Sazuna/UAT_keywords huggingface dataset:
Bistability of the Atmospheric Circulation on TRAPPIST-1e. Using a 3D general circulation model, we demonstrate that a confirmed rocky exoplanet and a primary observational target, TRAPPIST-1e presents an interesting case of climate bistability. We find that the atmospheric circulation on TRAPPIST-1e can exist in two distinct regimes for a 1 bar nitrogen-dominated atmosphere. One is characterized by a single strong equatorial prograde jet and a large day-night temperature difference; the other is characterized by a pair of mid-latitude prograde jets and a relatively small day-night contrast. The circulation regime appears to be highly sensitive to the model setup, including initial and surface boundary conditions, as well as physical parameterizations of convection and cloud radiative effects. We focus on the emergence of the atmospheric circulation during the early stages of simulations and show that the regime bistability is associated with a delicate balance between the zonally asymmetric heating, mean overturning circulation, and mid-latitude baroclinic instability. The relative strength of these processes places the GCM simulations on different branches of the evolution of atmospheric dynamics. The resulting steady states of the two regimes have consistent differences in the amount of water content and clouds, affecting the water absorption bands as well as the continuum level in the transmission spectrum, although they are too small to be detected with current technology. Nevertheless, this regime bistability affects the surface temperature, especially on the night side of the planet, and presents an interesting case for understanding atmospheric dynamics and highlights uncertainty in 3D GCM results, motivating more multimodel studies.

Keywords: Water vapor, Theoretical models, Atmospheric circulation, Planetary atmospheres, Transmission spectroscopy, Habitable zone, Habitable planets, Exoplanet atmospheres
Momentum Enhancement from a 3 cm Diameter Aluminum Sphere Striking a Small Boulder Assembly at 5.4 km s<SUP>-1</SUP>. An impact experiment was performed with a target of relevance to the upcoming DART impact. In this experiment, a collection of stones that is similar to a rubble pile was the target, though it was necessary to hold the stones in place (in this case with cement) since the target was hung vertically to perform the experiment. The stones-cement target has a higher density and a lower porosity than expected for Dimorphos, with the density being 2.92 g cm-3. A 3 cm diameter aluminum sphere was launched at a speed of 5.44 km s-1, which is similar to the anticipated 6.1 km s-1 impact speed of DART. The stones-concrete target was completely disassembled by the impact. The target was mounted on a pendulum. The swing of the pendulum was measured and from it the momentum enhancement $\beta ={3.4}_{-1.0}^{+0.1}$ was measured. Due to possible lateral expansion of debris material, this value is a lower bound on the momentum enhancement that would be imparted to an extended target.

Keywords: Impact phenomena, Near-Earth objects, Ejecta
Burial Depths of Extensive Shallow Cryptomaria in the Lunar Schiller-Schickard Region. Quantifying the volumes and geologic nature of lunar volcanic eruptions is important for constraining the thermal and geologic evolution of the Moon. Cryptomaria are effusive, basaltic lava flows on the Moon that were subsequently buried, and therefore hidden, by higher-albedo basin and crater ejecta. Radar offers the ability to probe the subsurface for geologic units not otherwise apparent at the surface. We use Arecibo/Green Bank Observatory and Lunar Reconnaissance Orbiter Mini-RF radar data sets to characterize maria and cryptomaria within the Schiller-Schickard region. We find significant variability in the radar backscatter across the region that does not correspond to previously mapped boundaries of maria and cryptomaria in the literature. We use the characteristic low backscatter (due to the attenuating nature in radio waves of some basaltic minerals) to analyze the distribution of cryptomaria. We use the reduction in radar backscatter to estimate burial depths of cryptomaria across the area. We present a new map of Schiller-Schickard cryptomaria and the local variability in the thicknesses of the light plains that bury the basalts. We find burial depths ranging from &gt;100 m in the deepest areas to just a few to tens of meters in areas with shallow cryptomaria (particularly prominent in the southeast). These areas are generally contiguous with maria, allowing us to track mare lava flow units into the subsurface at mare/highland margins. We propose that ~67% of the region contains surface or buried basaltic volcanism, which represents over twice (2.7× increase) the areal extent of cryptomaria reported in previous studies.

Keywords: Lunar maria, Planetary surfaces, Radar astronomy, Volcanism
The Contribution of Small Impact Craters to Lunar Polar Wander. Changes in mass distribution affect the gravitational figure and reorient a planetary body's surface with respect to its rotational axis. The mass anomalies in the present-day lunar gravity field can reveal how the figure and pole position have evolved over the Moon's history. By examining sequentially each individual crater and basin, working backward in time order through the catalog of nearly 5200 craters and basins between 1200 and 20 km in diameter, we investigate their contribution to the lunar gravitational figure and reconstruct the evolution of the pole position by extracting their gravitational signatures from the present-day Moon. We find that craters and basins in this diameter range, which excludes South Pole-Aitken, have contributed to nearly 25% of the present-day power from the Moon's degree-2 gravitational figure and resulted in a total displacement of the Moon's pole by ~10° along the Earth-Moon tidal axis over the past ~4.25 billion years. This also implies that the geographical location of the Moon's rotational pole has not moved since ~3.8 Ga by more than ~2° in latitude owing to impacts, and this has implications for the long-term stability of volatiles in the polar regions.

Keywords: Impact phenomena, Planetary polar regions, Lunar geodesy, Lunar gravitational field, The Moon, Lunar impacts, Lunar evolution, Planetary dynamics, Planetary structure
Spacecraft Geometry Effects on Kinetic Impactor Missions. The DART (Double Asteroid Redirection Test) mission will impact a spacecraft on the secondary (Dimorphos) of the binary asteroid system Didymos in 2022 September, with the goal of altering the orbital period of Dimorphos about Didymos sufficiently to be observed from ground-based observations. Numerical impact modeling is a crucial component in understanding the outcome of the DART experiment, and while many have investigated the effects of target properties, such as material strength and porosity (which remain unknown), an often overlooked factor is the importance of accurately representing the spacecraft itself in such models. Most impact modeling to date has considered simple impactor geometries such as a solid uniform sphere, but in reality the spacecraft is a complex shape full of different components, open spaces, and thin walled structures. At a minimum, a simple solid representation underestimates the surface area of the impact: for a small body such as Dimorphos (approximately 160 m in diameter), the difference between a spacecraft spanning 20 m (including solar arrays) impacting and a sub-1 m idealized shape may be important. In this paper, we compare models impacting high-fidelity models of the spacecraft based on the CAD geometry with various simplified impactors, in order to assess the potential importance of this effect. We find that the difference between the simplest impactor geometries (such as a uniform sphere) and the real spacecraft is measurable, and has an interesting dependence on the material properties of the asteroid itself.

Keywords: Impact phenomena, Space vehicles, Asteroids, Planetary science
A New Archive of Apollo's Lunar Seismic Data. The Apollo astronauts deployed seismic experiments on the nearside of the Moon between 1969 and 1972. Five stations collected passive seismic data. Apollo 11 operated for around 20 days, and stations 12, 14, 15, and 16 operated nearly continuously from their installation until 1977. Seismic data were collected and digitized on the Moon and transmitted to Earth. The data were recorded on magnetic reel-to-reel tapes, with timestamps representing the signal reception time on Earth. The taped data have been widely used for many applications and have previously been shared in various formats. The data have slightly varying sampling rates, due to random fluctuations of the data sampler and also its sensitivity to the significant temperature variations on the Moon's surface. Additionally, there were timing errors. Previously shared versions of the Apollo data were affected by these problems. We have reimported the passive data to SEED (Standard for the Exchange of Earthquake Data) format, and we make these data available via Incorporated Research Institutions for Seismology and the Planetary Data System. We have cleaned the timestamp series to reduce incorrectly recorded timestamps. The archive includes five tracks: three components of the mid-period seismometers, one short-period component, and a time track containing the timestamps. The seismic data are provided unprocessed in their raw format, and we provide instrument response files. We hope that the new archive will make it easier for a new generation of seismologists to use these data to learn more about the structure of the Moon.

Keywords: Lunar interior, Lunar seismology
Selenographic and Local Time Dependence of Lunar Exospheric Sodium as Observed by LADEE. Even though sodium (Na) has been known to be a constituent of the lunar exosphere for the past thirty years, limitations introduced by Earth-based observations make it difficult to determine how its distribution varies with local time. We used observations from the Ultraviolet and Visible Spectrometer instrument on board the NASA Lunar Atmosphere and Dust Environment Explorer mission to search for evidence of near-instantaneous dayside variation of exospheric Na across one lunation (2014 February-March). Through comparison with model simulations, the data appear to be consistent with persistent southern enhancements of Na, while no evidence of systematic depletion of the Na exosphere reservoir within two hours of local noon was obtained. The results indicate an enhancement of the gas density over Mare regions and the lunar nearside; though this finding could mean that the weak Na emission is lost in the scattering continuum over brighter soils. Day-to-day variability is observed and may reflect a changing solar wind and meteoroid environment combined with inhomogeneities in the gas-surface interaction parameters and Na distribution on the lunar surface. We found that, due to the limited viewing geometry and sensitivity of the instrument to scattering from the bright lunar surface, it is difficult to uniquely separate the latitudinal and local time variations of Na.

Keywords: Lunar composition, Exosphere, Lunar atmosphere
Tilting Uranus via Spin-Orbit Resonance with Planet Nine. Uranus's startlingly large obliquity of 98° has yet to admit a satisfactory explanation. The most widely accepted hypothesis involving a giant impactor that tipped Uranus onto its side encounters several difficulties with regard to Uranus's spin rate and prograde satellite system. An obliquity increase that was driven by capture of Uranus into a secular spin-orbit resonance remains a possible alternative hypothesis that avoids many of the issues associated with a giant impact. We propose that secular spin-orbit resonance could have excited Uranus's obliquity to its present-day value if it was driven by the outward migration of an as-yet-undetected outer solar system body commonly known as Planet Nine. We draw support for our hypothesis from an analysis of 123 N-body simulations with varying parameters for Planet Nine and its migration. We find that in multiple instances, a simulated Planet Nine drives Uranus's obliquity past 98°, with a significant number falling within 10% of this value. We note a significant caveat to our results in that a much faster than present-day spin axis precession rate for Uranus is required in all cases for it to reach high obliquities. We conclude that while it was, in principle, possible for Planet Nine (if it exists) to have been responsible for Uranus's obliquity, the feasibility of such a result hinges on Uranus's primordial precession rate.

Keywords: Celestial mechanics, Solar system gas giant planets, Trans-Neptunian objects
Arecibo Planetary Radar Observations of Near-Earth Asteroids: 2017 December-2019 December. We successfully observed 191 near-Earth asteroids using the Arecibo Observatory's S-band planetary radar system from 2017 December through 2019 December. We present radar cross sections for 167 asteroids; circular-polarization ratios for 112 asteroids based on Doppler-echo-power spectra measurements; and radar albedos, constraints on size and spin periods, and surface-feature and shape evaluation for 37 selected asteroids using delay-Doppler radar images with a range resolution of 75 m or finer. Out of 33 asteroids with an estimated effective diameter of at least 200 m and sufficient image quality to give clues of the shape, at least 4 (~12%) are binary asteroids, including 1 equal-mass binary asteroid, 2017 YE5, and at least 10 (~30%) are contact-binary asteroids. For 5 out of 112 asteroids with reliable measurements in both circular polarizations, we measured circular-polarization ratios greater than 1.0, which could indicate that they are E-type asteroids, while the mean and the 1σ standard deviation were 0.37 ± 0.23. Further, we find a mean opposite-sense circular-polarization radar albedo of 0.21 ± 0.11 for 41 asteroids (0.19 ± 0.06 for 11 S-complex asteroids). We identified two asteroids, 2011 WN15 and (505657) 2014 SR339, as possible metal-rich objects based on their unusually high radar albedos, and discuss possible evidence of water ice in 2017 YE5.

Keywords: Near-Earth objects, Asteroids, Radar telescopes, Remote sensing, Planetary science
Assessing Environmental Factors of Alluvial Fan Formation on Titan. Present-day environmental conditions on Titan, the largest moon of Saturn, may do active geomorphic work on its surface. On Earth, the hydrologic water cycle erodes and weathers its continents. Deluges over elevated terrain create debris flows and sheetfloods that spread into alluvial fans as the topographic slope decreases. Mars also shows evidence of past fluvial erosion, but fluvial activity cannot be ongoing in the present. On Titan, however, fluvial erosion is likely ongoing. In this study, we focus on understanding the environmental controls on the spatial distributions of alluvial fans, a type of fluvial depositional feature observed globally on the surface of Titan. To do this, we utilize probabilistic models to determine the strength of spatial correlations between spatial distributions of alluvial fans and present-day environmental factors. We find that the spatial distribution of alluvial fans on Titan correlates well with several present-day environmental conditions, including average precipitation, precipitation variability, and elevation. Based on our model, we also provide predictions of the likelihood of alluvial fan occurrences for areas of Titan not mapped with Cassini, which may be of interest for future missions to Titan.

Keywords: Planetary surfaces, Planetary atmospheres, Titan, Saturnian satellites, Land-atmosphere interactions
Surface Conditions and Resource Accessibility at Potential Artemis Landing Sites 007 and 011. International efforts are underway to explore the Moon's south polar region with robotic and human missions. These missions will address key scientific and exploration objectives in a region rich with possibilities, designed to develop a sustained lunar presence. To assist a trade study among six potential landing sites identified for Artemis astronauts, we examined two of those sites: 007 and 011. We find that (1) many craters in the vicinity of Site 007 excavated and expose ejecta from Shackleton and Slater; additionally, numerous craters around Site 011 expose Cabeus and de Gerlache ejecta; (2) dense boulder fields occur near a large permanently shadowed region (PSR) at Site 007 and near the point of highest surface illumination in Site 011, which may affect landing and surface exploration activities; (3) despite some surface roughness, both sites 007 and 011 are traversable and contain exploration targets suitable for in situ resource utilization; (4) sites 007 and 011 receive higher average illumination than previously reported for sites 001 and 004; and (5) PSRs, seasonally shadowed regions, and cold traps at both sites offer opportunities to sample volatiles.

Keywords: Selenology, Lunar surface
Let It Go: Geophysically Driven Ejection of the Haumea Family Members. We present a new model for Haumea's formation and evolution that relies on geophysical and geochemical data informed from observations of Haumea and meteorites to explain the characteristics of Haumea and its dynamical family. We hypothesize that after the impact of two partially differentiated Kuiper Belt objects, Haumea's rocky core grew, decreasing its moment of inertia (MOI), spinning it up to the point that icy material was ejected from its surface. This ice, carrying about 3% of Haumea's mass and 14% of its initial angular momentum, comprises the Haumean dynamical family and the ring system and moons observed today. Later, melted ice hydrated Haumea's core and it grew, increasing Haumea's MOI and spinning it down to the modern value. We use the geophysical code kyushu to demonstrate that solutions exist for a Haumea in hydrostatic equilibrium at each of these hypothesized stages. Geochemical modeling using the IcyDwarf code constrains the formation of Haumea's core and the creation of the collision family to have occurred after roughly 150-160 Myr of solar system evolution (4.41 ± 0.01 Gyr ago). Hydration of the core was complete by about 0.20 Gyr, but a substantial subsurface ocean with half the mass of Earth's oceans persisted until it froze at about 0.45 Gyr, making Haumea the solar system's most distant potential relict ocean world.

Keywords: Dwarf planets, Planetary interior, Kuiper belt
Physical Characterization of Near-Earth Asteroid (52768) 1998 OR2: Evidence of Shock Darkening/Impact Melt. We conducted photometric and spectroscopic characterization of near-Earth asteroid (52768) 1998 OR2 during a close approach to Earth in 2020 April. Our photometric measurements confirm the rotation period of the asteroid to be 4.126 ± 0.179 hr, consistent with the previously published value of 4.112 ± 0.001 hr. By combining our visible spectroscopic measurements (0.45-0.93 μm) with archival MITHNEOS near-infrared spectra (0.78-2.49 μm), we classify the asteroid as an Xn-type in the Bus-DeMeo taxonomy. The combined spectrum shows two weak absorption bands: Band I at 0.926 ± 0.003 μm and Band II at 2.07 ± 0.02 μm, with band depths of 4.5% ± 0.15% and 4.0% ± 0.21%, respectively. The band area ratio is 1.13 ± 0.05. These spectral band parameters plot at the tip of the S(IV) region of the Gaffey S-asteroid subtypes plot, suggesting an affinity to ordinary chondrite meteorites. We calculated the chemistry of olivine and pyroxene using the Band I center to be 20.1 ± 2.3 mol% fayalite and 18.2 ± 1.5 mol% ferrosilite, consistent with H-chondrites. Principal component analysis of 1998 OR2's combined visible-near-IR spectrum falls on the C/X-complex side of the α-line, near the end of the shock-darkening trend, consistent with its weak absorption bands (band depth &lt;5%). We use an areal mixing model with lab measurements of the shock-darkened H5 chondrite, Chergach, to constrain the amount of shock-darkened material on the asteroid's surface at ~63% dark lithology and ~37% light lithology.

Keywords: Observational astronomy, Near-Earth objects, Asteroids, Spectroscopy, Planetary science, Meteorites, Solar system astronomy
Momentum Enhancement during Kinetic Impacts in the Low-intermediate-strength Regime: Benchmarking and Validation of Impact Shock Physics Codes. In 2022 September, the DART spacecraft (NASA's contribution to the Asteroid Impact &amp; Deflection Assessment (AIDA) collaboration) will impact the asteroid Dimorphos, the secondary in the Didymos system. The crater formation and material ejection will affect the orbital period. In 2027, Hera (ESA's contribution to AIDA) will investigate the system, observe the crater caused by DART, and characterize Dimorphos. Before Hera's arrival, the target properties will not be well-constrained. The relationships between observed orbital change and specific target properties are not unique, but Hera's observations will add additional constraints for the analysis of the impact event, which will narrow the range of feasible target properties. In this study, we use three different shock physics codes to simulate momentum transfer from impactor to target and investigate the agreement between the results from the codes for well-defined target materials. In contrast to previous studies, care is taken to use consistent crushing behavior (e.g., distension as a function of pressure) for a given porosity for all codes. First, we validate the codes against impact experiments into a regolith simulant. Second, we benchmark the codes at the DART impact scale for a range of target material parameters (10%-50% porosity, 1.4-100 kPa cohesion). Aligning the crushing behavior improves the consistency of the derived momentum enhancement between the three codes to within +/-5% for most materials used. Based on the derived mass-velocity distributions from all three codes, we derive scaling parameters that can be used for studies of the ejecta curtain.

Keywords: Impact phenomena, Near-Earth objects, Asteroid satellites, Planetary science, A subgiant stars
The Horizontal Wavelength Spectrum of Gravity Wave Activity in Mars's Lower Atmosphere: The Perspective from MGS-TES Nadir Observations. Connecting upper-atmospheric gravity waves (GW) to their lower- and middle-atmospheric (0-30 and 30-100 km altitude) origins can improve understanding of the evolution of Mars's atmosphere as well as its present thermal structure and general circulation. A recent study using observations from the Mars Climate Sounder (MCS) on board the Mars Reconnaissance Orbiter (MRO) characterized the climatology of lower-atmospheric GW with 10-100 km horizontal wavelengths, but GW observed in the upper atmosphere have horizontal wavelengths of up to 500 km, motivating more careful attention to the horizontal wavelength spectrum of lower-atmospheric GW. A previous study of observations by the Thermal Emission Spectrometer (TES) on Mars Global Surveyor (MGS) reported substantial interannual variability in the horizontal wavelength spectrum of wave activity defined broadly, including GW. Here, we derive the horizontal wavelength spectrum of wave activity from the brightness temperature variance spectrum of MGS-TES observations resampled to the MRO-MCS spectral channels during L  s  = 120°-150°, Mars Years 24 and 25. Lower-atmospheric wave activity is strongest at wavelengths &lt;200 km, a population which resembles that observed by MRO-MCS and is likely GW activity. This short-wavelength population is distinct from a wave population with wavelengths &gt;1000 km, which appears to be a mixture of tides and planetary waves. We find that interannual variability in GW activity previously identified using MGS-TES data largely arises from a change in the instrumental noise characteristics of MGS-TES during the first quarter of MY 25.

Keywords: Mars, Planetary atmospheres, Atmospheric variability