Comets are a significant source of water on the Moon, suggests a study published online in Nature Geoscience. Because lunar water is geochemically distinct from water on Earth, the research suggests that it must have been acquired after the formation of the Moon.
James Greenwood and colleagues analysed lunar rock samples that were collected during the Apollo missions. They found significant amounts of water in the rocks with a specific geochemical signature that points to a source in the lunar mantle, solar-wind protons or comets. Based on similarities with the known characteristics of the comets Hale-Bopp, Hyakutake and P/Halley, the researchers conclude that comets are the most likely source of this water.