page_title: Lunar water
section_title: 21st century
hierarchical_section_title: Lunar water / History of observations / 21st century
caption_attribution_description: English: Direct evidence of lunar water though CHACE output profile
context_page_description: Lunar water is water that is present on the Moon. Liquid water cannot persist at the Moon's surface, and water vapor is decomposed by sunlight, with hydrogen quickly lost to outer space. However, scientists have conjectured since the 1960s that water ice could survive in 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, and the chemically related hydroxyl group, can also exist in forms chemically bound as hydrates and hydroxides to lunar minerals, 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. 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.
context_section_description: Deep Impact
  In 2005, observations of the Moon by the Deep Impact spacecraft produced inconclusive spectroscopic data suggestive of water on the Moon. In 2006, observations with the Arecibo planetary radar showed that some of the near-polar Clementine radar returns, previously claimed to be indicative of ice, might instead be associated with rocks ejected from young craters. If true, this would indicate that the neutron results from Lunar Prospector were primarily from hydrogen in forms other than ice, such as trapped hydrogen molecules or organics. Nevertheless, the interpretation of the Arecibo data do not exclude the possibility of water ice in permanently shadowed craters. In June 2009, NASA's Deep Impact spacecraft, now redesignated EPOXI, made further confirmatory bound hydrogen measurements during another lunar flyby.
  Kaguya
  As part of its lunar mapping programme, Japan's Kaguya probe, launched in September 2007 for a 19-month mission, carried out gamma ray spectrometry observations from orbit that can measure the abundances of various elements on the Moon's surface. Japan's Kaguya probe's high resolution imaging sensors failed to detect any signs of water ice in permanently shaded craters around the south pole of the Moon, and it ended its mission by crashing into the lunar surface in order to study the ejecta plume content. 
  Chang'e 1
  The People's Republic of China's Chang'e 1 orbiter, launched in October 2007, took the first detailed photographs of some polar areas where ice water is likely to be found. 
  Chandrayaan-1
  India's ISRO spacecraft Chandrayaan-1 released the Moon Impact Probe (MIP) that impacted Shackleton Crater, of the lunar south pole, at 20:31 on 14 November 2008 releasing subsurface debris that was analysed for presence of water ice. During its 25-minute descent, the impact probe's Chandra's Altitudinal Composition Explorer (CHACE) recorded evidence of water in 650 mass spectra gathered in the thin atmosphere above the Moon's surface and hydroxyl absorption lines in reflected sunlight.
  On September 25, 2009, NASA declared that data sent from its M³ confirmed the existence of hydrogen over large areas of the Moon's surface, albeit in low concentrations and in the form of hydroxyl group ( · OH) chemically bound to soil. This supports earlier evidence from spectrometers aboard the Deep Impact and Cassini probes. On the Moon, the feature is seen as a widely distributed absorption that appears strongest at cooler high latitudes and at several fresh feldspathic craters. The general lack of correlation of this feature in sunlit M³ data with neutron spectrometer H abundance data suggests that the formation and retention of OH and H₂O is an ongoing surficial process. OH/H₂O production processes may feed polar cold traps and make the lunar regolith a candidate source of volatiles for human exploration.
  Although M³ results are consistent with recent findings of other NASA instruments onboard Chandrayaan-1, the discovered water molecules in the Moon's polar regions is not consistent with the presence of thick deposits of nearly pure water ice within a few meters of the lunar surface, but it does not rule out the presence of small (<∼10 cm (3.9 in)), discrete pieces of ice mixed in with the regolith. Additional analysis with M³ published in 2018 had provided more direct evidence of water ice near the surface within 20° latitude of both poles. In addition to observing reflected light from the surface, scientists used M³'s near-infrared absorption capabilities in the permanently shadowed areas of the polar regions to find absorption spectra consistent with ice. At the north pole region, the water ice is scattered in patches, while it is more concentrated in a single body around the south pole. Because these polar regions do not experience the high temperatures (greater than 373 Kelvin), it was postulated that the poles act as cold traps where vaporized water is collected on the Moon.
  In March 2010, it was reported that the Mini-SAR on board Chandrayaan-1 had discovered more than 40 permanently darkened craters n
caption: Direct evidence of lunar water in the Moon atmosphere obtained by the Chandrayaan-1's Altitudinal Composition (CHACE) output profile
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