Influence of the Earthward and Tailward Ion Flows on the Lunar Surface Water in the Magnetotail

Earth wind, namely the particles from the Earth's magnetotail, is an important source of lunar water. Besides tailward flow incident on the lunar nearside when the Moon is in the magnetotail, there exists earthward flow bombarding the farside, affecting the distribution and preservation of lunar water. In this study, we determine the incident fluxes of both the tailward and earthward flows on the lunar surface with the ARTEMIS observations and examine their influences on the concentration and migration of lunar surface water and its reservation in the polar regions using Monte Carlo modeling. It is found that water molecules produced by the earthward flow can stay longer on the surface than those produced by the tailward flow. Our results suggest that the evolution of the Earth's magnetosphere can be inferred from Earth wind particles implanted in the soils of both the lunar nearside and farside.