Lunar water is water that is present on the Moon. Diffuse water molecules can persist at the Moon's sunlit surface, as discovered by NASA's SOFIA observatory in 2020. Some water vapor is decomposed by sunlight, with hydrogen quickly lost to outer space. Scientists have also confirmed that there's water ice in the cold, permanently shadowed craters at the Moon's poles. Water molecules are also detected in the thin layer of gases above the lunar surface
Water (H2O), and the chemically related hydroxyl group (-OH), can also exist in forms chemically bound as hydrates and hydroxides to lunar minerals (rather than free water), and evidence strongly suggests that this is indeed the case in low concentrations over much of the Moon's surface. In fact, adsorbed water is calculated to exist at trace concentrations of 10 to 1000 parts per million.[5] Inconclusive evidence of free water ice at the lunar poles had accumulated during the second half of the 20th century from a variety of observations suggesting the presence of bound hydrogen.
On 18 August 1976, the Soviet Luna 24 probe landed at Mare Crisium, took samples from the depths of 118, 143, and 184 cm of the lunar regolith, and then took them to Earth. In February 1978, it was published that laboratory analysis of these samples shown they contained 0.1% water by mass Spectral measurements shown minima near 3, 5, and 6 µm, distinctive valence-vibration bands for water molecules, with intensities two or three times larger than the noise level
On 24 September 2009, it was reported that the NASA's Moon Mineralogy Mapper (M3) spectrometer onboard India's ISRO Chandrayaan-1 probe had detected absorption features near 2.8–3.0 μm (0.00011–0.00012 in) on the surface of the Moon. On 14 November 2008, India made the Moon Impact Probe onboard Chandrayaan-1 orbiter crash into Shackleton crater and confirmed the presence of water ice. For silicate bodies, such features are typically attributed to hydroxyl- and/or water-bearing materials. In August 2018, NASA confirmed that M3 showed water ice is present on the surface at the Moon poles. Water was confirmed to be on the sunlit surface of the Moon by NASA on October 26, 2020.
Water may have been delivered to the Moon over geological timescales by the regular bombardment of water-bearing comets, asteroids, and meteoroids or continuously produced in situ by the hydrogen ions (protons) of the solar wind impacting oxygen-bearing minerals.
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 rendering long-term lunar habitation feasible.
