Sazuna/UAT_keywords huggingface dataset:
Constraining the Limitations of NEATM-like Models: A Case Study with Near-Earth Asteroid (285263) 1998 QE2. Near-Earth asteroids (NEAs) are a key test bed for investigations into planet formation, asteroid dynamics, and planetary defense initiatives. These studies rely on understanding NEA sizes, albedo distributions, and regolith properties. Simple thermal models are a commonly used method for determining these properties; however, they have inherent limitations owing to the simplifying assumptions they make about asteroid shapes and properties. With the recent collapse of the Arecibo Telescope and a decrease of direct size measurements, as well as future facilities such as LSST and NEO Surveyor coming online soon, these models will play an increasingly important role in our knowledge of the NEA population. Therefore, it is key to understand the limits of these models. In this work we constrain the limitations of simple thermal models by comparing model results to more complex thermophysical models, radar data, and other existing analyses. Furthermore, we present a method for placing tighter constraints on inferred NEA properties using simple thermal models. These comparisons and constraints are explored using the NEA (285263) 1998 QE2 as a case study. We analyze QE2 with a simple thermal model and data from both the NASA IRTF SpeX instrument and NEOWISE mission. We determine an albedo between 0.05 and 0.10 and thermal inertia between 0 and 425J m-2 s-1/2 K-1. We find that overall the simple thermal model is able to well constrain the properties of QE2; however, we find that model uncertainties can be influenced by topography, viewing geometry, and the wavelength range of data used.

Keywords: Near-Earth objects, Asteroids, Asteroid surfaces
The Water Activity of Mars-relevant Multicomponent Brines: The Changing Influence of Perchlorate on Habitability over Time. Low water activity limits the habitability of aqueous environments, and salts present on Mars are known to reduce water activity. As environmental brines are not pure solutions of a single salt, predicting their water activity is difficult without direct measurement. Martian brines are likely complex and dominated by ions including sulfates and perchlorates, unlike typical terrestrial aqueous environments dominated by sodium chloride. We used the Pitzer model to predict the water activity of multicomponent brines and tested against laboratory-produced brines, including for the first time perchlorate salts that are known to exist on Mars. Our calculations match measurements of single-salt solutions and predict the water activity of multicomponent brines with an accuracy dependent on the quality of thermodynamic data available for a given ion combination. We tested the hypothesis that some salts will dominate the water activity, and therefore habitability, of multicomponent brines. Some salts, such as sodium and magnesium sulfates, did not strongly modulate the water activity of the solution, whereas others such as magnesium chloride and some perchlorates did. Applied to the history of Mars, the data suggest that sulfates and sodium chloride present in Noachian and early Hesperian environments would not have limited habitability. Perchlorates produced photochemically later in the Amazonian could impose a water activity limit at high concentrations that is not significantly changed by other salts. Overall we found that magnesium and calcium chlorides mixed with perchlorates can reach the lowest water activity values and therefore the lowest habitability of the brines tested.

Keywords: Astrobiology, Habitable planets
Crystallization Kinetics of Vitreous Magnesium Sulfate Hydrate and Implications for Europa's Surface. Brines consistent with that expected for Europa's global subsurface ocean have been shown to form vitreous salt hydrates when frozen. We report experiments examining the crystallization kinetics of vitreous MgSO4 hydrate in order to better understand the stability of such materials on the surface of Europa. Vitreous MgSO4 hydrates formed from a 2 M parent solution were found to crystallize into MgSO4·11H2O (meridianiite) upon annealing at 195-225 K. Raman spectroscopy was used to monitor the crystallization and reaction rates were determined from the growth of the crystalline fraction as a function of time. Arrhenius analysis yielded an activation energy of 60 ± 9 kJ mol-1 for the vitreous to crystalline transition, implying that such transformation does not occur spontaneously at Europa's surface temperatures. If emplacement processes favor the formation of vitreous salt hydrates, they are likely to still be stable and could be an important non-ice component on Europa at present day.

Keywords: Chemical kinetics, Ice spectroscopy, Surface ices, Europa
Strongly Depleted Methanol and Hypervolatiles in Comet C/2021 A1 (Leonard): Signatures of Interstellar Chemistry?. We measured the chemical composition of comet C/2021 A1 (Leonard) using the long-slit echelle grating spectrograph iSHELL/IRTF on 2021 December 20 and on 2022 January 8 and 9. We sampled 11 primary volatiles (H2O, HCN, NH3, CO, C2H2, C2H6, CH4, CH3OH, H2CO, OCS, and HCl) and three product species (CN, NH2, and OH) and retrieved their molecular abundances, which can serve as important cosmogonic indicators. The abundance ratios, relative to water, of almost all trace volatiles appear to be depleted relative to reference values, with methanol abundance among the lowest observed in a comet. The observed stronger depletion of CH3OH, relative to CO, CH4, and C2H6, could be evidence of an interstellar medium (ISM) chemistry signature in comet/Leonard ices. Both the detection of HCl and the detection of OCS support the idea of interstellar origin for comet/Leonard ices, since they are preferentially formed via solid-phase interstellar chemistry and are then found depleted in dense molecular clouds and protoplanetary disks, suggesting that their abundances in comets might retain a signature from the ISM era. The comet also revealed a complex outgassing pattern, with volatiles largely shifted toward the sunward direction, relative to the dust profiles that appeared centered on the nucleus-centric position. Here we present emission profiles measured along the Sun-comet line for brightest lines of H2O, HCN, C2H6, and CO, and we show that they follow the release of water in similar fashion, interpreting this as indication of a not strict relationship between polar and apolar ices.

Keywords: High resolution spectroscopy, Long period comets, Infrared spectroscopy, Comae
Reassessment of the Volumes of Sediment Sources and Sinks on Venus. The dominant source of sediment on Venus is thought to be impact cratering, wherein crater ejecta is redistributed across the planet by winds. Here we provide a refined global sediment budget for Venus by mapping and quantifying the volume of sediment from impact craters observable in Magellan data using updated methodology. We improve on previous estimates of the volume of impact-generated sediment by mapping the impact deposits for all craters ≥11 km on Venus. We estimate the planet's total budget of impact sediment to be a minimum of 290,000 km3, which corresponds to a global layer of sediment 63 cm thick. If erosional processes have been active over the average surface age (500 Ma-1 Ga), the transportable fraction of this volume implies a sediment mobilization rate between 0.18 and 0.36 nm yr-1, comparable to the late Hesperian-Amazonian era of Mars. We requantify the volume of sediment held in recognized eolian features by (1) applying morphometric studies of planetary analogs to assess the volumes of observed Venusian dune and yardang fields and (2) estimating the volume of proposed microdune fields. We also identify a new yardang field near Mead crater. Globally, we find that &gt;100,000 km3 of available sediment is not accounted for by eolian deposits, concurring that lithification, resurfacing, and fields of as yet unidentified eolian features are other potential sinks for sediment. However, locally, individual eolian fields contain more sediment than can be derived from nearby craters, indicating that these fields contain additional sediment from other sources.

Keywords: Impact phenomena, Planetary surfaces, Surface processes, Venus, Solar system terrestrial planets, Craters
Exploring and Validating Exoplanet Atmospheric Retrievals with Solar System Analog Observations. Solar system observations that serve as analogs for exoplanet remote sensing data can provide important opportunities to validate ideas and models related to exoplanet environments. Critically, and unlike true exoplanet observations, solar system analog data benefit from available high-quality ground- or orbiter-derived "truth" constraints that enable strong validations of exoplanet data interpretation tools. In this work, we first present a versatile atmospheric retrieval suite, capable of application to reflected light, thermal emission, and transmission observations spanning a broad range of wavelengths and thermochemical conditions. The tool-dubbed rfast-is designed, in part, to enable exoplanet mission concept feasibility studies. Following model validation, the retrieval tool is applied to a range of solar system analog observations for exoplanet environments. Retrieval studies using Earth reflected light observations from NASA's EPOXI mission provide a key proof of concept for exo-Earth direct imaging concept missions under development. Inverse modeling applied to an infrared spectrum of Earth from the Mars Global Surveyor Thermal Emission Spectrometer achieves good constraints on atmospheric gases, including many biosignature gases. Finally, retrieval analysis applied to a transit spectrum of Titan derived from the Cassini Visual and Infrared Mapping Spectrometer provides a proof of concept for interpreting more feature-rich transiting exoplanet observations from NASA's James Webb Space Telescope. In the future, solar system analog observations for exoplanets could be used to verify exoplanet models and parameterizations, and future exoplanet analog observations of any solar system worlds from planetary science missions should be encouraged.

Keywords: Exoplanets, Titan, Earth (planet), Remote sensing, Radiative transfer simulations
An Ancient Martian Dynamo Driven by Hemispheric Heating: Effect of Thermal Boundary Conditions. Magnetic field observations from the MGS, MAVEN, and InSight missions reveal that a dynamo was active in Mars's early history. One unique feature of Mars's magnetic crustal field is its hemispheric dichotomy, where magnetic fields in the southern hemisphere are much stronger than those in the northern hemisphere. Here we use numerical dynamo simulations to investigate the potential hemispheric nature of Mars's ancient dynamo. Previous studies show that a hemispheric heat flux perturbation at the core-mantle boundary could result in either a stable hemispherical magnetic field or a constantly reversing field, depending on choices of parameters used in those models. These two scenarios lead to different implications for the origin of crustal fields. Here we test the dynamo sensitivity to varying hemispheric heat flux perturbations at the core-mantle boundary in a broader parameter regime to understand whether a hemispheric dynamo is likely for early Mars. We find that features of the dynamo change from stable, hemispheric magnetic fields to reversing, hemispheric fields, with increasing hemispheric heat flux perturbations at the core-mantle boundary. We also find that magnetic fields powered by bottom heating are more stable and transition from a nonreversing, hemispheric magnetic field to a multipolar field at higher hemispheric heat flux perturbations, while the transition happens at a much lower heat flux perturbation for magnetic fields powered by internal heating.

Keywords: Magnetohydrodynamics, Mars, Planetary interior, Magnetic fields
Probing Ganymede's Atmosphere with HST Lyα Images in Transit of Jupiter. We report results from far-ultraviolet observations by the Hubble Space Telescope of Jupiter's largest moon, Ganymede, transiting across the planet's dayside hemisphere. Within a targeted campaign on 2021 September 9 two exposures were taken during one transit passage to probe for attenuation of Jupiter's hydrogen Lyα dayglow above the moon limb. The background dayglow is slightly attenuated over an extended region around Ganymede, with stronger attenuation in the second exposure, when Ganymede was near the planet's center. In the first exposure, when the moon was closer to Jupiter's limb, the effects from the Ganymede corona are hardly detectable, likely because the Jovian Lyα dayglow is spectrally broader and less intense at this viewing geometry. The obtained vertical H column densities of around (1-2) × 1012 cm-2 are consistent with previous results. Constraining angular variability around Ganymede's disk, we derive an upper limit on a local H2O column density of (2-3) × 1016 cm-2, such as could arise from outgassing plumes in regions near the observed moon limb.

Keywords: Ultraviolet astronomy, Hubble Space Telescope, Galilean satellites, Ganymede
Electrostatic Repulsion of Dust from Planetary Surfaces. Surfaces of planetary bodies can have strong electric fields, subjecting conductive grains to repulsive electrostatic forces. This has been proposed as a mechanism to eject grains from the ground. To quantify this process, we study millimeter-sized basalt aggregates consisting of micrometer constituents exposed to an electric field in drop-tower experiments. The dust aggregates acquire high charges on subsecond timescales while sticking to the electrodes according to the field polarity. Charging at the electrodes results in a repulsive (lifting) force and continues until repulsion overcomes adhesion and particles are lifted, moving toward the opposite electrode. Some aggregates remain attached, which is consistent with a maximum charge limit being reached, providing an electrostatic force too small to counteract adhesion. All observations are in agreement with a model of moderately conductive grains with a small but varying number of adhesive contacts to the electrodes. This supports the idea that on planetary surfaces with atmospheres, electrostatic repulsion can significantly contribute to airborne dust and sand, i.e., decrease the threshold wind speed that is required for saltation and increase the particle flux as suggested before.

Keywords: Dust physics, Planetary surfaces, Charge transfer, Surface processes, Atmospheric dynamics
The Solar Wind Interaction with (1) Ceres: The Role of Interior Conductivity. As a potential "ocean world," (1) Ceres' interior may possess relatively high electrical conductivities on the order of 10-4-100 S m-1, suggesting that the solar wind interaction with Ceres may differ from other highly resistive objects such as the Moon. Here, we use a hybrid plasma model to quantify the solar wind interaction with Ceres over a range of scenarios for Ceres' internal conductivity structure and the upstream solar wind and interplanetary magnetic field (IMF) conditions. Internal models for Ceres include one-, two-, and three-layer conductivity structures that variously include a crust, mantle, and/or subsurface ocean, while modeled solar wind conditions include a nominal case, a high IMF case, and an "extreme" space weather case. To first order, Ceres' interaction with the solar wind is governed by the draping and enhancement of the IMF over its interior, whether from a moderate-conductivity mantle or a high-conductivity ocean. In turn, IMF draping induces compressional wings in the solar wind density and deceleration in the solar wind speed outside of Ceres. Together, all three effects are readily observable by a hypothetical orbital or landed mission with standard plasma and magnetic field instrumentation. Finally, we also consider the possible effects of unipolar induction within Ceres, which has been previously suggested as a mechanism for conducting bodies in the solar wind. Our model results show that the efficacy of unipolar induction is highly suppressed by the slow magnetic field-line diffusion through Ceres' interior and, thus, is not a significant contributor to Ceres' overall interaction with the solar wind.

Keywords: Ceres, Solar wind, Planetary interior, Interplanetary magnetic fields
Pluto's Surface Mapping Using Unsupervised Learning from Near-infrared Observations of LEISA/Ralph. We map the surface of Pluto using an unsupervised machine-learning technique using the near-infrared observations of the LEISA/Ralph instrument on board NASA's New Horizons spacecraft. The principal-component-reduced Gaussian mixture model was implemented to investigate the geographic distribution of the surface units across the dwarf planet. We also present the likelihood of each surface unit at the image pixel level. Average I/F spectra of each unit were analyzed-in terms of the position and strengths of absorption bands of abundant volatiles such as N2, CH4, and CO and nonvolatile H2O-to connect the unit to surface composition, geology, and geographic location. The distribution of surface units shows a latitudinal pattern with distinct surface compositions of volatiles-consistent with the existing literature. However, previous mapping efforts were based primarily on compositional analysis using spectral indices (indicators) or implementation of complex radiative transfer models, which need (prior) expert knowledge, label data, or optical constants of representative end-members. We prove that an application of unsupervised learning in this instance renders a satisfactory result in mapping the spatial distribution of ice compositions without any prior information or label data. Thus, such an application is specifically advantageous for a planetary surface mapping when label data are poorly constrained or completely unknown, because an understanding of surface material distribution is vital for volatile transport modeling at the planetary scale. We emphasize that the unsupervised learning used in this study has wide applicability and can be expanded to other planetary bodies of the solar system for mapping surface material distribution.

Keywords: Astroinformatics, Astrostatistics techniques, Astronomy data analysis, Surface ices, Pluto
Thermal Creep on Mars: Visualizing a Soil Layer under Tension. At low ambient pressure, temperature gradients in porous soil lead to a gas flow called thermal creep. In this regard, Mars is unique as the conditions for thermal creep to occur in natural soil only exist on this planet in the solar system. Known as a Knudsen compressor, thermal creep induces pressure variations. In the case of Mars, there might be a pressure maximum below the very top dust particle layers of the soil, which would support particle lift and might decrease threshold wind velocities necessary to trigger saltation or reduce angles of repose on certain slopes. In laboratory experiments, we applied diffusing wave spectroscopy (DWS) to trace minute motions of grains on the nanometer scale in an illuminated simulated soil. This way, DWS visualizes pressure variations. We observe a minimum of motion, which we attribute to the pressure maximum ~2 mm below the surface. The motion above but especially below that depth characteristically depends on the ambient pressure with a peak at an ambient pressure of about 3 mbar for our sample. This is consistent with earlier work on the ejection of particle layers and is in agreement with a thermal creep origin. It underlines the supporting nature of thermal creep for particle lift, which might be especially important on Mars.

Keywords: Mars
Impacts of Organic Ice Condensation on the Optical Properties of Haze on Pluto. The flyby of the New Horizons spacecraft in 2015 July revealed an unexpected cold atmosphere of Pluto and confirmed the existence of its atmospheric haze. The observed and simulated vertical profiles of chemical species and microphysical processes suggest that the haze particles in Pluto's middle and lower atmosphere may contain organic ice condensation. Such organic ice components can potentially affect Pluto's haze chemistry and optical properties, as well as its energy budget. This study investigates the influence of the ice components on the scattering properties of Pluto's haze by comparing New Horizons observations and simulated particle scattering properties. Comprehensive tests are performed for various haze particle parameters, including their size, chemical component, ice content, and morphology. Scattering properties of these ice-bearing haze particles are calculated by a discrete dipole approximation method and compared to multispectral observations obtained by four New Horizons instruments in spectral regions ranging from the ultraviolet to the near-infrared. The results indicate that the inclusion of the organic ice component leads to higher ratios of backscattering in the visible to extinction in the ultraviolet and provides better agreement with observations compared to monodispersed homogeneous aggregates. But it alone is not sufficient to explain the observed forward scattering values in the visible and near-infrared. Therefore, other scattering sources and/or mechanisms are still required to explain the full set of scattering observations. Further observations, as well as laboratory measurements and numerical tests, are anticipated to improve our understanding of the morphology and ice content of Pluto's haze.

Keywords: Atmospheric composition, Planetary atmospheres, Pluto
Shape Models of Lucy Targets (3548) Eurybates and (21900) Orus from Disk-integrated Photometry. We use our new light curves, along with historical data, to determine the rotation state, photometric properties, and convex shape models of the targets of the Lucy mission (3548) Eurybates and (21900) Orus. We determine a retrograde spin for both targets, with sidereal rotation periods of 8.7027283 ± 0.0000029 h and 13.486190 ± 0.000017 h, respectively. The phase curves of both objects are nearly linear in the phase-angle range observable from Earth and lack a pronounced opposition effect. Unsupervised classification of these phase curves by the Penttilä et al. tool suggests that Eurybates and Orus belong to the C and D taxonomic types, respectively, thereby independently confirming past classifications based on their spectral slope. Time-resolved color-index measurements show no systematic color variations correlated with rotation for either target at the 1% level, suggesting that no variegation is present on a hemispherical scale for any of the objects. Comparison of the shape models with stellar occultation data available for the two objects from the program by Buie et al. allows us to resolve the longitude ambiguity of the orientations of the spin axes and derive unique pole solutions for both targets. Furthermore, scaling the shape models to match the occultation chords produces accurate sizes and geometric albedos for both objects. The derived surface-equivalent spherical diameters are D  s  = 69.3 ± 1.4 km and D  s  = 60.5 ± 0.9 km for Eurybates and Orus, respectively, while the geometric albedo in the H, G 1, G 2 system is p  V (H, G 1, G 2) = 0.044 ± 0.003 and p  V (H, G 1, G 2) = 0.040 ± 0.002 for Eurybates and Orus, respectively.

Keywords: Light curves, Jupiter trojans, CCD photometry