Science Options for Sampling South Pole-aitken Basin

Introduction: Sample return from the huge South Pole-Aitken basin is one of the highest priority science missions recommend by the NRC/NAS for solar system exploration by NASA’s New Frontiers program, second only to Kuiper Belt/Pluto exploration [1]. The envisioned SPA mission is to address several key science issues concerning early evolution of solid bodies in the solar system. Since the Moon is a differentiated planetary body that shares the 1 AU environment with Earth, and SPA is among the largest basins in the solar system, mission goals identified by the NRC report include: • Obtain samples to constrain the early impact history of the inner solar system (including the possible 4.0 By “cataclysm”). • Assess the nature of the Moon’s interior and the style of the differentiation process. • Develop robotic sample acquisition, handling, and return technologies. Implementation of New Frontiers missions will be competed through a NASA AO process. The sample return mission to South Pole-Aitken Basin (SPA-SR) could be flown as early as 2008/9 [2]. Several aspects of this science opportunity involve community participation, most importantly analysis of the returned samples. Optimization of the specific site(s) selected for sampling also benefits from broad input, and several site selection options are discussed here. Minimum Science Requirements. In order for any SPA-SR mission to be selected, the science goals outlined by the NRC report must be met. These goals relate to the type of samples returned and translate into specific criteria. 1) Since SPA is the oldest known basin identified on the Moon [3], dating it will place substantial limits on the early impact history and the timing and duration of basin forming events in the inner solar system. Thus, samples of the SPA melt breccia must be returned to be dated. 2) As the largest, and deepest, accessible basin in the solar system, SPA basin interior would have originally exposed debris excavated from the lower portions of the crust or uppermantle. Returned samples should be selected to contain a significant portion of such material for analysis. The lack of extensive mare basalt fill [3, 4, 5] provides an unprecedented opportunity to sample this ancient basin interior. It is expected that 4 b. y. or more of surface reprocessing has occurred since basin formation and the actual challenge may be to recognize the original SPA melt breccia and lower crustal material. However, based on the assessment of SPA with remote data from Clementine and Lunar Prospector and the ground truth experience gained from Apollo and Luna for regolith evolution, the above requirements are easily met for a large number of regions within SPA. Key elements supporting this proposition are outlined here. SPA interior has not been later filled or covered by foreign material. Clementine images provide global