TITLE: Lunar Polar Volatiles: Assessment of the Current State of Knowledge
PRESENTER: Dana M Hurley
Johns Hopkins University Applied Physics Lab
Water is a useful resource for space exploration because it can be processed to make propellant and life-support consumables. Observations have confirmed that water ice exists on the Moon in some lunar persistently shadowed regions. Owing to the nature of instrumentation and remote sensing, nuances and assumptions are necessarily convolved with the data analysis to arrive at the published interpretations. We evaluate the observations related to the existence of water ice and other volatiles in the polar regions of the Moon to highlight the relative certainty of the published interpretation.
The spectral identification of water through the LCROSS impact experiment provides the strongest evidence of composition. This identification is supported by observations in the ultraviolet and the presence of H detected by neutron spectroscopy. The best evidence of the abundance of water comes from neutron spectroscopy owing to its ability to probe to depths of up to 1 m in the regolith. However the neutron spectra are not sensitive to the chemical form of H, leaving ambiguous whether the H is in the form of H2O, hydrated minerals, or other H-bearing material. The integrated total inventory of H poleward of 80° latitude is 1011 kg. The physical form of the water is poorly understood. Radar data are inconsistent with pervasive, contiguous ice blocks on the size scale of >10 cm, eliminating that as a possibility. However several alternatives exist including hydrated minerals, adsorbed molecules, pore-filling ice, and small ice grains mixed with regolith. Finally, observations indicate that water ice has a heterogeneous distribution both laterally and with depth on large spatial scales. Neutron data are consistent with a desiccated layer of a few 10s of cm overlying a richer layer in most cold polar regions. Surface frost observations indicate that not all persistently shadowed regions have the same amount of frost, and that heterogeneity persists to the > 200 m spatial resolution of the data.
The distribution at 1-100 m spatial scales critical for in situ resource utilization (ISRU) implementation has not been measured. We present modeling of impact gardening processes that redistribute volatiles in cold polar regions and the implications for setting measurement objectives for a landed, in situ sampling mission like Resource Prospector.