Solar wind and terrestrial atmosphere effects on lunar sample surface composition
Samples returned from the Apollo missions have been shown to have undergone a partial surface oxidation with the degree of oxidation being dependent on the intensity and duration of exposure to a terrestrial or other oxidizing atmosphere. Exposure to atomic hydrogen at room temperature, or molecular hydrogen above 100 C results in a surface reduction. The adsorption of water vapor on a test sample was found to be only slightly dependent on the state of surface oxidation, a situation consistent with the formation of hydroxyl groups on the surface when a sample is exposed to hydrogen. That hydroxyl groups are indeed formed is substantiated by the release of water vapor (and by release of heavy water following exposure to deuterium), indicating that water vapor can be synthesized from solar wind hydrogen and sample oxygen. Observations of trace amounts of methane indicate that the reduction process is by no means restricted to the formation of water vapor.