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Over the last four billion years, a large amount of cometary material is estimated to have impacted the Moon. Water ice is thought to be the major constituent of comet nuclei, and analysis of hydrogen isotopes present in lunar minerals suggests the possibility of a cometary source for lunar water. We simulate comet impacts on the Moon, with a view to studying the nature of deposition of cometary water in the Moon’s permanently shadowed craters (cold traps), where temperatures are low enough to trap water over geological time scales.
On impact, a comet vaporizes. The dense regions closest to the point of impact are simulated by our collaborators at the Planetary Science Institute in Arizona, using the SOVA hydrocode. We then use a Direct Simulation Monte Carlo (DSMC) code designed to handle rarefied planetary scale flows to track the evolution of the water vapor plume, and the eventual deposition of water molecules in cold traps. We are currently carrying out a parametric study of the influence of various parameters (comet density, impact angle, velocity, location etc.) on the final deposition pattern. Our aim is to investigate whether cometary delivery can account for current observations of hydrogen on the Moon, and the influence of parameters such as impact angle, velocity and location on the extent and nature of final retention of water.