Subsurface Migration of Water Vapor on Airless Bodies

The interaction of water molecules with the lunar surface is a key process for the transport and sequestration of water. Recent observations suggest that a desiccated layer overlies a more hydrated layer on the Moon, for reasons that are yet unexplained, but may be related to subsurface migration of water molecules. Subsurface migration may also lead to net sequestration of H2O in the polar regions of the Moon, outside the permanently shadowed regions. Proposed here is the development of more sophisticated models of the migration of water molecules in the subsurface of airless bodies, with the objective of gaining a clearer understanding of sequestration and subsurface migration of water molecules on the Moon.

Methodology: An existing model of water vapor migration in the subsurface of airless bodies will be enhanced in several ways: a more sophisticated model of adsorption energies will be developed; the role of three-dimensional effects will be studied; and the diffusion model will be coupled to a thermal model based on measured surface temperatures. This comprehensive numerical model will then be applied to two aspects: 1) the concentration of adsorbed water with depth, and 2) the concentration of thermally pumped ice as a function of depth.