On the Effect of Magnetospheric Shielding on the Lunar Hydrogen Cycle O. J. Tucker1*, W. M. Farrell1, and A. R. Poppe2 1NASA Goddard Space Flight Center, Greenbelt, Md, USA. 2Space Sciences Laboratory, University of California, Berkeley, CA, USA *Corresponding author: Orenthal Tucker (
[email protected]) NASA Goddard Space Flight Center, Magnetospheric Physics/Code 695, Greenbelt, MD 20771, USA Key Points: Low latitude nightside OH is depleted from waning gibbous to waxing crescent because of shielding when traversing the magnetotail. Low latitude dayside OH is decreased in the tail compared to out but the difference cannot be resolved with current observations. Magnetospheric shielding decreases the global H2 exosphere by an order of magnitude during the full Moon. 1 Abstract The global distribution of surficial hydroxyl on the Moon is hypothesized to be derived from the implantation of solar wind protons. As the Moon traverses the geomagnetic tail it is generally shielded from the solar wind, therefore the concentration of hydrogen is expected to decrease during full Moon. A Monte Carlo approach is used to model the diffusion of implanted hydrogen atoms in the regolith as they form metastable bonds with O atoms, and the subsequent degassing of H2 into the exosphere. We quantify the expected change in the surface OH and the H2 exosphere using averaged SW proton flux obtained from the Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) measurements. At lunar local noon there is a small difference less than ~10 ppm between the surface concentrations in the tail compared to out.