Journal: The Planetary Science Journal

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American Astronomical Society

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2632-3338

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2021 - 20253
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Publications 1 - 3 of 3
  • Science Goals and Objectives for the Dragonfly Titan Rotorcraft Relocatable Lander
    Item type: Journal Article
    Barnes, Jason W.; Stähler, Simon Christian; et al. (2021)
    The Planetary Science Journal
    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.
  • Human-assisted Sample Return Mission at the Schrödinger Basin, Lunar Far Side, Using a New Geologic Map and Rover Traverses
    Item type: Journal Article
    Czaplinski, Ellen C.; Harrington, Elise M.; Bell, Samantha K.; et al. (2021)
    The Planetary Science Journal
    The Schrödinger basin on the south polar lunar far side has been highlighted as a promising target for future exploration. This report provides a high-resolution geologic map in the southwest peak-ring (SWPR) area of the Schrödinger basin, emphasizing structural features and detailed mapping of exposed outcrops within the peak ring. Outcrops are correlated with mineralogical data from the Moon Mineralogical Mapper instrument. Geologic mapping reveals a complex structural history within the basin through a system of radially oriented faults. Further, the geologic map shows both faulted and magmatic contacts between peak-ring mineralogies, providing both structural and magmatic context for understanding lunar crustal evolution and polar region processes. To investigate these relationships and address key scientific concepts and goals from the National Research Council (NRC) report, we propose three traverse paths for a robotic sample return mission in the SWPR area. These traverses focus on addressing the highest priority science concepts and goals by investigating known outcrops with diverse mineralogical associations and visible contacts among them. Coinciding with the preparation for the 2024 Artemis III mission, NASA is increasing the priority of robotic exploration at the lunar south pole before the next crewed mission to the Moon. Through mapping the Schrödinger SWPR, we identified the extent of different lunar crustal mineralogies, inferred their geologic relationships and distribution, and pinpointed traversable routes to sample spectrally diverse outcrops and outcrop-derived boulders. The SWPR region is therefore a promising potential target for future exploration, capable of addressing multiple high-priority lunar science goals.
  • Supercooling, Glass Formation, and Mineral Assemblages upon Freezing of Salty Ice Grains from Enceladus's Ocean
    Item type: Journal Article
    Klenner, Fabian; Fifer, Lucas M.; Journaux, Baptiste; et al. (2025)
    The Planetary Science Journal
    The analysis of micrometer-sized ice grains emitted into space by Saturn's moon Enceladus suggests that the moon's subsurface ocean may be habitable. However, the formation conditions of these ice grains are largely unknown. Upon cooling, ocean droplets may supercool and then form a crystalline or glassy state, or a mixture of both. To investigate the processes of supercooling and glass formation in Enceladus's ice grains, we performed differential scanning calorimetry experiments with Enceladus-relevant salt mixtures at cooling rates ranging from 5 K minute$^{-1}$ to ~1227 K minute$^{-1}$ and extrapolated our results to faster cooling rates. We modeled the freezing of these solutions and associated mineral assemblages using the thermodynamic chemistry packages PHREEQC and Reaktoro. Our results indicate supercooling of ~25-30 K upon freezing from Enceladus's saline ocean. Freshly formed ice grains should be predominantly crystalline but contain up to 5% glass. Fast cooling rates and high salt concentrations favor the formation of glasses, potentially enabling the preservation of organics and cells, if present. Salts in the grains crystallize in the following sequence: first phosphate, followed by carbonates, and then chlorides. We find that the recently detected phosphates in Enceladus's ice grains are likely Na₂HPO₄:12H₂O. The pH values appear to vary among individual ice grains, depending on the stage of the freezing process, and these values may slightly differ from the pH of the moon's bulk ocean. Our experiments and models are relevant to other icy worlds with salty water reservoirs in their subsurfaces, such as Jupiter's moon Europa or the dwarf planet Ceres.
Publications 1 - 3 of 3