Sazuna/UAT_keywords huggingface dataset:
Seasonal Variations of Chemical Species and Haze in Titan's Upper Atmosphere. Seasonal variation is significant in Titan's atmosphere owing to the large change of solar insolation resulting from Titan's 26.7° axial tilt relative to the plane of Saturn's orbit. Here we present an investigation of hydrocarbon and nitrile species in Titan's upper atmosphere at 400-1200 km, which includes the mesosphere and the lower thermosphere, over more than one-fourth of Titan's year (2006-2014, L S = 318°-60°), using 18 stellar occultation observations obtained by Cassini/Ultraviolet Imaging Spectrograph. Vertical profiles of eight chemical species (CH4, C2H2, C2H4, C2H6, C4H2, C6H6, HCN, HC3N) and haze particles are retrieved from these observations using an instrument forward model, which considers the technical issue of pointing motion. The Markov Chain Monte Carlo algorithm is used to obtain the posterior probability distributions of parameters in the retrieval, which inherently tests the extent to which species profiles can be constrained. The results show that no change of the species profiles is noticeable before the equinox, while the decrease of atmospheric temperature and significant upwelling in the summer hemisphere are found five terrestrial years afterward. Altitude of the detached haze layer decreases toward the vernal equinox and then disappears, and no reappearance is identified within the time range of our data, which is consistent with observations from Cassini/Imaging Science Subsystem. This study provides observational constraints on the seasonal change of Titan's upper atmosphere and suggests further investigations of the atmospheric chemistry and dynamics therein.

Keywords: Upper atmosphere, Titan, Planetary atmospheres, Atmospheric composition, Atmospheric variability
Model of Double Asteroid Redirection Test Impact Ejecta Plume Observations. The Double Asteroid Redirection Test (DART) spacecraft will impact the moon Dimorphos of the [65803] Didymos binary in order to demonstrate asteroid deflection by a kinetic impactor. DART will measure the deflection by using ground-based telescopic observations of the orbital period change of Didymos and will carry the Light Italian CubeSat for Imaging of Asteroids (LICIACube) cubesat, which will perform a flyby of Didymos about 167 s after the DART impact, obtaining images of the DART impact ejecta plume. LICIACube images showing the ejecta plume spatial structure and temporal evolution will help determine the vector momentum transfer from the DART impact. A model is developed for the impact ejecta plume optical depth, using a point-source scaling model of the DART impact. The model is applied to expected LICIACube plume images and shows how plume images enable characterization of the ejecta mass versus velocity distribution. The ejecta plume structure, as it evolves over time, is determined by the amount of ejecta that has reached a given altitude at a given time. The evolution of the plume optical depth profiles determined from LICIACube images can distinguish between strength-controlled and gravity-controlled impacts, by distinguishing the respective mass versus velocity distributions. LICIACube plume images discriminate the differences in plume structure and evolution that result from different target physical properties, mainly the strength and porosity, thereby allowing inference of these properties to improve the determination of DART impact momentum transfer.

Keywords: Near-Earth objects, Close encounters
Moderately High Obliquity Promotes Biospheric Oxygenation. Planetary obliquity is a first-order control on planetary climate and seasonal contrast, which has a number of cascading consequences for life. How moderately high obliquity (obliquities greater than Earth's current obliquity up to 45°) affects a planet's surface physically has been studied previously, but we lack an understanding of how marine life will respond to these conditions. We couple the ROCKE-3D general circulation model to the cGENIE 3D biogeochemical model to simulate the ocean biosphere's response to various planetary obliquities, bioessential nutrient inventories, and biospheric structure. We find that the net rate of photosynthesis increased by 35% and sea-to-air flux of biogenic oxygen doubled between the 0° and 45° obliquity scenarios, which is an equivalent response to doubling bioessential nutrients. Our results suggest that moderately high obliquity planets have higher potential for biospheric oxygenation than their low-obliquity counterparts and that life on moderately high obliquity habitable planets may be easier to detect with next-generation telescopes. These moderately high obliquity habitable planets may also be more conducive to the evolution of complex life.

Keywords: Exoplanets, Ocean-atmosphere interactions, Astrobiology, Biosignatures, Habitable planets
Free Core Nutation and Its Relation to the Spin-over Mode. The time-varying response of Earth's and other planets' rotation to external gravitational torques depends strongly on their internal structure. In particular, the existence of the mode known as the free core nutation in the fluid core is known to amplify the forced nutations in the near-diurnal retrograde frequency band (as measured in the planetary frame of reference). Due to their proximity in shape and frequency, this mode is sometimes equated with the so-called spin-over mode, which denotes the free oscillation of a steadily rotating ellipsoidal fluid core. Through a careful study of the freely rotating two-layer planetary model with a rigid mantle and an inviscid fluid core, we show that the spin-over mode frequency corresponds to that where the sum of the external and internal torques on the mantle is balanced, causing it to rotate steadily. The presence of dissipation at the core-mantle boundary causes the free core nutation to become damped and slightly offsets its resonance frequency. We show that this offset, which is ≈-1 day for Earth, can be interpreted as the result of the proximity of the free core nutation frequency to that of the spin-over mode, which now corresponds to a minimum in the magnitude of the transfer function for nutations. We also show how this proximity leads to a slightly lower quality factor for the resonance than that computed from the usual formula. We conclude by discussing possible implications of this mechanism for Mars, the Moon, and the long-term evolution of Earth.

Keywords: Lunar geodesy, Mars, The Moon, Solar system, Earth (planet), Geodesics
New Polarimetric Data for the Galilean Satellites: Europa Observations and Modeling. This paper is dedicated to a long-standing problem of the shape of the negative branch of polarization (NBP) for Jupiter's moon Europa, determination of which is crucial for the characterization of the icy regolith on this satellite and similar objects, as well as for further progress in understanding light scattering by particulate surfaces. To establish the shape of Europa's NBP, in 2018-2021 we accomplished high-precision disk-integrated polarimetry of Europa in the UBVR I bands using the identical two-channel photoelectric polarimeters mounted on the 2.6 m Shajn reflector of the Crimean Astrophysical Observatory and the 2 m telescope of the Peak Terskol Observatory. We found that the polarization dependence on the phase angle in each filter is an asymmetric curve with a sharp polarization minimum ${P}_{\min }\approx -0.3 \% $ at phase angle ${\alpha }_{\min }\leqslant 0\buildrel{\circ}\over{.} 4$ , after which the polarization degree gradually increases to positive values, passing the inversion angle at α inv ≈ 6° - 7°. Within the error limits, the parameters P min, ${\alpha }_{\min }$ , and α inv of the NPB are independent of the wavelength in the visible spectrum. The polarization curve clearly demonstrates the so-called polarization opposition effect (POE). Our analysis of the previous and new polarimetric observations of Europa allows us to conclude that the POE is caused by coherent backscattering of sunlight on microscopic icy grains covering Europa's surface. Computer modeling with the numerical radiative transfer coherent backscattering method demonstrates that the best fit to the polarimetric observations and geometric albedo of Europa is provided by a regolith layer of elementary single-scattering albedo ~0.985 and extinction mean free path length 2π l/λ eff ≈ 150, λ eff representing the effective wavelength in the UBVR I spectral bands.

Keywords: Europa, Galilean satellites, Polarimetry, Jovian satellites
Dust Evolution in the Coma of Distant, Inbound Comet C/2017 K2 (PANSTARRS). C/2017 K2 (PANSTARRS) is an Oort Cloud comet previously observed to be active at heliocentric distances r &gt; 20 au on what is likely its first passage through the inner solar system. We observed the comet on 2021 March 19-20 at r = 6.82 au preperihelion and 8.°35 phase angle with the Hubble Space Telescope (HST), and obtained high spatial resolution photometry and polarimetry mapping the properties of dust over the coma prior to the onset of water ice sublimation activity on the nucleus. We found clear radial gradients in the color and polarization of the coma: the F475W-F775W ( $g^{\prime} -i^{\prime} $ ) reflectance slope increased from ~4.5% per 100 nm within ~10,000 km of the nucleus up to ~7% per 100 nm by ~50,000 km, while the negative polarization in F775W ( $i^{\prime} $ ) strengthened from about -2% to -3.5% over the same range. The radial intensity profiles moreover strongly deviate from profiles simulated for stable dust grains. Near-infrared imagery obtained with the Palomar Hale Telescope on 2021 May 18 at r = 6.34 au revealed a continued absence of micron-sized grains in the tail, but showed no clear spatial gradient in JHKs colors. The observed patterns collectively appear consistent with the inner coma being optically dominated by sublimating, micron-sized water ice grains, unlike the tail of more stable, millimeter-sized grains. Finally, we evaluated these results alongside other Oort Cloud comets, and found in a reanalysis of HST observations of C/2012 S1 (ISON) that the near-nucleus polarimetric halo reported for that comet is likely an observational artifact.

Keywords: Long period comets, Comets, Comae, Coma dust
Next-generation Laser Ranging at Lunar Geophysical Network and Commercial Lander Payload Service Sites. Five retroreflector arrays currently on the Moon reflect short laser pulses back to Earth, allowing range to be measured. Each array has multiple small corner cubes. Due to variable lunar optical librations of the direction to Earth, the tilted arrays spread return times of single photons in the returned laser pulse, degrading the synthesized multiphoton normal point range accuracy. The Next Generation Lunar Retroreflectors (NGLRs) and MoonLIGHT reflectors currently being fabricated are larger 10 cm single corner cubes that do not spread the pulse. The Lunar Geophysical Network (LGN) mission will place NGLRs at three separated sites on the lunar nearside. The Commercial Lander Payload Service (CLPS) and early Artemis missions will precede the LGN mission. Solutions that include 6 yr of simulated Lunar Laser Ranging (LLR) data to two sites in the north and two in the south show improvement in the uncertainties of many science parameters. Lunar solution parameters include displacement Love numbers h 2 and l 2, tidal dissipation at several frequencies, fluid-core/solid-mantle boundary (CMB) dissipation, and moment of inertia combinations (C-A)/B and (B-A)/C, with principal moments of inertia A &lt; B &lt; C. Submeter-accuracy coordinates of the new reflectors will result from the first month of well-distributed data. There are benefits other than lunar science: gravitational physics includes the equivalence principle; Earth science includes terrestrial tidal dissipation and ranging station positions and motions; and astronomical constants with GM(Earth+Moon) for the gravitational constant times the mass of the Earth-Moon system. Improvements are illustrated for h 2, l 2, (C-A)/B, (B-A)/C, equivalence principle, and GM(Earth+Moon).

Keywords: Space vehicle instruments, The Moon, Earth-moon system, Lunar science
The Outer Edge of the Venus Zone around Main-sequence Stars. A key item of interest for planetary scientists and astronomers is the habitable zone: the distance from a host star where a terrestrial planet can maintain necessary temperatures in order to retain liquid water on its surface. However, when observing a system's habitable zone, it is possible that one may instead observe a Venus-like planet. We define "Venus-like" as greenhouse-gas-dominated atmosphere occurring when incoming solar radiation exceeds infrared radiation emitted from the planet at the top of the atmosphere, resulting in a runaway greenhouse. Our definition of Venus-like includes both incipient and post-runaway greenhouse states. Both the possibility of observing a Venus-like world and the possibility that Venus could represent an end state of evolution for habitable worlds require an improved understanding of the Venus-like planet, specifically the distances where these planets can exist. Understanding this helps us define a "Venus zone"-the region in which Venus-like planets could exist-and assess the overlap with the aforementioned "habitable zone." In this study, we use a 1D radiative-convective climate model to determine the outer edge of the Venus zone for F0V, G2V, K5V, and M3V and M5V stellar spectral types. Our results show that the outer edge of the Venus zone resides at 3.01, 1.36, 0.68, 0.23, and 0.1 au, respectively. These correspond to incident stellar fluxes of 0.8, 0.55, 0.38, 0.32, and 0.3 S ⊙, respectively, where stellar flux is relative to Earth (1.0). These results indicate that there may be considerable overlap between the habitable zone and the Venus zone.

Keywords: Habitable zone, Venus, Carbon dioxide, Greenhouse gases
Radar and Optical Characterization of Near-Earth Asteroid 2019 OK. We conducted radar observations of near-Earth asteroid 2019 OK on 2019 July 25 using the Arecibo Observatory S-band (2380 MHz, 12.6 cm) planetary radar system. Based on Arecibo and optical observations the apparent diameter is between 70 and 130 m. Combined with an absolute magnitude of H = 23.3 ± 0.3, the optical albedo of 2019 OK is likely between 0.05 and 0.17. Our measured radar circular polarization ratio of μ  C  = 0.33 ± 0.03 indicates 2019 OK is likely not a V- or E-type asteroid and is most likely a C- or S-type. The measured radar echo bandwidth of 39 ± 2 Hz restricts the apparent rotation period to be approximately between 3 minutes (0.049 hr, D = 70 m) and 5 minutes (0.091 h, D = 130 m). Together, the apparent diameter and rotation period suggest that 2019 OK is likely not a rubble-pile body bound only by gravity. 2019 OK is one of a growing number of fast-rotating near-Earth asteroids that require some internal strength to keep them from breaking apart.

Keywords: Near-Earth objects, Asteroids, Small Solar System bodies, Close encounters, Apollo group
The Influence of Surface Binding Energy on Sputtering in Models of the Sodium Exosphere of Mercury. We have simulated the sodium (Na) exosphere of Mercury to show how the exosphere is affected by the assumed surface binding energy (SBE) of Na in the sputtered component. We constrained ion precipitation onto the surface using distributions for the cusp regions that are consistent with measurements by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging Fast Imaging Plasma Spectrometer instrument. We have simulated sputtering with SBEs of 0.27, 2.6, 4.4, and 7.9 eV, with the lowest value commonly used in exosphere models and the highest from recent molecular dynamics calculations for the Na-bearing feldspar end-member, albite. A gradual change in the exosphere is seen as the yield decreases and the ejecta energy increases with increasing SBE. We describe the corresponding exosphere source functions for ion sputtering (IS), as well as for the previously studied processes of micrometeoroid impact vaporization and photon-stimulated desorption (PSD), along with their release energy distributions and spatial distributions. We have summed the contributions of the various source processes to explain how and when the different sources can be distinguished by observations. The modeled exosphere scale heights range from 72 km for PSD to over 1000 km for IS using a SBE of 7.9 eV. We find that the processes responsible for generating Mercury's Na exosphere are separable by measuring line-of-sight column densities tangent to the planet at various altitudes and positions around the planet. Our initial results are consistent with the Na being sputtered from a high-SBE material such as feldspar, which has been predicted to be abundant on the Mercury's surface.

Keywords: Exosphere, Mercury (planet)
Double Asteroid Redirection Test (DART): Structural and Dynamic Interactions between Asteroidal Elements of Binary Asteroid (65803) Didymos. NASA's Double Asteroid Redirection Test (DART) mission is the first full-scale planetary defense mission. The target is the binary asteroid (65803) Didymos, in which the smaller component Dimorphos (~164 m equivalent diameter) orbits the larger component Didymos (~780 m equivalent diameter). The DART spacecraft will impact Dimorphos, changing the system's mutual orbit by an amount that correlates with DART's kinetic deflection capability. The spacecraft collision with Dimorphos creates an impact crater, which reshapes the body. Also, some particles ejected from the DART impact site on Dimorphos eventually reach Didymos. Because Didymos's rapid spin period (2.26 hr) may be close to its stability limit for structural failure, the ejecta reaching Didymos may induce surface disturbance on Didymos. While large uncertainties exist, nonnegligible reshaping scenarios on Didymos and Dimorphos are possible if certain conditions are met. Our analysis shows that given a surface slope uncertainty on Dimorphos of 45°, with no other information about its local topography, and if the DART-like impactor is treated as spherical, the ejecta cone crosses Didymos with speeds ≳14 m s-1 in 13% of simulations. Additional work is necessary to determine the amount of mass delivered to Didymos from the DART impact and whether the amount of kinetic energy delivered is sufficient to overcome cohesive forces in those cases. If nonnegligible (but small) reshaping occurs for either of these asteroids, the resulting orbit perturbation and reshaping are measurable by Earth-based observations.

Keywords: Near-Earth objects, Asteroids
The Possible Formation of Jupiter from Supersolar Gas. More than two decades ago, the Galileo probe performed in situ measurements of the composition of Jupiter's atmosphere and found that the abundances of C, N, S, P, Ar, Kr, and Xe were all enriched by factors of 1.5-5.4 times their protosolar value. Juno's measurements recently confirmed the supersolar N abundance and also found that the O abundance was enriched by a factor 1-5 compared with its protosolar value. Here, we aim at determining the radial and temporal evolution of the composition of gases and solids in the protosolar nebula (PSN) to assess the possibility that Jupiter's current composition was acquired via the direct accretion of supersolar gases. To do so, we model the evolution of a 1D α-viscous accretion disk that includes the radial transport of dust and ice particles and their vapors, with their sublimation and condensation rates, to compute the composition of the PSN. We find that the composition of Jupiter's envelope can be explained only from its accretion from PSN gas (α ≤ 10-3), or from a mixture of vapors and solids (α &gt; 10-3). The composition of the PSN at 4 au, namely between the locations of the H2O and CO2 icelines, reproduces the one measured in Jupiter between 100 and 300 kyr of disk evolution. Our results are found to be compatible with both the core accretion model, where Jupiter would acquire its metallicity by late accretion of volatile-rich planetesimals, and the gravitational collapse scenario, where the composition of proto-Jupiter would be similar to that of the PSN.

Keywords: Solar system gas giant planets, Jupiter, Protoplanetary disks, Planetary interior, Planet formation
Exploring the Shallow Subsurface of Mars with the Ma_MISS Spectrometer on the ExoMars Rover Rosalind Franklin. An essential part of the Exomars 2022 payload is the Mars Multispectral Imager for Subsurface Studies (Ma_MISS) experiment hosted by the drill system. Ma_MISS is a visible and near-infrared (0.4-2.3 μm) miniaturized spectrometer with an optical head inside the drill tip capable of observing the drill borehole with a spatial resolution of 120 μm. Here we report on how the Ma_MISS hyperspectral information provides in situ investigation of the subsurface at very fine resolution, prior to the collection of the samples that will be manipulated and crushed for further analysis by the analytical laboratory on the rover. Ma_MISS is the instrument that will closely investigate the subsurface mineralogical characteristics in its original geologic context at depths never reached before in Mars exploration. Ma_MISS recognizes all the major spectral features of the clays, basaltic, and minor phases expected at the ExoMars landing site, Oxia Planum. The high spatial resolution on the borehole wall is such that single grains of about 100 μm can be distinguishable in the assemblage of minerals observed by Ma_MISS. The spatial distribution of the mineralogies within the borehole walls is associated with the rocks and the processes that put these materials in place and possibly altered them with time, characterizing the habitats found in the stratigraphic record, indicating which ones are the most suitable to have held or to be holding nowadays traces of life.

Keywords: Mars
Comet 21P/Giacobini-Zinner: Narrowband Photometry of the Prototype of Carbon-chain Depleted Comets at Multiple Apparitions. We obtained extensive narrowband photoelectric photometry of Comet 21P/Giacobini-Zinner with observations spanning 33 yr. The original data from 1985 were re-reduced and are presented along with data from three additional apparitions, including 2018/19. The original conclusion regarding Giacobini-Zinner's chemical composition remains unchanged, with it having a 4-6× depletion in the carbon-chain molecules C2 and C3 and in NH, as compared with both OH and CN. The comet continues to exhibit a large asymmetry in production rates as a function of time and heliocentric distance, with production reaching a peak 3-5 weeks prior to perihelion. All species, including dust, follow the same general production rate curve each apparition, and the carbon-bearing species are always very similar to one another. However, OH and NH each differ in detail from the carbon-bearing species, implying somewhat varied composition between source regions. Longer term, there are only small secular changes among the apparitions before and near perihelion, but larger changes are evident as the comet recedes from the Sun, suggestive of a progressive precession of the rotation axis.

Keywords: Near-Earth objects, Comae, Comet nuclei, Short period comets, Comets, Comet volatiles