Sazuna/UAT_keywords huggingface dataset:
Detection of OH 18 cm Emission from Comet C/2020 F3 NEOWISE Using the Arecibo Telescope. We report the detection of emission from the OH 18 cm Λ-doublet transitions toward Comet C/2020 F3 NEOWISE using the Arecibo Telescope. The antenna temperatures are 113 ± 3 mK for the 1667 MHz line and 57 ± 3 mK for the 1665 MHz line. The beam-averaged OH column density (centered on the comet nucleus) derived from the 1667 transition is NOH = (1.11 ± 0.06) × 1013 cm-2. We implemented the Haser model to derive an OH production rate. The estimated OH production rate using the 1667 transition is QOH = (3.6 ± 0.6) × 1028 s-1, a factor of 2.4 lower than optically derived values for the same observing day, the difference of which is likely explained by quenching.

Keywords: Radio spectroscopy, Molecular spectroscopy, Comets, Comet volatiles , Hydroxyl sources
Regional Photometric Modeling of Asteroid (101955) Bennu. We present a regional photometric analysis of asteroid (101955) Bennu, using image data from the MapCam color imager of the OSIRIS-REx Camera Suite (OCAMS). This analysis follows the previously reported global photometric analysis of Bennu, which found that Bennu's roughness was difficult to photometrically model owing to unresolved surface variation. Here we find that, even with a high-resolution shape model (20 cm per facet) and automatic image registration (&lt;1 pixel error), Bennu remains a challenging surface to photometrically model: neither a suite of empirical photometric models nor the physically motivated Hapke model were able to eliminate the scatter in the data due to pixel-scale variations. Nonetheless, the models improved on the global analysis by identifying regional variations in Bennu's photometric response. A linear empirical model, when compared with independent measures of surface roughness and albedo, revealed correlations between those characteristics and phase slope. A regional Hapke analysis showed the same structure in its single-scattering albedo and asymmetry factors; although the Hapke parameters were loosely constrained, complicating interpretation of their spatial variation, the regional variation in relative parameter sensitivity also correlated with shallower phase slope, higher albedo, and less macroscopic roughness.

Keywords: Near-Earth objects, Asteroids, Surface photometry, Photometry, Asteroid surfaces
Asteroid 16 Psyche: Shape, Features, and Global Map. We develop a shape model of asteroid 16 Psyche using observations acquired in a wide range of wavelengths: Arecibo S-band delay-Doppler imaging, Atacama Large Millimeter Array (ALMA) plane-of-sky imaging, adaptive optics (AO) images from Keck and the Very Large Telescope (VLT), and a recent stellar occultation. Our shape model has dimensions 278 (-4/+8 km) × 238(-4/+6 km) × 171 km (-1/+5 km), an effective spherical diameter Deff = 222-1/+4 km, and a spin axis (ecliptic lon, lat) of (36°, -8°) ± 2°. We survey all the features previously reported to exist, tentatively identify several new features, and produce a global map of Psyche. Using 30 calibrated radar echoes, we find Psyche's overall radar albedo to be 0.34 ± 0.08 suggesting that the upper meter of regolith has a significant metal (i.e., Fe-Ni) content. We find four regions of enhanced or complex radar albedo, one of which correlates well with a previously identified feature on Psyche, and all of which appear to correlate with patches of relatively high optical albedo. Based on these findings, we cannot rule out a model of Psyche as a remnant core, but our preferred interpretation is that Psyche is a differentiated world with a regolith composition analogous to enstatite or CH/CB chondrites and peppered with localized regions of high metal concentrations. The most credible formation mechanism for these regions is ferrovolcanism as proposed by Johnson et al. (2020).

Keywords: Asteroids, Radar telescopes, Radar astronomy, Main belt asteroids, Asteroid surfaces
Characterization of Thermal-infrared Dust Emission and Refinements to the Nucleus Properties of Centaur 29P/Schwassmann-Wachmann 1. We present analyses of Spitzer observations of 29P/Schwassmann-Wachmann 1 using 16 μm IRS "blue" peak-up (PU) and 24 and 70 μm MIPS images obtained on UT 2003 November 23 and 24 that characterize the Centaur's large-grain (10-100 μm) dust coma during a time of non-outbursting "quiescent" activity. Estimates of ϵfρ for each band (16 μm (2600 ± 43 cm), 24 μm (5800 ± 63 cm), and 70 μm (1800 ± 900 cm)) follow the trend between nucleus size versus ϵfρ that was observed for the WISE/NEOWISE comet ensemble. A coma model was used to derive a dust production rate in the range of 50-100 kg s-1. For the first time, a color temperature map of SW1's coma was constructed using the 16 and 24 μm imaging data. With peaks at ~140 K, this map implies that coma water-ice grains should be slowly sublimating and producing water gas in the coma. We analyzed the persistent 24 μm "wing" (a curved southwestern coma) feature at 352,000 km (90″) from the nucleus attributed by Stansberry et al. to nucleus rotation and instead propose that it is largely created by solar radiation pressure and gravity acting on micron-sized grains. We performed coma removal to the 16 μm PU image in order to refine the nucleus' emitted thermal flux. A new application of the Near Earth Asteroid Thermal Model at five wavelengths (5.730, 7.873, 15.80, 23.68, and 71.42 μm) was then used to refine SW1's effective radius measurement to R = 32.3 ± 3.1 km and infrared beaming parameter to η = 1.1 ± 0.2, respectively.

Keywords: Centaur group, Comae, Short period comets, Infrared astronomy, Dust continuum emission, Infrared telescopes, Comets, Coma dust
Evidence that a Novel Type of Satellite Wake Might Exist in Saturn's E Ring. Saturn's E ring consists of micron-sized particles launched from Enceladus by that moon's geological activity. A variety of small-scale structures in the E ring's brightness have been attributed to tendrils of material recently launched from Enceladus. However, one of these features occurs at a location where Enceladus's gravitational perturbations should concentrate background E-ring particles into structures known as satellite wakes. While satellite wakes have been observed previously in ring material drifting past other moons, these E-ring structures would be the first examples of wakes involving particles following horseshoe orbits near Enceladus's orbit. The predicted intensity of these wake signatures is particularly sensitive to the fraction E-ring particles on orbits with low eccentricities and semimajor axes just outside of Enceladus's orbit, and so detailed analyses of these and other small-scale E-ring features should place strong constraints on the orbital properties and evolution of E-ring particles.

Keywords: Astrodynamics, Orbital motion, Planetary rings, Celestial mechanics, Three-body problem, Saturnian satellites
Consequences of Proposed Shoreline Deformation Scenarios for Jezero Crater, Mars. One of the most interesting questions about the climate and hydrology of early Mars is whether oceans existed and, if so, when. Various geologic features have been interpreted as ancient shorelines, but these features do not follow gravitational equipotentials. Prior work has shown that the elevation of the Arabia level, hypothesized to represent a large, early ocean, better conforms to an equipotential when correcting for global topographic change after its formation. Although the shoreline coordinates underlying these studies are debated, exploring the consequences of these topographic corrections allows additional observable consequences to be identified. Here we show that the topographic corrections cause Jezero crater, the landing site of the Perseverance rover, to be submerged under the proposed Arabia ocean. This precludes the ocean's existence during known fluvio-lacustrine activity at Jezero and suggests the ocean did not exist during the main era of valley network formation in the Noachian/Early Hesperian. We identify a period of ~108 yr years before fluvial activity at Jezero when the ocean could have existed and discuss potential observable consequences.

Keywords: Mars
The Likely Thickness of Europa's Icy Shell. The icy outer shell of Jupiter's moon Europa is believed to be geologically active, and geological processes within the ice may be key to sustaining chemical disequilibria and potentially habitable environments within the icy shell and ocean. Currently, there are insufficient observational data to determine the thickness of the icy shell, obfuscating crucial aspects of interior processes. Although a range of icy shell thicknesses (~10-1-102 km) have been proposed, not all are equally likely given the current knowledge of Europa. In this study, I construct a probability density distribution for Europa's present-day mean icy shell thickness using a heat flux balance, assuming a simple two-layered model consisting of a partially porous conductive upper layer, and a ductile interior layer that may be experiencing solid-state convection. Current best estimate (CBE) values and uncertainties for ~20 key parameters are propagated through this steady-state heat flux balance to construct ~107 independent simulations. Additionally, I estimate present-day values for the icy shell layer thicknesses, the rocky interior and icy heat fluxes, icy shell thermal properties, and convective ice viscosity. I predict Europa's total icy thickness to be ~23-47 km, with a CBE thickness of ${24.3}_{-1.5}^{+22.8}\,\mathrm{km}$ . This result is highly skewed; icy shells many tens of kilometers thick are much more probable than icy shells &lt;10 km thick. The resulting distributions have key implications for future spaceborne, landed, and subsurface exploration of Europa, as well as studies of icy shell processes, thermal and mechanical state, and habitability across the icy ocean worlds.

Keywords: Astrobiology, Tectonics, Europa
Science Goals and Objectives for the Dragonfly Titan Rotorcraft Relocatable Lander. NASA's Dragonfly mission will send a rotorcraft lander to the surface of Titan in the mid-2030s. Dragonfly's science themes include investigation of Titan's prebiotic chemistry, habitability, and potential chemical biosignatures from both water-based "life as we know it" (as might occur in the interior mantle ocean, potential cryovolcanic flows, and/or impact melt deposits) and potential "life, but not as we know it" that might use liquid hydrocarbons as a solvent (within Titan's lakes, seas, and/or aquifers). Consideration of both of these solvents simultaneously led to our initial landing site in Titan's equatorial dunes and interdunes to sample organic sediments and water ice, respectively. Ultimately, Dragonfly's traverse target is the 80 km diameter Selk Crater, at 7° N, where we seek previously liquid water that has mixed with surface organics. Our science goals include determining how far prebiotic chemistry has progressed on Titan and what molecules and elements might be available for such chemistry. We will also determine the role of Titan's tropical deserts in the global methane cycle. We will investigate the processes and processing rates that modify Titan's surface geology and constrain how and where organics and liquid water can mix on and within Titan. Importantly, we will search for chemical biosignatures indicative of past or extant biological processes. As such, Dragonfly, along with Perseverance, is the first NASA mission to explicitly incorporate the search for signs of life into its mission goals since the Viking landers in 1976.

Keywords: Planetary surfaces, Planetary atmospheres, Titan, Astrobiology, Pre-biotic astrochemistry
Six Outbursts of Comet 46P/Wirtanen. Cometary activity is a manifestation of sublimation-driven processes at the surface of nuclei. However, cometary outbursts may arise from other processes that are not necessarily driven by volatiles. In order to fully understand nuclear surfaces and their evolution, we must identify the causes of cometary outbursts. In that context, we present a study of mini-outbursts of comet 46P/Wirtanen. Six events are found in our long-term lightcurve of the comet around its perihelion passage in 2018. The apparent strengths range from -0.2 to -1.6 mag in a 5″ radius aperture and correspond to dust masses between ~104 and 106 kg, but with large uncertainties due to the unknown grain size distributions. However, the nominal mass estimates are on the same order of magnitude as the mini-outbursts at comet 9P/Tempel 1 and 67P/Churyumov-Gerasimenko, events that were notably lacking at comet 103P/Hartley 2. We compare the frequency of outbursts at the four comets, and suggest that the surface of 46P has large-scale (~10-100 m) roughness that is intermediate to that of 67P and 103P, if not similar to the latter. The strength of the outbursts appear to be correlated with time since the last event, but a physical interpretation with respect to solar insolation is lacking. We also examine Hubble Space Telescope images taken about two days following a near-perihelion outburst. No evidence for macroscopic ejecta was found in the image, with a limiting radius of about 2 m.

Keywords: Broad band photometry, Comets, Short period comets, Coma dust
The Science Case for a Return to Enceladus. The plume of Enceladus is unique in the solar system in providing direct access to fresh material from an extraterrestrial subsurface ocean. The Cassini Mission, though not specifically designed for it, was able to take advantage of the plume to conduct the best characterization to date of an extraterrestrial ocean. Evidence gathered from multiple instruments points to a global, subsurface liquid water ocean rich in salts and organic compounds, with water-rock interactions occurring presumably in hydrothermal systems at or below the moon's sea floor. Meeting the criteria of "extended regions of liquid water, conditions favorable for the assembly of complex organic molecules, and energy source(s) to sustain metabolism," the ocean of Enceladus can therefore be considered habitable. It is also the only confirmed place beyond the Earth where we can easily sample fresh material from a demonstrably habitable environment without the complications of digging or drilling. The next step is to investigate whether Enceladus' ocean is actually inhabited. Here, we summarize the evidence for Enceladus' ocean and its habitability, identify constraints and outstanding questions on the detectability of life within its ocean, and recommend a return to Enceladus with a dedicated search-for-life mission (or missions).

Keywords: Biosignatures, Astrobiology, Saturnian satellites, Ocean planets
Hydroxide Salts in the Clouds of Venus: Their Effect on the Sulfur Cycle and Cloud Droplet pH. The depletion of SO2 and H2O in and above the clouds of Venus (45-65 km) cannot be explained by known gas-phase chemistry and the observed composition of the atmosphere. We apply a full-atmosphere model of Venus to investigate three potential explanations for the SO2 and H2O depletion: (1) varying the below-cloud water vapor (H2O), (2) varying the below-cloud sulfur dioxide (SO2), and (3) the incorporation of chemical reactions inside the sulfuric acid cloud droplets. We find that increasing the below-cloud H2O to explain the SO2 depletion results in a cloud top that is 20 km too high, above-cloud O2 three orders of magnitude greater than observational upper limits, and no SO above 80 km. The SO2 depletion can be explained by decreasing the below-cloud SO2 to 20 ppm. The depletion of SO2 in the clouds can also be explained by the SO2 dissolving into the clouds, if the droplets contain hydroxide salts. These salts buffer the cloud pH. The amount of salts sufficient to explain the SO2 depletion entails a droplet pH of ~1 at 50 km. Because sulfuric acid is constantly condensing out into the cloud droplets, there must be a continuous and pervasive flux of salts of ≈10-13 mol cm-2 s-1 driving the cloud droplet chemistry. An atmospheric probe can test both of these explanations by measuring the pH of the cloud droplets and the concentrations of gas-phase SO2 below the clouds.

Keywords: Planetary atmospheres, Venus, Plasma clouds, Water vapor
Chandrayaan-2 Dual-frequency Synthetic Aperture Radar (DFSAR): Performance Characterization and Initial Results. The Dual-Frequency synthetic aperture radar (DFSAR) system manifested on the Chandrayaan-2 spacecraft represents a significant step forward in radar exploration of solid solar system objects. It combines SAR at two wavelengths (L and S bands) and multiple resolutions with several polarimetric modes in one lightweight (~20 kg) package. The resulting data from DFSAR support the calculation of the 2 × 2 complex scattering matrix for each resolution cell, which enables lunar near-surface characterization in terms of radar polarization properties at different wavelengths and incidence angles. In this paper, we report on the calibration and preliminary performance characterization of DFSAR data based on the analysis of a sample set of crater regions on the Moon. Our calibration analysis provided a means to compare on-orbit performance with prelaunch measurements, and the results matched with the prelaunch expected values. Our initial results show that craters in both permanently shadowed regions (PSRs) and non-PSRs that are classified as circular polarization ratio-anomalous in previous S-band radar analyses appear anomalous at the L band also. We also observe that material evolution and physical properties at their interior and proximal ejecta are decoupled. For the Byrgius C crater region, we compare our analysis of dual-frequency radar data with the predicted behaviors of theoretical scattering models. If crater age estimates are available, a comparison of their radar polarization properties at multiple wavelengths similar to that of the three unnamed south polar crater regions shown in this study may provide new insights into how the rockiness of craters evolves with time.

Keywords: Lunar craters, The Moon, Radar astronomy, Lunar science, Lunar features, Polarimetry
Propagation of Vertical Fractures through Planetary Ice Shells: The Role of Basal Fractures at the Ice-Ocean Interface and Proximal Cracks. The presence of smooth, young surfaces indicates that regions of Enceladus and Europa have been resurfaced through recent or ongoing activity related to the eruption of liquid water from subsurface reservoirs. For interior material to erupt or flow out onto the surfaces of these satellites, fractures would have to vertically penetrate the ice shell to the depth of a subsurface reservoir or ocean. Here we use linear elastic fracture mechanics to show that accounting for fracture interactions makes it much more difficult for fractures to penetrate the entire ice shell than previous estimates. We found that fractures that originate from the surface are unlikely to penetrate the entire shell thickness, even for the upper range of tectonic stresses estimated for each moon. Tensile fractures that initiate from the bottom of the icy shell-as observed in terrestrial ice shelves-propagate further into the icy shell than surface crevasses but still do not penetrate the entire ice thickness. However, full ice shell thickness fracture is possible if shear failure connects the surface with deep-penetrating basal fractures in thinner ice shell thicknesses and under certain stress conditions. This suggests that the combination of tensile and shear failure may be important and necessary for the formation of a connection from the surface to the ocean below.

Keywords: Ocean planets, Surface processes, Natural satellites (Solar system), Solar system, Saturnian satellites, Jovian satellites
The Scientific Value of a Sustained Exploration Program at the Aristarchus Plateau. The Aristarchus plateau hosts a diversity of volcanic features, including the largest pyroclastic deposit on the Moon, the largest sinuous rille on the Moon, and intrusive and extrusive examples of evolved, Th-rich silicic lithologies. We provide an overview of previous remote-sensing measurements of the Aristarchus plateau and provide new analyses of Diviner Lunar Radiometer thermal IR data, Lunar Prospector Gamma Ray Spectrometer Th data, Chang'e-5 Microwave Radiometer data, and hyperspectral and multispectral visible/near-infrared images and spectra from the Chandrayaan-1 Moon Mineralogy Mapper and the Kaguya Multispectral Imager. The rich diversity of volcanic features on the Aristarchus plateau presents an opportunity for a sustained science and exploration program. We suggest a series of missions to the Aristarchus crater floor or ejecta, the Cobra Head, and Herodotus Mons to investigate the link between pyroclastic, effusive basaltic, and silicic volcanism in the region. Such missions would enable analyses of silicic rocks that are rare in the Apollo sample collection and demonstrate in situ resource utilization of FeO- and H2O-bearing pyroclastic materials.

Keywords: The Moon, Lunar evolution, Volcanoes, Lunar science
Triton: Fascinating Moon, Likely Ocean World, Compelling Destination!. Triton is an important signpost in understanding the diverse populations of both ocean worlds and Kuiper Belt objects (KBOs). As a likely ocean world, it is unique by virtue of its kidnapped history from the Kuiper Belt: its large orbital inclination makes it the only ocean world thought to be primarily heated by obliquity tides. It is volatile-rich due to its formation in the outer solar system and its unusual surface geology may be the product of cryovolcanism. Observations from New Horizons and Cassini motivate re-examination of Triton data sets and models, with value for comparative planetology of ocean worlds and KBOs, most notably with Europa, Enceladus, Titan, and Pluto. We re-explore old data sets with the new perspective of the importance of ocean worlds in our solar system and the search for life.

Keywords: Triton
Habitability of Martian Noachian Hydrothermal Systems as Constrained by a Terrestrial Analog on the Colorado Plateau. Volcanic features and impact craters are ubiquitous features on Mars, and hydrothermal systems associated with the production of these features should have been abundant in Mars's early history. These hydrothermal systems represent potentially habitable environments and are therefore a high priority for continued investigations of the Martian crust. Here we present a Mars analog study where basaltic magma intruded water-bearing sediments to produce a high-temperature (as high as ~700°C) hydrothermal system, which we use to constrain the potential habitability of similar systems on Mars via mineralogy and geochemistry including S, C, and O isotopic systematics. Our analog site suggests evidence for a habitable environment once the system cooled below 120°C and the potential presence of microbial activity based on the combination of dolomite and C-isotopic systems in the same sample. These findings highlight the importance of future missions to investigate the interface of sediments with magmas and/or late-stage impact melts where microbial life may have taken hold when temperature conditions allowed.

Keywords: Mars