•Water on the Moon has two potential sources: water carried by comets and other bodies that impact the Moon, and in situ production. The latter is theorized to be produced in small amounts by the chemical combination of hydrogen ions (protons) in the solar wind with oxygen atoms in the Moon’s minerals (oxides, silicates, etc.), forming water or hydroxyl groups, the possible precursors of water. Water (H2O) and its chemical compound, the hydroxyl group (-OH), exist as hydrates and hydroxides of the Moon’s minerals, in low concentrations over a large portion of the Moon’s surface. Indeed, the presence of adsorbed water has been estimated at concentrations of one part per million to one part per thousand. This mineral-bound water, or hydroxylated mineral surface, should not be confused with water ice.
Uncertain evidence of the presence of liquid water on the Moon has been found in various models that assume the presence of bound hydrogen. Moon scientists have been debating the possibility of water deposits for decades. Now, they write in a report that they are “confident that the decades-long debate is over.” “There is water on the Moon everywhere, not just in minerals, but in fragmented form on the surface and probably in the form of ice blocks or slabs deep down.” In 1961, Caltech researchers Kenneth Watson, Bruce C. Murray and Harrison Brown first suggested that there might be ice in the bottoms of polar lunar craters. In 1978, it was reported that the samples returned by the Soviet Luna 24 probe contained 0.1% water by mass. In 1998, the Lunar Prospector spacecraft measured the amount of hydrogen in the regolith near the polar regions. This instrument is a neutron spectrometer that can detect the amount and location of hydrogen in up to 50 parts per million. In 2009, the Moon Mineralogy Mapper (M³) instrument on the Chandrayaan-1 spacecraft detected absorption characteristics on the Moon’s surface of about 2.8-3.0 micrometers. On November 13, 2009, NASA announced that the spectral presence of water had been confirmed in the debris cloud created by the impact of the LCROSS spacecraft on the Cabeus crater. However, what was detected was the hydroxyl group (·OH). The principal mission scientist, Anthony Colaprete, stated that the ejecta appeared to contain ice in a pure crystalline structure. Subsequent analysis determined that the water concentration was “5.6% ± 2.9% by mass.”
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