Modeling Lunar Water Formation Induced by Micrometeorite Impacts

Abstract:

While the existence of water has been confirmed on the Moon by observations, the exact process underlying the origin of water is still under debate. While solar wind proton implantation is a major source for hydrogen in the hydroxylation process on lunar surface, significant energy is required to trigger the chemical reactions for water formation. One of the broadly accepted triggering mechanisms is micrometeorite impacts. Recent laboratory experiments have shown that the heat generated by micrometeorite impacts is sufficient to trigger water formation in the regolith. However, at the same time, the heat generated could also vaporize most of the water molecules to the exosphere.

In this study, we apply reactive molecular dynamics (MD) simulations to simulate the water formation process induced by micrometeorite impacts. By mapping the temperature distribution and water distribution after impact, we find that the most favorable condition for water deposition in the regolith occurs at the rim of impact crater where the temperature is typically below the threshold for water vaporization due to heat conduction.Atomistic mechanisms that suggest the formation of highly-localized water distribution near crater rims will also be discussed.