Have Planets with Perpendicular Orbits?

Joshua N. Winn, Jack Lubin, Gu{\dh}mundur Stefánsson et al. (+5 more)

The two transiting planets of HD 3167 were reported to follow nearly perpendicular paths, with the inner orbit aligned with the stellar equator and the outer orbit nearly polar. This interpretation depends critically on a challenging single-transit detection of the Rossiter-McLaughlin effect of the inner planet. We observed three additional transits of the inner planet with the Keck Planet Finder and analyzed the new data together with two archival ESPRESSO transit datasets. We do not confirm the previously reported low obliquity. Our analysis favors a projected obliquity of $-66^{+14}_{-12}$ degrees, consistent with coplanar orbits. However, because the best-fit projected rotation velocity is higher than expected, and because the obliquity uncertainty grows substantially when the most discrepant of the five transit datasets is omitted, we regard the geometry of the HD 3167 system as still unsettled.
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All authors Joshua N. Winn, Jack Lubin, Gu{\dh}mundur Stefánsson, Haochuan Yu, Erik Petigura, Howard Isaacson, Andrew W. Howard, Fei Dai