Global distribution of lunar composition: New results from Lunar Prospector

Abstract

Maps of thorium [Th], [FeO], the ratio of epithermal to thermal neutrons (E/T), and fast neutrons (FN) from Lunar Prospector were studied to determine their global distribution on the Moon. These distributions are compared to that of the 750 nm lunar albedo from Clementine to aid in their interpretation. All distributions were parameterized using a spherical harmonic expansion out to order l = 30. Resultant harmonic coefficients generally decrease with increasing l value as a power law in l for all five variables. The axes of all dipole components (l = 1) cluster closely about a centroid given by +14.1° latitude and 16.4° west longitude. This location is very close to the symmetry axes of their quadrupole components (l = 2), which cluster about a centroid given by +24.6° latitude and 25.1° west longitude. Both centroids are near the center of a suggested Procellarum basin, given by Whitaker [1981] at +23° latitude and 15° west longitude. This suggestion is strengthened by a sharp decrease of the intensities of all three variables at ∼50° from the centroids, which is close to the boundary of the putative Procellarum basin. The coincidence of the global concentration of heat‐producing elements (through [Th]) and mare deposits on the lunar surface (through [FeO], [T/E], and [FN]) with the circular outline of a putative Procellarum basin suggests that the events that were responsible for producing Oceanus Procellarum (perhaps a single giant impact) must figure importantly in shaping the global distribution of surface composition. A second, apparently older circular structure having its center near −5° latitude and 65° east longitude and a radius of 50° is also hinted at in the data.