Sazuna/UAT_keywords huggingface dataset:
Photometry of Lunar Swirls in Comparison to Fresh Crater Ejecta. Swirls are sinuous high-reflectance lunar surface features collocated with crustal magnetic anomalies. These bright features and their geographical relationship to magnetic anomalies have been studied for decades, although their cause remains unclear. Several mechanisms for swirl formation have been proposed, including altered space weathering due to solar wind shielding, scouring of the surface by cometary impacts, and sorting of regolith materials. We use an empirical phase curve analysis and Hapke radiative transfer modeling of single-scattering albedo, bidirectional reflectance, and the angular width of the shadow hiding opposition effect to investigate regolith and crater ejecta properties at three prominent swirl sites: Reiner Gamma, Firsov, and Mare Ingenii. We assess the photometric differences between swirls, nearby background regolith, and fresh impact crater ejecta, and discuss implications for swirl formation. Our results suggest that both swirl and background regolith are consistently less backscattering than fresh crater ejecta, although swirl regolith and crater ejecta within swirls maintain higher single-scattering albedo values than the corresponding background materials. Physical processing via micrometeoroid impacts may explain the similar backscattering characteristics of swirl and background regolith, while additional space weathering of background regolith by solar wind causes differences in single-scattering albedo. In contrast, fresh crater ejecta is more backscattering than both swirl and background regolith, likely due to the impact process that exposes blocky material and alters the nearby surface. As a result, an anomalous space weathering environment caused by solar wind shielding remains a compelling hypothesis for the high-reflectance nature of lunar swirls.

Keywords: Lunar regolith, The Moon, Photometry, Albedo, Craters
Methods for Experimental Planetary Geology in Reduced-gravity Parabolic Flight: A Case Study of Researching Impact Crater Ejecta. Geologists have long conducted laboratory experiments to offer a controlled environment for understanding processes that occur in nature and linking those processes with natural geologic landforms. And, for over 70 yr, pilots and researchers have accessed reduced-gravity and microgravity conditions by flying aircraft in parabolic arc-shaped trajectories. However, only recently (technically since the 1980s but practically since the 2010s) has experimental geology begun to find a home in reduced-gravity flight with application to the solid-bodied worlds of the solar system. The methodology of our recent experimental campaign investigating impact crater ejecta emplacement serves as a case study in reduced-gravity experimental geology. We hope this case study will inspire future utilization of reduced-gravity flight as a laboratory method for better understanding geological processes on worlds throughout the solar system.

Keywords: Ejecta, Lunar craters, Experimental data, Mars, Experimental techniques, Planetary geology, Craters, Asteroid surfaces
A Pre-flyby View on the Origin of Asteroid Donaldjohanson, a Target of the NASA Lucy Mission. The NASA Lucy mission is scheduled to fly by the main-belt asteroid (52246) Donaldjohanson on 2025 April 20. Donaldjohanson (DJ hereafter) is a member of the primitive (C-type class) Erigone collisional asteroid family located in the inner main belt in proximity of the source regions of asteroids (101955) Bennu and (162173) Ryugu, visited respectively by the OSIRIS-REx and Hayabusa2 missions. In this paper we provide an updated model for the Erigone family age and discuss DJ evolution resulting from nongravitational forces (namely Yarkovsky and Yarkovsky–O'Keefe–Radzievski–Paddack (YORP)), as well as its collisional evolution. We conclude that the best-fit family age is 155 Myr and that, on such timescales, both Yarkovsky and YORP effects may have affected the orbit and spin properties of DJ. Furthermore, we discuss how the NASA Lucy mission could provide independent insights on such processes, namely by constraining DJ shape, surface geology, and cratering history.

Keywords: Main belt asteroids
Thermophysical Model of (269) Justitia—Main Belt Asteroid Possibly Implanted from Trans-Neptunian Region. Asteroid Justitia is a special main-belt object, being an extremely red body with a steeper spectral slope than any other D-type asteroid. Conversely, its spectral and polarimetric properties resemble organics-rich Centaurs and trans-Neptunian objects. For this reason, it was chosen as a main target of the MBR Explorer space mission. It is crucial for space mission planning and operations to have in advance the best estimate of the target size, spin, shape, and properties of the surface. In particular, the size determination was in high demand before the extensive stellar occultation campaign in 2023 August, for station deployment and observation planning. We utilized multiple lightcurves from our campaign on slow rotators and from the literature to reconstruct the spin and shape of Justitia via lightcurve inversion. Then we applied the Convex Inversion Thermophysical Model to simultaneously optimize the fit to visible lightcurves and to thermal data from infrared space observatories. We present here the pair of most precise physical models of Justitia possible before the occultation campaign, with similar properties of both solutions. The size range of Justitia was narrowed here to 55–60 km, so by a factor of 4 compared with previous estimates, and also the shape model's resolution was improved. An estimate of thermal inertia and surface roughness was also obtained, with implications for surface texture and regolith properties.

Keywords: Asteroid rotation, Asteroids, Asteroid surfaces
Occultation-based Size and Shape of (269) Justitia. We present results from an occultation of a star by the asteroid (269) Justitia on 2023 August 31 UT using a deployment of 34 stations. Of the deployed stations, 29 were successful in collecting useful data and 19 recorded a positive occultation event. All stations were regularly spaced 2.45 km apart in the cross-track direction to cover ±3σ of the ephemeris uncertainty with a planning diameter of 59 km. We find that the shape of Justitia is irregular, with large-scale facets and a circular-equivalent radius in the range of 28.5–28.9 km. The inferred albedo is pV = 0.072 ± 0.007 using a rotation-corrected absolute magnitude of HV = 9.72. Astrometry from the occultation is provided.

Keywords: Astrometry, Main belt asteroids, Albedo, Asteroid occultation
Radiance Contrasts at Possible Lunar Water Ice Exposures Seen by ShadowCam. Surface water ice within lunar permanently shadowed regions (PSRs) could have an enhanced visible wavelength reflectance relative to lunar regolith. Moon Mineralogy Mapper (M3) infrared spectroscopic detections compose one data set previously interpreted as surface ice occurrences within the PSRs. Here we investigate the M3 water ice identifications at higher resolution with broadband visible-wavelength mosaicked images (60 m pixel scale) obtained by the ShadowCam instrument aboard the Korea Aerospace Research Institute Korea Lunar Pathfinder Orbiter. Individual M3 positive water ice detections show no radiance contrast with their surroundings. However, north polar PSRs with at least one M3 water ice detection have a ∼4.4× higher modal radiance than those lacking M3 water ice detections, although this cannot be definitively attributed to water ice. Our findings are consistent with previous estimates of ice abundance as being less than ∼30 wt%, resulting in contrast too small to be detected by the ShadowCam instrument.

Keywords: The Moon, Surface ices, Planetary polar regions
Transport and Mixing in Planetary Polar Vortices with Annular and Monopolar Potential Vorticity Structures. Polar vortices are a common feature in the solar system, but their structure varies between planets. Although polar vortices are characterized by a coherent region of high potential vorticity (PV) in the polar regions, the meridional variation of PV ranges from strong monopolar to annular distributions. The reduced stability of an annular vortex compared to a monopolar vortex may lead to increased horizontal transport between the midlatitudes and the poles, but this has yet to be thoroughly investigated. Here we perform such an investigation by quantifying the horizontal mixing in polar vortices of varying PV structure, for both a two-dimensional shallow-water model and a three-dimensional general circulation model (GCM). Good agreement is found between the models, with both models indicating that both vortices maintain a horizontal mixing barrier that isolates the polar regions from the extratropics. The primary difference between the two vortex structures is on the interior of the vortex edge, where there is increased mixing inside the annular vortex but a clear reduction of mixing inside the monopolar vortex. In the three-dimensional GCM, a "subvortex" region is identified below the annular polar vortex that allows for more transport of material into the polar regions than the subvortex of the monopolar vortex. This suggests a potential pathway for transport into annular vortices that does not occur for monopolar vortices. Although we start from a Mars-like atmosphere for simplicity and flexibility, our results should describe other terrestrial planets/moons with broad polar vortices with coherent regions of high PV.

Keywords: Atmospheric circulation, Mars, Titan, Polar jets, Atmospheric dynamics, Atmospheric variability
Glycine Partitioning in Frozen Putative Europan Brines. Europa is considered a leading target in the search for extraterrestrial life because it may host conditions conducive to habitability, including a persistent energy source, access to biologically critical elements, and a vast subsurface ocean of liquid water. This study examines the behavior of glycine, an amino acid, in simulated Europan brines subjected to various freezing conditions to understand its potential distribution and preservation on Europa. Equimolar brines containing 0.1 M of Na+, Cl‑, Mg2+, SO42‑, and glycine (C2H5NO2) were exposed to flash- and slow-freezing conditions to simulate different emplacement processes onto Europa's icy surface environment. Analyses using Raman imaging revealed that glycine preferentially associates with salt phases rather than water ice, where the cooling rate influences both the species of salt that precipitates and their spatial distribution. These findings suggest that salt-rich ice particles could be valuable targets for remote and in situ detection of organic molecules and potential biosignatures in future exploration. Notably, solid CO2 was observed in isolated inclusions within slow-frozen samples, suggesting a glycine-driven mechanism for CO2 entrapment during freezing. Diffuse reflectance infrared measurements of the observed CO2 showed some consistencies but did not produce an identical match of the recent JWST spectra of CO2 on Europa's surface, implying that this mechanism is unlikely to be the pathway for CO2 production on this icy body.

Keywords: Vibrational spectroscopy, Europa, Planetary science, Astrochemistry
Supercooling, Glass Formation, and Mineral Assemblages upon Freezing of Salty Ice Grains from Enceladus's Ocean. The analysis of micrometer-sized ice grains emitted into space by Saturn's moon Enceladus suggests that the moon's subsurface ocean may be habitable. However, the formation conditions of these ice grains are largely unknown. Upon cooling, ocean droplets may supercool and then form a crystalline or glassy state, or a mixture of both. To investigate the processes of supercooling and glass formation in Enceladus's ice grains, we performed differential scanning calorimetry experiments with Enceladus-relevant salt mixtures at cooling rates ranging from 5 K minute‑1 to ∼1227 K minute‑1 and extrapolated our results to faster cooling rates. We modeled the freezing of these solutions and associated mineral assemblages using the thermodynamic chemistry packages PHREEQC and Reaktoro. Our results indicate supercooling of ∼25–30 K upon freezing from Enceladus's saline ocean. Freshly formed ice grains should be predominantly crystalline but contain up to 5% glass. Fast cooling rates and high salt concentrations favor the formation of glasses, potentially enabling the preservation of organics and cells, if present. Salts in the grains crystallize in the following sequence: first phosphate, followed by carbonates, and then chlorides. We find that the recently detected phosphates in Enceladus's ice grains are likely Na2HPO4:12H2O. The pH values appear to vary among individual ice grains, depending on the stage of the freezing process, and these values may slightly differ from the pH of the moon's bulk ocean. Our experiments and models are relevant to other icy worlds with salty water reservoirs in their subsurfaces, such as Jupiter's moon Europa or the dwarf planet Ceres.

Keywords: Space probes, Ice formation, Very small grains, Experimental data, Enceladus, Planetary mineralogy, Europa, Astrobiology, Surface ices, Planetary science, Saturnian satellites
In situ, Surface-deployed Distributed Instruments for Planetary Science: Scientific Opportunities and Technology Feasibility. In this paper, we assess the scientific promise and technology feasibility of in situ distributed instruments for planetary surface and atmospheric science. A distributed instrument is an instrument designed to collect spatially and temporally correlated data from multiple networked, geographically distributed point sensors. Distributed instruments are ubiquitous in Earth science, where they are routinely employed for weather and climate science, seismic studies and resource prospecting, and detection of industrial emissions. However, to date, their adoption in planetary science has been minimal. It is natural to ask whether this lack of adoption is driven by low potential to address high-priority questions in planetary science, immature technology, or both. To address this question, we survey high-priority planetary science questions that are uniquely well suited to distributed, surface-deployed, in situ instruments. We identify four areas of research where such distributed instruments hold promise to unlock answers that are largely inaccessible to monolithic sensors or remote sensing approaches, or can complement existing approaches, namely, in weather and climate studies; localization of seismic events on rocky and icy bodies; localization of trace gas emissions; and magnetometry studies of internal planetary composition. Next, we survey enabling technologies for distributed sensors and assess their maturity. We identify sensor placement (including descent and landing on planetary surfaces), power, and instrument autonomy as three key areas requiring further investment to enable future distributed instruments. Overall, this work shows that distributed instruments hold great promise for planetary science, and paves the way for follow-up studies of future distributed instruments for solar system science.

Keywords: Lunar probes, Lunar seismology, Planetary atmospheres, Planetary probes, Landers, Planetary science, Planetary magnetospheres, Planetary interior, Planetary dynamics
Curtain-based Maps of Eruptive Activity in Enceladus's South-polar Terrain at 15 Cassini Epochs. We map surface eruptive activity in Cassini images of Enceladus's south-polar terrain (SPT) at 15 epochs spanning late 2009 to late 2015 using a refined curtain approach derived from that of J. N. Spitale et al. (S2015). This refined approach gives a better representation of the uncertainties in identifying source fractures by allowing for multiple candidate sources to be identified for an observed eruption. Our analysis includes the five epochs studied by S2015, which were independently reexamined here. The results in this work are intended to supersede those of S2015. About 80% of the currently active fracture system in the SPT (by length) was observed to be erupting at a level detectable in Cassini images during every epoch. On/off variability is observed almost exclusively at the fringes of the fracture system, possibly reflecting a thickening ice shell away from the pole. No definitive connection between surface activity and the roughly factor of 3 plume optical depth variation with mean anomaly is made here, but our results do not rule out a scenario where the pattern of eruptive activity on the surface is correlated with the mean anomaly, provided only the fractures at the fringe of the SPT ever turn completely off during the tidal cycle. Our results are best explained by eruptions sourced directly from the ocean.

Keywords: Enceladus, Saturnian satellites
A Pluto─Charon Sonata. V. Long-term Stability of the HST State Vector. We analyze a new set of ∼275 n-body calculations designed to place limits on the masses of the small circumbinary satellites in the Pluto─Charon system. Together with calculations reported in previous papers, we repeat that a robust upper limit on the total mass of the four satellites is ≍9.5 × 1019 g. For satellite volumes derived from New Horizons, this mass limit implies a robust upper limit on the bulk densities of Nix and Hydra, ≲1.7 g cm−3, that is comparable to the bulk density of Charon. Additional calculations demonstrate that satellite systems with masses ≲8.25 × 1019 g are robustly stable over the current age of the Sun. The bulk densities of Nix and Hydra in these lower-mass systems are clearly smaller than the bulk density of Charon. These new n-body results enable accurate measurements of eccentricity and inclination for Nix, Kerberos, and Hydra that agree well with orbital elements derived from numerical calculations with new Hubble Space Telescope and New Horizons state vectors. With these new state vectors, Styx has a 37% larger eccentricity and an 85% smaller inclination, which makes it more prone to gravitational perturbations from Nix.

Keywords: Natural satellite formation, Plutonian satellites, Dynamical evolution, Pluto
Spectral Effects of Shock Darkening on Ordinary Chondrite and Howardite, Eucrite, and Diogenite Meteorites. Impacts are the most ubiquitous processes on planetary bodies in our solar system. During these impact events, shock waves can deposit enough energy to produce shock-induced darkening in the target material, resulting in an alteration of its spectral properties. This spectral alteration can lead to an ambiguous taxonomic classification of asteroids and an incorrect identification of meteorite analogs. In this study, we investigated the effects of shock darkening on the visible and near-infrared spectra of ordinary chondrites and members of the howardites, eucrites, and diogenites clan. A decrease in albedo and suppression of the absorption bands with increasing shock darkening was observed for all the samples. We found that adding ≳50% of shock-darkened material to an unaltered sample was enough to change the taxonomic classification of an ordinary chondrite from S-complex to C- or X-complex. A similar amount was sufficient to change the taxonomic classification of a eucrite from V type to O type, whereas a eucrite composed of 100% shock-darkened material was classified as a Q type. We discuss the limitations of using just albedo for taxonomic classification of asteroids, which has implications for future space-based infrared surveys. We also investigated if shock darkening is responsible for a bias against the discovery of near-Earth objects (NEOs) with H and L chondrite-like compositions, which could explain the abundance of LL chondrites among NEOs.

Keywords: Meteorites, Asteroids, Spectroscopy
Setting the Stage for Uranian Seismology from Rings and Radial Velocities. A Uranus orbiter would be well positioned to detect the planet's free oscillation modes, whose frequencies can resolve questions about Uranus's weakly constrained interior. We calculate the spectra that may manifest in resonances with ring orbits or in Doppler imaging of Uranus's visible surface, using a wide range of interior models that satisfy the present constraints. Recent work has shown that Uranus's fundamental (f) and internal gravity (g) modes have appropriate frequencies to resonate with Uranus's narrow rings. We show that even a single ℓ = 2 f- or g-mode detected in ring imaging or occultations can constrain Uranus's core extent and density. Fully fluid models typically have ℓ = 2–7 f-mode frequencies slightly too high to resonate among the narrow rings. If Uranus has a solid core that f-modes cannot penetrate, their frequencies are reduced, rendering them more likely to be observed. A single ℓ ≳ 7 f-mode detection would constrain Uranus's unknown rotation period. Meanwhile, the different technique of Doppler-imaging seismology requires specialized instrumentation but could deliver many detections, with best sensitivity to acoustic (p) modes at mHz frequencies. Deviations from uniform frequency spacing can be used to locate density interfaces in Uranus's interior, such as a sharp core boundary. Shallower nonadiabaticity and condensation layers complicate this approach, but higher-order frequency differences can be analyzed to disentangle deep and near-surface effects. The detection of normal modes by a Uranus orbiter would help to discern among the degenerate solutions permitted by conventional measurements of the planet's static gravity field.

Keywords: Ring resonance, Orbiters, Doppler imaging, Planetary rings, Solar system gas giant planets, Orbital resonances, Non-radial pulsations, Planetary interior, Uranus
Probing Lateral Density Variations in the Crust from Gravity and Topography: Applications to the Moon and Mars. We present a constraint matrix to be used in the determination of gravity field models from spacecraft tracking data that uses information from topography and that allows for the direct determination of lateral variations in crustal density. Our approach is based on a matrix formulation of Bouguer corrections using a spherical harmonics expansion for density. This formulation also allows us to directly determine the spherical harmonics coefficients for density in the crust from a set of gravity coefficients. We validate this by comparison with an approach using localization and show that both methods result in comparable density maps. We then apply the constraint matrix on a test case using lunar data from before the Gravity Recovery and Interior Laboratory (GRAIL) mission and compare this with results from GRAIL, showing that we can obtain density results similar to those from GRAIL data. We also apply this constraint to the determination of the gravity field of Mars. While our results for Mars tentatively suggest a hemispherical density contrast separated by the north–south dichotomy, the resolution of Martian gravity is currently too low to robustly determine large-scale density variations.

Keywords: Mars, The Moon
Dielectric and Polarimetric Radar Properties of Suspected Surficial Ice Exposures at the Lunar South Pole. Various active and passive orbital measurements have provided evidence for surficial water ice within some lunar permanently shadowed regions (PSRs), especially from near-infrared observations by the M3 instrument. However, radar identification of lunar ice has so far remained ambiguous. Here, we examine the radar-inferred dielectric properties of lunar PSRs and illuminated craters to investigate the potential for ice. We show that the dielectric permittivity of proposed surficial ice-bearing PSRs is lower and has a different distribution than illuminated crater floors of the same diameter range. This difference is confirmed via polarimetric analysis. However, we find that regions with fewer or greater numbers of M3 detections do not have meaningfully different dielectric properties. The lack of correlation with M3 detections suggests the differences in radar properties are likely due to a smoother surface at the wavelength scale, perhaps as a consequence of the presence of deeper ice, as suggested by prior studies.

Keywords: Lunar surface, Radar observations, Lunar science