Sazuna/UAT_keywords huggingface dataset:
Juno Spacecraft Measurements of Jupiter's Gravity Imply a Dilute Core. The Juno spacecraft measured Jupiter's gravity field and determined the even and odd zonal harmonics, J  n , with unprecedented precision. However, interpreting these observations has been a challenge because it is difficult to reconcile the unexpectedly small magnitudes of the moments J 4 and J 6 with conventional interior models that assume a large, distinct core of rock and ice. Here we show that the entire set of gravity harmonics can be matched with models that assume an ab initio equation of state, wind profiles, and a dilute core of heavy elements that are distributed as far out as 63% of the planet's radius. In the core region, heavy elements are predicted to be distributed uniformly and make up only 18% by mass because of dilution with hydrogen and helium. Our models are consistent with the existence of primary and secondary dynamo layers that will help explain the complexity of the observed magnetic field.

Keywords: Solar system gas giant planets
Statistical Significance of Mission Parameters on the Deflection Efficiency of Kinetic Impacts: Applications for the Next-generation Kinetic Impactor. Understanding how to deflect an incoming asteroid is of great importance and a focus of research undertaken internationally by the planetary defense community. Deflection of an asteroid by a kinetic impactor is one such mitigation method that has a high degree of technological maturity. In 2022, NASA's planetary defense mission, the Double Asteroid Redirection Test (DART), will provide the first full-scale technology demonstration of a kinetic impactor. However, the DART mission is just a single test of one kinetic impactor design, prompting the question: Is it possible to optimize the design of a kinetic impactor to make it the most efficient deflector that it can be? In this paper, we use high-fidelity hydrodynamic simulations to examine the effect of five mission parameters (impactor mass, impact velocity, impactor composition, impactor geometry, and target strength) on three observables related to deflection efficiency (crater morphology, ejecta distribution, and momentum transfer) resulting from kinetic impacts. We find that the most significant mission parameters for determining postimpact factors are the impact velocity, impactor mass, and target strength. The impactor geometry and impactor composition emerge as statistically nonsignificant. Overall, we find that the ogive impactor geometry results in the highest variance in predicting the momentum enhancement factor (β), and that generally, impactors with smaller volumes and flat leading edges (plates and rings) produce smaller craters and less ejecta mass compared to impactors with larger volumes and sharper leading edges (spheres, ogives, and cones).

Keywords: Impact phenomena, Planetary science
Surface Properties of Near-Sun Asteroids. Near-Earth asteroids (NEAs) with small perihelion distances reach subsolar temperatures of ≥1000 K. They are hypothesized to undergo "supercatastrophic" disruption, potentially caused by near-Sun processes such as thermal cracking, spin-up, meteoroid impacts, and subsurface volatile release, all of which are likely to cause surface alteration, which may change the spectral slope of the surface. We attempted to observe 35 of the 53 known near-Sun asteroids with q ≤ 0.15 au from 2017 January to 2020 March to search for trends related to near-Sun processes. We report the optical colors and spectral slopes of 22 objects that we successfully observed and the measured rotation periods for three objects. We find the distribution of colors to be overall bluer than the color distribution of NEAs, though there is a large overlap. We attribute the large scatter to unknown dynamical histories and compositions for individual objects, as well as competing surface altering processes. We also investigated potential correlations between colors and other properties (e.g., perihelion distance, Tisserand parameter, rotation period) and searched for evidence of activity. Finally, we have compiled all known physical and dynamical properties of these objects, including probabilistic source regions and dwell times with q ≤ 0.15 au.

Keywords: Near-Earth objects, Asteroids, Small Solar System bodies, Optical astronomy, Ground-based astronomy, Solar system astronomy
New Constraints on the Volatile Deposit in Mercury's North Polar Crater, Prokofiev. We present new high-resolution topographic, illumination, and thermal models of Mercury's 112 km diameter north polar crater, Prokofiev. The new models confirm previous results that water ice is stable at the surface within the permanently shadowed regions (PSRs) of Prokofiev for geologic timescales. The largest radar-bright region in Prokofiev is confirmed to extend up to several kilometers past the boundary of its PSR, making it unique on Mercury for hosting a significant radar-bright area outside a PSR. The near-infrared normal albedo distribution of Prokofiev's PSR suggests the presence of a darkening agent rather than pure surface ice. Linear mixture models predict at least roughly half of the surface area to be covered with this dark material. Using improved altimetry in this crater, we place an upper limit of 26 m on its ice deposit thickness. The 1 km baseline topographic slope and roughness of the radar-bright deposit are lower than the non-radar-bright floor, although the difference is not statistically significant when compared to the non-radar-bright floor's natural topographic variations. These results place new constraints on the nature of Prokofiev's volatile deposit that will inform future missions, such as BepiColombo.

Keywords: Mercury (planet)
Physical Characterization of 2015 JD<SUB>1</SUB>: A Possibly Inhomogeneous Near-Earth Asteroid. The surfaces of airless bodies such as asteroids are exposed to many phenomena that can alter their physical properties. Bennu, the target of the OSIRIS-REx mission, has demonstrated how complex the surface of a small body can be. In 2019 November, the potentially hazardous asteroid 2015 JD1 experienced a close approach of 0.033 1 au from the Earth. We present results of the physical characterization of 2015 JD1 based on ground-based radar, spectroscopy, and photometric observations acquired during 2019 November. Radar polarimetry measurements from the Arecibo Observatory indicate a morphologically complex surface. The delay-Doppler images reveal a contact binary asteroid with an estimated visible extent of ~150 m. Our observations suggest that 2015 JD1 is an E-type asteroid with a surface composition similar to aubrites, a class of differentiated enstatite meteorites. The dynamical properties of 2015 JD1 suggest that it came from the ν 6 resonance with Jupiter, and spectral comparison with major E-type bodies suggests that it may have been derived from a parental body similar to the progenitor of the E-type (64) Angelina. Significantly, we find rotational spectral variation across the surface of 2015 JD1 from the red to blue spectral slope. Our compositional analysis suggests that the spectral slope variation could be due to the lack of iron and sulfides in one area of the surface of 2015 JD1 and/or differences in grain sizes.

Keywords: Near-Earth objects, Asteroids, Radar astronomy, Photometry, Spectroscopy, Asteroid surfaces
Ultraviolet Spectroscopy of Lucy Mission Targets with the Hubble Space Telescope. The recently launched Lucy mission aims to understand the dynamical history of the solar system by examining the Jupiter Trojans, a population of primitive asteroids co-orbital with Jupiter. Using the G280 grism on the Hubble Space Telescope's Wide Field Camera 3, we obtained near-ultraviolet spectra of four of the five Lucy mission targets-(617) Patroclus-Menoetius, (11351) Leucus, (3548) Eurybates, and (21900) Orus-to search for novel spectral features. We observe a local reflectance minimum at 0.4 μm accompanied by an increase in reflectance from 0.35 to 0.3 μm in the spectra of Patroclus and Orus. We use the principles of Rayleigh scattering and geometric optics to develop a Hapke optical model to investigate whether this feature can be explained by the presence of submicroscopic grains on Trojan surfaces. The near-ultraviolet "bump" feature can be explained by scattering due to fine-grained opaques (iron, amorphous carbon, or graphite) with grain sizes ranging from 20 to 80 nm.

Keywords: Hubble Space Telescope, Jupiter trojans, Near ultraviolet astronomy, Spectroscopy
Chemical Fractionation Modeling of Plumes Indicates a Gas-rich, Moderately Alkaline Enceladus Ocean. Enceladus harbors an ocean beneath its ice crust that erupts spectacular plumes from fissures at the south pole. The plume composition was measured by the Cassini spacecraft, and provides evidence for the ocean's gas content, salinity, pH, and potential for life. Understanding the ocean's composition is complicated by physicochemical processes that alter the plume composition during eruption, such as water vapor condensation in the icy fissures and gas exsolution from the ocean surface. We developed a model that includes key fractionation processes, in particular fractionation during gas exsolution, which has not been previously considered. Our model predicts a moderately alkaline (pH 7.95-9.05), gas-rich ocean (~10-5-10-3 molal) with high concentrations of ammonium ions (10-2-10-1 molal). Our derived dissolved gas concentrations are higher than in recent studies because we account for gas exsolution, which depletes gases in the plume compared to the ocean, and because our model conserves mass flow rates between gas exsolution from the ocean and eruption from the tiger stripe fissures. We find carbon dioxide and hydrogen concentrations that could provide sufficient chemical energy for oceanic life in the form of hydrogenotrophic methanogens. Carbon dioxide concentrations of 10-5-10-3 molal indicate a more Earth-like pH than the pH ~8.5-13.5 in previous studies. The inferred bulk ammonium and total inorganic carbon concentrations are consistent with cometary levels. This corroborates evidence from cometary deuterium-hydrogen (D/H) ratios that Enceladus formed from comet-like planetesimals. Our results suggest a gas-rich ocean that inherited its high volatile concentrations from comet-like building blocks.

Keywords: Water vapor, Methane, Chemical abundances, Carbon dioxide, Astrobiology, Saturnian satellites, Comet volatiles
Dione's Thermal Inertia and Bolometric Bond Albedo Derived from Cassini/CIRS Observations of Solar Eclipse Ingress. On 2010 May 18 Cassini's Composite Infrared Spectrometer (CIRS) observed Dione's leading hemisphere as its surface went into solar eclipse. Surface temperatures derived from each of CIRS' focal plane 3 (FP3, 600-1100 cm-1) show a rapid decrease in Dione's surface temperature upon eclipse ingress. This change was compared to the model surface emission to constrain bolometric Bond albedo and thermal inertia. Seven FP3 detectors were able to constrain the observed surface's thermophysical properties. The bolometric Bond albedo derived from these detectors are consistent with one another (0.54 ± 0.05 to 0.62 ± 0.03) and that of diurnal studies (e.g., 0.49 ± 0.11, Howett et al. 2014). This indicates that Dione's albedo is uniform to within the uncertainties across the observed region of its leading hemisphere. The derived thermal inertias are consistent across detectors, 9 ± 4 J m-2 K-1 s-1/2 (MKS) to 16 ± 8 MKS, and with previous diurnal studies (e.g., 8 to 12 MKS, Howett et al. 2014). The skin depth probed by the eclipse thermal wave is ~0.6-1 mm, which is much shallower than that probed by diurnal cycles (~50 mm). Thus, the agreement in thermal inertia between the eclipse and diurnal studies indicates that Dione's subsurface structure is uniform from submillimeter to subcentimeter depths. This is different from the Jovian system, where eclipse-derived thermal inertias are much lower than those derived from diurnal studies. The cause of this difference is not known, but one possibility is that the E-ring grains that bombard Dione's leading hemisphere overturn it, causing uniformity to centimeter depths.

Keywords: Natural satellite surfaces, Surface ices, Saturnian satellites
Topographically Influenced Evolution of Large-scale Changes in Comet 67P/Churyumov-Gerasimenko's Imhotep Region. Large portions of comet 67P/Churyumov-Gerasimenko's northern hemisphere are blanketed by fallback material consisting of centimeter-sized particles termed the smooth terrains. Observations from the Rosetta mission show that the most drastic transient changes during 67P's 2015 perihelion passage occurred within a subset of these deposits. However, we still do not understand the processes driving these changes, limiting our overall understanding of how comets evolve over both seasonal and multiorbit timescales. Herein we provide a complete documentation of scarp-driven activity on 67P's largest smooth terrain deposit, a highly active portion of the Imhotep region that is the southernmost of all smooth terrain basins on 67P. We also present a thermal model that accurately predicts when and where scarps originate during the course of the observed activity. Assuming a uniform surface composition, our model shows that activity is heavily controlled by local topography rather than the presence of ice-enhanced hot spots on the surface. Scarps within the smooth terrain deposits in central Imhotep also exhibit a peculiar behavior, where three scarps originate from the same location but at different times and migrate in opposite directions. This behavior indicates that the landscape retains a memory of previous cycles of erosion and deposition, reflected by the depth of the volatile-rich layer. Future work will need to couple our thermal model with a landscape evolution model in order to explain the complete dynamic evolution of these terrains.

Keywords: Comet nuclei, Comets, Small Solar System bodies
Ring Seismology of the Ice Giants Uranus and Neptune. We assess the prospect of using ring seismology to probe the interiors of the ice giants Uranus and Neptune. We do this by calculating normal-mode spectra for different interior models of Uranus and Neptune using the stellar oscillation code GYRE. These spectra provide predictions of where in these planets' ring systems the effects of interior oscillations might be detected. We find that f-mode resonances with azimuthal order m = 2 or 7 ≤ m ≤ 19 fall among the inner rings (6, 5, 4, α, and β) of Uranus, while f-mode resonances with 2 ≤ m ≤ 12 fall in the tenuous ζ ring region. In addition, f-mode resonances with m = 2 or 6 ≤ m ≤ 13 may give azimuthal structure to Neptune's tenuous Galle ring. We also find that g-mode resonances may fall in the middle to outer rings of these planets. Although an orbiter is most likely required to confirm the association between any waves in the rings and planetary normal modes, the diversity of normal-mode spectra implies that identification of just one or two modes in the rings of Uranus or Neptune would eliminate a variety of interior models and thus aid in the interpretation of Voyager observations and future spacecraft measurements.

Keywords: Neptune, Orbits, Planetary rings, Orbital resonances, Solar system gas giant planets, Planetary dynamics, Uranus
Releasing Atmospheric Martian Dust in Sand Grain Impacts. Emission of dust up to a few microns in size by impacts of sand grains during saltation is thought to be one source of dust within the Martian atmosphere. To study this dust fraction, we carried out laboratory impact experiments. Small numbers of particles of about 200 μm in diameter impacted a simulated Martian soil (bimodal Mars Global Simulant). Impacts occurred at angles of ~18° in vacuum with an impact speed of ~1 m s-1. Ejected dust was captured on adjacent microscope slides and the emitted particle size distribution (PSD) was found to be related to the soil PSD. We find that the ejection of clay-sized dust gets increasingly harder the smaller these grains are. However, in spite of strong cohesive forces, individual impacts emit dust of 1 μm and less, i.e., dust in the size range that can be suspended in the Martian atmosphere. More generally, the probability of ejecting dust of a given size can be characterized by a power law in the size range between 0.5 and 5 μm (diameter).

Keywords: Mars, Exoplanet atmospheres
The Geologic Impact of 16 Psyche's Surface Temperatures. NASA's Discovery mission Psyche will soon be launched to visit the asteroid 16 Psyche. In this work, we model the surface temperatures of 16 Psyche. Our modeling is focused on capturing the diurnal and seasonal surface temperature variations caused by 16 Psyche's large obliquity (95°) and moderately high eccentricity (0.134). Using a semianalytic framework, we predict that large thermal variations (including at the poles) can cause cracking of boulders leading to a porous surface regolith. This prediction is consistent with a high-porosity surface regolith inferred from thermal inertia measurements. We also find that water ice is not likely to be stable at any latitude.

Keywords: Asteroids, Asteroid surfaces
Assessing the Detectability of Europa's Seafloor Topography from Europa Clipper's Gravity Data. Due to its size and tidal heating, Europa may potentially possess active volcanism and hydrothermal circulation at its seafloor. The upcoming Europa Clipper mission provides the opportunity to obtain global gravity maps over a range of spatial scales, up to degree l ≈ 10. We assess the ability of such gravity measurements to determine Europa's seafloor topography, building on and extending previous work in this area. We create a suite of models that test the gravity signature of a wider range of possible topographies and lithospheric thicknesses, spacecraft close-approach altitudes, and the effect of a gypsum layer on the seafloor. Additionally, we model Europa's seafloor scaled from other geologically active bodies, i.e., Earth, Venus, and Io, investigating the distinguishability of volcanic or plate tectonic features. We find that seafloor topography should be detectable at the resolution of Clipper, while the ice shell characteristics (e.g., via admittance analysis) are not resolvable globally. In our baseline scenario, seafloor topography dominates the total gravity signal up to degree l = 22, while for planetary analogs this proves true up to degree l = 11 for an Earth-scaled seafloor, as well as l = 42 and l = 54 for a Venus- or Io-scaled seafloor. Finally, we find that a putative layer of gypsum on the seafloor reduces the gravity signal by flattening out the seafloor, though its presence will not be detectable absent independent determination of its topographic amplitude.

Keywords: Gravitational fields, Galilean satellites, Europa
Insight into the Distribution of High-pressure Shock Metamorphism in Rubble-pile Asteroids. Shock metamorphism in ordinary chondrites allows for reconstructing impact events between asteroids in the main asteroid belt. Shock-darkening of ordinary chondrites occurs at the onset of complete shock melting of the rock (&gt;70 GPa) or injection of sulfide and metal melt into the cracks within solid silicates (~50 GPa). Darkening of ordinary chondrites masks diagnostic silicate features observed in the reflectance spectrum of S-complex asteroids so they appear similar to C/X-complex asteroids. In this work, we investigate the shock pressure and associated metamorphism pattern in rubble-pile asteroids at impact velocities of 4-10 km s-1. We use the iSALE shock physics code and implement two-dimensional models with simplified properties in order to quantify the influence of the following parameters on shock-darkening efficiency: impact velocity, porosity within the asteroid, impactor size, and ejection efficiency. We observe that, in rubble-pile asteroids, the velocity and size of the impactor are the constraining parameters in recording high-grade shock metamorphism. Yet, the recorded fraction of higher shock stages remains low (&lt;0.2). Varying the porosity of the boulders from 10% to 30% does not significantly affect the distribution of pressure and fraction of shock-darkened material. The pressure distribution in rubble-pile asteroids is very similar to that of monolithic asteroids with the same porosity. Thus, producing significant volumes of high-degree shocked ordinary chondrites requires strong collision events (impact velocities above 8 km s-1 and/or large sizes of impactors). A large amount of asteroid material escapes during an impact event (up to 90%); however, only a small portion of the escaping material is shock-darkened (6%).

Keywords: Main belt asteroids, Chondrites, Asteroid dynamics, Computational methods
Callisto and Europa Gravity Measurements from JUICE 3GM Experiment Simulation. The JUpiter Icy Moons Explorer is an ESA mission set for launch in 2023 April and arrival in the Jovian system in 2031 July to investigate Jupiter and its icy satellites with a suite of 10 instruments. The mission will execute several flybys of the icy moons Europa, Callisto, and Ganymede before ending the mission with a 9-month orbit around Ganymede. The 3GM experiment on board the spacecraft will exploit accurate range and Doppler (range-rate) measurements to determine the moons' orbit, gravity field, and tidal deformation. The focus of this paper is on the retrieval of Europa's and Callisto's gravity field, without delving into the modeling of their interior structures. By means of a covariance analysis of the data acquired during flybys, we assess the expected results from the 3GM gravity experiment. We find that the two Europa flybys will provide a determination of the J 2 and C 22 quadrupole gravity field coefficients with an accuracy of 3.8 × 10-6 and 5.1 × 10-7, respectively. The 21 Callisto flybys will provide a determination of the global gravity field to approximately degree and order 7, the moon ephemerides, and the time-variable component of the gravitational tide raised by Jupiter on the moon. The k 2 Love number, describing the Callisto tidal response at its orbital period, can be determined with an uncertainty σ  k2 ~ 0.06, allowing us to distinguish with good confidence between a moon with or without an internal ocean. The constraints derived by 3GM gravity measurements can then be used to develop interior models of the moon.

Keywords: Gravitational fields, Tides, Galilean satellites, Orbit determination, Jovian satellites
Observations and Modeling of the Opposition Surges of the Icy Moons of Saturn Based on Cassini Visual Infrared Mapping Spectrometer Data. Observations of the opposition surges on the main moons of Saturn (Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus) during Cassini's prime and extended missions are reduced and analyzed. The main data set comes from the Visual Infrared Mapping Spectrometer (VIMS) with wavelength coverage in the visible and near-infrared out to 3.60 μm, covering 99% of the solar spectrum. Imaging Science Subsystem images and Ultraviolet Imaging Spectrometer data augment the VIMS data set. Hapke models are fit to Dione and Rhea, and Irvine's simpler shadowing model is fit to the sparser data sets of Enceladus, Dione, and Rhea. The high porosities (~95% void space in the optically active portion of the regolith) and forward-scattering properties of the surfaces are similar to other icy moons and to Pluto. A change in the character of their opposition surge at 3.60 μm can be attributed largely to the noninteraction of long-wavelength photons with small particles on these moons' surfaces. The opposition surge on the low- and high-albedo regions of Dione are similar. However, the low-albedo terrain of Iapetus exhibits a less robust surge than the high-albedo regions, which we attribute to differences in surface texture. The low-albedo hemisphere of Iapetus seems to be akin to the small number of bodies in the solar system that lack an appreciable opposition surge, possibly due to the accumulation of low-albedo dust. With observations over the range of the solar spectrum, we compute new values for the bolometric Bond albedos of these moons.

Keywords: Saturnian satellites, Opposition, Infrared photometry