A Tale of Two Planet(ary bodie)s: The Origin of Ice on Mercury and the Moon

The low obliquity of Mercury and the Moon causes topographic depressions located near their poles to cast persistent shadows, which may cold-trap volatiles for geologic time periods. Despite their similar thermal environments, telescopic and remote sensing observations have previously detected thick, pure water ice deposits near the poles of Mercury but not the Moon - where ice was found to be superficial or mixed with the regolith. This work attempts to resolve the apparent difference between the two planetary bodies employing physical models and spacecraft observations. We study how topographic roughness affects the temperature distribution and the ensuing prevalence of cold-traps, and constrain the amount, age and origin of polar ice deposits on Mercury and the Moon. Our results suggest that the difference between the amount of cold-trapped volatiles on these planetary bodies may not be as significant as previously thought, and that the presence of heavier carbonaceous volatiles on Mercury may explain the higher purity of its ice deposits relative to the Moon