The Spatial Distribution of Lunar Polar Hydrogen Deposits After SELENE/Kaguya

Feldman et al (1998, 2000, 2001) found evidence of hydrogen near the lunar poles using data collected by the neutron spectrometer carried by the Lunar Prospector. Eke et al (2009) strongly suggested the hydrogen is concentrated into the permanently shaded "cold traps" near the lunar poles. This is important because if the hydrogen is in the form of a volatile compound, then it is only stable in these cold traps. As the most likely candidate volatile is water ice (Vasavada et al, 1999), this is of interest both for improving the understanding of the solar system and for the upcoming lunar exploration. On the other hand, if the hydrogen is distributed throughout the polar regions in a more uniform way, then it is more plausibly the result of the solar wind implantation of hydrogen into the regolith (Starukhina and Shkuratov, 2000). The excess of polar hydrogen would then be a consequence of the the lower polar temperatures reducing the rate at which it diffuses out of cold regolith grains. Determining which of these two scenarios is dominant, requires an improved determination of the spatial distribution and concentration of the polar hydrogen using a more sophisticated method of analysis and a better map of permanent shadow. This talk will present the results of applying a Pixon image reconstruction approach to the Lunar Prospector epithermal neutron data coupled to the new permanent shadow maps drawn from the preliminary SELENE/Kaguya laser altimetry observations (Noda et al. 2008). The reconstruction results point to several south pole features, including the large degraded crater Cabaeus (85.6S, 308.9E), where inferred concentrations exceed 0.5 wt% water-equivalent hydrogen. These results have been provided to the LCROSS team to assist in targeting.