Lunar water

Although liquid water cannot persist at the Moon's surface, and water vapour is quickly decomposed by sunlight and lost to space, scientists have thought since the 1960s that water ice, deposited by impacting comets or produced by the reaction of oxygen-rich lunar rocks and hydrogen in the solar wind, could survive in the cold, permanently shadowed craters at the Moon's poles.^[56] These craters have been in shadow for the past two billion years,^[57] and computer simulations suggest that up to 14,000 km² might be in permanent shadow.^[58] The presence of usable quantities of water on the Moon is an important factor in rendering lunar habitation cost-effective, since transporting from Earth would be prohibitively expensive.^[59]

Many different signatures of lunar water have since been found.^[60] In 1994, Clementine's bistatic radar experiment found indications of small, frozen pockets of water close to the surface (though later Arecibo radar observations suggested these might be rocks ejected from young impact craters);^[61] the Lunar Prospector's neutron spectrometer indicated in 1998 that high

Lunar south pole as imaged by Clementine: note permanent polar shadowconcentrations of hydrogen are present in the upper metre of the regolith near the polar regions;^[62] in 2008, new analysis found small amounts of water in the interior of volcanic lava beads brought to Earth by Apollo 15.^[63] In September 2009, Chandrayaan-1, the first Indian lunar mission, detected water and hydroxyl absorption lines in reflected sunlight using NASA's Moon Mineralogy Mapper instrument, evidence of large quantities of water on the Moon's surface, possibly as high as 1,000 ppm.^[64] Weeks after, NASA's LCROSS mission flew its 2300 kg impactor into a permanently shadowed polar crater, and detected at least 100 kg of water in the plume of ejected materia