Ostrach, Lillian - Characterization of Smooth Deposits Within South-Pole Aitken Basin: The Search for Impact Melt Deposits

Abstract: 
Recent lunar missions, including the Lunar Reconnaissance Orbiter (LRO), Chandryaan-1, Kaguya/SELENE, and the Gravity Recovery and Interior Laboratory (GRAIL), enable researchers to answer outstanding questions critical to lunar science in preparation for future robotic and human exploration. The South Pole-Aitken basin (SPA) is identified as one of the highest-priority targets for future exploration and sample return because multiple science objectives can be addressed, including investigations related to the bombardment history of the Solar System, the lunar interior (including crustal structure and mantle composition), and the volcanic evolution of the Moon [1,2]. Impact melts form during the impact process; radiometric ages for melts therefore date an impact event. Although SPA is heavily modified by subsequent basin, crater, and mare materials, by identifying the oldest surfaces from remote sensing data, it may be possible date the SPA event (and those impact basins located within SPA) via a future sample return mission (e.g., MoonRise).

Previous investigations employed multiple techniques and datasets [e.g.,3-6], and we build upon these findings to further characterize geology within SPA. Our efforts place particular emphasis on smooth deposits interpreted to be impact melt or basin ejecta interior to and surrounding “young” impact craters (e.g., Alder, Bhabha, Bose, Finsen), although we do include mare and cryptomare deposits in our survey. Our primary objectives are to (1) determine smooth deposit origin on the basis of albedo, composition, embayment relations, and stratigraphic relations to crater ejecta, (2) determine the relative ages of both the smooth deposit and its associated crater, placing the unit into stratigraphic context with other SPA basin materials, and (3) identify locations hosting the oldest surfaces (presumed to be SPA-derived impact melt) in SPA. In a comprehensive mapping effort to better understand the geology of the SPA basin using new remote sensing data, we utilize multiple datasets (e.g., LRO, M3) at high resolution to characterize geologic units on the basis on morphology (e.g, degradation state, stratigraphic relations), composition, and in some cases, crater densities [7].

[1]Committee on the Scientific Context for Exploration of the Moon National Research Council (2007), “The Scientific Context for Exploration of the Moon: Final Report”, National Academies Press.
[2]Committee on the Planetary Science Decadal Survey (2011) “Vision and Voyages for Planetary Science in the Decade 2013-2022”, National Academies Press.
[3]Wilhelms, D. (1987) The Geologic History of the Moon, USGS Prof. Pap. 1348.
[4]Pieters, C.M. et al. (2001) JGR 106, 28001-28022.
[5]Petro, N.E., Pieters, C.M. (2004) JGR 109, E06004.
[6]Moriarty et al. (2013) JGR Planets 118, 2310-2322.
[7]Kirchoff, M.R. et al. (2013) Icarus 225, 325-341.