There is evidence that water ice crystals do exist on the surface of the Moon. In 1994 the Clementine lunar probe made radar measurements of the Moon’s south pole that indicated the possible presence of frozen water mixed into the lunar soil and rocks. The particular location where the measurement was made is about the size of four football fields, and reaches a depth of about sixteen feet (five meters). The ice is thought to be inside a deep crater, and may have been deposited there when comets, which are composed mostly of of water ice, crashed into the Moon’s surface. Deep inside the craters, where sunlight does not shine, the ice may have accumulated without being melted by the Sun’s heat.

Since 1994, scientists have launched numerous scientific missions to the Moon, including Lunar Prospector, Chandrayaan-1, LCROSS, LRO, and GRAIL. They have uncovered substantial further evidence of large amounts of ice on and near the Moon’s surface.