Models of the distribution and abundance of hydrogen at the lunar south pole

Abstract

Permanently shadowed locations at the lunar poles are potential sites for significant concentrations of cold‐trapped volatiles, including water ice. Hydrogen enhancements are seen at the poles, but the physical form, abundance and distribution of this hydrogen remains controversial. Using a pixon‐based image reconstruction algorithm to effectively improve spatial resolution, we derive maps of the lunar south polar water‐equivalent hydrogen concentration that are fully consistent with the orbital neutron measurements, with abundances greater than 0.5 wt% in some permanently shadowed locations. This is much greater than the highest solar wind hydrogen abundance in returned lunar samples, and may indicate ice between regolith grains. If the hydrogen distribution is inhomogeneous within a permanently shadowed crater, then even higher abundances are implied. In Shackleton crater, for example, the derived count rates are consistent with 10% of the crater floor area having 20‐wt% water‐equivalent hydrogen, and the remainder at 0.25 wt%.