Lunar water

Lunar water is water that is present on the Moon. The search for the presence of lunar water has attracted considerable attention and motivated several recent lunar missions, largely because of water's usefulness in making long-term lunar habitation feasible.^[1]

The moon was believed to be completely dry after analysis of Apollo mission soil samples; it was understood that any water vapor on the surface would generally be decomposed by sunlight, leaving hydrogen and oxygen lost to outer space. However, subsequent robotic probes found evidence of water, especially of water ice in some permanently-shadowed craters on the Moon; and in 2018 water ice was confirmed in multiple locations.^[2][3][4][5] This water ice is not in the form of sheets of ice on the surface nor just under the surface, but there may be small (less than about 10 centimetres (3.9 in)) chunks of ice mixed into the regolith, and some water is chemically bonded with minerals.^[6][7][8] Other experiments have detected water molecules in the negligible lunar atmosphere,^[9] and even some in low concentrations at the Moon's sunlit surface.^[10]

Water (H₂O) and the related hydroxyl group (-OH) exist in forms chemically bonded as hydrates and hydroxides to lunar minerals (rather than free water), and evidence strongly suggests that this is the case in low concentrations for much of the Moon's surface.^[11][12] In fact, of surface matter, adsorbed water is calculated to exist at trace concentrations of 10 to 1000 parts per million.^[13]

Water may have been delivered to the Moon over geological timescales by the regular bombardment of water-bearing comets, asteroids, and meteoroids^[14] or continuously produced in situ by the hydrogen ions (protons) of the solar wind impacting oxygen-bearing minerals.^[15]

NASA's Ice-Mining Experiment-1 (set to launch on the PRIME-1 mission no earlier than late 2024) is intended to answer whether or not water ice is present in usable quantities in the southern polar region.^[16]