Lunar crustal mixing and compositional contamination: New perspectives from spectral mixture analysis of Clementine data and numerical modeling of impact cratering

During the Apollo exploration of the Moon, a significant amount (10%–30%) of nonmare materials was found in returned mare soils, and both lateral and vertical mixing processes on the Moon were proposed to explain the origin of “exotic” components. As no definitive data existed at that period, the vigorous debate on the relative importance of lateral versus vertical mixing quieted down and had been largely dormant over the last 20 years.; New exploration of the Moon by Clementine spacecraft in the 1990's opened up new avenues of investigation of material mixing on the Moon. The research presented here relies extensively on remote sensing observations of varying compositional gradients combined with numerical modeling of impact cratering. The observations are made on the basis of traditional and multiple endmember spectral mixture analyses of Clementine ultraviolet-visible (UV-VIS) multispectral data. Impact cratering is assumed to be a random process and responsible for material mixing on the Moon. An anomalous diffusion model, a model based on the assumption of linearly additive ejects and a deterministic model are developed to accommodate different scenarios of material lateral mixing due to small and large craters.; The observations at many geological boundaries reveal that lateral mixing dominates over vertical mixing and the anomalous diffusion model suggests that high-velocity ejecta play a significant role in delivering materials. The study also shows that material lateral mixing processes due to small and large craters are different scenarios and that it is necessary to make such distinction in order to develop physically meaningful models. Such a distinction was unfortunately ignored in previous studies.; The results from quantitative analyses of compositional variations over large regions indicate that large craters are responsible for the formation of large-scale compositional gradients and play a significant role in delivering highland materials into mare. In addition, the contribution of “exotic” components from nearby large craters to specific sites on the Moon should be considered deterministically because a statistical model might commit a large error in this case.