Sazuna/UAT_keywords huggingface dataset:
Formation of Water-rich Giant Planet Satellites at Decretion Disk Ice Lines. The volatile budgets of giant planet satellites are critical to unraveling the origin of their building blocks within the circumplanetary disks that hosted them. The Galilean moons Ganymede and Callisto, as well as the Saturnian moon Titan, are known to be anomalously water rich on the basis of their mean densities and interior models informed by gravity data from Galileo and Cassini, characterized by ice-to-rock ratios around unity. Here, we show that the water-ice sublimation line in a decreting circumplanetary disk lends itself to the formation of a water-rich solid reservoir, serving as a natural site for the birthplace of icy satellites. Fundamentally, this reflects how interior to the ice line, water vapor is advected outward, while beyond it, water ice drifts inward as pebbles. Using a semianalytic model for dust and vapor evolution, we simulate vapor and ice accumulation at the ice line, showing that solids just beyond it achieve steady-state ice-to-rock ratios a factor of a few higher than elsewhere in the disk. For typical disk parameters, this ice buildup occurs within a timescale of a few thousand years. We propose this as a first-order process that explains, at least to some extent, the compositions of three aforementioned satellites. We explore the impact of uncertain turbulence parameters on our results, namely the turbulent Schmidt number and Shakura─Sunyaev α, before discussing them in the context of icy satellite D/H ratios. We conclude by evaluating alternative scenarios for explaining water-rich satellites, based on the conversion of CO to CH4, with water as a by-product.

Keywords: Ganymede, Callisto, Titan, Galilean satellites, Saturnian satellites
Inferring Exoplanet Parameters from Transit Timing Variations Using LSTM Networks. Transit timing variation (TTV) analysis provides a valuable complement to traditional transit and radial-velocity techniques, particularly in compact, near-resonant planetary systems where dynamical interactions amplify timing signals and refine mass and orbital estimates. Traditional approaches—such as Markov Chain Monte Carlo—are computationally demanding, particularly for high-dimensional orbital configurations. In this study, we present a machine learning framework based on long short-term memory networks to estimate key planetary parameters, including mass, orbital period, and argument of periastron, using TTV signals along with known properties of the transiting planet. The model is trained on synthetic systems generated with TTVFast and employs Monte Carlo dropout to quantify prediction uncertainties. We applied the model on two observed systems: Kepler-277 and Kepler-36. For Kepler-277, the model achieves a mass estimate of 57.25 ± 10.56M⊕, an orbital period of 26.76 ± 2.73 days, and provides a novel constraint on the argument of periastron of 297 .° 29 ± 22 .° 26. For Kepler-36, the model yields a mass estimate of 51.53 ± 14.61M⊕, a period of 10.31 ± 2.666 days, and an argument of periastron of 261 .° 90 ± 16 .° 09. These estimates are obtained under the assumption of near-circular orbits, and in this context, the argument of periastron primarily describes the relative difference in ω between the two planets rather than an absolute orbital orientation. Although the predicted parameters are not highly accurate, the model reliably captures their overall magnitude, providing a useful first-order estimate that can serve as a prior for more detailed dynamical or photodynamical analysis.

Keywords: Exoplanet dynamics, Transit timing variation method, Astronomy data analysis
Surface Properties, Orbital Dynamics, and Thermophysical Modeling of the Primitive Asteroid (269) Justitia. The Emirates Mission to the Asteroid Belt (EMA) will study the ultrared asteroid (269) Justitia. In this work, we present the first detailed investigation of Justitia's surface dynamics using the newly developed 3D polyhedral shape model with 574 vertices and 1144 faces. We analyze its geopotential, surface acceleration, escape speeds, slopes, and equilibrium points, and we also search for planar symmetric periodic orbits using an equivalent ellipsoidal approximation. Our results indicate that the lowest geopotential values occur at the poles, which also correspond to regions of maximum surface acceleration. The global slope distribution suggests preferred zones of material accumulation or migration, offering clues to Justitia's long-term morphological evolution. Most slopes remain below 40∘, implying that loose particles may settle stably across large portions of the surface. We identify five equilibrium points consistent with Justitia's estimated density and slow rotation period. Two external points (E2 and E4) exhibit linear stability, and all equilibrium locations lie relatively far from the surface owing to the body's slow spin. Additionally, we discover 28 new families of planar symmetric periodic orbits and then classify their topologies and determine their linear stability, providing a dynamical framework relevant to future spacecraft operations near Justitia. Finally, thermal modeling reveals how thermal inertia and heliocentric distance shape Justitia's temperature distribution. The south pole receives more insolation than the north pole, reaching minimum temperatures of about 102 and 87 K, respectively. These combined dynamical and thermal results offer valuable insights for the EMA mission and for understanding slowly rotating small bodies.

Keywords: Main belt asteroids, Celestial mechanics, Computational methods, Asteroid dynamics
Thermophysical Modeling of Asteroid (15) Eunomia from Spatially Resolved ALMA and VLA Data. Asteroid (15) Eunomia is the largest S-type asteroid in the main belt and the largest member of the Eunomia asteroid family. Previous visible-to-mid-infrared data suggested that Eunomia's hemispheres have different olivine-to-pyroxene ratios and that ∼2% of asteroids in its family belong to the X-complex, a taxonomic class possibly associated with iron meteorites. This led to the proposal that Eunomia is partially differentiated. In this work, we searched for metallic regions on Eunomia's surface diagnostic of differentiation by analyzing new brightness temperature data collected with the Atacama Large Millimeter/Submillimeter Array (ALMA) at 1.3 mm and the Karl G. Jansky Very Large Array at 1 and 2 cm, which are particularly sensitive to surface metal content. The ALMA data are resolved at 30 km and allow us to characterize spatial variations in surface properties. We derived best-fit disk-averaged thermal inertia Γ = 75─135 J m−2 s−0.5 K−1 and dielectric constant ϵ = 7─8 ( χr2=15.5 ; high  χr2  could be due to insufficient data quality or large-scale topography not captured by the shape model). The thermal inertia derived here from 1.3 mm observations may be different from that derived from mid-infrared observations, as the ALMA observations at 1.3 mm probe deeper into the subsurface than mid-infrared observations, where the regolith properties may be different. We do not find hemispherical-scale variations in the thermal inertia and dielectric constant. This suggests that the metal contents of any distinct olivine-rich and pyroxene-rich regions are not significantly different. Overall, our results do not provide conclusive evidence for the state of differentiation of Eunomia.

Keywords: Radio interferometers, Asteroid surfaces
UV─Vis─NIR Reflectance Spectra of Ilmenite Mixtures: Implications for Estimation of TiO<SUB>2</SUB> Content in Lunar Mare Regions. We performed spectral measurements on mixtures of ilmenite powder (&lt;48 μm) and clinopyroxene or gabbro powder (&lt;155 μm) to investigate the effect of ilmenite content on the spectral characteristics in the ultraviolet (UV), visible (Vis), and near-infrared (NIR) ranges. We found that increasing ilmenite content leads to (1) a darkening of Vis and NIR reflectance, (2) a decrease of the UV slope, (3) a weakening of band depths around 950─1050 nm and 1250─1300 nm, and (4) a neutralization of the Vis─NIR slope. For lunar mare regions, which have ∼7wt% ilmenite, it was estimated that the albedo in the Vis─NIR reflectance would decrease by 25%─29%, the Vis─NIR slope would decrease by 9%─26%, and the UV slope would decrease by 4%─5%. We also examined the effect of the addition of clinopyroxenes and gabbro on the spectral characteristics of ilmenite. The results indicate that most diagnostic features of ilmenite were masked, except for a distinct peak near 900 nm, which can thus serve as a reliable indicator of the presence of ilmenite in mixed compositions. Furthermore, we evaluated existing methods for estimating TiO2 content in lunar mare regions using spectral band ratios. The results indicate that ratios that incorporate UV reflectance are more sensitive to ilmenite content than those that incorporate reflectance only at Vis and/or NIR wavelengths longer than 415 nm. This suggests that UV reflectance is more reliable for the estimation of ilmenite abundance on the lunar surface.

Keywords: Infrared spectroscopy, Lunar maria, Planetary mineralogy, Ultraviolet spectroscopy, Lunar mineralogy, Spectroscopy
The Flux of Large Impacts on the Moon Enhanced near the Beginning of the Copernican Period. The size─frequency distribution (SFD) of lunar impactors was believed to be time independent for the last 3.5 billion years (Gyr). Here, I use linear and nonlinear topographic diffusion models to determine the degradation states (the integral of diffusivity over time) of 13,103 craters on the lunar maria, and find that the degradation rate (the degradation state per unit of crater production density), which should be constant if the impactor SFD is unchanged, varies with crater production density by a factor of 3.0─3.7. This crater density-dependent degradation rate results from the time-dependent SFD shape of lunar impactors, with the flux of large (greater than about 50 m in diameter) impactors increasing about 1.5─1.6 ± 0.1 billion years age (Ga). The enhanced flux potentially results from the formation of large asteroid families near resonances. This work emphasizes the importance of future missions to explore young surfaces to remove the age gap of lunar samples between 53 Ma and 2 Ga.

Keywords: Lunar maria, Near-Earth objects, Lunar craters
Distribution of Buried Volcanic Deposits in the Schiller─Schickard Region of the Moon. Cryptomaria are ancient volcanic units on the Moon that are key to understanding early lunar thermal history but are difficult to study because they have been buried and obscured from direct view by later impact ejecta. The Schiller─Schickard region is one of the most studied locations of cryptomaria because evidence for cryptomare deposits exist in a variety of datasets, but the three-dimensional distribution of deposits at local scales is debated. Here, we study cryptomare distribution within Schiller─Schickard at local scales using image data from the Lunar Reconnaissance Orbiter Camera data and FeO abundance maps from Kaguya and Clementine datasets. We map dark halo craters (DHCs) in this region between 30°─60°S and 290°─320°E that excavate through surface material and reveal darker material with higher FeO abundances in the crater ejecta. These findings show 531 such craters ranging from 0.1 to 22.6 km in diameter, which reveal a highly heterogeneous distribution of cryptomaria throughout the region in basin and nonbasin settings that are buried as shallow as 8 m beneath the surface and may be as deep as 1.8 km. We compare our results to previous studies that used radar, mineralogical, gravity, and topography data to map cryptomaria in Schiller─Schickard, finding that between 3% and 26% of this region's area contains cryptomaria as inferred from the DHC inventory. This comparison reveals new, local sites of potential cryptomaria and shows the most promising locations for a potential landed mission that studies cryptomaria from the ground.

Keywords: Lunar maria, Lunar craters, The Moon, Volcanism
A Comprehensive Spectroscopic Reference of the Solar System and Its Application to Exoplanet Direct Imaging. We present a calibrated database of reflectance spectra for the solar system planets (i.e., Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune) and for Titan, spanning from the ultraviolet to the near infrared. We considered data collected over 60 yr of planetary observations, employing a broad range of geometries and facilities (spacecraft and ground-based observatories). To correct for differences in observational geometries and data quality, we adopted a two-step calibration process that standardized each spectrum to the planet's geometric albedo values and corrected for planetary heterogeneity and calibration effects. The calibrated datasets were then combined across wavelengths, leading to a reference composite reflectance spectrum for each planet. As an application of this spectral library for exoplanetary research, we simulated direct imaging observations of the Proxima Centauri and HD 219134 systems as solar system analogs, as well as the solar system at a distance of 10 pc. We also explored the detection limitations of direct imaging instruments imposed by the inner and outer working angles for Earth- and Jupiter-like exoplanets as a function of system distance. Additionally, we used the visible light portion of the results to produce realistic color reconstructions of each planet. Standardizing reflectance spectra in this work improves our baseline for interpreting new reflected light observations of exoplanets through comparative planetology. This spectral library (available on Zenodo at doi:10.5281/zenodo.17470004) can then serve as a calibrated and validated reference in the modeling and preparation for the characterization of exoplanet atmospheres with future direct imaging missions and for astronomical studies of the solar system.

Keywords: Planetary surfaces, Exoplanets, Planetary atmospheres, Coronagraphic imaging, Spectroscopy
Origin of Hyperion and Saturn's Rings in a Two-stage Saturnian System Instability. The age of the rings and some of the moons of Saturn is an open question, and multiple lines of evidence point to a recent (few hundred Myr ago) cataclysm involving the disruption of past moons. The main driver of the evolution of the Saturnian system is the relatively rapid tidal expansion of its largest moon, Titan, which is likely driven by resonant tides within Saturn. The obliquity of Saturn and the orbit of the small moon Hyperion both serve as a record of the past orbital evolution of Titan. Saturn's obliquity was likely generated by a secular spin─orbit resonance with the planets, while Hyperion is caught in a mean-motion resonance with Titan, with both phenomena driven by Titan's orbital expansion. We propose that the breaking of Saturn's spin resonance was also the event in which Hyperion formed, when an outer mid-sized satellite ("Proto-Hyperion") was destabilized and collided with Titan, with some of the debris accreting into Hyperion. During the instability, Proto-Hyperion's perturbations produced the observed orbital inclination of Iapetus. The same event also excited the eccentricity of Titan, which then, through Titan's resonant interaction with the inner moons, led to destabilization, collisional disruption, and re-accretion of the inner moon system, including the rings. We present numerical integrations that show that this chain of events has a relatively high probability, and discuss how it fits within our knowledge of the Saturnian system.

Keywords: Celestial mechanics, Saturnian satellites, Orbital resonances, N-body simulations
Impact-driven Deposition of Metallic Titanium on the Moon. Impact-induced high temperatures are a key driver of titanium (Ti) redistribution in Ti-bearing phases, which is crucial for understanding element cycling on the Moon. However, direct mineralogical evidence for the redistribution pathways of Ti during extreme impact processes is still lacking. In this study, we report the first discovery of metallic Ti grains preserved in Chang'e-6 lunar regolith. These grains are characterized by their microscale size, droplet morphology, native Ti composition, and polycrystalline structure. The presence of Np─Fe0-bearing silicate glass inclusions within the metallic Ti indicates a lunar surface origin rather than terrestrial contamination. Our results reveal that the coexistence of metallic Ti and Np─Fe0 grains formed via the impact-induced vaporization of ilmenite (FeTiO3), followed by Ti and Fe vapor deposition on the Moon. The discovery of lunar metallic Ti documents a novel impact-driven vapor-deposition process on the Moon. This finding also suggests that impact heating on the Moon and other airless planetary bodies is a viable mechanism for generating high-purity metallic Ti resources.

Keywords: Lunar impacts, The Moon, Impact gardening
Haze, Methane, and Carbon Monoxide in Titan's North Polar Atmosphere from a Cassini/VIMS Specular Transmission Spectrum on the T104 Flyby. We analyze a specular reflection of the Sun off of Titan's largest sea, Kraken Mare, observed by the Cassini Visual and Infrared Mapping Spectrometer on the T104 flyby (2014 August 21). We use the specularly reflected I/F signal to derive a transmission spectrum. Owing to the low incidence and emission angles (51°) of the reflection, the specular signal is visible down to the 1.3 and 1.6 μm windows, as well as the 2.0, 2.7/2.8, and 5 μm windows as had been seen previously on T85. We confirm the T85 result that Titan's atmosphere absorbs more at 2.7 μm than it does at 2.8 μm and that the "notch" between those windows results from absorption in the atmosphere and not from the surface. We compare our derived T104 spectrum to numerically integrated optical depths calculated using Huygens-derived haze properties and correlated-k gas absorption coefficients. We fit the T104 observation using 63% ± 3% greater haze abundance than derived from Huygens and a wavelength exponent of 2.50 ± 0.03, steeper than the 2.0 derived from Huygens. We measure a surface methane fraction of 0.043 ± 0.001 over Kraken Mare at 68°N latitude, slightly lower than the Huygens measurement of 0.0539 ± 0.0014 in Titan's tropics. The comparison shows the utility of specular reflection transmission spectra for quantitative determination of Titan's atmospheric properties. Fitting of carbon monoxide (CO) absorption places a constraint of 22.6 ± 0.3 ppm on the fraction of CO in Titan's atmosphere. Mismatches between our model and these specular transmission observations may allow quantitative estimation of the effects of unknown composition gaseous absorbers throughout Titan's atmosphere.

Keywords: Natural satellite atmospheres, Titan, Transmission spectroscopy
Hydration Features on Near-Earth Objects: Integrating New Data with Prior Results. Near-Earth objects (NEOs) are excellent laboratories for testing processes that affect airless bodies, as well as informing us about solar system history. Though most NEOs are nominally anhydrous because they formed inside the solar system frost line and their surface temperatures are high enough to remove volatiles, a 3 μm feature typically indicative of OH/H2O has been identified on several such bodies. Possible sources for OH/H2O on these bodies include carbonaceous chondrite impactors or interactions with protons implanted by solar wind. The MIT-Hawaii Near-Earth Object Spectroscopic Survey (or MITHNEOS) began its 3 μm observation campaign of NEOs in 2022 and has obtained spectral data of 15 predominantly nominally anhydrous (i.e., mostly S-complex or V-type) targets using NASA's Infrared Telescope Facility's near-infrared spectrometer, SpeX. Spectra were collected using both prism (0.7─2.52 μm) and long-wavelength cross-dispersed short (LXD_short; 1.67─4.2 μm) modes to accurately characterize asteroid spectral type and the 3 μm region. Four of the 15 NEOs observed exhibit a 3 μm feature, exhibiting band shapes similar to those identified in a previous NEO survey, which found a trend between hydration band presence and large aphelion (i.e., Q &gt; 2.06 au). Combining our new observations with the preexisting database of NEO 2─4 μm data revealed that band depth increases with decreasing orbital inclination and that all NEOs with hydration bands have i &lt; 27°, with most having i &lt; 14°. We find that NEOs with low inclinations and large aphelia are the most likely bodies in near-Earth space to possess surficial OH/H2O.

Keywords: Near-Earth objects, Ground-based astronomy, Near infrared astronomy
The Fate of Frozen Carbonated Water at Europa-like Conditions. We present the results of experiments probing the retention of CO2 in crystalline water ice, frozen sodium chloride (NaCl) brines, and flash-frozen carbonated water using diffuse reflectance infrared spectroscopy. Characteristic absorptions alluding to the formation of clathrate hydrates in crystalline ices and frozen brines are observed. NaCl in frozen brines does not qualitatively affect the formation of clathrate hydrates. Generation and stability of clathrates in crystalline ice transiently subjected to pressure─temperature (P─T) conditions in the stability region is observed, despite conditions being unviable at the onset of freezing. Retention of CO2 in flash-frozen carbonated water is observed to be dependent on the temperature of the substrate during freezing. The state of CO2 retained in the resulting ices differs from clathrate hydrates, as inferred from the respective infrared spectra. Both mechanisms of CO2 retention are stable up to 140 K and under evacuated conditions. In the context of Europa, the P─T states traversed by the samples plausibly represent the typical conditions around endogenous CO2, if it is indeed transported from the subsurface ocean to the surface while being retained in ice/frozen brines and/or liquid emerging on the surface. However, the absorptions of CO2 in laboratory infrared spectra do not match those detected on the leading side of Europa by the NIRSpec instrument on board JWST. Therefore, it is unlikely that the endogenous CO2 observed at the surface of Europa is sourced directly from the ocean, unless additional processes affect the observed bands of CO2 on Europa.

Keywords: Ice composition, Infrared spectroscopy, Ice spectroscopy, Europa, Surface ices
Early Observations of New Active Asteroid 2025 VZ<SUB>8</SUB>. We report observations of main-belt asteroid 2025 VZ8 using multiple telescopes from UT 2025 November 24 to UT 2025 December 23 that confirm the presence of visible comet-like activity. These observations were motivated by online reports that an abrupt brightening event may have led to the object's discovery on UT 2025 November 9. In all observations reported here, the object displays a tapered tail approximately 3″ long aligned with the antisolar direction. The object has an asteroidal Tisserand parameter value with respect to Jupiter (TJ = 3.371), and is thus considered an active asteroid. We measure an average apparent  r' -band magnitude of mr ∼ 21.6 mag over the reported observing period. Due to the sudden appearance of activity far from perihelion, we suggest that the activity is more likely due to an impact or rotational destabilization, rather than sublimation.

Keywords: Main belt asteroids, Comets
Infrared Spectroscopy of the Nova V5115 Sagittarii during Its Fe II Phase. V5115 Sagittarii was a very fast nova (t2 = 7 days) from a massive white dwarf (1.2 M⊙). Our 0.8─5.0 μm spectrum from 19 days after discovery shows numerous Fe II lines and weak, just emerging He I emission and falls clearly within the Fe II-type nova classification. At this epoch, the nova had sufficient excitation that N I features were plentiful but Na I emission was absent and only the brightest C I features were detectable.

Keywords: Classical novae