For consideration in the next New Frontiers Announcement of Opportunity, the committee offers descriptions of eight candidate missions and an innovative mission option. The eight mission options, described below in the same order as they appeared in the decadal survey, are followed by a description of the innovative mission option. No science prioritization is implied by their order.

The South Pole-Aitken Basin Sample Return mission, as described in the decadal survey, is an inner-solar-system mission to study basin-forming processes and impact chronology by returning samples from the deepest, most heavily cratered—and, hence inferred to be the oldest—impact structure preserved on the Moon (Figure 2.1). Another goal of the mission is to use these returned samples to understand the nature of the Moon’s deep crust and upper mantle and the planetary processes that produced these features. These goals are to be accomplished through the intensive study of the returned materials in Earth-based laboratories.

Heavy bombardment in the very early history of the solar system is a paradigm established from analysis of the samples returned by the Apollo and the Soviet robotic Luna missions. Careful site selection and the study of new samples of the Moon will result in detailed verification and extension of this central concept for the formation and early history of the terrestrial planets and its implications for the earliest appearances and evolution of life. In particular, this mission would allow a test of theories that have been proposed about the early impact history of the inner solar system, notably the “lunar cataclysm” model.

FIGURE 2.1 South Pole-Aitken Basin. The basin is clearly visible in both the topography and iron projections, illustrating how a large impact affected the Moon. The black area at the pole was not imaged. SOURCE: Courtesy of Clementine Science Group, Lunar and Planetary Institute.