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The implications of possibly large volatile reservoirs on the Moon are significant for the future of manned activity there and for space science and exploration in general. In autumn of 2008 NASA will launch the LCROSS mission to impact two spacecraft into a permanently shadowed crater—a cold trap—at the south pole of the Moon. The lead spacecraft will excavate its own several meter crater. The process will be observed by the following smaller vehicle and by orbiting and Earth-based instruments in hopes of observing the release of volatiles—predominantly water—from the lunar soil. The following vehicle will then impact as well. We examine the plausible vapor dynamics following the impacts and concentrate on the observability of the gas from Earth or lunar orbit. In the free-molecular computational model of the vapor motion, water and OH molecules move ballistically, have a temperature-dependent surface residence time, and are subject to photo-dissociation and ionization losses. Sunlight shadowing, separation of the vapor from the dust grains, dust thermodynamics and different impact plume models are considered. [ABSTRACT FROM AUTHOR]

It has now been firmly established from both theoretical calculations and observations, that the exospheres of the terrestrial planets have extended coronae of translational energetic oxygen atoms. The current model generally accepted as the source of these hot atoms is the dissociative recombination of O[SUP +,SUB 2], that is, O[SUP +,SUB 2] + e[SUP-] → O* + O* where the product O* atoms are translationally energetic. The determination of the extent of this population of superthermal atoms is an important endeavor. The present paper considers a simple model based on the Boltzmann equation for the energy and altitude dependence of the oxygen atom distribution function. The density and temperature distributions are determined with this distribution. [ABSTRACT FROM AUTHOR]