ALT We present JWST/MIRI Low Resolution Spectroscopy (LRS) of 3I/ATLAS obtained post-perihelion at a heliocentric distance of 2.21 au. Our spectrum contains a prominent 10 micron silicate emission feature with a broad, smooth shape that is distinct from those commonly observed in Solar System comets. We model the spectrum using thermal emission from amorphous carbon, amorphous olivine, and amorphous pyroxene grains. Our models strongly favor a pyroxene-dominated, amorphous silicate composition and show a degeneracy between silicate grain size and the relative abundance of silicate and carbon dust. Across a set of representative models, the best-fitting crystalline abundance is zero, and we place an upper limit of 5.3% on the crystalline fraction of the silicates. We identify an emission feature near 6.83 microns that is consistent with aliphatic C-H-bearing material. The overwhelmingly amorphous silicate composition supports previous work that measured unusual volatile and isotopic composi

ALT Context. Some debris discs contain cold molecular gas. The origin of this gas is one of the key questions in our understanding of the evolution of planetary systems. The effect of gas on the smallest dust grains, which are expected to be unbound due to radiation pressure, is not well understood. The unbound grains contribute to the brightness of scattered light and thermal emission from the disc halo at short wavelengths. Aims. We explored the conditions under which gas can prevent or slow down the escape of unbound grains and increase their number density in the disc halo sufficiently to affect its brightness and reveal properties of the gas. Methods. We numerically integrated the equations of motion of dust grains released on unbound orbits in optically thin, gaseous debris discs, taking into account stellar gravity, radiation pressure, Poynting-Robertson drag, and gas drag. Results. We find that gas drag can significantly slow down the escape of unbound grains only for very high gas

ALT Venus is home to vivid sulfur chemistry, with SO₂ as the major sulfur gas species and a global cloud layer between 47 and 70 km composed of H₂SO₄ and H₂O. The chemistry in the clouds has been extensively studied with 1D models, but none is able to reproduce the three orders of magnitude decrease of SO₂ inside the clouds. Sulfur allotrope chemistry could be a candidate for buffering sulfur atoms, as it can grow into long chains. Sulfur hydrides such as H₂S is considered as one of the main sulfur-bearing compounds, possibly linked to surface reactions or have a volcanic origin like on Earth. In this study, we use for the first time a 3D model to study the climatology of the sulfur allotrope in gas and condensed phase and hydride chemistry in the clouds with an explicit photolysis calculation and updated UV cross-section. H₂S is close to ppmv levels below the cloud base, the third most abundant sulfur-bearing species in this region after SO₂ and OCS. Below the clouds, S₈ gas phase is the

ALT T. Mazeh and coworkers pioneered a method using rotational photometric modulation as a proxy to infer stellar obliquities in Kepler transiting planetary systems, based on the expected positive correlation between spot-induced modulation amplitudes and stellar inclinations. They found that planet hosts cooler than the Sun showed larger modulation amplitudes than comparison stars, consistent with low stellar obliquities. For hotter hosts, however, they reported the opposite - a negative amplitude difference (hosts minus comparison stars) - which is difficult to interpret in terms of viewing geometry. We show that this comparison is affected by confounding variables not controlled for in the sample selection. One such confounder is apparent magnitude, whose distributions differ markedly between the two samples for hotter stars and affect the observed modulation amplitudes. We develop resampling and likelihood-based approaches that enable comparison of the amplitude distributions at fixed

ALT Rocky planets the size of Earth or larger are expected to undergo one or more giant impacts during the final stages of their formation. Some of these collisions occur after protoplanetary disk dissipation, potentially driving the loss of primordial hydrogen-rich atmospheres through elevated surface temperatures. However, whether giant impacts promote atmospheric loss or retention remains unclear because they both heat planetary interiors and increase atmospheric gravitational binding. Here we model the evolution of rocky planets after their largest post-disk giant impact, accounting self-consistently for the concurrent increase in gravitational binding energy and mantle thermal energy. Whereas the entire accreted mass contributes to the increase in gravitational binding energy, only part of the impact energy raises mantle temperature. Mantle melting consumes energy as latent heat, while the impactor's metallic core transfers little energy to the mantle and remains superheated at depth.

ALT Eclipse mapping is a well-established technique for constraining the spatial emission of hot Jupiter exoplanets. Brown dwarfs in ultra-short orbits around white dwarfs are an analog to hot Jupiters that can only ever be eclipsed within a limited range of latitudes. We adapt the eigenmapping method to disentangle the signals from the ever- and never-occulted regions. The result of this signal separation is a super-position of map structures, yielding sharp boundaries at the occultation region. We introduce a model that penalizes the harmonic complexity of the model map with Tikhonov regularization, whose parameters are tuned to reproduce the fit quality of the eigenmapping model. We use JWST NIRSpec/PRISM full-orbit observations of the eclipsing WD 1202-024 system as a template to construct and run injection-recovery tests on simulated light curves, isolating both latitudinal structures as well as emission from a physically-realistic general circulation model (GCM). In the latter, the n

ALT The small Solar System bodies (SSSBs) preserve records of the formation and evolution of the Solar System. In particular, the near-infrared wavelength region around 3 μm provides crucial insights into the origin and transport of hydrated materials and organics, although it is difficult to observe from the ground because of strong telluric absorption. We assess the observability of SSSBs as complementary science to the ESA Ariel space mission, operating in the visible to mid-infrared wavelength range (0.5–7.8 μm). Using the NASA JPL Horizons ephemeris system, we evaluate the visibility of known SSSBs from 2032 to 2035. Our analysis shows that Ariel can spectroscopically characterize up to 402 unique SSSBs under a conservative limiting visual magnitude of V=13.6. If observations can be extended to somewhat fainter targets (V=16), the number of observable SSSBs could increase to 2144. Assuming operational scenarios in which one SSSB is observed every 3, 7, or 30 days over a four-year miss

ALT Context. The DART impact might have substantially modified the surface and near-surface structure of Dimorphos, affecting the morphology and gravity field that is to be measured by ESA's Hera mission. Aims. We investigate the post-impact redistribution of ejecta and its dependence on the assumed internal structure of Dimorphos. Methods. We performed high-resolution SPH simulations of the DART impact into two low-cohesion rubble-pile models, with and without a large central boulder. We followed the processes of ejecta re-accumulation and gravity evolution for six hours. Results. The impact ejects about 13% of Dimorphos's mass, most of which is re-accreted, producing near-global resurfacing. The ejecta blanket exceeds 8 m around the impact depression but is only a few tens of centimetres thick near the antipode, with similar large-scale deposition in both interior models. Local gravity changes reach about 10% of the pre-impact value. The central boulder affects the surface gravity only w

ALT The diversity of planetary orbital architectures calls for observational constraints on radial variations in disk-plane orientation, or warps, yet such variations in dust disks remain poorly characterized. CQ Tau is a promising target because its misaligned inner disk and candidate gas warp suggest a radially extended warp. We present the ALMA 1.3 mm dust continuum image reconstructed from the real part of the visibilities, extracting the centro-symmetric disk structure. At an effective spatial resolution of 0.052” × 0.042” (7.8 × 6.3 au), the image reveals a bright main ring at radii of ∼20–70 au and an unresolved compact emission component tracing the inner disk around the central star. Ellipse fits centered on the stellar position to contours tracing the inner and outer edges of the ring reveal radial variations in position angles and inclinations. At the inner edge (∼21–26 au), the position angle and inclination span 214°–233° and 23°–39°, respectively, while they span 231°–235° an

ALT The knowledge of Titan's near-surface atmosphere is sparse. The Huygens descent probe measured winds, and the multiple dune field observations and possible dust storms suggest active near-surface dynamics. The Dragonfly rotorcraft lander will fly close to the surface in the Shangri-La region, near the Huygens landing site, where complex dune orientations were observed. This study presents the first mesoscale modelling of the near-surface dynamics in this region. However, due to a lack of high-resolution topography data, synthetic maps of surface properties were built. The surface was divided into different topographical units, such as plains, mountains, etc. The slopes and height of those units were then parametrised. Maps of thermal inertia, albedo and the aerodynamic roughness height were also built. The mesoscale model is coupled to a comprehensive radiative transfer code and forced by a global climate model. No moist processes are considered in this study. Topography has a major im

ALT In the outer regions of protoplanetary disks, dust grains are often mantled with a layer of ice containing simple molecules. The irradiation of the disk by far-ultraviolet (FUV) photons breaks such molecules, producing photoproducts (radicals, ions, and intermediary molecules) in the ice layer that can act as precursors to complex organics. As grains drift towards the warmer, inner region of the disk, their consequent sublimation of ices causes organic synthesis on their surfaces, potentially enhancing grain sticking and dust growth. In addition to interstellar medium radiation, FUV emission from the central star and nearby massive stars can contribute to photoproduct formation. We perform a vertical dust size evolution simulation including grain growth and fragmentation, and calculate photoproduct formation under irradiation from these three sources, treating the central star's FUV continuum and Lyman-α emission separately. We find that enhanced UV irradiation, particularly from stell

ALT A recent study reported a transiting giant-planet candidate with a mass of 9.4⁺⁴.⁹₋₄.₁ M_J and a radius of 1.7±0.1 R_J on a wide orbit around Boyajian's star (KIC 8462852, also called Tabby's star), which is well known for its irregular, deep flux dips. The reported radius is puzzling, because cool giant planets of ∼10 MJup are expected to have radii close to Jupiter's, so the companion appears ∼60–70% larger than standard models allow. Here we explore the solution that the planet is actually ringed. We develop a fast and accurate code to compute the transit light curve due to a ringed planet, and apply it to the TESS light curve. The ring model is marginally favoured by the data by Δχ²>10 and a difference in Bayesian information criterion (BIC) of <2. The preferred configuration is a Jupiter-sized (1.1 R_J) planet surrounded by an opaque, highly flattened ring extending to 3.1–4.4 planetary radii with a nearly polar obliquity. While the ring geometry is uncertain, simple estimates sug

ALT We present time-series observations of the long period comet C/2025 K1 (ATLAS) obtained in 2025-2026, bracketing the comet's fragmentation in early November 2025. We show that a simple radiation pressure model can explain many of the comet's properties: the rapid fading after fragmentation, the increasing mean particle size in the projected photometry aperture, and the time dependence of the surface brightness profile. Small dust particles (≲ 100 μm) dominate the coma, with average dust velocity ∼ a few × 1 meter s⁻¹. The nucleus radius is estimated at ∼0.5 km and the dust properties are consistent with, but do not prove, an origin in nucleus rotational breakup, followed by being swept down the tail by radiation pressure.

ALT Comet C/2025 K1 (ATLAS) underwent major fragmentation after its 2025 October 8 perihelion passage at q 0.33 au. We present four epochs of Johnson-Cousins BVR imaging obtained with the Mount Laguna Observatory 40-inch reflector on 2025 November 26, November 29, December 5, and December 8, sampling the subsequent evolution of the integrated fragment-coma complex. The images were homogenized to common circular two-dimensional effective point-spread functions before morphology was measured along the projected fragment axis. We evaluated 324 profile-extraction configurations and removed solutions whose localized peak landed on the search-window boundary. The fragment-axis surface-brightness enhancement relocates inward between November 26 and 29 and outward between December 5 and 8; the sign of both changes is recovered in every valid configuration and at all tested common target PSFs from 5.3 to 6.0 arcsec. Calibrated BVR photometry using Gaia DR3 synthetic Johnson-Kron-Cousins standards i

ALT The regular satellites of Jupiter and Saturn are substantially enriched in ice relative to the rock-rich solids of the outer Solar System. In addition, the satellites interior to Titan and distant Iapetus are icier than Titan itself. Collisional processes and subsequent migration can readily alter compositions deep in the planetary potential well, but producing a distant, ice-rich satellite with Iapetus's radius of about 700 km is a challenge. We show that differential ablation and capture of icy and rocky fragments from differentiated outer Solar System bodies can explain the bulk Jovian and Kronian satellite ice enrichment and supply the substantial ice-rich inventory needed for Iapetus. For 1 m–1 km fragments with the canonical size-distribution index p=3.5 and a source containing 30% ice by mass, the fixed radial distance Saturn calculation deposits material with ice fractions of 0.66 (delivery of vapor-only rock) or 0.50 (with retained rock melt) at 20 Saturn radii and nearly pure

ALT Rocky exoplanets orbiting M dwarf stars are often assumed to be synchronously rotating, such that water-trapping in ice sheets on the permanent nightside may pose a threat to habitability. However, in compact M dwarf systems, gravitational interactions between planets may cause the substellar point to librate or circulate on millennial timescales and sporadically change direction or speed. Here, we use a 3D global climate model to quantify, for the first time, the water-trapping capabilities of these "near"-synchronously rotating exoplanets, with TRAPPIST-1e as our test case. Across a range of synodic day lengths, we find that there is a permanent polar ice reservoir and an increasingly large build-up of lower-latitude transient nightside ice for longer days. A persistent ice-free region develops on the dayside where surface conditions can sustain liquid water. However, this steady-state ice distribution may never be realized since the accumulation timescale may be slower than changes

ALT Close-in gas giant atmospheres are in chemical disequilibrium. Solving 3D kinetics to capture one source of this disequilibrium, transport-induced quenching, is computationally demanding, so simplifications are used. General circulation models (GCMs) relax abundances on the timescale of a single conversion pathway. 1D models place a quench level and hold abundances vertically uniform above it. We test both simplifications on CH4 against aerosol-free, solar-composition GCM simulations with thermochemical kinetics for HAT-P-11b, HD 189733b, HD 209458b and WASP-17b. We find ten CH4-to-CO conversion pathways, varying with depth, longitude and planet. A single pathway controls CH4 quenching on the three cooler planets; on WASP-17b two compete. The CH4 quench level is 3D: where the atmosphere is hotter, or a faster pathway takes over, the conversion timescale shortens, the quench level rises and the quench-level abundance falls. On WASP-17b the pathway switch lifts the quench level over the

ALT Saturn's bulk metallicity and atmospheric volatile enrichments exceed those of Jupiter. Combined with their similar heavy-element masses, this suggests that Saturn formed farther out in a protoplanetary disk whose metallicity increased with heliocentric distance. Numerous models argue that Jupiter formed near the H₂O iceline; Saturn's composition is therefore expected to reflect accretion beyond this region. We test whether Saturn's elemental enrichments can be reproduced by formation near the CO₂ or CO icelines using a one-dimensional viscous α-disk model that tracks the transport, sublimation, and recondensation of 13 volatile carriers. We compute time-dependent radial distributions of solids and vapors for α=5×10⁻⁴–5×10⁻³ and varied CO/CO₂ abundance ratios, and compare the resulting metallicities and enrichments with Saturn's observed composition. Strong carbon and oxygen enrichment peaks result from the cold-finger effect, most prominently at the CO₂ iceline, where supersolar metal

ALT Around luminous A-type stars, retaining micrometer-sized dust grains is difficult owing to the high radiation pressure that repels particles with sizes below the blowout limit. Yet such particles have been evidenced in the terrestrial zone around those stars, via pronounced silicate spectral features. An in situ planetesimal belt that collisionally replenishes the dust is expected to deplete quickly, limiting the lifetime of observable features. However, modeling of such systems often relies on a power-law description of the grain size distribution that has a lower size limit owing to blowout. Using more complex, collisional simulations instead, we investigated the temporal evolution of hypothetical planetesimal belts in the terrestrial zone around five A-type stars showing strong spectral silicate features. A collisional cascade that is modified by radiation pressure results in dust distributions that replicate observed spectral features without requiring other physical processes. Whi

ALT Recent studies have shown the traditional comet brightening model, Hn, with a constant activity index n (i.e., single slope in log₁₀(rₕ)), fails to accurately describe heliocentric lightcurves at large distances, where water-ice sublimation is inefficient. We present a new empirical model, Hab, for distant comet brightening in which the effective brightening slope varies with heliocentric distance, rₕ. Using a multi-year pre-perihelion dataset from uniform instrumentation for 23 comets, we found that Hab provides the best match to long inbound arcs spanning a wide range in rₕ. The best-fit coefficients a and b cluster tightly for our best-observed comets, suggesting a common brightening behavior; we therefore also tested one- and two-parameter Hab variants in which a and/or b are fixed to anchor values derived from these comets (A₁ = 0.40 ± 0.09, B₁ = -1.78 ± 0.68), either individually, jointly, or via a linear relation. The three-parameter Hab model is strongly favored by the Bayesian