Date/Time: Tuesday, May 17, 2011 9:00AM PST, 16:00 UTC
Presenter: Thomas Orlando and Gregory A. Grieves
TITLE: Experimental and theoretical investigations regarding water on the Moon
Increasing evidence supports the notion that water is present on the Moon in significant quantities, both from primordial and exogenic sources. The mechanisms of retention and the stabilities of hydrogen absorption from such sources are poorly constrained, though ongoing theoretical and experimental work is being pursued to address these issues. We present experimental and theoretical results regarding the presence and evolution of H2O and OH in the top meter of regolith that may have been formed on and in grain surfaces from solar wind bombardment. Specifically, temperature program desorption (TPD) experiments were performed to explore the thermal stability of adsorbed water and hydroxyl on lunar regolith surrogates. Mechanically micronized JSC-1A was chosen to simulate the mare regions, while micronized albite was used to represent the lunar highlands. Both samples were found to have a continuous distribution of molecular chemisorption sites with binding energies ranging from 0.5 eV up to 1.3 eV. There is also evidence in the TPD and diffuse IR reflectance data for the recombinative desorption of hydroxyl at temperatures above 500 K. This recombination process produces water and may be a primary source term. Water desorbs but does not re-adsorb on the annealed samples. This suggests that in the absence of solar wind bombardment, the accumulation of adsorbed hydroxyl and water is a very ‘slow’ process. Using the extracted binding energies, estimated recombinative desorption rates, and the known lunar temperature distributions, we attempt to model the time evolution of water production as well as lunar spatial distribution maps. These results offer one, perhaps partial, explanation for the observed distributions of both OH and H2O on the surface of the Moon.