Livengood, Timothy - Evidence for Diurnally Varying Hydration at the Moon's Equator from the Lunar Exploration Neutron Detector (LEND)

We detect hydrogen-bearing volatiles, most likely water and hydroxyl, concentrated near the Moon’s dawn terminator by an active daily cycle of surface hydration and dehydration. This represents a potential volatile resource for  in situ resource utilization (ISRU) that is distilled by natural processes and thus may be accessible at minimal energy cost. Measurements by the Lunar Exploration Neutron Detector (LEND) on the polar-orbiting Lunar Reconnaissance Orbiter (LRO) spacecraft detect hydrogen in the regolith through the localized suppression of epithermal neutron flux from the Moon’s surface. At low latitude, the greatest flux suppression is found at dawn, with the least suppression and least hydrogenation in the lunar afternoon. This non-uniform and asymmetric distribution can persist only if a population of hydrogen-bearing volatiles is mobile across the sunlit lunar sur-face in the morning sector with an average horizontal velocity of 4.3 m/s in the anti-sunward direction, enabling the detected hydrogen to remain fixed with respect to the Sun while the Moon rotates.