Exploring The Volcanic And Impact Histories Of The Moon Through Analyses Of Material In Western Orientale Basin
Several fundamental questions about the geologic history of the Moon remain open, despite the wealth of available orbital data. Certain questions can be more readily addressed by exploration of the lunar surface, including constraining the bombardment history of the Moon and planetary-scale impact processes (i.e., basin formation), characterizing the diversity of lunar crustal rocks, and measuring mare basalts to constrain the compositional evolution of the Moon. A rover landed in a region with diverse geology, such as the Orientale basin, would be able to address many of these fundamental lunar questions. The proposed landing site (Fig. 1) is a large mare pond (935 km2 ) located on the western side of Orientale at the base of the Outer Rook Ring. Due to its location, this mare pond can be considered farside material and provides an opportunity to study lunar materials outside of the Procellarum KREEP terrain; it is located within the region of thicker crust (~45 km) . This particular mare pond is an ideal landing site due to its proximity to Outer Rook Ring (OR) and Maunder Formation (MF) materials. The OR contains material with up to ~95% plagioclase , hypothesized to be crustal materials that were uplifted during the Orientale impact event. Moon Mineralogy Mapper (M3) spectral data indicate that immature material are available for sampling from at least three sample sites: (1) the OR (18.12oS, 104.36oW), (2) the MF (18.09oS, 103.92oW), and (3) the mare (ejecta from the immature crater at 17.50oS, 104.15oW) (Fig. 1). At Sample Site 1, several large boulders that have mass-wasted from outcrops further up slope on this OR massif are present on the flat mare surface and would be easily accessible for measurement. There are other relatively immature impact craters between Sample Site 1 and 2, but Sample Site 3 is the largest and has the strongest spectral absorption features. Thus, that crater is a first choice for mare basalt investigations. This proposed landing site and sampling plan (anorthosite, impact melt, mare) in western Orientale would address several key NRC science concepts , including constraining the bombardment history of the Moon (Goal 1), characterizing the diversity of lunar crustal rocks (Goal 3), measuring volcanic materials to constrain the thermal and compositional evolution of the Moon (Goal 5), study impact processes on planetary scales (Goal 6), and investigate regolith processes and weathering on anhydrous airless bodies (Goal 7). Both mobility and in situ sample analyses are necessary to address the NRC science objectives listed above. Exploration of a companion site on the east side of Orientale (Needham et al., this meeting) could be used to compare geologic variations across the lunar crustal thickness boundary. References:  Whitten, J.L., et al. (2011) JGR 116.  Wieczorek, M.A. et al. (2012) Science 5.  Cheek, L.C., et al. (2013) JGRP 118.  National Research Council (2007) Sci. Context Expl. Moon.