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Microsymposium 57: Polar Volatiles on the Moon and Mercury: Nature, Evolution, and Future Exploration

Ariel Deutsch
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Abstract Text: 

The discovery of polar volatiles on Mercury and the Moon has revolutionized our understanding of the origin and evolution of volatiles in the inner Solar System, and has subsequently inspired the exploration of these significant scientific legacies and potential future resources. At Mircosymposium 57, we discussed the formation, distribution, abundance, age, and preservation of these materials. Volatiles hold records of the geological, geochemical, and orbital histories of Mercury and the Moon, and understanding the source of these volatiles may provide insight into the degassing history of these bodies and the flux of impactors in the Solar System. Exploring these materials with future missions is critical in answering these questions and assessing their potential for supporting human exploration. At Microsymposium 57, we explored our current knowledge of these materials and identified the key questions and objectives in order to underpin and motivate future exploration. We reviewed current exploration plans, including the U.S. Resource Prospector, Russian Luna 25-27, and ESA BepiColombo missions.

Permanently shadowed regions (PSRs) are unique environments in which cryogenic temperatures can trap solar system volatiles, which record evidence of planetary formation and evolution. While water-ice deposits are strictly found within PSRs on Mercury, evidence for water ice existing only within PSRs on the Moon is less conclusive. Thermal modeling using topographic datasets indicates that surface and subsurface water-ice deposits are stable on both bodies. Earth-based radar measurements and high circular polarization ratios are consistent with the presence of water ice at both poles of Mercury, however a better understanding of surface roughness is required for interpreting the orbital and bi-static measurements indicating water ice on the Moon. Orbit-measured hydrogen concentrations indicate broad spatial suppression near the north pole of Mercury, consistent the presence of pure water ice in the PSRs. Neutron measurements of the Moon show hydrogen enhancements at both poles, and suggest layering of hydrogen in the PSRs. Reflectance measurements of Mercury reveal that most PSRs are anomalously dark, consistent with the presence of lag deposits of carbon-rich volatiles that insulate water-ice deposits. Reflectance measurements of the Moon indicate larger porosities and higher albedos within PSRs, and the presence of water frost is consistent with these regions of low temperatures. In-situ measurements indicate that multiple volatile species are present at the lunar poles, including H2O, H2, OH, and CO. Understanding the similarities and differences between mercurian and lunar volatiles will lend insight into the possible sources of these inventories. We discussed the possibilities of volatiles being delivered via water-rich comets or asteroids, planetary outgassing, solar-wind interactions, and micrometeorite bombardment. Our discussions laid out key avenues for future research and mission directions.

" M. Sarantos (Heliophysics Science Division, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA; 3Solar System Exploration Division, NASA Goddard Space Flight, Center, Greenbelt, Maryland, USA)...
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Recognizing that science and human exploration are mutually enabling, NASA created the Solar System Exploration Research Virtual Institute (SSERVI) to address basic and applied scientific questions fundamental to understanding the Moon, Near Earth Asteroids, the Martian moons Phobos and Deimos, and the near space environments of these target bodies. As a virtual institute, SSERVI funds investigators at a broad range of domestic institutions, bringing them together along with international partners via virtual technology to enable new scientific efforts."