Modeling of the vapor release from the LCROSS impact: Parametric dependencies

Abstract

The Lunar Crater Observation and Sensing Satellite (LCROSS) mission included an intentional impact into the Cabeus crater, a permanently shadowed region near the Moon's south pole. The impact produced a vapor plume of volatile species liberated from the impact site. Using a Monte Carlo model to simulate the vapor plume expansion, this paper investigates the expansion as a function of the physical properties of the gas. For a thermal release scenario, the cloud expands with the highest density at the center, with the density dropping within the cloud in time as the cloud expands. When a significant non-thermal component to the velocity (a bulk speed) exists, the vapor expands as a hemispheric shell outward from the impact site. For heavier species, the high bulk velocity produces a hemisphere of higher density of gas that appears as a ring from above. For lighter gases like H2, the thermal velocity is on the same order as the bulk velocity. If the source is prolonged, the source rate is dominant in determining the local density, however. Gases produced by photodissociation have a prolonged source close to the impact site compared to promptly produced vapors. Copyright 2011 by the American Geophysical Union.