Far-ultraviolet reflectance properties of the Moon's permanently shadowed regions

Although of great interest for science and resource utilization, the Moon's permanently shadowed regions (PSRs) near each pole present difficult targets for remote sensing. The Lyman Alpha Mapping Project (LAMP) instrument on the Lunar Reconnaissance Orbiter (LRO) mission is able to map PSRs at far-ultraviolet (FUV) wavelengths using two faint sources of illumination from the night sky: the all-sky Ly alpha glow produced as interplanetary medium (IPM) H atoms scatter the Sun's Ly alpha emissions, and the much fainter source from UV-bright stars. The reflected light from these two sources produces only a few hundred events per second in the photon-counting LAMP instrument, so building maps with useful signal-to-noise (SNR) ratios requires the careful accumulation of the observations from thousands of individual LRO orbits. In this paper we present the first FUV albedo maps obtained by LAMP of the Moon's southern and northern polar regions. The results show that (1) most PSR regions are darker at all FUV wavelengths, consistent with their surface soils having much larger porosities than non-PSR regions (e.g., similar to 70% compared to similar to 40% or so), and (2) most PSRs are somewhat redder (i.e., more reflective at the longer FUV wavelengths) than non-PSR regions, consistent with the presence of similar to 1-2% water frost at the surface.