A New Moon for the Twenty-First Century

Thirty years of lunar sample studies supplemented by spotty remote sensing and geophysical data gave us the broad outline of the nature and geologic history of the Moon. Many cherished beliefs are now being questioned on the basis of global data returned by two bargain-basement missions sent to the Moon in the 1990s, Clementine and Lunar Prospector. These data are being integrated with new and old lunar sample data, to give us new, though still controversial, ideas about the nature of the Moon. Two articles in a special section of the Journal of Geophysical Research (Planets) illustrate the point. Brad Jolliff and his colleagues at Washington University in St. Louis, Jeff Gillis, Larry Haskin, Randy Korotev, and Mark Wieczorek (now at the Massachusetts Institute of Technology) divide the Moon's crust into distinct geochemical provinces quite different from the traditional highlands (or terra) and maria. In a separate paper, Randy Korotev presents a detailed analysis of a common rock type among the samples returned by the Apollo missions. This rock type, nicknamed enigmatically "LKFM," was thought by many of us to represent the composition of the lower crust everywhere on the Moon. Korotev argues that it is confined to only one of Jolliff's provinces. If correct, this changes our estimates of the composition of the lunar crust, hence of the entire Moon. Although other lunar scientists will scrutinize these new views of the Moon, it is clear that some long-held ideas about the Moon might be modified significantly, if not tossed out completely.