LRO-LAMP Survey of Lunar South Pole Cold Traps: Implication for the Presence of Condensed H2O

We employ nighttime observations from the Lyman Alpha Mapping Project (LAMP) ultraviolet (UV) spectrograph onboard the Lunar Reconnaissance Orbiter to investigate the presence of condensed water ice within lunar south pole cold traps. This study incorporates LAMP observations between 2009 and 2016, which more than doubles the number of observations from previous LAMP Permanently Shadowed Regions (PSRs) studies. In this study, we focus on cold traps within five south polar craters: Faustini, Shoemaker, Haworth, Cabeus, and Amundsen. An unnamed cold trap region adjacent to Haworth and Shoemaker was also investigated. We present On-band (148-162 nm), Edge-band (164-173 nm), and Off-band (175-190 nm) albedo maps at 4-km spatial resolution and far-UV albedo spectra of cold traps at 2-nm spectral resolution. We find Off-band to On-band albedo ratios (the UV wavelength ranges with high and low H2O ice reflectivity, respectively) within cold traps that are consistent with previous PSR studies. Spectral intimate mixture models considering 5 mu m H2O grains and a range of regolith grain sizes (20-74 mu m) with porosities between 0.3 and 0.75 yields abundances of similar to 0.9-4.9 wt.%, where increasing the range of H2O and regolith grain sizes may increase the range of water abundance. We further find generally lower albedos within the cold trap regions than at the surrounding non-cold trap regions across all wavelengths, consistent with increased regolith porosity within cold traps as suggested by Gladstone et al. (2012), .