Composition variations of major lunar elements: Possible impacts on lunar albedo spectra

Abstract

Understanding the elemental composition of the lunar regolith is important for expanding our knowledge of the history and geology of the Moon. Several methods have already been used to achieve this purpose, including direct analysis of lunar samples and satellite spectroscopy. Since computer modeling is important for processing the collected data, and for the preparation of future missions, this work uses Monte Carlo simulations to study the radiation emitted by the lunar surface, via nuclear interactions between the incident radiation environment and lunar regolith, to characterize the elemental composition of the Moon. When high energy primary galactic cosmic rays and solar energetic particles strike the lunar surface, they either scatter to free space or produce secondaries through cascades of interactions, some of which escape the lunar surface. Both the scattered primaries and escaping secondaries constitute the lunar “albedo” particles studied in this paper. The purpose of this work is to determine whether enhancing the abundances of any of the major lunar elements (O, Na, Mg, Al, Si, Ca, Ti, Mn, and Fe) causes an observable difference in the spectra of albedo particles emitted by the regolith. The model-based results herein show that charged albedo particles do not display any significant differences for any element. They also confirm that low-energy neutrons and gamma rays produce observable variations with different lunar compositions. This provides evidence that albedo neutrons and/or gamma rays, and not protons, are the source of the variations observed in a recent map of the lunar albedo, generated by the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument.