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Solar wind interactions and the evolution of hydroxyl on the Moon

Thomas Orlando
Delivered As: 
Abstract Text: 

Recent orbital observations of the Moon’s surface show an infrared absorption feature at 2.8 µm indicating the presence of hydroxylated silicates, which may have been formed by proton implantation from the solar wind. A model is presented that takes into account proton induced formation of hydroxyl sites within the regolith followed by temperature dependent first order loss processes. These are mainly photodegradation/photodesorption of terminal SiOH groups and hot H atom reactive scattering with SiOH forming molecular hydrogen and SiO lattice sites. Diffusive transport of H and OH plays a minor role relative to the solar wind induced removal processes of the hydroxyl sites. The model predicts solar wind production and release of mainly molecular hydrogen with little to no molecular water formation and retention, particularly in sun-lit regions. Instead, an OH signature within the sampling depth of the space-craft reflection measurements is produced and preserved over long time scales with a defined temperature and spatial variability. The overall model shows general agreement with the observed hydroxyl abundances and likely captures most of the essential physics and chemistry underlying these observations. The model can also be used to make predictions regarding OH and water abundances on other airless solar system bodies such as asteroids and Mercury.

James W. Head, Brown University
SSERVI Identifier: 

Recognizing that science and human exploration are mutually enabling, NASA created the Solar System Exploration Research Virtual Institute (SSERVI) to address basic and applied scientific questions fundamental to understanding the Moon, Near Earth Asteroids, the Martian moons Phobos and Deimos, and the near space environments of these target bodies. As a virtual institute, SSERVI funds investigators at a broad range of domestic institutions, bringing them together along with international partners via virtual technology to enable new scientific efforts."