Sazuna/UAT_keywords huggingface dataset:
Porosity-filling Metamorphic Brines Explain Ceres's Low Mantle Density. Recent work has sought to constrain the composition and makeup of the dwarf planet Ceres's mantle, which has a relatively low density, between 2400 and 2800 kg m-3, as inferred by observations by the Dawn mission. Explanations for this low density have ranged from a high fraction of porosity-filled brines to a high fraction of organic matter. We present a series of numerical thermodynamic models that yield the mineralogy and fluid composition in the mantle as a function of Ceres's thermal evolution. We find that the resulting phase assemblage could have changed drastically since the formation of Ceres, as volatile-bearing minerals such as serpentine and carbonates would partially destabilize and release their volatiles as temperatures in the mantle reach their maximum about 3 Gyr after Ceres's formation. These volatiles consist mainly of aqueous fluids containing Na+ and HS- throughout the metamorphic evolution of Ceres and, in addition, high concentrations of CO2 at high temperatures relatively recently. The predicted present-day phase assemblage in the mantle, consisting of partially devolatilized minerals and 13-30 vol% fluid-filled porosity, is consistent with the mantle densities inferred from Dawn. The metamorphic fluids generated in Ceres's mantle may have replenished an ocean at the base of the crust and may even be the source of the Na2CO3 and NaHCO3 mineral deposits observed at Ceres's surface.

Keywords: Ceres, Planetary interior, Mantle
Processing and Analysis for Radio Science Experiments (PARSE): Graphical Interface for Bistatic Radar. Opportunistic bistatic radar (BSR) observations of planetary surfaces can probe the textural and electrical properties of several solar system bodies without needing a dedicated instrument or additional mission requirements, providing unique insights into volatile enrichment and supporting future landing, anchoring, and in situ sampling. Given their opportunistic nature, complex observation geometries, and required radiometric knowledge of the received radio signal, these data are particularly challenging to process, analyze, and interpret for most planetary science data users, who can be unfamiliar with link budget analysis of received echoes. The above impedes real-time use of BSR data to support mission operations, such as identifying safe landing locations on small bodies, as was the case for the Rosetta mission. To address this deficiency, we develop an open-source graphical user interface-Processing and Analysis for Radio Science Experiments (PARSE)-that assesses the feasibility of performing BSR observations and automates radiometric signal processing, power spectral analysis, and visualization of DSN planetary radio science data sets acquired during mission operations or archived on NASA's Planetary Data System. In this first release, PARSE automates the processing chain developed for Dawn at Asteroid Vesta, streamlining the detection of DSN-received surface-scatter echoes generated as the spacecraft enters/exits occultations behind the target. Future releases will include support for existing Arecibo data sets and other Earth-based radio observatories. Our tool enables the broader planetary science community, beyond planetary radar signal processing experts, to utilize BSR data sets to characterize electrical and textural properties of planetary surfaces. Such tools are becoming increasingly important as the number of space missions-and subsequent opportunities for orbital radio science observations-continue to grow.

Keywords: Small Solar System bodies, Astronomy software, Solar system, Radar astronomy, Doppler shift
Optical Constants of a Titan Haze Analog from 0.4 to 3.5 μm Determined Using Vacuum Spectroscopy. Titan's thick atmosphere is primarily composed of nitrogen and methane. Complex chemistry happening in Titan's atmosphere produces optically thick organic hazes. These hazes play significant roles in Titan's atmosphere and on its surface, and their optical properties are crucial for understanding many processes happening on Titan. Due to the lack of such information, the optical constants of laboratory-prepared Titan haze analogs are essential inputs for atmospheric modeling and data analysis of remote-sensing observations of Titan. Here we perform laboratory simulations in a Titan-relevant environment, analyze the resulting Titan haze analogs using vacuum Fourier transform infrared spectroscopy, and calculate the optical constants from the measured transmittance and reflectance spectra. We provide a reliable set of optical constants of Titan haze analogs in the wavelength range from 0.4 to 3.5 μm and will extend it to 28.5 μm in the near future, which can be used for analyzing both existing and future observational data of Titan. This study establishes a feasible method to determine optical constants of haze analogs of (exo)planetary bodies.

Keywords: Titan
The Extent, Nature, and Origin of K and Rb Depletions and Isotopic Fractionations in Earth, the Moon, and Other Planetary Bodies. Moderately volatile elements (MVEs) are depleted and isotopically fractionated in the Moon relative to Earth. To understand how the composition of the Moon was established, we calculate the equilibrium and kinetic isotopic fractionation factors associated with evaporation and condensation processes. We also reassess the levels of depletions of K and Rb in planetary bodies. Highly incompatible element ratios are often assumed to be minimally affected by magmatic processes, but we show that this view is not fully warranted, and we develop approaches to mitigate this issue. The K/U weight ratios of Earth and the Moon are estimated to be 9704 and 2448, respectively. The 87Rb/86Sr atomic ratios of Earth and the Moon are estimated to be 0.072 5 and 0.015 4, respectively. We show that the depletions and heavy isotopic compositions of most MVEs in the Moon are best explained by evaporation in 99%-saturated vapor. At 99% saturation in the protolunar disk, Na and K would have been depleted to levels like those encountered in the Moon on timescales of ~40-400 days at 3500-4500 K, which agrees with model expectations. In contrast, at the same saturation but a temperature of 1600-1800 K relevant to hydrodynamic escape from the lunar magma ocean, Na and K depletions would have taken 0.1-103 Myr, which far exceeds the 1000 yr time span until plagioclase flotation hinders evaporation from the magma ocean. We conclude that the protolunar disk is a much more likely setting for the depletion of MVEs than the lunar magma ocean.

Keywords: Isotopic abundances, Lunar composition, Chemical abundances, Earth-moon system
Analysis of Four-band WISE Observations of Asteroids. We analyzed 82,548 carefully curated observations of 4420 asteroids with Wide-field Infrared Survey Explorer (WISE) four-band data to produce estimates of diameters and infrared emissivities. We also used these diameter values in conjunction with absolute visual magnitudes to infer estimates of visible-band geometric albedos. We provide solutions to 131 asteroids not analyzed by the NEOWISE team and to 1778 asteroids not analyzed with four-band data by the NEOWISE team. Our process differs from the NEOWISE analysis in that it uses an accurate solar flux, integrates the flux with actual bandpass responses, obeys Kirchhoff's law, and does not force emissivity values in all four bands to an arbitrary value of 0.9. We used a regularized model-fitting algorithm that yields improved fits to the data. Our results more closely match stellar-occultation diameter estimates than the NEOWISE results by a factor of ~2. Using 24 high-quality stellar-occultation results as a benchmark, we found that the median error of four-infrared-band diameter estimates in a carefully curated data set is 9.3%. Our results also suggest the presence of a size-dependent bias in the NEOWISE diameter estimates, which may pollute estimates of asteroid size distributions and slightly inflate impact-hazard risk calculations. For more than 90% of asteroids in this sample, the primary source of error on the albedo estimate is the error on absolute visual magnitude.

Keywords: Near-Earth objects, Main belt asteroids, Asteroids, Asteroid surfaces
An Energy Balance Model for Rapidly and Synchronously Rotating Terrestrial Planets. This paper describes the habitable energy balance model for exoplanet observations (HEXTOR), which is a model for calculating latitudinal temperature profiles on Earth and other rapidly rotating planets. HEXTOR includes a lookup table method for calculating the outgoing infrared radiative flux and the planetary albedo, which provides improvements over other approaches to parameterizing radiative transfer in an energy balance model (EBM). Validation cases are presented for present-day Earth and other Earth-sized planets with aquaplanet and land planet conditions from 0° to 45° obliquity. A tidally locked coordinate system is also implemented in the EBM, which enables calculation of the horizontal temperature profile for planets in synchronous rotation around low-mass stars. This coordinate-transformed model is applied to cases for TRAPPIST-1e as defined by the TRAPPIST Habitable Atmosphere Intercomparison protocol, which demonstrates better agreement with general circulation models than with the latitudinal EBM. Advances in applying EBMs to exoplanets can be made by using general circulation models as a benchmark for tuning as well as by conducting intercomparisons between EBMs with different physical parameterizations.

Keywords: Computational methods, Astrobiology, Planetary climates, Hierarchical models, Exoplanet atmospheres
Radar and Lightcurve Observations and a Physical Model of Potentially Hazardous Asteroid 1981 Midas. We report observations of the Apollo-class potentially hazardous asteroid 1981 Midas, which passed 0.090 au from Earth (35 lunar distances) on 2018 March 21. During this close approach, Midas was observed by radar both from the Arecibo Observatory on March 21 through 25 (five nights) and from NASA's Goldstone Deep Space Communications Complex on March 19 and 21. Optical lightcurves were obtained by other observers during four apparitions (1987, 1992, 2004, and 2018), which showed a rotation period of 5.22 hr. By combining the lightcurves and radar data, we have constructed a shape model for Midas. This model shows that Midas has two lobes separated by a neck, which, at its thinnest point, is about 60% of the width of the largest lobe. We also confirm the lightcurve-derived rotation period and show that Midas has a pole direction within 6° of ecliptic longitude and latitude (λ, β) = (39°, -60°) and dimensions of (3.41 ± 9%) × (1.90 ± 11%) × (1.27 ± 29%) km. Analysis of gravitational slopes on Midas indicates that nearly all of the surface has a slope less than the typical angle of repose for granular materials, so it does not require cohesion to maintain its shape. In addition, we measured a circular polarization ratio of 0.83 ± 0.04 at Arecibo's 13 cm wavelength, which is the highest seen to date for any near-Earth asteroid with visible and near-infrared spectral type V.

Keywords: Near-Earth objects, Asteroids, Light curves, Radar telescopes, Radar astronomy
The Lunar Geophysical Network Landing Sites Science Rationale. The Lunar Geophysical Network (LGN) mission is proposed to land on the Moon in 2030 and deploy packages at four locations to enable geophysical measurements for 6-10 yr. Returning to the lunar surface with a long-lived geophysical network is a key next step to advance lunar and planetary science. LGN will greatly expand our primarily Apollo-based knowledge of the deep lunar interior by identifying and characterizing mantle melt layers, as well as core size and state. To meet the mission objectives, the instrument suite provides complementary seismic, geodetic, heat flow, and electromagnetic observations. We discuss the network landing site requirements and provide example sites that meet these requirements. Landing site selection will continue to be optimized throughout the formulation of this mission. Possible sites include the P-5 region within the Procellarum KREEP Terrane (PKT; (lat: 15°; long: -35°), Schickard Basin (lat: -44.°3; long: -55.°1), Crisium Basin (lat: 18.°5; long: 61.°8), and the farside Korolev Basin (lat: -2.°4; long: -159.°3). Network optimization considers the best locations to observe seismic core phases, e.g., ScS and PKP. Ray path density and proximity to young fault scarps are also analyzed to provide increased opportunities for seismic observations. Geodetic constraints require the network to have at least three nearside stations at maximum limb distances. Heat flow and electromagnetic measurements should be obtained away from terrane boundaries and from magnetic anomalies at locations representative of global trends. An in-depth case study is provided for Crisium. In addition, we discuss the consequences for scientific return of less than optimal locations or number of stations.

Keywords: Lunar composition, Lunar interior, Lunar seismology, The Moon, Lunar science, Lunar rilles
Dark-flight Estimates of Meteorite Fall Positions: Issues and a Case Study Using the Murrili Meteorite Fall. Fireball networks are used to recover meteorites, with the context of orbits. Observations from these networks cover the bright flight, where the meteoroid is luminescent, but to recover a fallen meteorite, these observations must often be predicted forward in time to the ground to estimate an impact position. This dark-flight modeling is deceptively simple, but there is hidden complexity covering the precise interactions between the meteorite and the (usually active) atmosphere. We describe the method and approach used by the Desert Fireball Network, detailing the issues we have addressed, and the impact that factors such as shape, mass, and density have on the predicted fall position. We illustrate this with a case study of Murrili meteorite fall that occurred into Lake Eyre-Kati Thanda in 2015. The fall was very well observed from multiple viewpoints, and the trajectory was steep, with a low-altitude endpoint, such that the dark flight was relatively short. Murrili is 1.68 kg with a typical ordinary chondrite density but with a somewhat flattened shape compared to a sphere, such that there are discrepancies between sphere-based predictions and the actual recovery location. It is notable that even in this relatively idealized dark-flight scenario, modeling using spherically shaped projectiles resulted in a significant distance between predicted fall position and recovered meteorite.

Keywords: Meteorites, Meteoroids
Thermophysical Investigation of Asteroid Surfaces. II. Factors Influencing Grain Size. Asteroid surfaces are subjected to mechanical weathering processes that result in the development and evolution of regolith. Two proposed mechanisms—impact bombardment and thermal fatigue—have been proposed as viable and dominant weathering processes. Previously, we compiled and estimated thermal inertias of several hundred asteroids (mostly in the main belt) for which we determined dependencies on temperature, diameter, and rotation period. In this work, we estimate grain sizes of asteroid regoliths from this large thermal inertia data set using thermal conductivity models. Following our previous work, we perform multivariate linear model fits to the grain size data set and quantify its dependency on diameter and rotation period. We find that the preferred model indicates that asteroid grain sizes are inversely dependent on object size for &lt;10 km asteroids and exhibit no relationship above this size cutoff. Rotation period and grain size show a positive relationship when the rotation period is greater than ∼5 hr and an inverse relationship below this rotation period. These results indicate that both impact weathering and thermal fatigue are relevant regolith evolution mechanisms. We run post-hoc t-tests between spectral groups to infer the influence of composition on regolith grain sizes. We find that M-type (including suspected metal-rich objects) and E-type asteroids have larger grain sizes relative to our population sample and that P-type asteroids have distinctly smaller grains than other groups.

Keywords: Near-Earth objects, Asteroids, Main belt asteroids, Asteroid rotation, Linear regression, Asteroid belt, Asteroid surfaces
Identifying Impact Melt from the Smythii Basin: Toward an Improved Chronology for Lunar Basin Formation. At c. 820 km in diameter, the Smythii impact basin is one of the large lunar basins (&gt;200 km diameter) thought to have formed during the pre-Nectarian period. We combine Lunar Reconnaissance Orbiter imagery, topography, and Moon Mineralogy Mapper compositional data to interpret the surface and subsurface geology of the Smythii basin with the goal of identifying datable impact melt for investigation by a future lunar lander. Surface outcrops exposed on the central peak of the Schubert C crater are identified as uplifted deposits of Smythii impact melt, and a mission concept is presented for sampling these exposures in order to establish the absolute age of the Smythii basin using radioisotopic geochronology. This mission concept is in line with one of the current top-tier priorities for lunar science: determining the age of large basins and thus constraining the impact flux during the Moon's first billion years, which is a proxy record for the role of impacts on the surface environment and habitability of early Earth and the inner solar system during this interval.

Keywords: Isotopic abundances, Lunar craters, Lunar petrology, Selenology, The Moon, Lunar geochronology, Lunar impacts, Lunar surface, Lunar mineralogy
The Arecibo Observatory as an Instrument for Investigating Orbital Debris: Legacy and Next Generation Performance. In this paper, we investigate the ability of the Arecibo Observatory to characterize the orbital debris environment and compare it to the primary instrument used by NASA's Orbital Debris Program Office, the Haystack Ultra-Wideband Satellite Imaging Radar (HUSIR). Arecibo's location (18.°3 N) increases the percentage of observable orbits (relative to HUSIR) by 27%, which gives Arecibo access to a much larger and previously unmeasured portion of the environment. Due to the recent collapse of the Arecibo dish, in addition to exploring historic capabilities of the Legacy Arecibo Telescope, estimates of the performance of the proposed Next Generation Arecibo Telescope (NGAT) are explored. We show that the current NGAT design could have a sensitivity comparable to the Goldstone Orbital Debris Radar, currently NASA's most sensitive orbital debris radar. Additionally, design suggestions are presented that would significantly improve the capabilities of the NGAT for orbital debris investigations. We show that, with appropriate hardware upgrades, it would be possible to achieve a minimum-detectable debris size as small as 1 mm. These capabilities would allow data from Arecibo to significantly improve short-term debris environment models, which are used to inform spacecraft design and operations, particularly for orbital debris smaller than 3 mm, which pose the highest penetration risk to most spacecraft.

Keywords: Space debris, Radar telescopes
Probing the Icy Shell Structure of Ocean Worlds with Gravity-Topography Admittance. The structure of the icy shells of ocean worlds is important for understanding the stability of their underlying oceans as it controls the rate at which heat can be transported outward and radiated to space. Future spacecraft exploration of the ocean worlds (e.g., by NASA's Europa Clipper mission) will allow for higher-resolution measurements of gravity and shape than currently available. In this paper, we study the sensitivity of gravity-topography admittance to the structure of icy shells in preparation for future data analysis. An analytical viscous relaxation model is used to predict admittance spectra given different shell structures determined by the temperature-dependent viscosity of a tidally heated, conductive shell. We apply these methods to the ocean worlds of Europa and Enceladus. We find that admittance is sensitive to the mechanisms of topography support at different wavelengths and estimate the required gravity performance to resolve transitions between these mechanisms. We find that measuring admittance would be complementary to ice-penetrating radar in constraining shell thickness as it would cover the cases for which a direct ice-ocean interface detection is less favorable with radar, i.e., for warmer and thicker shells. Finally, we find that admittance may be used to constrain the tidal dissipation within the icy shell, which would be complementary to a more demanding measurement of the tidal phase lag.

Keywords: Tides, Saturnian satellites, Ocean planets, Europa
Serpentinization in the Thermal Evolution of Icy Kuiper Belt Objects in the Early Solar System. Here we present an improved algorithm to model the serpentinization process in planetesimals in the early solar system. Although it is hypothesized that serpentinization-like reactions played an important role in the thermal evolution of planetesimals, few and restricted models are available in this topic. These processes may be important, as the materials involved were abundant in these objects. Our model is based on the model by Góbi &amp; Kereszturi and contains improvements in the consideration of heat capacities and lithospheric pressure and in the calculation of the amount of interfacial water. Comparison of our results with previous calculations shows that there are significant differences in, e.g., the serpentinization time-the time necessary to consume most of the reactants at specific initial conditions-or the amount of heat produced by this process. In a simple application we show that in icy bodies, under some realistic conditions, below the melting point of water ice, serpentinization reaction using interfacial water may be able to proceed and eventually push the local temperature above the melting point to start a "runaway" serpentinization. According to our calculations in objects with radii R ≳ 200 km, serpentinization might have quickly reformed nearly the whole interior of these bodies in the early solar system.

Keywords: Planetary interior
Arecibo Radar Maps of Venus from 1988 to 2020. Over its 57 yr history, the Arecibo telescope was used to produce radar maps of Venus that pioneered our understanding of surface landforms and geologic processes. The best spatial resolution of 1-2 km achievable with the S-band (2380 MHz) transmitter was first used to map the surface in 1988, providing dual-circular polarization images ahead of the Magellan mission. Along with the 1988 observations, high-resolution images from observing runs in 2012, 2015, 2017, and 2020 have been archived with the NASA Planetary Data System to preserve these legacy data sets. We document the data collection and processing methods for the Arecibo Venus data, discuss unique aspects of the delay-Doppler imaging, and derive relative calibration factors linking the final multilook maps and Magellan data. The observations also allow for derivation of the circular polarization ratio and, potentially, the Stokes vector components. These results are particularly relevant for long-term monitoring of the spin rate, surface change detection, and planning for S-band polarimetry from the EnVision orbiter mission.

Keywords: Venus, Radar astronomy