Analyses of Lunar Orbiter Laser Altimeter 1,064-nm Albedo in Permanently Shadowed Regions of Polar Crater Flat Floors: Implications for Surface Water Ice Occurrence and Future In Situ Exploration

Abstract

Potential water ice concentrated within the permanently shadowed regions (PSRs) near lunar poles is both scientifically significant and of value for future explorations. However, after decades of observations, the existence and characteristics of PSR water ice remain controversial. The 1,064-nm laser reflectance measurements collected by the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter (LRO) provide a unique opportunity to detect and characterize PSR water ice. In this work, we focus on all major PSRs on the flat floors of lunar polar craters and analyze their detailed LOLA 1,064-nm albedo and then compare this with the adjacent flat non-PSRs. We find that the LOLA albedo of the majority of these PSRs is systematically higher than their adjacent non-PSRs. Potential contributions of various factors to the observed LOLA albedo are individually quantitatively evaluated; we show that each of them is unable to account for the observed LOLA albedo anomalies and that the presence of surface water ice is the most likely explanation. Combined characterization of LOLA albedo and substrate impact cratering records (crater populations and depths) reveals that the inferred PSR water ices are in very small quantity (probably in the form of a surface frost layer or admixture with regolith) and are laterally heterogeneous in model ice concentration, ranging from negligible to ~6%. We recommend that these PSRs as priority targets for future surface in situ exploration endeavors, and a case assessment of Amundsen crater is presented.