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Physics Astrophysics Earth and Planetary Astrophysics

astro-ph.EP Watch Earth and Planetary Astrophysics

Friday 4 September

Earth and Planetary Astrophysics

Evidence for LP 890-9d via Transit Timing Variations

Kevin B. Stevenson, Guangwei Fu, Kristin S. Sotzen et al. (+10 more)

LP 890-9, also known as SPECULOOS-2 and TOI-4306, is a nearby late-M dwarf hosting two confirmed transiting rocky exoplanets. We analyze 20 JWST/NIRSpec PRISM transits of LP 890-9b and LP 890-9c obtained as part of GO program 7073 and detect statistically significant transit timing variations (TTVs), with peak-to-peak amplitudes of ~17 s and ~35 s, respectively. Using analytic linear TTV theory, we find that the known two-planet configuration cannot reproduce the measured TTV amplitudes or super-period, whereas three-planet models provide substantially better fits. The best-fit configuration places the candidate third planet, LP 890-9d, between planets b and c, with an orbital period of ~4.4 days; however, the current data do not uniquely determine its orbital architecture, and periods spanning 4.0-6.9 days remain plausible. TESS is insensitive to transits of LP 890-9d and we find no evidence for the candidate in JWST observations, although the phase coverage (ranging from ~50% to ~80%) depends strongly on the candidate orbital period. Additional high-precision transit observations of LP 890-9b and LP 890-9c are needed to refine their TTV solutions and further constrain the orbital properties of the third planet.
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All authors Kevin B. Stevenson, Guangwei Fu, Kristin S. Sotzen, E. M. May, Larissa Palethorpe, Jacob Lustig-Yaeger, Ted M. Johnson, Eric Agol, Katherine A. Bennett, Carlos Gascón, David K. Sing, Jeff A. Valenti, Hannah R. Wakeford

Earth and Planetary Astrophysics

JWST Excludes Exomoons Down to 0.1 Earth Radii Around a Rocky, Temperate Exoplanet

David Kipping

To date, even with JWST, it has not been possible to test for exomoons as small as the Moon. Only two reported searches for exomoons around bound planets have been attempted with JWST, both of which relied on a single JWST transit. We suggest that the below expectation sensitivity to date is, in part, a product of the considerable intrinsic flexibility of the planet+moon transit model when confronted with a single event, and the presence of unanticipated systematic noise. To test this, we present a search around the rocky, temperate-zone exoplanet LP 890-9c using twelve JWST transits. We find no evidence for an exomoon but exclude $0.1R_{\oplus}$ moons to 95% confidence across the entire Hill region, representing by far the most sensitive search to date. Our limits exclude analogs to many real Solar System moons, such as Europa, Rhea and Umbriel. However, we emphasize that the close-in orbit of LP 890-9c (0.04au) would make any moons larger than ${\sim}0.1R_{\oplus}$ unlikely to survive for many Gyr due to tides. Regardless, our study firmly establishes that JWST can indeed probe down to remarkably small moons. Further, we find that even a single transit can deliver impressive limits, with the exception of one epoch that is contaminated by red noise. However, by pairing it with just one cleaner epoch, the sensitivity recovers to a level indistinguishable from any other pairing, which bodes well for a potential second JWST transit of Kepler-167e.
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Earth and Planetary Astrophysics

Enabling Metallicity Measurements of M-dwarf Microlensing Lenses out to the Galactic Bulge

Jiyuan Zhang, Gregory Green, Weicheng Zang et al. (+2 more)

We demonstrate that metallicity becomes identifiable for M-dwarf microlensing lenses out to bulge distances when multi-band lens photometry is combined with the angular Einstein radius, thereby defining the photometric–microlensing metallicity method. The cool atmospheres of M dwarfs contain abundant molecules, whose broad absorption bands make their positions in an optical–NIR color–absolute magnitude diagram sensitive to metallicity. The angular Einstein radius provides the mass–distance constraint needed to infer the lens absolute magnitude, while the intrinsic M-dwarf locus and reddening vector are non-parallel in color–color space, allowing the lens extinction and intrinsic color to be inferred simultaneously from its multi-band photometry, thereby recovering the lens intrinsic position in the metallicity-sensitive color–absolute magnitude diagram. The method requires three-band lens photometry spanning roughly the R, Z, and K bands, making it particularly well suited to Roman through its high-resolution F062, F087, and F213 imaging. With the planned Roman Galactic Bulge Time-Domain Survey (GBTDS) observations plus an additional $\sim$8 hr of F062 imaging per field ($\sim$40 hr in total) roughly a decade after Roman launch, host metallicities could be measured for $\sim$150 planetary systems under the GBTDS yield forecast, with a typical $1\sigma$ precision of $\sim$0.25 dex from our mock-recovery analysis. Applied homogeneously to GBTDS microlensing events with and without detected planets, the method would enable the first measurement of the occurrence–metallicity relation for cold low-mass planets beyond the snow line, constrain the low-metallicity cutoff for their formation, and extend occurrence–metallicity studies into the inner Galaxy.
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All authors Jiyuan Zhang, Gregory Green, Weicheng Zang, Hongjing Yang, Shude Mao

Earth and Planetary Astrophysics

A Homogeneous Survey of JWST MIRI Transmission Spectra of 10 Exoplanets

Martin Binet, Nikku Madhusudhan, Måns Holmberg et al. (+1 more)

The launch of JWST has enabled unprecedented atmospheric characterization of exoplanets. In particular, the JWST-MIRI instrument in the mid-infrared enables probing of molecular species that are harder to detect in the near-infrared. This has come to the fore with the first MIRI-LRS observation of a candidate hycean world, K2-18 b, with potential signs of dimethyl sulfide in its atmosphere. The statistical significance of this result has been debated in subsequent works, arguing instead for the possibility of random noise, instrumental systematics, or a different molecule. The same applies to similar spectra reported for several other exoplanets using MIRI-LRS and interpreted with similar retrieval architectures. In this work, we distinguish between these possibilities with a homogeneous survey of MIRI-LRS transmission spectra of 10 diverse exoplanets, from temperate sub-Neptunes to hot rocky planets and gas giants. We first perform a comparative assessment of the spectra, considering fits with featureless models and pairwise correlations, followed by extensive atmospheric retrievals. With the retrievals, we search for over 150 trace species in the atmosphere of each planet. We find hints of complex molecules in the temperate sub-Neptunes and candidate hycean worlds K2-18 b, TOI-732 c and TOI-270 d, similar to previous works, but not in the other seven planets. Our results indicate that the observed spectral features are likely due to molecular absorption rather than instrument systematics or noise, and underscore these temperate sub-Neptunes as a unique class of planets. More observations are required to robustly identify the specific molecules and constrain the underlying chemical processes, biotic or abiotic.
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All authors Martin Binet, Nikku Madhusudhan, Måns Holmberg, Subhajit Sarkar

Earth and Planetary Astrophysics

Planetary gas gaps and kinematic signatures in the planet forming disk around WISPIT 2

Nienke van der Marel, Jochen Stadler, Andres F. Izquierdo et al. (+7 more)

The giant planet formation process in disks of gas and dust surrounding young stars is observationally still poorly constrained. Direct detection of protoplanets within the disk remains limited with current facilities. Indirect observational evidence of protoplanets through substructures or deviations from Keplerian rotation in the gas remains ambiguous in absence of detected planets. The lack of the combined detection of substructures and their corresponding planets makes it challenging to connect the planet formation process to the host environment. Observations with the Atacama Large Millimeter Array (ALMA) reveal clear detections of gas gaps and kinematic signatures in the WISPIT 2 protoplanetary disk that are cospatial with the locations of previously detected giant protoplanets. The newly identified gas gaps, observed in both the 12CO integrated intensity map and its rotation curve, correspond with the previously identified gaps in scattered light. Their morphologies are shown to be consistent with eccentric gaps, as expected from planet-disk interaction models of massive planets. The lack of eccentricity in the outer disk can be explained if a third planet is present in the system. The observations of WISPIT 2 provide a long-sought empirical bridge between kinematic signatures, gas gaps and giant planet formation in disks.
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All authors Nienke van der Marel, Jochen Stadler, Andres F. Izquierdo, Ruobing Dong, Bertram Bitsch, Jake Byrne, Richelle van Capelleveen, Chloe Lawlor, Christian Ginski, Matthew Kenworthy.

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

Active focal plane phase mask coronagraphy with a discrete pixelated device: I. Study of the theoretical performance trade space

Liurong Lin, Axel Potier, Ruben Tandon et al. (+2 more)

Recent advances in high-contrast exoplanet imaging instrumentation have introduced the concept of adaptive coronagraphy. For example, liquid-crystal-on-silicon spatial light modulators can be used as programmable phase masks or digital micro-mirror devices as configurable pupil apodizers. Adaptive coronagraphy offers the ability to adjust in real time to changing observing conditions and science goals, such as switching between blind surveys and follow-ups of known objects, or optimizing observations of multiple star systems including binaries and triples. At the same time, these active devices present challenges: finite spatial sampling, limited phase resolution, and the scalar nature of their modulation can all reduce coronagraphic performance. We look at the performance of a coronagraph utilizing pixelated discrete focal plane masks in function of various key parameters, notably spatial sampling, phase resolution, temporal jitter, and calibration errors. The analysis includes several FPM designs: vortex, four-quadrant phase mask, Roddier and Roddier, dual-zone phase mask, and azimuthal cosine phase mask. Both monochromatic and 20% broadband imaging conditions are considered, along with the absence or presence of a central obstruction from a secondary mirror in the telescope pupil, associated with variations in Lyot stop sizing. Our results identify the main error sources and limiting parameters of scalar, pixelated FPM coronagraphs. Under ideal conditions, performance is mainly limited by spatial sampling and chromaticity of scalar phase modulation. These devices are therefore primarily relevant to ground-based high-contrast imaging rather than the deeper contrast regimes required by future space observatories. Although motivated mainly by SLM implementations, the conclusions should also apply to other discrete pixelated focal-plane phase masks.
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All authors Liurong Lin, Axel Potier, Ruben Tandon, Lucas Marquis, Jonas G. Kühn

Earth and Planetary Astrophysics

Stability of circumbinary planets: the role of binary properties and migration scenarios

Romain Grane, Nicolás Cuello, Mario Sucerquia et al. (+4 more)

Among the thousands of exoplanets detected to date, only a very small fraction are classified as circumbinary planets, and this number becomes negligible when considering low-mass planets. This rarity may partly result from observational biases, but also from the challenging dynamical environment of binary systems, which can prevent the long-term stability of planetary orbits. It is therefore essential to investigate the conditions that enable the formation and survival of stable circumbinary planets, particularly in the low-mass regime. To this end, we performed N-body simulations coupled with a planet migration prescription to study the post-formation dynamics of two 10 Earth-mass circumbinary planets in a protoplanetary disc. Based on more than 1,000 simulations, we find that inward migration can, in some cases, be halted through resonance capture with the binary. In contrast to some previous purely N-body studies, these configurations appear to remain stable over long timescales. We further find that the binary mass ratio $q_B$ and eccentricity $e_B$ strongly influence the stability of multi-planet systems. Within the explored parameter space, some regions support long-term stability, whereas others are highly unstable. These stability regions are also sensitive to the migration timescales, and therefore to disc properties and planetary masses. Finally, our simulations suggest that systems in which two planets enter resonance while migrating together are more likely to form stable multi-planet configurations, particularly around highly eccentric binaries. These results provide a first step toward identifying binary star systems that are most promising for hosting multiple low-mass circumbinary planets.
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All authors Romain Grane, Nicolás Cuello, Mario Sucerquia, Emmanuel Gianuzzi, Milenne Ávila-Bravo, Carolina Charalambous, Amaury H. M. J. Triaud

Earth and Planetary Astrophysics

Modelling Palomar Transients: Constraints from Reflection Geometry and Orbital Altitude

Beatriz Villarroel, Alina Streblyanska, Hichem Guergouri et al. (+3 more)

Recent searches of digitised photographic plates from the Palomar Observatory have uncovered tens of thousands of short-lived transients, each visible in only a single exposure. Their morphologies indicate sub-second flashes, consistent with specular reflections from highly reflective objects in near-Earth orbits. In this paper, we present a modelling study using geometric shadow modelling, Monte Carlo simulations, and photometric constraints to infer their physical properties. We examine the observed groupings and alignments, which appear to be consistent with sudden changes in attitude. Assuming a spherical-shell model, the angular profile of the measured transient deficit around the antisolar point is consistent with a population at characteristic altitudes of $\sim 20,000$–25,000 km. A complementary estimate, based on the altitude dependence of the global Earth-shadow deficit, yields a broader characteristic range of $\sim$ 20,000–35,000 km above Earth's surface, extending into the geosynchronous orbital (GSO) region. Under simplified geometric and photometric assumptions and assuming $\sim20{,}000$ to $35{,}786$ km above the Earth's surface, the inferred sizes of the specularly reflecting facets range from centimetre scales up to $\sim3$ m, with characteristic flash durations of $\sim320$ ms and slow rotation rates. We explore both natural and non-natural toy models consistent with the data, and provide constraints to guide future observational searches.
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All authors Beatriz Villarroel, Alina Streblyanska, Hichem Guergouri, Brian Doherty, Matthew Shultz, Stephen Bruehl

Earth and Planetary Astrophysics

Gravitational instability in planet-forming discs

Cristiano Longarini and Giuseppe Lodato

During the earliest phases of star and planet formation, a young star is surrounded by a disc that can become gravitationally unstable. Indeed, if the protoplanetary disc is sufficiently massive, its self-gravity triggers the formation of large scale spiral arms, transporting angular momentum, trapping solid particles and, potentially, collapsing to form sub-stellar companions. In this paper, we review the theoretical and observational advances in the study of gravitational instability in protoplanetary discs over the last 10 years, since the advent of ALMA. These developments have transformed our understanding of gravitational instability, moving beyond its historical role as a theoretical mechanism for giant planet formation toward a physically rich framework that can be directly tested against high-resolution observations.
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Earth and Planetary Astrophysics

Updated in-flight calibration of the Hayabusa2/NIRS3 spectrometer: new global near-infrared photometric properties of asteroid (162173) Ryugu

Antonin Wargnier, Eri Tatsumi, Koki Yumoto et al. (+10 more)

The Near InfraRed Spectrometer (NIRS3) onboard Hayabusa2 observed asteroid (162173) Ryugu, searching especially for signatures of water-bearing minerals. However, during the mission, absolute reflectance measured by the Telescopic Optical Navigation Camera (ONC-T) and NIRS3 showed a systematic offset. Additionally, touchdown operations have modified the instrumental response, which has made post-second-touchdown data less reliable. Correction of these issues is crucial to interpret the subtle spectroscopic differences across the surface, better understand the origin and evolution of carbonaceous asteroids, and support the Hayabusa2$\sharp$ mission's future observations of the asteroids (98943) Torifune and 1998 KY26. We used Ryugu observations at different mission phases for relative calibrations and lunar observations for the absolute calibration. Moon spectra acquired during the first Earth swing-by were compared to simulated ones from photometric models based on lunar orbiter and ground-based data. We then applied the updated calibration to the full Hayabusa2 proximity phase dataset, enabling disk-resolved global and regional photometric analyses. We showed that the data obtained following the first and second touchdowns required downscaled corrections of $5.4 \pm 1.8 $% and $10.3 \pm 0.4 $% at 2 $\mu m$, respectively, while the absolute calibration revealed that NIRS3 reflectance was underestimated by about 8% compared with the original calibration. Our new photometric parameters are consistent with previous studies and indicate a weak east-west dichotomy in phase ratio and phase reddening, pointing to higher surface roughness and higher abundance of fine-grained regolith in Ryugu eastern hemisphere.
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All authors Antonin Wargnier, Eri Tatsumi, Koki Yumoto, Mayumi Ichikawa, Shin-ya Murakami, Yuichiro Nagai, Kazuhiro Honda, Yasuhiro Yokota, Toru Kouyama, Takahiro Iwata, Moe Matsuoka, Satoshi Tanaka, Kohei Kitazato

Earth and Planetary Astrophysics

Mapping the WISPIT2 Planet-Hosting Cavity at Sub-Hill-Radius scales

Myriam Benisty, Stefano Facchini, Richard Teague et al. (+6 more)

We present new deep, very high angular resolution observations of the sub-mm continuum (19x13 mas) and 12CO (67x52 mas) emission from the disk surrounding the planet host WISPIT2. Our analysis reveals a clear gas gap carved by WISPIT 2b and an empty cavity within the orbit of WISPIT 2c. We also find a gaseous and optically thin dusty ring located between the orbits of the two planets. Channel maps show a pronounced change in the emission surface height of the disk, which transitions from flat within the cavity to strongly flared beyond the orbit of planet b, producing clear breaks in the velocity channels. A pronounced thunderbolt-shaped feature, identified as a kinematic planetary signature (KPS), is detected at the location of WISPIT 2b, in agreement with predictions from planet-disk interaction simulations. This constitutes the first system with a confirmed kinematic signature associated with a directly imaged planet. By mirroring opposite velocity-channel maps about the systemic velocity, we further investigate the KPS and identify spatially resolved excess emission in the vicinity of WISPIT 2b. We find that this emission is resolved across the full Hill sphere of the planet, significantly exceeding the expected extent of a circumplanetary disk. We therefore suggest that the observed emission arises from a combination of processes, including prominent planet-driven spiral wakes, localized heating induced by the planet and a circumplanetary disk. Although higher spectral resolution is required to disentangle these contributions, our observations demonstrate the potential to directly characterize the birth environment of forming massive planets at scales down to sub-Hill radius.
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All authors Myriam Benisty, Stefano Facchini, Richard Teague, Francesco Zagaria, Pietro Curone, Viviana Pezzotta, Jaehan Bae, Gabriele Cugno, Daniel J. Price

Earth and Planetary Astrophysics

The metallicity of giant exoplanets around low-mass stars and how Ariel can help

Ravit Helled, Sho Shibata, Shubham Kanodia et al. (+1 more)

Giant planets orbiting low-mass stars represent a unique population of giant planets that can be studied to constrain planet formation theory. Surveys of transiting giant exoplanets around M-dwarfs (GEMS) allow for measurement of their masses and radii, which in turn can be used to estimate their bulk densities. Coupling these observations to interior structure and evolution models can yield the bulk metallicity of these planets, however there are degeneracies to this that are improved by measurements of atmospheric metallicity. Estimates of bulk metallicity can be crucial to our understanding of planet formation timescales and mass budgets, particularly in these extreme (planet-to-star) mass ratio systems. Here we show that GEMS are expected to have a low bulk metallicity as a natural result of the planet formation process, and the low efficiency of planetesimal capture post-formation. To test this empirically, we need a larger sample of GEMS with atmospheric measurements, which can reduce some of the degeneracies with the interior modelling of planets. Measuring the atmospheric composition of GEMS with JWST and Ariel will be crucial for better understanding this unique planetary type, which sits at the tail of standard planet formation conditions.
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All authors Ravit Helled, Sho Shibata, Shubham Kanodia, Billy Edwards

Earth and Planetary Astrophysics

Multi-Wavelength Post-Perihelion Polarimetry of Interstellar Comet 3I/ATLAS

Zuri Gray, Galin Borisov, Ludmilla Kolokolova et al. (+15 more)

We present new post-perihelion polarimetric observations of the third discovered interstellar object, 3I/ATLAS (C/2025 N1; hereafter 3I), obtained using FORS2 at the Very Large Telescope, ALFOSC at the Nordic Optical Telescope, and FoReRo2 at the 2 m Ritchey-Chrétien-Coudé telescope. The observations span phase angles 1-30$^{\circ}$, providing the most extensive polarimetric phase angle coverage obtained for an interstellar object to date. The post-perihelion measurements reveal that the unusual polarimetric properties of 3I persist across perihelion and match recent independent post-perihelion observations, indicating no significant evolution in the polarimetric properties. The increased phase angle coverage allowed us to further constrain the minimum polarisation to $-2.9\%$ at phase angle $5.5^{\circ}$. Multi-band BVRI observations reveal a wavelength dependence of polarisation, with the negative polarisation branch becoming deeper and shifted toward smaller phase angles at longer wavelengths. The polarimetric colour is predominantly red and increases with phase angle, consistent with behaviour observed in other comets. Imaging and polarimetric maps show a substantially more extended coma after perihelion, while the polarisation distribution itself remains smooth and spatially homogeneous. Numerical modelling suggests that the unusually deep polarisation phase curve originates from moderately porous dust aggregates consisting of weakly absorbing sub-micron monomers, resulting in much brighter dust than that in typical solar system comets.
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All authors Zuri Gray, Galin Borisov, Ludmilla Kolokolova, Johannes Markkanen, Yuna G. Kwon, Stefano Bagnulo, Alberto Cellino, Rosemary C. Dorsey, Grigori Fedorets, Mikael Granvik, Eric MacLennan, Antti Penttilä, Karri Muinonen, Olga Muñoz, Philippe Bendjoya, Maxime Devogèle, Simone Ieva, Francisco J. García-Izquierdo

Earth and Planetary Astrophysics

Disk dispersal freezes overstable resonant librations

Linghong Lin and Beibei Liu

Context. Convergent migration in a gaseous protoplanetary disk can capture a planet pair into mean-motion resonance. Eccentricity damping can subsequently make the resonant libration overstable and drive the pair out of resonance. Most studies of this process, however, assume a static disk. Aims. We examine how the decay of disk torques during dispersal changes this outcome and whether it can freeze an overstable libration before the pair escapes. Methods. We describe disk dispersal by allowing the migration and eccentricity-damping timescales to increase exponentially on a local timescale $\tau_{\rm d}$. Integrating the time-dependent growth rate predicts $\tau_{\rm d,crit}\propto\tau_{e,0}$. We test this scaling with direct $N$-body integrations and relate $\tau_{\rm d}$ to the time taken by a photoevaporative cavity edge to cross the local torque-producing region. Results. The simulations recover a linear boundary, $\tau_{\rm d,crit}\simeq S\tau_{e,0}$, with $S\simeq3$ over the explored parameter range. In a fiducial minimum-mass solar nebula, faster propagation of the cavity edge shortens the local dispersal time. The ratio $\tau_{\rm d}/\tau_{\rm d,crit}$ also decreases with orbital radius, so both effects favour resonant survival. Conclusions. When local disk dispersal is sufficiently rapid, the libration amplitude can freeze and the planet pair can remain in resonance instead of escaping through overstability. Late disk evolution can therefore alter the outcome of resonant overstability.
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Earth and Planetary Astrophysics

Habitable-zone Earths at the detection frontier: Measured completeness and false-alarm rate of a transit pipeline for the PLATO M-dwarf sample

Yohann Tschudi

The PLATO mission will observe its first long-pointing field, LOPS2 (Long-duration Observation Phase, South field), for at least two years, bringing the habitable zones (HZ) of its M-dwarf sample within reach of a transit search. The completeness and false-alarm rate of a pipeline validated on TESS M dwarfs are measured on simulated PLATO photometry and converted into a candidate-level forecast for the LOPS2 M dwarfs. Simulated PLATO light curves (717 d baseline; three stellar cells of the faint half of the sample) were processed end to end in two arms, without and with a pre-launch model of the instrument systematics: 930 in the first (465 realisations, 525 injected planets, 465 noise-only twins) and 790 in the second. Injected planets measure completeness against the expected signal-to-noise ratio (S/N), separately for the long-period regime of the HZ; noise-only twins measure the false-alarm rate against the floor on the red-noise-aware statistic S/N_pink. Completeness reaches 50% at S/N = 7.7 +/- 0.15 over all periods and 8.6 +/- 0.3 in the long-period regime. The false-alarm rate falls from 79 +/- 2% to 0.6% as the S/N_pink floor rises from 6 to 8, and 6 +/- 1% at the adopted floor 7.5 (completeness 54 +/- 2%). In the field, the 50 known transiting objects of interest (19 confirmed planets, 31 candidates) would all be recovered; a transiting HZ planet of 1.0 (1.5) Earth radii would be recovered as a candidate with ~40% (65%) probability, giving about 4 HZ Earths and 7 super-Earths over 16 929 field M dwarfs. The systematics arm shifts the 50% point by +0.54 (+0.27/-0.22) in S/N, a penalty localised on the transition, leaving the floor robust and negligible on the long-period injections that feed the HZ. Habitable-zone Earths around the PLATO M dwarfs sit at the measured detection frontier, where completeness and reliability, both measurable before launch, decide the yield.
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Earth and Planetary Astrophysics

Signatures of rocky debris accretion in AF-Type planet hosts

J. Maldonado, I. Mendigutía, S. Barceló Forteza et al. (+3 more)

The gas-giant planet-metallicity correlation plays a fundamental role in our understanding of planet formation. We determine in a homogeneous way the metallicity and individual abundances of a sample of A and early-F stars, with and without known planetary companions, and discuss their abundance distribution and trends. We find that stars with planets generally exhibit higher abundances of both iron-peak and volatile elements compared to stars without known planets although in most cases this tendency is not statistically significant. The $\rm {C/O}$ ratio remains similar between both samples, while the $\rm {Mg/Si}$ ratio is shifted towards higher values in the general planet host sample. When the sample is limited to fully radiative stars (spectral type earlier than F5), the statistical significance of carbon overabundances vanishes. In contrast, elements such as O and Ni remain significantly overabundant. The $\rm {C/O}$ and $\rm {Mg/Si}$ ratios in this radiative subsample are statistically indistinguishable from that of the comparison sample. The persistent overabundance of O and Ni, combined with $\rm {C/O}$ and $\rm {Mg/Si}$ ratios similar to those of stars without planets in fully radiative hosts, points to the ongoing surface pollution by volatile-poor, silicate-rich rocky debris, rather than the accretion of gas giants. These findings might position early-type main-sequence stars as a crucial dynamical missing link in the chemical life-cycle of planetary systems: bridging the initial dust-trapping phase in pre-main sequence transition discs, the dilution of this superficial pollution during the fully convective red giant phase, and the eventual dynamically-driven accretion of asteroid material observed in polluted white dwarfs
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All authors J. Maldonado, I. Mendigutía, S. Barceló Forteza, G. M. Mirouh, B. Montesinos, E. Villaver

Earth and Planetary Astrophysics

Retrieving Ocean Glint Reflectance Signatures from Directly Imaged Earth-like Exoplanets

Eleanor Cornish and Tyler D. Robinson

Future space telescopes searching for extraterrestrial life require methods to detect environments that can potentially support life. Liquid water is considered essential for life as we know it and its presence is therefore an important observable when characterizing potentially Earth-like exoplanets. Remotely inferring the presence of surface liquid water on a world from spatially unresolved observations is an outstanding challenge where the detection of ocean glint could provide supporting evidence. This study assesses the feasibility of detecting ocean glint from Earth-like exoplanets using simulated data from NASA's Habitable World Observatory (HWO). We conducted retrievals on these simulated observations using a model that included a glint contribution and performed model selection against retrievals that did not include glint. We find that over a range of spectral signal-to-noise ratios from 5 to 25, a phase angle of at least 120 deg is necessary for glint detection. Our results offer the opportunity to shape mission development by providing constraints on key telescope observing requirements.
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Thursday 3 September

Earth and Planetary Astrophysics

A Cross-Laboratory Comparison Study of Titan Haze Analogs: Surface Energy II

Eric C. Austin, Xinting Yu, Chao He et al. (+10 more)

The organic haze particles on Titan play important roles in atmospheric cloud formation and aerosol-lake interactions. These processes are strongly influenced by the surface energy of the haze particles, which controls cohesion and wetting behavior. This study presents a comparative analysis of 32 laboratory-produced haze analog samples ("tholins") synthesized across three laboratories. Using contact angle measurements, we determine the total surface energy and its dispersive and polar components for all samples, systematically evaluating the effects of substrate choice, air exposure, initial N2/CH4 gas mixture, and experimental setup. We find that tholin samples exhibit minimal substrate dependence, whereas exposure to ambient air substantially modifies the surface chemistry, altering the balance between dispersive and polar components. Thus, future Titan-relevant surface property measurements may use any substrate but must keep samples pristine. Surface energies vary weakly across methane concentrations, from 1-10% CH4 in N2, indicating that Titan's hazes formed at different altitudes should exhibit broadly similar cohesiveness. In contrast, experimental conditions such as gas exposure time and energy source produce the dominant differences in surface energy, driven largely by variations in polar components. Despite these differences, tholin samples exhibit high dispersive components, implying that Titan's hazes should act as efficient cloud condensation nuclei for hydrocarbon clouds and should generally sink into Titan's lakes. Given observed ethane ice clouds, we conclude that cold plasma tholins may be better physical analogs for Titan's hazes than samples produced with far-ultraviolet irradiation, though intrinsic surface energies of UV tholins remain uncertain due to film thickness limitations.
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All authors Eric C. Austin, Xinting Yu, Chao He, Cara Pesciotta, Ella Sciamma-O'Brien, Joshua A. Sebree, Jose Raul Montes-Bojorquez, Adis Husić, Erik White, Christopher R. Bond, Sarah Hörst, Farid Salama, Patricia McGuiggan

Earth and Planetary Astrophysics

Circumbinary planets in coplanar triple-star systems: I. Minimum eccentricity variation region

Emmanuel Gianuzzi, Mario Sucerquia, Nicolás Cuello et al. (+1 more)

We aim to determine the conditions under which Lidov-Kozai oscillations can arise for circumbinary planets in hierarchical triple-star systems, and to identify the orbital regions where competing secular perturbations minimize eccentricity excitation. We analyzed the statistical properties of hierarchical triples from the Multiple Star Catalog to construct representative synthetic configurations. We then performed N-body simulations of circumbinary planets embedded in these systems, systematically exploring their orbital evolution and long-term stability across a range of semimajor axes and inclinations. For representative compact hierarchical triple-star systems with masses $m_0 \sim m_1 \approx 0.75\,{\rm M}_\odot$ and $m_2 \approx 0.6\,{\rm M}_\odot$ and eccentricities $e_1 \sim 0.1$ and $e_2 \sim 0.4$, dynamically significant stable circumbinary regions exist only in sufficiently hierarchical configurations, with period ratios $P_2 /P_1 \gtrsim 10^2$. In this regime, the secular competition between the tertiary perturbations and the apsidal precession induced by the compact inner binary determines both the onset of Lidov-Kozai oscillations beyond a critical distance ($a_{\rm LK}$) and the location of a region where eccentricity variations are minimized, i.e., the minimum eccentricity variation region (MER). We derived analytical estimates for these dynamical features, showing that the MER is well described by the analytical quantity $a_{\rm short}$ on short and intermediate timescales, while on secular timescales it converges toward the equilibrium prediction $a_{\rm ME}$. These analytical estimates agree well with N-body simulations. Application to the observed triple system WDS 08403+1921 confirms that $a_{\rm LK}$ and $a_{\rm ME}$ accurately identify the main dynamical features of the stability map.
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All authors Emmanuel Gianuzzi, Mario Sucerquia, Nicolás Cuello, Cristian Giuppone

Earth and Planetary Astrophysics

Composition gradients in sub-Neptunes: K2-18 b and TOI-270 d as case studies

Luca Morf and Ravit Helled

Structure models of sub-Neptunes commonly assume purely adiabatic interiors with distinct layers of homogeneous composition. We assess how allowing for more complex interiors with composition gradients affects the inferred internal structure and bulk compositions of the sub-Neptunes K2-18 b and TOI-270 d. We compare purely adiabatic models with distinct layers against models that include composition gradients and stable non-convective regions. We present solutions that are consistent with the observed masses, radii, and atmospheric boundary conditions. We find that composition gradients significantly increase the range of viable interior structures: For example, the interior degeneracy remains substantial even for fixed mass and radius and the maximum hydrogen-helium (H-He) mass fraction can increase by up to a factor of five for K2-18 b. We further show that correlations, such as those between the H-He abundance and the ice-to-rock or rock-to-iron ratios, can weaken when composition gradients are introduced. For example, the Spearman rank correlation coefficient between the H-He and iron abundances decreases from $\sim0.7$ to $\sim0.4$ for TOI-270 d in our models. Purely adiabatic models underestimate the range of plausible compositions and overestimate the impact of more precise measurements, atmosphere models, and host star constraints on a more accurate characterization. We suggest that interior models of sub-Neptunes should by default include more complex interiors, such as composition gradients and non-convective regions, when using data for interpreting the planetary structure, formation, and evolution.
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Earth and Planetary Astrophysics · Cross-listed from astro-ph.IM

TNFlow: Amortized Posterior Inference for Trans-Neptunian Object Surface Composition

Agastya Gaur, Cristina M. Dalle Ore and Alessandra Ricca

We present TNFlow, a transformer and normalizing flow architecture for inferring the surface composition of Trans-Neptunian Objects (TNOs) from their reflectance spectra. TNFlow is trained on synthetic spectra generated by the Shkuratov radiative transfer model to act as its inverse. TNFlow takes ${\sim}$0.7s to invert one spectrum on a single CPU core, returning a multimodal posterior over simplex-valid compositions and grain sizes. On synthetic spectra, the highest-weight mode achieves a mean total-variation distance of 0.149 from ground truth on the test split, and the model generalizes well to unseen combinations of known components. Qualitative tests on real JWST spectra show blindness or bias towards some materials. We suggest this could be attributed to either simulator fidelity or the training set.
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Earth and Planetary Astrophysics

Detection of hydrocarbons in Titan using high-resolution cross-correlation spectroscopy

Maria Coelho, Rafael Rianço-Silva, Diogo Gonçalves et al. (+2 more)

High-resolution cross-correlation spectroscopy (HRCCS) is a powerful technique for detecting molecules whose individual spectral lines are too weak to be identified directly, but its sensitivity is limited by the availability and quality of high-resolution opacity data. Many molecules of atmospheric and astrobiological interest lack complete line lists, restricting traditional template-based searches. In this work, we use Titan as a controlled testbed to develop and validate a new cross-section-based methodology for HRCCS template construction. We analyse K-band CRIRES+ observations of Titan (1.99 - 2.48 {\mu}m), and compute cross-correlation functions using both line-by-line and cross-section-based templates. Our analysis recovers known hydrocarbons such as methane (CH4) and acetylene (C2H2), and yields the first HRCCS detection of ethane (C2H6) with a significance of SNRpeak = 5.17 {\pm} 0.07. The ethane detection was made possible exclusively through cross-section-based templates, as no high-resolution line list currently exists for this molecule. These results demonstrate that cross-section-based template construction is a practical and powerful strategy for extending HRCCS to molecules that currently lack reliable line lists, and establish Titan as a benchmark for calibrating molecular detection techniques that can be applied to both solar system and exoplanet atmospheres. Future applications of this approach to other ground-based high-resolution spectrographs, as well as to JWST's highest-resolution modes and next-generation facilities such as the ELT, could significantly expand the inventory of molecules detectable in planetary atmospheres.
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All authors Maria Coelho, Rafael Rianço-Silva, Diogo Gonçalves, Pedro Machado, Zita Martins

Earth and Planetary Astrophysics

Properties of Seasonal Ice at Sisyphi Cavi and Implications for Current Modification of Martian Gullies

Apolline Leclef, Mathieu Vincendon, Cateline Lantz et al. (+7 more)

Martian gullies are geologically recent landforms that may form either through liquid-water activity and/or through processes involving CO2 ice. We investigated the mechanisms responsible for the formation or modification of these features by focusing on the active site of Sisyphi Cavi (68{\deg}S, 1{\deg}E), located outside the typical latitude range of gully presence. Using CRISM and OMEGA infrared data, we characterized the composition and physical state of seasonal surface ices to test the relevance of H2O and CO2 ice driven mechanisms. Our analysis shows that H2O ice is not detected as an independent surface deposit, although it may be present as minor inclusions within the CO2 ice layer. In particular, during the final phase of CO2 ice sublimation in late spring, no H2O ice signature is observed. In the area, faint spectral signatures of sulfate salts are observed, but their distribution and amount do not suggest any direct link with gully activity. Available observations during early and mid-spring reveal that CO2 ice is translucent during these times, suggesting that it likely remains in this state through most of the ice season. However, a temporal mismatch between dark spot formation - indicative of CO2 geysers through translucent ice - and gully modification (respectively occurring late winter to early spring, and mid to late spring) exists. This does not suggest a systematic link between both processes. Overall, the available observations provide no evidence that liquid water contributes to present-day gully activity at Sisyphi Cavi, while offering no support either for the hypothesis that gully modifications are mainly driven by the formation of CO2 geysers. Gully modifications at Sisyphi Cavi, observed during the late sublimation stages of CO2 ice, may be rather more appropriately explained by CO2-ice-based fluidization or avalanche processes.
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All authors Apolline Leclef, Mathieu Vincendon, Cateline Lantz, François Andrieu, Marie Ausseresse, John Carter, Susan J. Conway, Marion Massé, Kelly Pasquon, Frédéric Schmidt

Earth and Planetary Astrophysics

Disk survey in the Serpens star-forming region: Environmental effects in nearby star-forming regions

Simin Tong, Nienke van der Marel, Jonathan P. Williams et al. (+1 more)

The external environment where protoplanetary disks are embedded regulates disk evolution. External irradiation, which heats and evaporates gas, as well as frequent stellar encounters, which truncate disks, can reduce disk sizes and masses. Disk surveys in nearby star-forming regions with various environments can help us understand how external environments impact disk evolution. The Serpens star-forming region, which is thought to be dense but not highly irradiated by massive stars, is an ideal laboratory to study the dynamical effects on disk properties. We aim to study how dynamical interactions modify disk dust masses by comparing Serpens with other nearby star-forming regions through their disk masses and 3D stellar densities. We survey 321 young stellar objects from Class I to III in Serpens using ALMA at 0.25 arcsec. We measure disk dust masses from millimeter observations under the optically thin assumption and recompute the 3D stellar density using Gaia data. We apply the same method to other nearby star-forming regions for direct comparison with Serpens. The cumulative disk dust mass distribution of Serpens is similar to those of similarly aged nearby star-forming regions, such as Lupus and Taurus. Along with re-assessment of the 3D stellar density, it suggests that Serpens is not likely to have experienced strong tidal truncation capable of producing lower disk dust masses. We also find that the low disk dust mass tension in Ophiuchus and Corona Australis can be resolved when only disks that have been explicitly identified as members of young (1-2 Myr) sub-clusters are considered. Disks without Gaia identifications, especially in Ophiuchus, are spatially clustered in the 2D projected sky plane and less massive than nearby disks with Gaia identifications, possibly tracing the effects of tidal truncation in denser environments at earlier evolutionary stages.
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All authors Simin Tong, Nienke van der Marel, Jonathan P. Williams, Alexa R. Anderson

Earth and Planetary Astrophysics

Trans-Neptunian Object dynamics even better explained by a stellar flyby after 4.5 Gyr of evolution

Susanne Pfalzner, Frank W. Wagner and Marco Bischoff

The Trans-Neptunian objects (TNOs) formed together with the planets from a flat disc of gas and dust but now orbit the Sun mostly on inclined, eccentric orbits. One explanation for the TNOs' orbits is a close flyby of another star. One with a mass of $M_p =$0.8 Msun at $q_p =$ 110 au and $i_p =$70{\deg} fits the observations. However, such close encounters were more frequent when the Sun was young and still part of its birth cluster. Assuming that the flyby happened then, we use numerical $N$-body simulations to model how the TNOs' orbits changed due to interactions with the planets over the 4.56 Gyr since the Sun formed. We find that the cold Kuiper belt region lost about 80% and the hot Kuiper belt population about 40% of its initial population. About 7% –8% of the TNOs were injected into the planet region, but almost all (99%) were ejected afterwards. By contrast, the orbital parameters of distant Sedna-like objects ($q >$60 au) remained basically unchanged. Surprisingly, in sum, these changes improve the fit to the observed TNO population even more, strengthening the argument for a close flyby to the Solar System. The remaining differences concern the location of the cold population and the inclination distribution of the Sedna population. We discuss possible reasons and steps to resolve these issues.
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Earth and Planetary Astrophysics

Effect of stellar spot-only spectral lines in high-resolution transit spectroscopy

W. Dethier, E. Cristo, O. D. S. Demangeon et al. (+3 more)

We investigate how a representative single spectral line present only in a stellar spot can introduce distortions in high-resolution planetary absorption spectra. Specifically, we assess whether such spot-induced features may resemble planetary atmospheric absorption and the observational or stellar conditions under which they become significant. Using the SOAPv4 code, we simulated transit observations of an atmosphere-less planet across a star with a spot containing an additional absorption line compared to the photosphere's spectrum. Two systems were modelled: a close-in Jupiter-sized planet and a distant Earth-sized planet transiting a Sun-sized star. We varied the stellar rotation period and the spot size, and ensured that the planet transits the spot. Spectral lines were idealised Gaussians to isolate the impact of the spot-specific feature. We show that a single stellar spot line can generate spurious features in the absorption spectrum. These features contaminate the absorption spectrum in ways that may lead to misinterpretation if not accounted for. For Jupiter-sized planets with short transits, the features are mainly emission-like, but can nonetheless dampen a potential true atmospheric absorption signature. For Earth-sized planets with long transits, the distortion is mainly absorption-like and could be interpreted as planetary absorption. These results highlight the importance of accounting for stellar heterogeneity and activity in the analysis of high-resolution absorption spectra.
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All authors W. Dethier, E. Cristo, O. D. S. Demangeon, J. P. Lucero, N. C. Santos, B. Tessore

Earth and Planetary Astrophysics

Dynamically favorable hosts for submoons around Jupiter and Saturn

Ryan Dahoumane, Valéry Lainey and Kevin Baillié

The long-term stability of small bodies orbiting natural satellites (submoons) in the Solar System has been previously investigated using an analytical approximation of a three-body problem, focusing mainly on tidal forces and neglecting other perturbations. This approach suggests that submoons around most of the regular satellites in the Solar System could be stable. However, no such object has been detected to date. In this work, we extend these previous results by numerically testing the survival of submoons around a large number of satellites of Jupiter and Saturn. Our goal is to rank the satellites of Jupiter and Saturn according to how dynamically favorable they are for submoon survival over the simulated timescales. For each regular or irregular satellite considered, we performed 130 separate N-body integrations, each containing one hypothetical submoon with a different initial semimajor axis and inclination. From the 1 Myr survival fractions, we rank the satellites according to their dynamical favorability for submoon survival over the simulated timescale. We find that, after 1 Myr, the satellites with the highest survival fractions (above 30%) are Iapetus ($\approx 37\%$), Titan ($\approx 35\%$), Rhea ($\approx 32\%$), Phoebe ($30\%$), Callisto ($\approx 34\%$), and Ganymede ($30\%$). Rather than providing absolute probabilities for the existence of submoons, these survival fractions identify the most dynamically favorable hosts. Iapetus, Titan, Rhea, Phoebe, Callisto, and Ganymede are the most dynamically favorable submoon hosts among the tested satellites.
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Wednesday 2 September

Earth and Planetary Astrophysics

Evolutionary pathways toward survival of a thick CO2- or SO2-rich atmosphere on the lava world TOI-561 b

Emma Postolec, Tim Lichtenberg, Johanna K. Teske et al. (+10 more)

Rocky planets evolve through the exchange of volatiles between their interiors and atmospheres, an interplay still poorly constrained by observations. Remarkably, highly irradiated ultrashort-period (USP) exoplanets may offer a window into this exchange – some retain low bulk densities compatible with volatile-rich envelopes surrounding rocky interiors, indicating possible secondary atmospheres. TOI-561 b is a prime example, with a bulk density of $4.3\pm0.4$ g cm$^{-3}$ and recent JWST observations favoring a thick volatile atmosphere overlying a dayside magma ocean. Here, we investigate the evolutionary pathways allowing TOI-561 b to retain a substantial atmosphere over gigayears using the PROTEUS coupled interior–atmosphere framework. We explore different core radius fractions, Bond albedos, atmospheric escape efficiencies, mantle redox states, and initial C–H–O–N–S volatile inventories, under in situ evolution and late inward migration. Over half of our simulations leave a bare interior too dense to match observations. Successful cases favor a volatile-rich origin ($\lesssim200$ Earth oceans of hydrogen, S/H $\le10$, and N/H $\le1$), an oxidized mantle ($f$O$_2 \gtrsim \mathrm{IW}+4$), a small iron core ($\le 0.40$ for the core radius fraction), and low escape efficiency ($\epsilon \lesssim 10^{-3}$) in the hydrodynamic escape regime. At present, TOI-561 b is consistent with a global magma ocean beneath a thick (surface pressure $\approx 10^{3}$–$10^{4}$ bar), high mean molecular weight atmosphere ($38$–$60$ g mol$^{-1}$). Two archetypes emerge, differentiated by bulk sulfur content: a CO$_2$-dominated and an SO$_2$-dominated atmosphere. Migration is viable but not required to reproduce the observations. Our study illustrates how interior–atmosphere coupling governs atmospheric retention on irradiated rocky planets.
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All authors Emma Postolec, Tim Lichtenberg, Johanna K. Teske, Harrison Nicholls, Mara Attia, Anjali Piette, Lisa Dang, Nicole L. Wallack, Mykhaylo Plotnykov, Alex McGinty, Samuel Boucher, Bo Peng, Diana Valencia

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

Infrared-excess sources in VVV: candidate debris discs, SED characterization, and variability analysis

P. Esteves, R. K. Saito, C. Chavero et al. (+9 more)

Debris disks around main-sequence stars provide important insights into planetary formation and evolution; however, identifying these systems in the Galactic plane, where high interstellar extinction and source crowding are significant, remains challenging. Deep, wide-area surveys such as the VISTA Variables in the Via Lactea (VVV) ESO Public Survey provide multi-epoch infrared observations, enabling systematic searches in these environments. We present a method to construct a refined sample of main-sequence candidates by cross-matching data from Gaia DR3, GLIMPSE, DECaPS, and VIRAC2, to identify infrared excesses through spectral energy distribution (SED) analysis, and to analyse time-series data to detect variability potentially associated with circumstellar material or other astrophysical phenomena. Although infrared excess is commonly associated with debris disks, contributions from unresolved binaries or line-of-sight contamination cannot be excluded. Applying this methodology to the VVV tile d077 using the VIRAC2 catalogue, we analyse an initial sample of 879,556 sources and identify 446 sources flagged by the VO SED Analyser (VOSA) excess-detection algorithm as having infrared excess, of which 171 show candidate periodic variability in the VIRAC2 Ks-band light curves. We further perform SED fitting using theoretical models to derive physical parameters and approximate spectral types for these sources. This work provides a catalogue of infrared-excess candidates in a Galactic field affected by high extinction, along with a reproducible method suitable for future large-scale applications.
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All authors P. Esteves, R. K. Saito, C. Chavero, V. Fermiano, D. Minniti, B. W. Borges, C. Cáceres, Z. Guo, V. D. Ivanov, R. G. Kurtev, D. Quispe, R. M. Torres

Earth and Planetary Astrophysics

Low-energy ring particle accretion as the origin of Pan's equatorial ridge

Marco Baj, Iosto Fodde, Lucia Francesca Civati et al. (+1 more)

Pan is a small Saturnian satellite embedded within the planet's A ring, characterized by a polygonal equatorial ridge whose formation mechanism remains debated. A proposed explanation is ring particle accretion, yet previous simplified models could not address the ridge's complex multi-lobed morphology without ad hoc assumptions, and the cause of its latitudinal spread remains unclear. This work studies the complex low-energy dynamics around Pan to verify whether the ring particle accretion paths are consistent with the observed ridge morphology. We model particle motion using a CR3BP with spherical harmonic perturbations. Accretion paths are analyzed via grid-search simulations of trajectories transiting the $L_1$ and $L_2$ necks, using backward propagation from Pan's surface to determine the impacting material's original orbital characteristics. Asymmetric accreting particle populations, with inner-ring particles located closer to Pan and contributing more significantly to the impact flux, produce impact distributions that correlate with the ridge structure, especially for the Saturn-facing hemisphere. The ridge latitudinal spread is recovered only when the out-of-plane position and velocity of the accreting particles are strictly limited, consistent with accretion from a thin disk such as Saturn's rings. Furthermore, analysis of the particles' impact conditions revises the previously estimated minimum accretion duration downward by an order of magnitude, to $10^4$ yr, while accreting material is shown to originate from ring particles that once populated the Encke Gap. By systematically sampling admissible low-energy trajectories near Pan, our grid-search approach resolves the complex accretion dynamics that previous simplified narrow-stream models do not capture, revealing that the ridge's main morphological features emerge naturally from the local low-energy dynamical environment.
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All authors Marco Baj, Iosto Fodde, Lucia Francesca Civati, Fabio Ferrari