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Physics Astrophysics Earth and Planetary Astrophysics

astro-ph.EP Watch Earth and Planetary Astrophysics

Wednesday 2 September

Earth and Planetary Astrophysics

New and Updated Rossiter-McLaughlin Measurements for Three Hot Jupiter-Hosting M Dwarfs

Drew Weisserman, Ryan Cloutier, Alexandra Rochon et al. (+12 more)

Evidence suggests that Kozai-Lidov high-eccentricity migration (HEM) is the dominant migration channel for short-period Giant Exoplanets around M dwarf Stars (GEMS). However, it is unlikely that all short-period GEMS form via HEM, given that most systems lack known massive companions capable of driving HEM. Characterizing the stellar obliquities of GEMS via the Rossiter-McLaughlin (RM) effect can help shed light on the dynamical histories of GEMS. We present RM effect detections for the GEMS TOI-5205 b, TIC 46432937 b, and TOI-3714 b using the Gemini-North/MAROON-X spectrograph, bringing the total number of GEMS with RM detections to five. Our systems are well-aligned, with sky-projected obliquities of $\lambda = 0 \pm 6^\circ$, $3_{-3}^{+4}$$^\circ$, and $15_{-8}^{+12}$$^\circ$, respectively, and we measure a deprojected obliquity of $\psi = 24_{-8}^{+7}$ $^\circ$ for TOI-3714. We analyze archival radial velocities, astrometry, and speckle imaging data to search for additional companions around all five known GEMS with RM detections. We find tentative evidence for a new massive companion around one of these GEMS, TOI-5293 A, in Gaia DR2+DR3 data, though further follow-up is needed for confirmation. We rule out massive companions between $\sim 1-10\textrm{ AU}$ in the remaining systems, but cannot rule out all companions capable of driving HEM. Our findings present further evidence that short-period GEMS are preferentially aligned. While current results remain consistent with both primordial alignment and HEM plus tidal damping, we offer future directions for studies to further constrain the dominant migration channel for GEMS.
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All authors Drew Weisserman, Ryan Cloutier, Alexandra Rochon, Ze'ev Vladimir, Bertram Bitsch, Ritvik Basant, Jacob L. Bean, Tanya Das, Emily Deibert, Thomas M. Evans-Soma, Michael Line, Ralph Pudritz, Andreas Seifahrt, Evgenya L. Shkolnik, Luis Welbanks

Earth and Planetary Astrophysics

JWST MIRI reveals a potential atmosphere on the ultra-hot rocky planet TOI-431b

Cole Smith, Brandon Park Coy, Megan Weiner Mansfield et al. (+13 more)

An open question in exoplanet science is whether rocky exoplanets extremely close in to their host stars, `lava worlds', can retain significant atmospheres. Thermal emission observations via secondary eclipse can be used to determine whether a rocky exoplanet possesses an atmosphere. It is expected that an atmosphere could increase the planet's albedo and/or redistribute heat away from the dayside, reducing the secondary eclipse depth measured. Recent eclipse observations of lava planets, rocky planets hot enough to have liquid magma surfaces, have suggested the presence of atmospheres. Here, we present a single JWST MIRI/LRS partial secondary eclipse of the lava planet TOI-431b. We measure an eclipse depth of 81 $\pm$ 16 ppm, which corresponds to a brightness temperature of $1967^{+237}_{-253}$ K and a brightness temperature ratio R = $0.81\pm0.10$, being 1.2 $\sigma$ higher than the value reported by Spitzer. The observed brightness temperature ratio is 1.8$\sigma$ below that of a zero-albedo, zero heat redistribution bare rock (R=1). Given that magma pools are expected to have low albedos, we find that our results are best explained by the presence of an atmosphere. Future work to measure the exact composition of TOI-431b's atmosphere and improve models of lava planet atmospheres would better constrain the nature and evolution of lava planets.
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All authors Cole Smith, Brandon Park Coy, Megan Weiner Mansfield, Rafael Luque, Anjali A. A. Piette, Qiao Xue, Michael Zhang, Jacob L. Bean, Madison Brady, Peter Gao, Jegug Ih, Eliza M.-R. Kempton, Edwin Kite, Daniel Koll, Jaume Orell, Enric Palle

Earth and Planetary Astrophysics

Radial velocity detection of the TRAPPIST-1 planetary system with SPIRou and NIRPS

Alexandrine L'Heureux, René Doyon, Charles Cadieux et al. (+57 more)

The TRAPPIST-1 system is well-known for its seven transiting Earth-sized exoplanets. It has been extensively studied and characterized, notably with transit timing variations (TTVs) to precisely measure the mass of the planets. Using near-infrared spectroscopic observations obtained as part of the SPIRou Legacy Survey and the NIRPS Guaranteed Time Observation programs, we aimed to verify those values through radial velocity (RV) measurements of the system. Our RV analysis reveals that the current data do not have the precision required to individually detect the TRAPPIST-1 planets. However, we confidently detect ($\Delta\ln\mathcal{Z}=7.53$, 1860:1 odds) the combined RV signature of the planets by informing their relative masses on the TTV analysis, with TRAPPIST-1 b as a proxy of the whole system. For the first time, the RV signal of the TRAPPIST-1 system is recovered: we find a RV semi-amplitude of $K_b=3.65^{+0.78}_{-0.83}$ m s$^{-1}$ corresponding to a planetary mass of $M_{p,\,b}=1.31\pm0.29$ M$_\oplus$, demonstrating that the RV measurements are consistent with the TTV model ($M_{p,\,b;\,\text{TTV}}=1.374\pm0.069$ M$_\oplus$). Additionally, the NIRPS RVs constrain the presence of giant planets beyond the snow line, excluding Saturn-mass planets out to 2.7-yr orbits and Neptune-mass objects out to 20 d. Through RV, we determined the stellar activity period to be of $3.22^{+0.22}_{-0.20}$ d. Its agreement with photometric measurements (K2 and TESS) confirms stellar rotation as the origin of the $\sim3.3$-d periodicity observed for TRAPPIST-1. We further investigated stellar activity with SPIRou polarimetric measurements, placing an upper limit on the longitudinal field ($|B_l|<40$ G, $3\sigma$). This limit is compatible with a weak multipolar large-scale magnetic geometry, as observed in some of the later-type rapidly rotating M dwarfs.
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All authors Alexandrine L'Heureux, René Doyon, Charles Cadieux, Pascal Petit, Olivia Lim, Étienne Artigau, Neil J. Cook, Eric Agol, Xavier Bonfils, Julien Morin, Stefano Bellotti, Claire Moutou, Leslie Moranta, Jean-François Donati, Luc Arnold, Xavier Delfosse, Guillaume Hébrard, Romain Allart, François Bouchy, Lucile Mignon, Izan de Castro Leão, Dany Mounzer, Khaled Al Moulla, Frédérique Baron, Björn Benneke, Mathis Bouffard, Casey Brinkman, Bruno L. Canto Martins, Andres Carmona, Ryan Cloutier, Marion Cointepas, Nicolas B. Cowan, Eduardo Cristo, Roseane de Lima Gomes, Jose Renan De Medeiros, Xavier Dumusque, Dasaev O. Fontinele, Thierry Forveille, Yolanda G. C. Frensch, Jonathan Gagné, Jonay I. González Hernández, Nicole Gromek, Melissa J. Hobson, Vigneshwaran Krishnamurthy, Pierrot Lamontagne, Lison Malo, Eder Martioli, Yuri S. Messias, Louise D. Nielsen, Ares Osborn, Léna Parc, Caroline Piaulet-Ghorayeb, Nuno C. Santos, Bennett Neil Skinner, Avidaan Srivastava, Atanas K. Stefanov, Alejandro Suárez Mascareño, Gregg Wade, Joost P. Wardenier, Drew Weisserman

Earth and Planetary Astrophysics

POSEIDON III: The Aligned Orbit of the Hot Neptune Around the Hot Star WASP-195

Juan I. Espinoza-Retamal, Joshua N. Winn, Rafael Brahm et al. (+33 more)

Stellar obliquities provide important clues as to the formation and migration histories of planetary systems, but measurements remain scarce for Neptune-mass planets, especially those orbiting hot stars (above the Kraft break). Here we present observations of the Rossiter-McLaughlin effect in the hot-star/hot-Neptune system WASP-195 ($T_{\rm eff}=6470\pm100$ K, $v\sin{i_\star}=10.5\pm1.1$ km s$^{-1}$) obtained with the Keck Planet Finder and NEID spectrographs. A joint analysis of these observations, archival photometry, and archival radial velocities yields a sky-projected stellar obliquity of $\lambda=-10\pm7^\circ$, consistent with spin-orbit alignment. This makes WASP-195 one of the few hot-star/hot-Neptune systems with a measured obliquity. Archival radial velocities from SOPHIE exclude Jupiter-mass planets within approximately 3 au at $5\sigma$ confidence. The aligned and nearly circular orbit is naturally consistent with a history of disk-driven migration, although coplanar high-eccentricity migration or Roche-lobe overflow cannot be ruled out. We also investigate why so few Neptunes around hot stars have measured obliquities. Their scarcity likely reflects a combination of the lower intrinsic occurrence of short-period Neptunes around hot stars and the difficulty of confirming planet candidates in this regime, where rapid stellar rotation broadens spectral lines and hampers conventional radial-velocity confirmation. Rapid rotation also increases the detectability of the Rossiter-McLaughlin effect, a feature that could help to widen the planet confirmation bottleneck while expanding the obliquity census of small planets around hot stars.
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All authors Juan I. Espinoza-Retamal, Joshua N. Winn, Rafael Brahm, Luke B. Handley, Elise Koo, Caleb Lammers, Cristobal Petrovich, Gu{\dh}mundur Stefánsson, Andrés Jordán, Xian-Yu Wang, Songhu Wang, Nicholas Saunders, Erik A. Petigura, Lauren M. Weiss, Ashley D. Baker, Theron W. Carmichael, Fei Dai, Jerry Edelstein, Jack Foley, Benjamin J. Fulton, Steven Giacalone, Steven R. Gibson, Samuel Halverson, Andrew W. Howard, Howard Isaacson, Emma McIntyre, Pranav H. Premnath, Maleah Rhem, Kodi Rider, Ryan A. Rubenzahl, Arpita Roy, Christopher Smith, Judah Van Zandt, Josh Walawender, Elina Y. Zhang, Jingyi Zhang

Earth and Planetary Astrophysics

The Ultraviolet Spectrograph on ESA's Jupiter Icy Moons Explorer Mission (JUICE-UVS)

Kurt D. Retherford, Philippa M. Molyneux, Thomas K. Greathouse et al. (+51 more)

The Jupiter Icy Moons Explorer (JUICE) mission, led by ESA, has an Ultraviolet Spectrograph (JUICE-UVS) contributed by NASA and built at Southwest Research Institute. JUICE-UVS is designed to provide a diversity of measurements to further our understanding of the potential habitability of icy ocean worlds at Jupiter and to study Jupiter and the Jovian system as an archetype for gas giants. JUICE-UVS observes photons in the 50-204 nm wavelength range at moderate spectral and spatial resolution along a 7.5 deg slit composed of 7.3 deg x 0.1 deg and 0.2 deg x 0.2 deg contiguous sections. JUICE-UVS performs a comprehensive study of icy satellite atmospheres, plumes, surfaces, and local space environments; Jupiter's atmosphere and aurora; Io and its Io Plasma Torus; and other Jupiter system targets (rings, small moons, etc.) as available. The variety of observational techniques employed include: nadir push-broom imaging, disk scans, limb stares, stellar and solar occultations, Jupiter transit observations, and neutral cloud/plasma torus stares and scans. This paper describes the UVS investigation's science plans, instrument details, concept of operations, and data formats in the context of the JUICE mission's habitability and Jupiter system goals.
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All authors Kurt D. Retherford, Philippa M. Molyneux, Thomas K. Greathouse, Michael W. Davis, G. Randall Gladstone, Steven C. Persyn, Maarten H. Versteeg, Mary F. Araujo, Fran Bagenal, Tracy M. Becker, Arnaud Beth, Ronald K. Black, Bertrand Bonfond, Shawn M. Brooks, Emma J. Bunce, Alain Carapelle, Steven Cortinas, Gregory J. Dirks, Bryan Esquivel, Paul D. Feldman, Sue Ferrell, Mark Ferris, Leigh N. Fletcher, Matthew A. Freeman, Marina Galand, Rohini S. Giles, Denis Grodent, Vincent Hue, Erica Johnson, Joshua A. Kammer, Cynthia Kempe, Laurent Lamy, Adrian Martin, Melissa A. McGrath, Edward G. Nerney, Carlos Nuñez, Zachary Olsen, Norman Pelletier, Brandon Perez, Kristian B. Persson, Eric Quémerais, Rick Raffanti, Ujjwal Raut, Ryan Rickerson, Lorenz Roth, Oswald H. W. Siegmund, John R. Spencer, Andrew J. Steffl, Bradley J. Trantham, John V. Vallerga, Todd J. Veach, Michael A. Velez, Brandon C. Walther, the JUICE-UVS Team

Earth and Planetary Astrophysics

Revisiting orbital recurrence in the dimmings of Boyajian's star (KIC~8462852)

Hector Socas-Navarro

KIC~8462852 (Boyajian's star) shows deep, asymmetric, and highly irregular dimming events with no simple repetition pattern. A symmetric 1.1% transit detected by TESS in 2019 has been interpreted as a possible giant planet or brown dwarf, while the irregular dips are generally attributed to transiting dust from exocomets or planetesimal fragments. We test whether the broader dip families may nevertheless recur orbitally. Our scenario assumes a major disruption that produced fragments with slightly different periods, causing successive returns to spread progressively in orbital phase. We compare this recurrent model with a null hypothesis of chronologically independent family centers, accounting for the observing window, and marginalize over the recurrence period $P$ and dispersion scale $\sigma_P$. We obtain $B_{10}=44.9$ in favor of recurrence, corresponding to “very strong” evidence on the Jeffreys scale. The maximum-likelihood solution is $P_{\rm ML}=781.6$~d and $\sigma_{P,\rm ML}=80.0$~d, close to the 776.1-d timescale obtained if D800 and the 2019 TESS event are separated by four revolutions. Independently of the timing fit, this period predicts a transit duration of about 20.5~h for the published stellar and transit parameters, in close agreement with the observed $\sim21$~h. The result is conditional on the adopted topology, priors, family definition, and observing selection function, and does not prove orbital recurrence. Nevertheless, the family timings strongly favor this specific recurrent-fragment model over independent occurrence, making progressive orbital phase dispersion a viable and physically motivated interpretation.
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Earth and Planetary Astrophysics

The Hill sphere transits of Beta Pictoris c and the search for another 1981-like event

V.E.C. Bakker, M.A. Kenworthy, R. Stuik et al. (+17 more)

Beta Pictoris is a young and nearby planetary system hosting an edge-on debris disk and at least three gas-giant planets. Their circumplanetary environments could host exomoons and rings, a detection of which would be highly informative for moon and planet formation theories. A photometric fluctuation of about 4% was seen towards Beta Pictoris in 1981, indicating the transit of dust in the system, which could be associated with the Hill spheres of the two inner planets. We search for the origin of the 1981 event by searching for an analogous event in multi-epoch photometry from 2017 to 2023, and look for signs of circumplanetary material in transits of the Hill sphere of Beta Pictoris c. Observations from the BRITE satellite, and the bRing and ASTEP observatories are fitted to a model of the 1981 event to search for a similar event, and also search for a signal consistent with a circumplanetary disk transit using a simple flat disk model. No compelling evidence for a 1981 event during a Hill sphere primary transit is found, although we do find a candidate event around 2019 July 26. Due to the uncertainty in the time of closest projected separation of Beta Pictoris c, a search for a disk during the primary transit of 2018 could not be robustly determined, but bRing photometry for the second primary transit places an upper limit on the dust content of the Hill sphere of ~ $10^{22}$ grams of material. With no compelling detection of an event similar to that seen in 1981 during the transits of Beta Pictoris c in the photometric time series, we rule out the hypothesis that this event was related to the Hill spheres of Beta Pictoris c and Beta Pictoris b. Future observations of the next Hill sphere transit in 2028 can be realised with both ground-based observatories and with PLATO, whose first long duration science pointing will include Beta Pictoris.
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All authors V.E.C. Bakker, M.A. Kenworthy, R. Stuik, K. Zwintz, T. Guillot, S. Vach, J. Wang, J. Kammerer, W. Balmer, S. Lacour, S. Zieba, E.E. Mamajek, G.-D. Marleau, R.B. Kuhn, P. Kalas, Y. De Pra, E.J.W. de Mooij, N. Crouzet, M. Buttu, J.I. Bailey III

Earth and Planetary Astrophysics

Galactic tides in the Solar System within a non-axisymmetric Milky Way model adjusted to Gaia data

Alexandre Bougakov, Yassin Rany Khalil, Marc Fouchard et al. (+4 more)

Context. Galactic tides are external differential forces acting on extended systems immersed in the Galactic potential. They play a key role in the dynamics of comets in the Oort cloud. Aims. We aim to establish the strength of Galactic tides from the non-axisymmetric potential of the Milky Way revealed by the Gaia mission, and how this strength evolves along the Galactic trajectory of the Solar System. Methods. We derived expressions for Galactic tide parameters independently of any simplified trajectory for a star in the Galaxy or any specific symmetry of the Galactic potential. We obtained six parameters, $G_1$ to $G_6$, that quantify the influence of tides. Using the most up-to-date Galactic potential model, extended here to three dimensions, we studied the time evolution of these parameters along the Sun's trajectory using a statistical approach. Results. Even for Galactic trajectories featuring modest radial and vertical excursions, as investigated here, the dominant Galactic parameter, $G_3$, is found to vary by an order of magnitude along the solar trajectory. $G_1$ and $G_2$ reach up to about one half and one quarter, respectively, of $G_3$ along the solar trajectory, whilst parameters $G_4$ to $G_6$ reach up to one tenth of $G_3$. Conclusions. Contrary to what is often assumed, all Galactic tide parameters vary widely along the Galactic trajectory of the Solar System. Two consequences can be expected: First, $G_3$ directly affects the flux of observable long-period comets and the extent of the fossilised Sednoids region; second, $G_1$ and $G_2$, and to a lesser extent, $G_4$ to $G_6$, break the integrability of the dynamics, potentially affecting the long-term structure of the Oort cloud. Additionally, the new parameters $G_4$ to $G_6$, while small for the Solar System, may strongly impact extrasolar systems with a large out-of-the-plane excursion in the Galaxy.
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All authors Alexandre Bougakov, Yassin Rany Khalil, Marc Fouchard, Melaine Saillenfest, Benoit Famaey, Paola Di Matteo, Misha Haywood

Earth and Planetary Astrophysics

Drift-dominated dust evolution. A multiwavelength analysis of dust rings in CY Tau and DoAr25

Anastasia Topalidou, Nienke van der Marel, Paola Pinilla et al. (+3 more)

Context. Protoplanetary disks are the birthplaces of planets, and understanding the distribution and evolution of dust within them is essential for tracing the early stages of planet formation. Aims. Following the DSHARP survey, we aim to constrain the radial distribution of the dust surface density and the maximum emitting grain size in the disks of CY Tau and DoAr 25 and assess the relative importance of dust trapping and radial drift in shaping the dust population in disks. Methods. We present multiwavelength continuum observations of CY Tau and DoAr 25 from ALMA at 2.4 and 1.25 mm and archival VLA data at 8.8 mm. Combining the observations with dust continuum forward modeling, we sought to infer a radial profile of the two systems of the dust surface density and maximum emitting grain size. Results. For DoAr 25, the results reveal a prominent dust ring at 111 AU and evidence for large (centimeter-sized) grains extending to the outer disk. In contrast, CY Tau exhibits a more compact and smoother structure, with both the dust surface density and grain size decreasing monotonically with radius. A tentative shoulder feature in the radial profiles, located between 20-40 AU, may point to a marginal substructure, possibly a weak dust trap. Conclusions. DoAr 25 shows evidence for a dust trap capable of halting inward drift, while CY Tau exhibits behavior consistent with evolution dominated by radial drift. Together, these results highlight how dust evolution processes shape the disk morphology and grain-size distributions, even in the low-mass stellar regime.
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All authors Anastasia Topalidou, Nienke van der Marel, Paola Pinilla, Haochang Jiang, Osmar M. Guerra-Alvarado, Brodie J. Norfolk

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

3.5-meter Segmented-Mirror Robotic Space Telescope Mission White Paper III. Key Scientific Mission: Exoplanet Science with a Coronagraph

Juhan Kim, Sang Hyun Lee, Yong-Woo Kang et al. (+22 more)

This volume defines the exoplanet science program enabled by the dedicated high-contrast coronagraph in the baseline science payload of the 3.5-meter Segmented-Mirror Robotic Space Telescope. The observatory architecture incorporates the optical interfaces, wavefront sensing and control, pointing stability, and operations software required for coronagraphic observations from the outset. The observing strategy gives priority to the nearest stellar systems because they provide the most accessible laboratories for planetary exploration and the most likely destinations of future interstellar missions. The diffraction limit sets a reflected-light horizon of roughly 10–15 pc for planets at 1 AU and roughly 50–80 pc for Jupiter analogs. Within those horizons, the telescope can image nearby giant planets, obtain reflected-light spectra of their atmospheres, survey young systems and circumstellar disks, and support the habitability and biosignature programs that larger future missions will pursue. The wide-field imager complements the coronagraph through transit photometry, occurrence-rate statistics, and long-term monitoring of stellar magnetic activity. A systematic census of the nearest stellar neighbors provides a lasting reference for exoplanet science and future space exploration.
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All authors Juhan Kim, Sang Hyun Lee, Yong-Woo Kang, Jeong-Yeol Han, Sungwook E. Hong, Bongkon Moon, Donguk Song, Juhyung Kang, Myeong-Gu Park, Sang Chul Kim, Chung-Uk Lee, Sangmo Tony Sohn, Arman Shafieloo, David Parkinson, Hong Soo Park, Dohyeong Kim, Chan Park, Jungjoo Sohn, Young-Beom Jeon, Jong-Hak Woo, Hyung Mok Lee, Hong Bae Ann, Myungkook James Jee, Mansoo Choi, Changbom Park

Earth and Planetary Astrophysics

Photometric characterization of near-Earth asteroids: rotation, taxonomy, and candidate evidence for internal cohesion

A. Carbognani, A. Buzzoni, M. Barbetta et al. (+1 more)

We present the results of a survey of previously uncharacterized near-Earth asteroids (NEAs) conducted between the second half of 2024 and the first months of 2026 using broadband $BVR_{c} I_{c}$ photometry and time-resolved lightcurve observations. Color indices were obtained for 14 NEAs of the 15 observed, with a dimension range between 0.11 and 2.5 km, and used to derive taxonomic classifications through comparison of a sample of reference reflectance curves. The sample appears to be dominated by S-, X-, and C-complex and V-type asteroids; absolute magnitudes and effective diameters were estimated using taxonomically appropriate albedos. Rotation periods were determined or constrained for several targets. Some large objects appear to rotate faster than the classical cohesionless spin barrier at $P\simeq 2.2$~h, although in some cases the period determinations remain tentative due to limited temporal coverage. A cohesive rubble-pile model provides a plausible explanation for the observed rapid rotation within the uncertainties of the derived physical parameters, and modest cohesive strengths of order $10^{2}$–$10^{4}$~Pa are sufficient to account for the observed rotation rates.
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All authors A. Carbognani, A. Buzzoni, M. Barbetta, R. Gualandi

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

Multiplicity of Cool Stars and their Evolution

Matthew I. Swayne, Leen Decin, Theo Khouri et al. (+12 more)

Making up a sizeable portion of the galactic census, stellar multiples are experiencing a renaissance. Enabling the study of multiple strands of the study of cool stars, stellar multiples have been found and characterised in great numbers by the missions of the last decade, allowing the exploration of stellar parameters and populations, observation of stellar interactions, studies into stellar formation and evolution, and characterisation of circumbinary systems. This exciting explosion of science is only set to continue, with future missions set to offer even further insights into the topic. Within these proceedings we will summarise the presentations and discussions on cool stellar multiplicity within our splinter sessions at the 23rd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, as we examine the present state of the field and look to what the future may bring.
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All authors Matthew I. Swayne, Leen Decin, Theo Khouri, Ayush Moharana, Léa Planquart, John Southworth, Nikki J. Miller, José A. Caballero, Orsolo De Marco, Krzysztof G. Hełminiak, Swetlana Hubrig, Valentin D. Ivanov, Pierre Kervella, Thibault Merle, Dorota M. Skowron

Earth and Planetary Astrophysics

The NC-CC dichotomy in ruthenium isotopes: Implications for the origin of the late veneer

Jonas Pape, Emily A. Worsham and Thorsten Kleine

High-precision mass-independent Ru isotope data for iron meteorites reveal that in three-isotope diagrams including the p-process Ru nuclides 96Ru or 98Ru, non-carbonaceous (NC) meteorites plot along an s-process mixing line, while the carbonaceous (CC) type irons plot as a cluster off the NC-line. As previously observed for Mo, this offset can be accounted for by an r-process excess in CC over NC materials. As a highly siderophile element, Ru in the bulk silicate Earth (BSE) is thought to predominantly derive from the late veneer, making the Ru isotope dichotomy a powerful genetic tracer of Earth's late accretionary epoch. The BSE and the isotopically anomalous Itsaq Gneiss Complex as defined in prior studies plot on the NC-line defined in this study, suggesting a predominantly NC late veneer that may have evolved over time from more s-process-enriched to more s-process-depleted compositions. However, more precise 96Ru and 98Ru measurements of the BSE's composition are needed to more reliably determine the genetic heritage of the late veneer and to quantify as to whether it contains CC material.
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Earth and Planetary Astrophysics

Double Gravity-Assist Rendezvous Trajectory to Halley's Comet Using Deep-Space Low Thrust

Roberto Flores, Alessandro Beolchi, Chiara Pozzi et al. (+4 more)

The perihelion of comet 1P/Halley in 2061 is an excellent chance to revisit this object of outstanding scientific and cultural relevance. During its 1986 approach to the Sun, it was targeted by several flyby missions. Due to its retrograde, highly-inclined orbit, the relative velocities during the encounter were large, limiting the scientific return due to the short time spent inside the coma. A rendezvous trajectory would overcome this limitation, but the design is challenging due to the limitations of current propulsion technology. Given the lead times of spacecraft development and the long duration of the interplanetary transfer to the comet, it is imperative to start mission planning as soon as possible. We present a novel rendezvous strategy, combining unpowered Jupiter and Saturn gravity-assists with deep-space low-thrust arcs. It minimizes launch energy and propellant budget, constraining the arrival to occur before the onset of high activity. The double flyby strategy reduces the otherwise prohibitive cost of the plane change maneuver. Closed expressions for the optimal flyby geometry, together with an explicit low-thrust transcription technique, reduce the number of design parameter to three, improving computational efficiency. Crucially, this is the first rendezvous mission concept achievable with well-proven technology (standard radioisotope thermoelectric generators and a Hall-effect thruster) and compatible with several existing launchers. We describe the trajectory optimization strategy and perform a comprehensive exploration of the design space. Finally, we present two promising proof-of-concept trajectories in detail.
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All authors Roberto Flores, Alessandro Beolchi, Chiara Pozzi, Mauro Pontani, Ivano Bertini, Cesare Barbieri, Elena Fantino

Tuesday 1 September

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

Mass-dependent multiplicity fraction in low mass stars revealed by Gaia astrometry

Ben Pennell, Hans-Walter Rix, Kareem El-Badry et al. (+3 more)

Stellar multiplicity at different orbital periods is probed by different techniques: radial velocities at the shortest periods, direct imaging at the longest, and astrometry in between. Gaia DR3 provides unprecedented astrometric information to constrain binary populations with periods of tens to thousands of days. Beyond the small fraction of direct orbit solutions, Gaia publishes coarser astrometric diagnostics for all objects, such as on-sky accelerations, jerks, or the single-star goodness-of-fit measure, RUWE. We show that these diagnostics together are sensitive to a far wider range of orbital periods than orbit solutions alone. Built on the Gaiamock emulator, we develop a forward-modelling framework to constrain rates of multiplicity from Gaia data, using all astrometric solution types. We apply this framework to $366~027$ primaries of $0.2$–$0.75\,M_\odot$ between $50$ and $200$ pc, including vastly more M-dwarfs than previous multiplicity studies. For fiducial models of the period and mass-ratio distributions, the inferred multiplicity fraction is approximately constant at ${\sim}45\%$ from the solar-type regime down to $0.4\,M_\odot$, only then dropping to ${\sim}15\%$ by $0.2\,M_\odot$. This mass-multiplicity relationship revises the conventional picture of a monotonically rising mass–multiplicity relation, and aligns the upper M-dwarf regime with solar-type stars rather than placing it on a continuous decline.
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All authors Ben Pennell, Hans-Walter Rix, Kareem El-Badry, Sahar Shahaf, Johanna Müller-Horn, Jiadong Li

Earth and Planetary Astrophysics

Precise Stellar Age Constraints and Habitable Zone Evolution in Exoplanet Systems

Grace Henry, Ted von Hippel and Anna Childs

Accurate stellar ages are fundamental to interpreting the evolutionary histories of habitable zone (HZ) planets. Because stellar luminosity evolves over time, HZ boundaries migrate outward, meaning that present-day HZ planets may have experienced different irradiation environments earlier in their evolution. Accurate ages are therefore required to estimate HZ residence times and place planetary habitability in an evolutionary context. We use the Bayesian Analysis of Stellar Evolution with nine parameters (BASE-9) code to constrain ages and masses for exoplanet host stars with planets located in the HZ. Our sample includes single stars with effective temperatures of 4475-7200 K that host planets within their calculated HZ boundaries. We fit isochrones to broadband photometry from Gaia DR3, Pan-STARRS, and 2MASS jointly with Gaia parallaxes, spectroscopic metallicities, and extinction estimates, and assess the resulting age posterior distributions. Using these age constraints, we track HZ migration along stellar evolutionary sequences to estimate continuous HZ residence times, allowing us to identify ideal targets for followup high resolution characterization. Because isochrones separate most strongly near and beyond the main-sequence turnoff, our analysis emphasizes evolved and turnoff hosts, where BASE-9 produces the tightest constraints. We quantify age precision across the sample, yielding highly precise ages for subgiants and evolved main-sequence or turnoff stars, and less precise but measurable ages for lower main-sequence hosts. The final catalog provides our age constraints for 149 HZ planets around 146 host stars and supports evolutionary interpretations of planetary histories.
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Earth and Planetary Astrophysics

IFU Observations of Comet 3I/ATLAS = C/2025 N1 (ATLAS) using the Hobby-Eberly Telescope with the VIRUS Instrument

Anita Cochran, Gregory Zeimann, Emmanuel Jehin et al. (+2 more)

We observed interstellar object 3I/ATLAS = C/2025 N1 (ATLAS) on 9 December 2025 UT with the VIRUS spectrograph on the Hobby-Eberly Telescope. VIRUS is a low spectral resolving power, multi-IFU, optical spectrograph. We used a single IFU for the observations and were able to obtain spectra spaced every one arcsec (1327 km) from the optocenter out to about 85,000 km in the sunward direction. The spectra include molecular features normally seen in the optical for spectra of Solar System comets, with the addition of many very strong lines of FeI and NiI. We modeled these observations using the Haser (1957) model framework and find that the data can only be fit if we assume that the outflow velocity of the gas is half that of comets in our Solar System observed at the same heliocentric distance. We derived Haser model scale lengths for three NiI and four FeI lines. We discuss the implication of the similarities and differences between this object and normal Solar System comets. The excellent spatial resolution of VIRUS, coupled with a FOV of 50X50 arcsecs and a geocentric distance of 1.83 au, allowed us to probe the coma of 3I in great detail.
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All authors Anita Cochran, Gregory Zeimann, Emmanuel Jehin, Hideyo Kawakita, Adam McKay

Earth and Planetary Astrophysics

From orbit to ground: pre-impact meteorite strewn field predictions for imminent impactors and meteorite recovery

Anna Moscati, Marco Fenucci, Laura Faggioli et al. (+3 more)

The flux of meteoroids reaching the Earth is continuous, ranging from microscopic grains to occasional metre and decametre scale bodies. The smallest ones fully ablate in the upper atmosphere, whereas sufficiently large or strong objects survive entry and deposit fragments on the ground as meteorites. Predicting where these fragments land, and reconstructing the atmospheric trajectory and fragmentation sequence that produced them, is central both to hazard assessment and to the recovery of freshly fallen material. The accuracy of such predictions, however, remains limited by poorly constrained fragmentation processes and by sparse, heterogeneous observational coverage of individual events. Traditional strewn field simulations rely on detailed fireball data and event-specific assumptions on fragment masses, aerodynamics, and breakup. These approaches are effective for well-instrumented events, but their applicability degrades rapidly when observations are sparse, often resulting in huge uncertainties. We present an ab initio framework predicting strewn fields of near-Earth asteroids directly from pre-impact orbital solutions. It propagates luminous trajectory and dark flight using a physics-based translational dynamics model and realistic atmospheric conditions, without requiring fireball triangulation or event-specific tuning. Validation against recent asteroid falls with recovered meteorites shows agreement with observations, with nominal solutions reproducing fall locations within 100-200 m. The new method has been integrated into the ESA Aegis pipeline, which now enables hours-ahead computation of impact locations, supporting recovery efforts, minimizing contamination, and, where warranted by object size and predicted ground hazard, civil-protection decision making.
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All authors Anna Moscati, Marco Fenucci, Laura Faggioli, Marco Micheli, Francisco Ocaña, Juan Luis Cano

Earth and Planetary Astrophysics

Mass constraints for the K2-223 system planets: An ultra-short-period sub-Earth, a short-period super-Earth, and a tentative long-period giant planet

Dawid Jankowski, Grzegorz Nowak, Gaia Lacedelli et al. (+23 more)

We present mass constraints of two short-period Earth-sized planets transiting K2-223 based on high-precision radial velocity measurements from HARPS-N and ESPRESSO, as well as a tentative indication of an outer Jupiter-like planet orbiting the G1V dwarf K2-223. With a radius of $R_\mathrm{b}=0.79\pm0.10$ $\mathrm{R_{\oplus}}$ and a 3$\sigma$ upper mass limit $M_\mathrm{b}<2.8$ $\mathrm{M_{\oplus}}$, K2-223 b belongs to the small group of known sub-Earth planets and is currently the smallest known ultra-short-period planet ($P_\mathrm{b}\approx$ 0.5 day) transiting a solar-type star. With a radius of $R_\mathrm{c}=1.41\pm0.15$ $\mathrm{R_{\oplus}}$, a mass of $M_\mathrm{c}=4.2\pm1.3$ $\mathrm{M_{\oplus}}$, and a density of $\rho_\mathrm{c}=8.3\pm3.7$ $\mathrm{g\,cm^{-3}}$, K2-223 c is a short-period ($P_\mathrm{c}\approx$ 4.5 days) super-Earth. Based on almost 6.5 years of radial velocity monitoring of K2-223 with the HARPS-N spectrograph, we identified a tentative giant planet with an orbital period of $P_\mathrm{d}=4.53^{+0.32}_{-0.34}$ $\mathrm{years}$ and a minimum mass of $1.29^{+0.23}_{-0.17}$ $\mathrm{M_{\rm Jup}}$. Two close-in small planets accompanied by a distant candidate Jupiter-like companion would make K2-223 a system with a rare architecture. This is valuable for testing scenarios of planetary formation and evolution. The extreme proximity of K2-223 b to the parent star means that relativistic and tidal perturbations to Newtonian gravity need to be considered. We discuss the timescales and amplitudes of these effects in the context of the radial velocity model and dynamical simulations of the K2-223 multiple-planet system. We also present a parametrisation of the planets with directly measured masses, radii, and bulk densities in terms of the orbital period normalised by the Roche period. This provides an alternative representation in the context of the Neptune desert.
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All authors Dawid Jankowski, Grzegorz Nowak, Gaia Lacedelli, Enric Pallé, Krzysztof Goździewski, Thomas Masseron, Ilaria Carleo, Rafael Luque, Felipe Murgas, Davide Gandolfi, Artie P. Hatzes, William Cochran, Pedro Figueira, Rafael A. García, Samuel Geraldía-González, Judith Korth, Pierrot Lamontagne, John H. Livingston, Savita Mathur, Giuseppe Morello, Jaume Orell-Miquel, Dinil B. Palakkatharappil, Carina M. Persson, Seth Redfield, Atanas K. Stefanov, Vincent Van Eylen

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

Amortized Opacity Marginalization Improves C/O Interval Calibration for Brown-Dwarf Retrievals

Kellen Heraty

Molecular line lists disagree at a level that measurably shifts retrieved C/O, so retrievals conditioned on a single list omit a dominant systematic from their error bars. Classical marginalization re-runs a full retrieval under K opacity realizations per object. We move that cost into simulation: while generating the training set we randomize opacities (smooth multiplicative Fourier fields in $\log\nu$ plus a discrete line-list mixture, under a deliberately broad prior informed by measured inter-list differences), so a neural posterior estimator learns an already-marginalized posterior. Conceptually, this is the amortized analogue of repeating a conventional retrieval under many plausible opacity realizations and averaging the resulting posteriors. On perturbed held-out spectra (n=2048) a standard NPE covers nominal 90% C/O intervals 43.3% of the time against 82.4% for a compute-matched marginalized network; three-seed control ensembles reach 93.2% on clean data but 61.4% under perturbation, against 89.4% marginalized, isolating the deficit as opacity-induced (TARP joint expected-coverage deviation 0.005 against 0.035 for a single control network). An axis ablation traces the gain to the continuous field (45.4% for the discrete swaps alone, 79.3% for the field alone). Applying the 105 real bad-pixel masks with median filling then collapsed the ensemble's C/O coverage from 0.901 to 0.479; retraining on the same mask distribution and pooling three such seeds returns a nominal 0.905 C/O and 0.891 overall under the full deployment path, still in simulation (n=1024, same 105 masks), at 0.21 to 0.31 of the prior width. On 105 JWST/G395H spectral products of 13 late-T/Y dwarfs, single marginalized networks bracket the Hood et al. (2024) T8 benchmark C/O where the control excludes it, a consistency check rather than a validation, at 1.6-2.6x wider intervals.
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Earth and Planetary Astrophysics

Constraining the Planetary Obliquity Distribution of Warm Jupiters

Caleb Lammers and Joshua N. Winn

Warm Jupiters are an intriguing class of planets with uncertain origins. Their planetary obliquities could help distinguish between different formation pathways: planet-planet scattering and migration across resonances can excite large obliquities, whereas in-situ formation would more naturally produce low obliquities. We searched for oblateness-related anomalies in the transit light curves of six observationally favorable warm Jupiters: TOI-201b, TOI-1670c, TOI-199b, Kepler-9c, Kepler-30c, and Kepler-553c. Each planet's light curve is consistent with a spherical planet and provides degenerate constraints on the planet's sky-projected oblateness and obliquity. To overcome these limitations, we performed hierarchical Bayesian modeling of the population-level obliquity distribution. Assuming warm Jupiters are as oblate as Saturn ($f \approx 0.1$), we find their median obliquity to be below $12^\circ$ with $90$% confidence and below Saturn's obliquity ($27^\circ$) with $93$% confidence. Jupiter-like oblateness ($f \approx 0.06$) and larger obliquities are allowed. Simulations of JWST observations predict that significantly tighter constraints can be derived.
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Earth and Planetary Astrophysics · Cross-listed from math.DS

Families of relative periodic orbits in the planar three-body problem via consecutive alignments

Joan Gimeno, Marc Jorba-Cuscó and Begoña Nicolás

Relative periodic orbits (RPOs) are solutions of the three-body problem that are periodic in a uniformly rotating reference frame and, in general, quasi-periodic in inertial coordinates. We present a numerical procedure for computing and continuing one-parameter families of RPOs of the planar Newtonian three-body problem. The method exploits consecutive syzygies, understood here as configurations in which the three bodies are aligned and their velocities satisfy the corresponding symmetry conditions. Matching the positions and momenta at two consecutive alignments reduces the computation of RPOs to a low-dimensional nonlinear problem. Its solutions are then numerically continued, and linear stability is determined from the nontrivial eigenvalues of the rotated monodromy matrix after removing the neutral directions associated with conserved quantities and continuous symmetries. The procedure is applied to several mass distributions and initial configurations, producing families of Poincaré, Hill, and binary-type solutions. These families exhibit transitions from nearly circular to highly eccentric motion, changes of stability near resonances and turning points, and absolute periodic solutions when the rotation angle is a rational multiple of 2{\pi}. In the Hill families, the continuation connects satellite configurations with circumstellar motion as the smallest body loses its gravitational binding to the intermediate body. Circumbinary and circumstellar configurations are also obtained in the binary regime. The results illustrate the dynamical diversity of RPOs and provide coherent three-body motions that can be used as prescribed trajectories in restricted four-body models.
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Earth and Planetary Astrophysics

Beyond Five Scale Heights: Composition- and Cloud-dependent Ariel Tier-2 Requirements for sub-Neptunes

Vigneshwaran Krishnamurthy, Nicolas B. Cowan, Misato Fukagawa et al. (+1 more)

The Ariel Mission Candidate Sample (MCS) Tier-2 requirements provide a common screening reference by assuming a clear H$_2$/He atmosphere and a five-scale-height transmission signal. We quantify how those requirements change for 197 known planets with $1.5\leq R_{\rm p}/R_\oplus<4.0$ when composition and clouds are specified explicitly. Equilibrium-chemistry transmission spectra at $1\times$, $10\times$, and $100\times$ solar metallicity are evaluated for clear atmospheres and idealized 1-mbar cloud decks, binned to the 47 AIRS Tier-2 channels, and combined with target-specific MCS-calibrated noise curves. For each atmosphere, we calculate the number of transits required for a featureless spectrum to be rejected at a $3\sigma$ confidence in at least 90% of repeated observations. The clear $1\times$-solar atmosphere closely follows the MCS prediction. At $10\times$ solar metallicity, stronger molecular opacity generally improves detectability, whereas at $100\times$ solar metallicity the increased mean molecular weight dominates and roughly doubles the required number of transits. Cloudy atmospheres follow the same non-monotonic trend but at substantially greater cost: the $1\times$-solar, 1-mbar case requires nearly an order of magnitude more transits than the MCS prediction, while the enriched cloudy cases still require several times more. Overall, in most atmospheric scenarios tested, small planets require more transits to robustly detect spectral features than listed in the MCS. A literature crossmatch further identifies Ariel targets with detected metastable helium, for which Tier-2 molecular spectra could connect lower-atmosphere composition and clouds to an extended, escaping H$_2$/He upper atmosphere.
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All authors Vigneshwaran Krishnamurthy, Nicolas B. Cowan, Misato Fukagawa, Teruyuki Hirano

Earth and Planetary Astrophysics

Transiting Planetary Systems with Distant Giant Companions Remain Moderately Coplanar

Guang-Yao Xiao, Huan-Yu Teng, Xiumin Huang et al. (+4 more)

The mutual inclination between inner planets and distant giant companions provides an important probe of planetary system formation and dynamical evolution, yet direct measurements of this quantity remain scarce. We combine radial velocity (RV) observations with Hipparcos–Gaia astrometry to constrain the orbital architecture of 19 planetary systems hosting at least one transiting inner planet and one outer giant companion. Using a hierarchical Bayesian framework, we infer the population-level distribution of the minimum mutual inclination, $\Delta I$, between the inner and outer planetary orbits. We find that the $\Delta I$ distribution is well described by a Rayleigh model with a scale parameter of $\sigma = 15.8^{+2.8}_{-2.6}\deg$, which is strongly preferred over an isotropic distribution ($\Delta\log Z=5.45$). This result suggests that transiting systems hosting distant giant companions remain substantially more coplanar than expected for an isotropic population, consistent with the partial preservation of primordial coplanarity. A division by the mass ($0.3\,M_{\rm Jup}$) of the inner transiting planet suggests that giant-inner-planet systems may have lower $\Delta I$ than small-inner-planet systems, with $P(\sigma_{\rm giant}<\sigma_{\rm small})=0.952$; however, the current data do not significantly favor a model allowing different $\sigma$ values for the two subsamples over one in which they share a common $\sigma$. Future Gaia DR4 astrometry will enable more robust population-level studies of the three-dimensional architectures of systems with distant giant companions.
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All authors Guang-Yao Xiao, Huan-Yu Teng, Xiumin Huang, Fabo Feng, Dong Lai, Fei Dai, Yu-Juan Liu

Earth and Planetary Astrophysics

Optical Colors as Compressed Spectral Information for Trans-Neptunian Objects

Hsing-Wen Lin, Larissa Markwardt, Kevin Napier et al. (+3 more)

Broadband optical colors have long been recognized as tracers of the surface spectral properties of trans-Neptunian objects (TNOs), yet their relationship to near-infrared (NIR) spectra has not been quantitatively characterized. We construct an empirical optical-NIR spectral manifold from JWST spectroscopy of 40 TNOs and 8 Neptune Trojans and interpret broadband photometry as compressed representations of this manifold. Using the spectral manifold as a prior, the model conditions on observed broadband optical colors to infer a posterior distribution in the spectral latent space. We then evaluate filter combinations through posterior entropy and Kullback-Leibler information gain and found that the gr colors provide broad localization on the manifold, while additional filters substantially reduce posterior uncertainty. Independently defined optical color populations map coherently onto the major compositional classes of the spectral manifold, providing a physical interpretation of previously identified color groups. The learned manifold also enables the inverse mapping back to optical color space. Sampling and decoding the manifold reproduces the observed topology of optical color space, indicating that these color populations arise naturally as low-dimensional projections of a continuous optical-NIR compositional manifold rather than isolated empirical clusters. The forward and inverse mappings provide a unified interpretation of optical colors as compressed representations of an optical-NIR spectral manifold. As JWST expands the manifold and Rubin maps millions of objects onto it, this framework provides an innovated approach to population-scale compositional studies and the discovery of rare surface types.
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All authors Hsing-Wen Lin, Larissa Markwardt, Kevin Napier, Fred Adams, Renu Malhotra, David Gerdes

Earth and Planetary Astrophysics

Current water trapping micro-habitats on the surface of Mars

Anna Bognar, Bernadett D. Pal and Akos Kereszturi

This paper presents a conceptual model exploring how liquid water could be maintained in direct contact with hypothetical microorganisms during warm daytime periods on Mars. Hygroscopic surface salts (e.g., NaCl, CaCl$_2$, Ca(ClO$_4$)$_2$, gypsum, MgSO$_4$) can absorb water vapor and form liquid solutions; however, daytime exposure normally causes rapid drying. We propose a mechanism where diurnal temperature fluctuations drive thermal expansion and contraction cycles that open and close micro-cracks in salt crystals. Nighttime-condensed deliquescent liquid penetrates these fractures, which then partially close during warmer daytime hours, trapping liquid water inside and preventing immediate evaporation. Thermally induced volume changes (ranging from ~0.5-0.9% in crystalline phases up to several percent in concentrated solutions) support the feasibility of this cyclic aperture dynamic. Modeling deliquescence and salt distribution indicates that nighttime microscopic liquid can form for ~100-130 sols per Martian year near Acidalia Planitia. At depths of 2-3 mm within soil or salt structures, hypothetical microorganisms would gain partial UV shielding while retaining access to visible light. Overall, internal crystal micro-fractures may offer transient daytime liquid microenvironments, highlighting these locations as potential candidate habitats for photosynthetic life on modern Mars.This study serves as a conceptual feasibility analysis for near-surface brine retention within hygroscopic salt structures under present-day Martian conditions.
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Earth and Planetary Astrophysics

Exoplanets in star clusters

T. Broza and E. Paunzen

The field of exoplanetary research is rapidly evolving, thanks to TESS and Kepler/K2. With the latest data release, Gaia DR3, Gaia has transformed the study of star clusters. By combining the known properties of exoplanets and those of star clusters, in which they are found, it is possible to study the planets in greater detail and test theories of planetary evolution. We aim to create a catalogue of Gaia IDs for known exoplanets and use it to link the planets to a catalogue of star clusters. We utilised the NASA Exoplanet Archive and the Extrasolar Planets Encyclopaedia to compile a catalogue of known exoplanets. We then cross-matched the data with Gaia DR3 sources to obtain the Gaia IDs of the exoplanets. Using this information, we inferred the potential association of these exoplanets with star clusters. We described the statistical properties of these exoplanets. We compiled a catalogue of Gaia IDs for known exoplanets and identified those associated with star clusters. This resource facilitates detailed studies of exoplanet properties and their evolutionary contexts within stellar clusters.
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Earth and Planetary Astrophysics

Doubling Sunlight for a Human Mars Base With Orbiting Solar Reflectors

Ari Essunfeld, Yuji Takubo, Adrian Dumitrescu et al. (+4 more)

The Sun's faintness at Mars' orbit makes producing energy, melting ice, and staying warm more difficult. Orbiting solar reflectors (OSRs) can augment sunlight at Mars, but the area of OSRs needed to double sunlight at a Mars base is not known. Here, we analyze Sun-synchronous Mars orbits to find the OSR area that doubles insolation to a Mars base. We show that the reflectors can deliver sunlight and maintain a stable orbit via attitude control and solar-sail propulsion, with no propellant. We also show that these Mars orbits can be reached via solar sailing from low Earth orbit, reducing delivery cost. Doubling sunlight is viable with an orbiting solar reflector areal density of $20 {\rm g/m^2}$, a 7-fold improvement over flight-proven solar sails. However, designing a spacecraft with low areal density, agile maneuverability (for accurate pointing), high tension in the sail membrane (to smooth wrinkles), and mass-manufacturability (to enable a constellation of reflectors) would be challenging. Still lower areal density of $<5 {\rm g/m^2}$ would be needed for more ambitious applications, such as sublimating the CO$_2$ ice at Mars' south pole to aid in terraforming.
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All authors Ari Essunfeld, Yuji Takubo, Adrian Dumitrescu, Alexandre Kling, Fabrizio Pisani, Casey Handmer, Edwin S. Kite

Monday 31 August

Earth and Planetary Astrophysics

An Upper Limit on Turbulent Viscosity in the Circumjovian Nebula

Konstantin Batygin and Fred C. Adams

Circumplanetary disks are open, dynamic systems sustained by a meridional circulation that draws gas and dust from the parent nebula along nearly polar streamlines, and ultimately returns some of this material through a viscously driven, in-plane outflow. In such a disk, the water ice line acts as a site of solid-mass accumulation: inward-drifting icy solids sublimate interior to the ice line, the resulting vapor is advected outward by the gas, and recondensation beyond the ice line resets the material to a small Stokes number. The operation of this drift-mediated loop requires the fragmentation-limited Stokes number of the mass-dominant icy aggregates to exceed the equilibrium Stokes number at which the radial drift of solids reverses. Because the former scales inversely with the Shakura-Sunyaev viscosity parameter $\alpha$ while the latter is directly proportional to it, this requirement yields a compact upper bound on the vigor of turbulence in the satellite-forming region. Adopting an actively heated, steady-state circumjovian disk truncated at the tidal radius, we find a marginal bound of $\alpha\lesssim 10^{-3}$ for an icy-particle fragmentation threshold of $v_f\simeq1\,{\rm m\,s^{-1}}$ - appropriate for cold ice with sticking properties similar to silicate dust. This bound scales linearly with $v_f$, reaching $\alpha\lesssim5\times10^{-3}$ for more adhesive, warm ice ($v_f\simeq5\,{\rm m\,s^{-1}}$). The bound carries no explicit dependence on the disk's mass flux, and is set entirely by the local thermal state, pressure gradient, and geometry of the circumjovian nebula.
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Earth and Planetary Astrophysics

Accelerating Chemical Kinetics for Exoplanet Atmospheres using Neural Networks

Isaac Malsky, Xi Zhang, Tiffany Kataria et al. (+5 more)

Observations increasingly reveal the coupled radiative, chemical, and dynamical processes that shape exoplanet atmospheres. Interpreting these atmospheres requires models that can capture this complexity. However, multidimensional models remain fundamentally limited by computational cost, and answering key questions requires simulating the governing physical mechanisms at speeds classical methods cannot achieve. As a result, models often rely on simplifying approximations, such as equilibrium chemistry, even when those assumptions miss important effects. There is a pressing need for fast and accurate chemical kinetics solvers to model planetary atmospheres. Here we present a machine learning local-box chemical kinetics solver for exoplanet atmospheres using a residual flow-map architecture. We demonstrate that this surrogate model is several orders of magnitude faster than a classical solver, achieving microsecond-scale inference while retaining percent-level accuracy. The surrogate model covers a parameter space that spans $T=300$-$3000$ K, $P=10^{-6}$-$10^{4}$ bar, $\Delta t=10^{-3}$-$10^{8}$ s, and compositions ranging from $10^{-2}$ to $10^{3}$ times solar in both C/O ratio and metallicity. Our model outperforms several commonly used machine learning architectures and performs robustly under the extreme stiffness characteristic of atmospheric chemistry. The machine learning framework presented here is a flexible and efficient approach to emulating state-to-state flow-map problems that commonly arise in numerical simulations.
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All authors Isaac Malsky, Xi Zhang, Tiffany Kataria, Matthew Graham, Ziyu Huang, Boris Bonev, Shang-Min Tsai, Elspeth K.H. Lee