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[[File:Direct evidence of lunar water.jpg|thumb|right|350px|Direct evidence of lunar water in the Moon atmosphere through Chandrayaan-1 Chandra's Altitudinal Composition (CHACE) output profile]]
[[File:Chandrayaan1 Spacecraft Discovery Moon Water.jpg|thumb|right|350px|These images show a very young lunar crater on the side of the Moon that faces away from Earth, as viewed by Chandrayaan-1's Moon Mineralogy Mapper equipment <!-- icleshow/5057854.cms -->]]

'''Lunar water''' is water that is present on the [[Moon]]. Liquid water cannot persist at the Moon's surface, and [[water vapor]] is [[photodissociation|decomposed by sunlight]], with [[hydrogen]] quickly lost to outer space. However, scientists have since the 1960s conjectured that [[ice|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.<ref name="space">{{cite web|url=http://www.space.com/18067-moon-atmosphere.html|title=Atmosphere of the Moon|publisher=space.com|accessdate=2015-05-25}}</ref><ref name="nasa">{{cite web|url=http://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphere.html#.VCzkF2eSxQA|title=Is There an Atmosphere on the Moon? &#124; NASA|publisher=nasa.gov|accessdate=2015-05-25}}</ref>

[[dihydrogen oxide|Water (H<sub>2</sub>O)]], and the chemically related [[hydroxyl]] group (-OH), can also exist in forms chemically bound as [[hydrates]] and [[hydroxide]]s 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.<ref name=Lucey>{{Cite journal|title=A Lunar Waterworld|journal=Science|date=23 October 2009|first=Paul G.|last=Lucey|pmid=19779147|volume=326|issue= 5952|pages=531–532|doi= 10.1126/science.1181471|url=http://www.sciencemag.org/cgi/content/summary/sci;326/5952/531?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=lunar+water&searchid=1&FIRSTINDEX=10&resourcetype=HWCIT|format=|accessdate=2009-11-18 |bibcode = 2009Sci...326..531L }}</ref> In fact, [[Adsorption|adsorbed]] water is calculated to exist at trace concentrations of 10 to 1000 [[parts per million]].<ref>{{Cite journal|title=Detection of Adsorbed Water and Hydroxyl on the Moon|journal=Science|date=23 October 2009|first=Roger N.|last=Clark|pmid=19779152|volume=326|issue= 5952|pages= 562–564|doi= 10.1126/science.1178105|url=http://www.sciencemag.org/cgi/content/abstract/sci;326/5952/562|format=|accessdate=2009-11-20 |bibcode = 2009Sci...326..562C }}</ref> In 1978 it was reported that samples returned by the [[USSR|Soviet]] [[Luna 24]] probe contained 0.1% water by mass sample.<ref name="Geokhimiya_rus">{{cite journal |last1= Akhmanova|first1= M|last2= Dement'ev|first2= B|last3= Markov|first3= M|date=February 1978|language= russian|title= Water in the regolith of Mare Crisium (Luna-24)?|journal= Geokhimiya|issue= 285}}</ref><ref name="Geochemistry_eng">{{cite journal |last1= Akhmanova|first1= M|last2= Dement'ev|first2= B|last3= Markov|first3= M|date= 1978|title= Possible Water in Luna 24 Regolith from the Sea of Crises|journal= Geochemistry International|volume= 15|issue= 166}}</ref> Inconclusive evidence of free water ice at the lunar poles was accumulated from a variety of observations suggesting the presence of bound hydrogen.

On 18 November 2008, the Moon Impact probe was released from India's ''[[Chandrayaan-1]]'' at a height of {{convert|100|km}}. During its 25-minute descent, the impact probe's Chandra's Altitudinal Composition (CHACE) recorded evidence of water in 650 mass spectra gathered in the thin atmosphere above the Moon's surface.<ref>[http://www.planetary.org/blogs/emily-lakdawalla/2010/2430.html Water on the Moon: Direct evidence from Chandrayaan-1's Moon Impact Probe]. Published on 2010/04/07.</ref> In September 2009, NASA payload [[Moon Mineralogy Mapper]] onboard Chandrayaan-1 detected water on the Moon surface<ref>{{cite web|url=http://planetary.org/news/2009/1113_LCROSS_Lunar_Impactor_Mission_Yes_We.html |title=LCROSS Lunar Impactor Mission: "Yes, We Found Water!" |last=Lakdawalla |first=Emily |date=13 November 2009 |publisher=The Planetary Society |accessdate=2010-04-13 |deadurl=yes |archiveurl=https://web.archive.org/web/20100122233405/http://www.planetary.org/news/2009/1113_LCROSS_Lunar_Impactor_Mission_Yes_We.html |archivedate=22 January 2010 |df= }}</ref><ref>{{cite journal|authors=Pieters, C. M.; Goswami, J. N.; Clark, R. N.; Annadurai, M.; Boardman, J.; Buratti, B.; Combe, J.-P.; Dyar, M. D.; Green, R.; Head, J. W.; Hibbitts, C.; Hicks, M.; Isaacson, P.; Klima, R.; Kramer, G.; Kumar, S.; Livo, E.; Lundeen, S.; Malaret, E.; McCord, T.; Mustard, J.; Nettles, J.; Petro, N.; Runyon, C.; Staid, M.; Sunshine, J.; Taylor, L. A.; Tompkins, S.; Varanasi, P.|date=2009|title=Character and Spatial Distribution of OH/H2O on the Surface of the Moon Seen by M3 on Chandrayaan-1|journal=Science|volume=326|issue=5952|pages=568–72|doi=10.1126/science.1178658|pmid=19779151|bibcode = 2009Sci...326..568P }}</ref> and [[hydroxyl]] absorption lines in reflected sunlight.
In November 2009, [[NASA]] re-confirmed water on moon with its [[LCROSS]] space probe which detected a significant amount of hydroxyl group in the material thrown up from a south polar crater by an impactor;<ref name=spectraResult>{{Cite news
| first=Jonas
| last=Dino
| author2=Lunar Crater Observation and Sensing Satellite Team
| authorlink=
| title=LCROSS Impact Data Indicates Water on Moon
| date=November 13, 2009
| publisher=[[NASA]]
| url=http://www.nasa.gov/mission_pages/LCROSS/main/prelim_water_results.html
| accessdate = 2009-11-14
| language = }}</ref> this may be attributed to water-bearing materials<ref name='hydroxyl'>{{Cite journal|title=Character and Spatial Distribution of OH/H2O on the Surface of the Moon Seen by M3 on Chandrayaan-1|journal=Science|date=23 October 2009|first=C. M.|last=Pieters|author2=J. N. Goswami |author3=R. N. Clark |display-authors=etal |pmid=19779151|volume=326 |issue= 5952|pages=568–572|doi= 10.1126/science.1178658|url=http://www.sciencemag.org/cgi/content/abstract/sci;326/5952/568|format=|accessdate=2009-11-20|bibcode=2009Sci...326..568P}}</ref> – what appears to be "near pure [[crystalline]] water-ice".<ref name=BBC2Mar2010>[http://news.bbc.co.uk/1/hi/sci/tech/8544635.stm "Ice deposits found at Moon's pole"], BBC News, 2 March 2010</ref>
In March 2010, it was reported that the Mini-SAR on board Chandrayaan-1 had discovered more than 40 permanently darkened craters near the Moon's north pole that are hypothesized to contain an estimated 600&nbsp;million [[metric tonne]]s (1.3&nbsp;trillion pounds) of water-ice.<ref name=BBC2Mar2010 /><ref name="additional evidence">{{cite news |title=NASA Radar Finds Ice Deposits at Moon's North Pole |date=March 2010 |url=http://www.nasa.gov/mission_pages/Mini-RF/multimedia/feature_ice_like_deposits.html |work=[[NASA]] |accessdate=2012-03-26}}</ref>

Water may have been delivered to the Moon over geological timescales by the regular bombardment of water-bearing [[comet]]s, [[asteroid]]s and [[meteoroid]]s <ref>
Elston, D.P. (1968) "Character and Geologic Habitat of Potential Deposits of Water, Carbon and Rare Gases on the Moon", Geological Problems in Lunar and Planetary Research, Proceedings of AAS/IAP Symposium, AAS Science and Technology Series, Supplement to Advances in the Astronautical Sciences., p. 441</ref> or continuously produced ''in situ'' by the hydrogen ions ([[proton]]s) of the [[solar wind]] impacting oxygen-bearing minerals.<ref name="nasa2">{{cite web |url=http://lunar.arc.nasa.gov/project/faq.htm#18 |title=NASA – Lunar Prospector |publisher=lunar.arc.nasa.gov |accessdate=2015-05-25 |deadurl=yes |archiveurl=https://web.archive.org/web/20160914115221/http://lunar.arc.nasa.gov/project/faq.htm#18 |archivedate=2016-09-14 |df= }}</ref>

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.

==Lunar water discovery==

[[File:LRO Peers into Permanent Shadows.ogg|thumb|300px|Beginning with a full-frame Moon in this video, the camera flies to the lunar south pole and shows areas of permanent shadow. Realistic shadows evolve through several months.]]

On 24 September 2009 [[Science (journal)|''Science'']] magazine reported that the [[Moon Mineralogy Mapper]] (M<sup>3</sup>) on the [[Indian Space Research Organisation]]'s (ISRO) ''[[Chandrayaan-1]]'' had detected water on the Moon.<ref>{{Cite journal | last1 = Pieters | first1 = C. M. | last2 = Goswami | first2 = J. N. | last3 = Clark | first3 = R. N. | last4 = Annadurai | first4 = M. | last5 = Boardman | first5 = J. | last6 = Buratti | first6 = B. | last7 = Combe | first7 = J. -P. | last8 = Dyar | first8 = M. D. | last9 = Green | first9 = R. | last10 = Head | first10 = J. W. | last11 = Hibbitts | first11 = C. | last12 = Hicks | first12 = M. | last13 = Isaacson | first13 = P. | last14 = Klima | first14 = R. | last15 = Kramer | first15 = G. | last16 = Kumar | first16 = S. | last17 = Livo | first17 = E. | last18 = Lundeen | first18 = S. | last19 = Malaret | first19 = E. | last20 = McCord | first20 = T. | last21 = Mustard | first21 = J. | last22 = Nettles | first22 = J. | last23 = Petro | first23 = N. | last24 = Runyon | first24 = C. | last25 = Staid | first25 = M. | last26 = Sunshine | first26 = J. | last27 = Taylor | last28 = Tompkins | first28 = S. | first29 = P. | last29 = Varanasi | first27 = L. A. | doi = 10.1126/science.1178658 | title = Character and Spatial Distribution of OH/H2O on the Surface of the Moon Seen by M3 on Chandrayaan-1 | journal = Science | volume = 326 | issue = 5952 | pages = 568–572 | year = 2009 | pmid = 19779151| pmc = | bibcode = 2009Sci...326..568P }}</ref>
M<sup>3</sup> detected absorption features near {{convert|2.8-3.0|µm|abbr=on}} on the surface of the Moon. For silicate bodies, such features are typically attributed to [[hydroxyl]]- and/or [[Water (properties)|water]]-bearing materials. 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 M<sup>3</sup> data with neutron spectrometer H abundance data suggests that the formation and retention of OH and H<sub>2</sub>O is an ongoing surficial process. OH/H<sub>2</sub>O production processes may feed polar cold traps and make the lunar regolith a candidate source of volatiles for human exploration.

The Moon Mineralogy Mapper (M<sup>3</sup>), an imaging spectrometer, was one of the 11 instruments on board Chandrayaan-1, whose mission came to a premature end on 29 August 2009.<ref name="isro_pressrel_090829">{{cite web|title=Welcome To ISRO:: Press Release:: 29 August 2009|url=http://www.isro.org/pressrelease/scripts/pressreleasein.aspx?Aug29_2009|deadurl=yes|archiveurl=https://web.archive.org/web/20120903104432/http://www.isro.org/pressrelease/scripts/pressreleasein.aspx?Aug29_2009|archivedate=3 September 2012|df=}} 101004 isro.org</ref> M<sup>3</sup> was aimed at providing the first mineral map of the entire lunar surface.

Lunar scientists had discussed the possibility of water repositories for decades. They are now increasingly "confident that the decades-long debate is over" a report says. "The Moon, in fact, has water in all sorts of places; not just locked up in [[minerals]], but scattered throughout the broken-up [[planetary surface|surface]], and, potentially, in blocks or sheets of ice at depth." The results from the ''[[Chandrayaan]]'' mission are also "offering a wide array of watery signals."<ref>{{cite news | url =https://www.usatoday.com/tech/science/2009-09-23-moon-water_N.htm | title =It's not lunacy, probes find water in Moon dirt | date =23 September 2009 | accessdate =2009-09-26 | publisher =USA Today}}</ref><ref>{{cite news | url =http://www.hindu.com/2009/09/23/stories/2009092357770100.htm | title =Water discovered on Moon?: "A lot of it actually" | date =23 September 2009 | accessdate =2009-09-26 | publisher =The Hindu}}</ref>

==History of observations==

===20th century===
;Apollo Program
The possibility of ice in the floors of polar lunar craters was first suggested in 1961 by [[Caltech]] researchers Kenneth Watson, Bruce C. Murray, and Harrison Brown.<ref>Watson, K., B. C. Murray, and H. Brown (1961), The Behavior of Volatiles on the Lunar Surface, J. Geophys. Res., 66(9), 3033–3045.</ref> Although trace amounts of water were found in [[lunar rock]] samples collected by [[Apollo program|Apollo]] astronauts, this was assumed to be a result of contamination, and the majority of the lunar surface was generally assumed to be completely dry.<ref name="space.com">[http://www.space.com/scienceastronomy/090923-moon-water-discovery.html "It's Official: Water Found on the Moon"], ''Space.com'', 23 September 2009</ref><ref>{{Cite journal|title=Water on The Moon, I. Historical Overview|journal=Astronomical Review|date=October 2011|first=Arlin |last=Crotts|pmid=|volume=6|issue= 8|pages= 4–20|doi= |url=http://astroreview.com/issue/2012/article/water-on-the-moon-i-historical-overview|format=|accessdate=2012-10-03 |bibcode = 2011AstRv...6h...4C }}</ref> However, a 2008 study of lunar rock samples revealed evidence of water molecules trapped in volcanic glass beads.<ref name="sciam 9-Jul-08">[http://www.sciam.com/article.cfm?id=moon-once-harbored-water Moon Once Harbored Water, Lunar Lava Beads Show], ''Scientific American'', July 9, 2008</ref>

The first direct evidence of water vapor near the Moon was obtained by the [[Apollo 14]] [[ALSEP]] Suprathermal Ion Detector Experiment, SIDE, on March 7, 1971. A series of bursts of water vapor ions were observed by the instrument mass spectrometer at the lunar surface near the Apollo 14 landing site.<ref>Freeman, J.W., Jr., H.K. Hills., R.A. Lindeman, and R.R. Vondrak, Observations of Water Vapor at the Lunar Surface, ''The Moon'', 8, 115–128, 1973</ref>

;Luna 24
In February 1978 Soviet scientists M. Akhmanova, B. Dement'ev, and M. Markov of the Vernadsky Institute of Geochemistry and Analytic Chemistry published a paper claiming a detection of water fairly definitively.<ref name=Geokhimiya_rus /><ref name=Geochemistry_eng /> Their study showed that the samples returned to Earth by the 1976 Soviet probe [[Luna 24]] contained about 0.1% water by mass, as seen in infrared absorption spectroscopy (at about {{convert|3|µm|abbr=on}} wavelength), at a detection level about 10 times above the threshold.<ref name="Crotts_hist">{{cite arXiv |last= Crotts|first= Arlin|eprint= 1205.5597v1|title= Water on The Moon, I. Historical Overview|class= astro-ph. EP|date= 2012}}</ref>

;Clementine mission
[[File:Moon South Pole.jpg|thumb|200px|Composite image of the Moon's south polar region, captured by NASA's [[Clementine mission|Clementine probe]] over two [[lunar day]]s. Permanently shadowed areas could harbour water ice.]]

A proposed evidence of water ice on the Moon came in 1994 from the United States military [[Clementine probe]]. In an investigation known as the '[[bistatic radar]] experiment', Clementine used its transmitter to beam radio waves into the dark regions of the south pole of the Moon.<ref>[http://www.sciencemag.org/cgi/content/full/274/5292/1495 The Clementine bistatic radar experiment] — Science</ref> Echoes of these waves were detected by the large dish antennas of the [[Deep Space Network]] on Earth. The magnitude and [[Polarization (waves)|polarisation]] of these echoes was consistent with an icy rather than rocky surface, but the results were inconclusive,<ref name=Clementine>[http://lunar.arc.nasa.gov/results/ice/clem.htm Clementine Probe] {{webarchive |url=https://web.archive.org/web/20080724111724/http://lunar.arc.nasa.gov/results/ice/clem.htm |date=July 24, 2008 }}</ref> and their significance has been questioned.<ref>{{cite journal | doi = 10.1029/1998JE900038 | title = Reanalysis of Clementine bistatic radar data from the lunar South Pole | date = 1999 | last1 = Simpson | first1 = Richard A. | last2 = Tyler | first2 = G. Leonard | journal = Journal of Geophysical Research | volume = 104 | page = 3845 | bibcode=1999JGR...104.3845S}}</ref><ref>{{cite journal | doi = 10.1038/nature05167 | title = No evidence for thick deposits of ice at the lunar south pole | date = 2006 | last1 = Campbell | first1 = Donald B. | last2 = Campbell | first2 = Bruce A. | last3 = Carter | first3 = Lynn M. | last4 = Margot | first4 = Jean-Luc | last5 = Stacy | first5 = Nicholas J. S. | journal = Nature | volume = 443 | issue = 7113 | pages = 835–7 | pmid = 17051213 | url=http://ssedso.gsfc.nasa.gov/initiatives/lunar/LESWG/pubs_presentations/misc/nature05167.pdf |format=PDF|bibcode = 2006Natur.443..835C }}</ref> Earth-based radar measurements were used to identify the areas that are in permanent shadow and hence have the potential to harbour lunar ice: Estimates of the total extent of shadowed areas poleward of 87.5 degrees latitude are {{convert|1030 and 2550|km2}} for the north and south poles, respectively.<ref name="Margot1999">{{cite journal|last1=Margot|first1=J. L.|title=Topography of the Lunar Poles from Radar Interferometry: A Survey of Cold Trap Locations|journal=Science|volume=284|issue=5420|date=1999|pages=1658–1660|issn=0036-8075|doi=10.1126/science.284.5420.1658|bibcode = 1999Sci...284.1658M|pmid=10356393}}</ref> Subsequent computer simulations encompassing additional terrain suggested that an area up to {{convert|14,000|km2}} might be in permanent shadow.<ref name="M03">{{cite web| url = http://www.psrd.hawaii.edu/June03/lunarShadows.html | title=The Moon's Dark, Icy Poles| last = Linda | first=Martel | date = June 4, 2003}}</ref>

;Lunar Prospector
The [[Lunar Prospector]] probe, launched in 1998, employed a neutron spectrometer to measure the amount of [[hydrogen]] in the lunar [[regolith]] near the polar regions.<ref>{{cite web|url=http://lunar.arc.nasa.gov/results/ice/eureka.htm |title=Eureka! Ice found at lunar poles |date=August 31, 2001 |deadurl=yes |archiveurl=https://web.archive.org/web/20061209110937/http://lunar.arc.nasa.gov/results/ice/eureka.htm |archivedate=December 9, 2006 }}</ref> It was able to determine hydrogen abundance and location to within 50 parts per million and detected enhanced hydrogen concentrations at the lunar north and south poles. These were interpreted as indicating significant amounts of water ice trapped in permanently shadowed craters,<ref>[http://nssdc.gsfc.nasa.gov/planetary/lunar/lp_science.html Lunar Prospector Science Results] NASA</ref> but could also be due to the presence of the [[hydroxyl radical]] (<sup>•</sup>OH) chemically bound to minerals. Based on data from Clementine and Lunar Prospector, NASA scientists have estimated that, if surface water ice is present, the total quantity could be of the order of {{convert|1-3|km3}}.<!-- Weight in the Moon is not as in the Earth; instead must mention mass or volume.--><ref>[https://science.nasa.gov/headlines/y2005/28apr_lro.htm Prospecting for Lunar Water], NASA</ref><ref>[http://lunar.arc.nasa.gov/results/neures.htm Neutron spectrometer results] {{webarchive |url=https://web.archive.org/web/20090117210125/http://lunar.arc.nasa.gov/results/neures.htm |date=January 17, 2009 }}</ref> In July 1999, at the end of its mission, the Lunar Prospector probe was deliberately crashed into [[Shoemaker (lunar crater)|Shoemaker crater]], near the Moon's south pole, in the hope that detectable quantities of water would be liberated. However, spectroscopic observations from ground-based telescopes did not reveal the spectral signature of water.<ref>[http://nssdc.gsfc.nasa.gov/planetary/text/lp_pr_19991013.txt No water ice detected from Lunar Prospector], NASA website</ref>

;Cassini–Huygens
More suspicions about the existence of water on the Moon were generated by inconclusive data produced by [[Cassini–Huygens]] mission,<ref name=Kemm>{{Cite news| first=Kelvin | last=Kemm | title=Evidence of water on the Moon, Mars alters planning for manned bases | date=October 9, 2009 | publisher=Engineering News | url =http://www.engineeringnews.co.za/article/evidence-of-water-on-the-moon-mars-alter-planning-for-manned-bases-2009-10-09 | work = | pages = | accessdate = 2009-10-09 | language = }}</ref> which passed the Moon in 1999.

===21st century===
;Deep Impact
In 2005, observations of the Moon by the ''[[Deep Impact (spacecraft)|Deep Impact]]'' spacecraft produced inconclusive spectroscopic data suggestive of water on the Moon. In 2006, observations with the [[Arecibo Observatory|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.<ref>{{cite web |author=Paul Spudis |title=Ice on the Moon |url=http://www.thespacereview.com/article/740/1 |publisher=The Space Review |date=2006 |accessdate=2013-09-27}}</ref> In June 2009, NASA's ''Deep Impact'' spacecraft, now redesignated [[EPOXI]], made further confirmatory bound hydrogen measurements during another lunar flyby.<ref name="space.com"/>

;Kaguya
As part of its lunar mapping programme, Japan's [[SELENE|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.<ref>[http://www.kaguya.jaxa.jp/en/equipment/grs_e.htm Kaguya Gamma Ray Spectrometer], JAXA</ref> 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,<ref>{{cite web |url=http://www.spaceflightnow.com/news/n0907/06kaguya/ |title=Japan's now-finished lunar mission found no water ice |publisher=Spaceflight Now |date=July 6, 2009 |accessdate=2013-09-27}}</ref> and it ended its mission by crashing into the lunar surface in order to study the ejecta plume content.<ref>{{cite web|url=http://news.bbc.co.uk/1/hi/sci/tech/8094863.stm |title=Japanese probe crashes into Moon |publisher=BBC News |date=2009-06-11 |accessdate=2013-09-27}}</ref> <!-- Results of this?? -->

;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.<ref name="who's orbiting">[https://science.nasa.gov/headlines/y2008/20feb_orbitingthemoon.htm "Who's Orbiting the Moon?"], NASA, February 20, 2008</ref> <!-- results of this?? -->

[[File:Water Detected at High Latitudes on the Moon.jpg|thumb|Image of the Moon taken by the [[Moon Mineralogy Mapper]]. Blue shows the spectral signature of [[hydroxide]], green shows the brightness of the surface as measured by reflected infrared radiation from the [[Sun]] and red shows a mineral called [[pyroxene]].]]
[[Image:LCROSS Centaur Sep.jpg|thumb|On Friday 9 October 2009, as the spent upper stage of NASA's [[Lunar Reconnaissance Orbiter]] launcher smashed into the [[Cabeus (crater)|Cabeus lunar crater]], the [[LCROSS]] probe attempted to detect water in the ejecta plume before it also crashed itself onto the lunar surface.]]
;Chandrayaan-1
On November 14, 2008, the [[India]]n 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 analyzed for presence of water ice.<ref>{{cite web|title=Chandrayaan team over the Moon|date=2008-11-15|publisher=The Hindu|url=http://www.hindu.com/2008/11/15/stories/2008111560851200.htm}}</ref> On 25 September 2009, ISRO announced that the MIP had discovered water on the moon just before impact.<ref>{{cite web|title=MIP detected water on Moon way back in June: ISRO Chairman|date=2009-09-25|publisher=The Hindu|url=http://www.thehindu.com/sci-tech/science/mip-detected-water-on-moon-way-back-in-june-isro-chairman/article24854.ece}}</ref> This announcement was made after the discovery of water was announced on September 24, 2009 by Science magazine by the NASA payload Moon Mineralogy Mapper carried on board Chandrayaan-1.<ref>{{cite web|title=Water on moon ?|date=2009-09-25|publisher=Science Magazine|url=http://science.sciencemag.org/content/169/3952/1309}}</ref> MIP discovered water on moon before NASA's Moon Mineralogy Mapper but the announcement of this discovery was not made until NASA confirmed it.<ref>{{cite web|title=Chandrayaan first discovered water on moon, but ?|date=2009-09-25|publisher=DNA|url=http://www.dnaindia.com/scitech/report-chandrayaan-first-discovered-water-on-moon-but-1292942}}</ref><ref>{{cite web|title=Did India beat NASA to find water on moon?|date=2009-09-25|publisher=NDTV|url=http://www.ndtv.com/offbeat/did-india-beat-nasa-to-find-water-on-moon-402138}}</ref>

On September 25, 2009, [[NASA]] declared that data sent from its [[Moon Mineralogy Mapper]] (M3) instrument aboard Chandrayaan-1 orbiter confirmed the existence of hydrogen over large areas of the Moon's surface,<ref name=Kemm /> albeit in low concentrations and in the form of [[hydroxyl]] group ({{·}}OH) chemically bound to soil.<ref name='hydroxyl'/><ref>[http://news.bbc.co.uk/2/hi/science/nature/8272144.stm "Spacecraft see 'damp' Moon soils"], BBC, 24 September 2009</ref><ref>{{Cite news| first=George | last=Leopold | title=NASA confirms water on Moon | date=2009-11-13 | publisher= | url =http://www.industrialcontroldesignline.com/news/221800240;jsessionid=B43OJXVJWWI15QE1GHOSKHWATMY32JVN | work = | pages = | accessdate = 2009-11-18 | language = }}</ref> This supports earlier evidence from spectrometers aboard the ''[[Deep Impact (spacecraft)|Deep Impact]]'' and [[Cassini–Huygens|Cassini]] probes.<ref name="space.com"/><ref name="timesonline.co.uk">[http://www.timesonline.co.uk/tol/news/science/space/article6859492.ece "Moon crash will create six-mile plume of dust as Nasa searches for water"], ''The Times'', October 3, 2009</ref><ref>[https://www.theguardian.com/science/2009/sep/24/discovery-water-moon-lunar-base Discovery of water on Moon boosts prospects for permanent lunar base], ''The Guardian'', 24 September 2009</ref>

On March 2010, it was reported that the [[Mini-RF|Mini-SAR]] on board Chandrayaan-1 had discovered more than 40 permanently darkened craters near the Moon's north pole that are hypothesized to contain an estimated 600&nbsp;million metric tonnes of water-ice.<ref name=BBC2Mar2010 /><ref name="additional evidence" /> The radar's high CPR is not uniquely diagnostic of either roughness or ice; the science team must take into account the environment of the occurrences of high CPR signal to interpret its cause. The ice must be relatively pure and at least a couple of meters thick to give this signature.
<ref name="additional evidence"/> The estimated amount of water ice potentially present is comparable to the quantity estimated from the previous mission of [[Lunar Prospector]]'s neutron data.<ref name="additional evidence"/>

Although the results are consistent with recent findings of other NASA instruments onboard Chandrayaan-1 (the Moon Mineralogy Mapper (MP3) discovered water molecules in the Moon's polar regions, while water vapor was detected by NASA's [[Lunar Crater Observation and Sensing Satellite]], or LCROSS<ref name="additional evidence"/>) this observation 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 (<∼{{convert|10|cm|abbr=on}}), discrete pieces of ice mixed in with the regolith.<ref>{{cite journal | title = The nature of lunar volatiles as revealed by Mini-RF observations of the LCROSS impact site | journal = Journal of Geophysical Research: Planets | date = 13 January 2011 | first = C. D. |last=Neish | author2 = D. B. J. Bussey |author3=P. Spudis |author4=W. Marshall |author5=B. J. Thomson |author6=G. W. Patterson |author7=L. M. Carter. | volume = 116 | issue = E01005 | page = 8| id = | url = http://www.agu.org/pubs/crossref/2011/2010JE003647.shtml | accessdate = 2012-03-26| doi=10.1029/2010JE003647 | bibcode=2011JGRE..11601005N| quote = the Mini-RF instruments on ISRO's Chandrayaan-1 and NASA's Lunar Reconnaissance Orbiter (LRO) obtained S band ({{convert|12.6|cm|abbr=on}}) synthetic aperture radar images of the impact site at 150 and 30&nbsp;m resolution, respectively. These observations show that the floor of Cabeus has a circular polarization ratio (CPR) comparable to or less than the average of nearby terrain in the southern lunar highlands. Furthermore, <2% of the pixels in Cabeus crater have CPR values greater than unity. This observation 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 (<∼{{convert|10|cm|abbr=on}}), discrete pieces of ice mixed in with the regolith.}}</ref>

;Lunar Reconnaissance Orbiter
The search for lunar ice continued with NASA's [[Lunar Reconnaissance Orbiter]] (LRO) / [[LCROSS]] mission, launched June 18, 2009. LRO's onboard instruments carried out a variety of observations that may provide further evidence of water. On October 9, 2009, the [[Centaur (rocket stage)|Centaur]] upper stage of its [[Atlas V]] carrier rocket was directed to impact [[Cabeus (crater)|Cabeus crater]] at 11:31 UTC, followed shortly by the LCROSS spacecraft that flew into the ejecta plume and attempted to detect the presence of water vapor in the debris cloud.<ref>[http://lcross.arc.nasa.gov/mission.htm LCROSS mission overview] {{webarchive|url=https://web.archive.org/web/20090613115731/http://lcross.arc.nasa.gov/mission.htm |date=2009-06-13 }}, NASA</ref> Although no immediate spectacular plume was seen, time was needed to analyze the spectrometry data. On November 13, 2009 NASA reported that after analysis of the data obtained from the ejecta plume, the spectral signature of water had been confirmed.<ref name=spectraResult/><ref>[http://www.huffingtonpost.com/randall-amster/moon-river-what-water-in_b_373832.html Moon River: What Water in the Heavens Means for Life on Earth], by [[Randall Amster]], ''The Huffington Post'', November 30, 2009.</ref> However, what was actually detected was the chemical group hydroxyl ({{·}}OH), which is suspected to be from water,<ref name=Lucey /> but could also be [[hydrate]]s, which are inorganic salts containing chemically-bound water molecules. The nature, concentration and distribution of this material requires further analysis;<ref name=spectraResult/> chief mission scientist Anthony Colaprete has stated that the ejecta appears to include a range of fine-grained particulates of near pure crystalline water-ice.<ref name=BBC2Mar2010/> A later definitive analysis found the concentration of water to be "5.6 ± 2.9% by mass".<ref name="Colaprete2010">{{Cite journal
|author1=Colaprete, A. |author2=Schultz, P. |author3=Heldmann, J. |author4=Wooden, D. |author5=Shirley, M. |author6=Ennico, K. |author7=Hermalyn, B. |author8=Marshall, W |author9=Ricco, A. |author10=Elphic, R. C. |author11=Goldstein, D. |author12=Summy, D. |author13=Bart, G. D. |author14=Asphaug, E. |author15=Korycansky, D. |author16=Landis, D. |author17=Sollitt, L. | title=Detection of Water in the LCROSS Ejecta Plume
| journal=Science|date=22 October 2010|volume=330
| issue=6003
| pmid=20966242|pages=463–468
| doi=10.1126/science.1186986
| bibcode=2010Sci...330..463C
}}</ref> The [[Mini-RF]] instrument on LRO observed the LCROSS landing site and did not detect any evidence of large slabs of water ice, so the water is most likely present as small pieces of ice mixed in with the lunar regolith.<ref name=NozetteEtAl10>{{cite journal|title=The Lunar Reconnaissance Orbiter Miniature Radio Frequency (Mini-RF) Technology Demonstration|last1=Nozette|first1=Stewart|last2=Spudis|first2=Paul|last3=Bussey|first3=Ben|last4=Jensen|first4=Robert|last5=Raney|first5=Keith|display-authors=etal|journal=Space Science Reviews|date=January 2010|volume=150|pages=285–302|bibcode = 2010SSRv..150..285N |doi = 10.1007/s11214-009-9607-5 }}</ref><ref name=NeishEtAl11>{{cite journal | title = The nature of lunar volatiles as revealed by Mini-RF observations of the LCROSS impact site | journal = Journal of Geophysical Research: Planets | date = 13 January 2011 | first = C. D. |last=Neish | author2 = D. B. J. Bussey |author3=P. Spudis |author4=W. Marshall |author5=B. J. Thomson |author6=G. W. Patterson |author7=L. M. Carter. | volume = 116 | issue = E01005 | page = 8| id = | url = http://www.agu.org/pubs/crossref/2011/2010JE003647.shtml | accessdate = 2012-03-26| doi=10.1029/2010JE003647 | bibcode=2011JGRE..11601005N }}</ref>

LRO's laser altimeter's examination of the Shackleton crater at the lunar south pole suggests up to 22% of the surface of that crater is covered in ice.<ref>[http://www.nasa.gov/mission_pages/LRO/news/crater-ice.html Researchers Estimate Ice Content of Crater at Moon's South Pole] (NASA)</ref>

;Melt inclusions in Apollo 17 samples
In May 2011, Erik Hauri et al. reported<ref name="hauri">{{Cite journal
| last = Hauri
| first = Erik
| authorlink =
| author2=Thomas Weinreich
| author3=Alberto E. Saal
| author4=Malcolm C. Rutherford
| author5=James A. Van Orman
| title = High Pre-Eruptive Water Contents Preserved in Lunar Melt Inclusions
| journal = Science Express
| volume = 10
| issue = 1126
| pages = 213–215
| publisher = AAAS
| location =
| date = 26 May 2011
| url = http://www.sciencemag.org/content/early/2011/05/25/science.1204626.abstract
| jstor =
| issn = 1095-9203
| doi = 10.1126/science.1204626
| id =
| mr =
| zbl =
| jfm =
| accessdate = 2011-05-31
| bibcode=2011Sci...333..213H}}</ref> 615-1410 ppm water in [[melt inclusions]] in lunar sample 74220, the famous high-titanium "orange glass soil" of volcanic origin collected during the [[Apollo 17]] mission in 1972. The inclusions were formed during explosive eruptions on the Moon approximately 3.7&nbsp;billion years ago.

This concentration is comparable with that of magma in Earth's [[upper mantle]]. While of considerable selenological interest, this announcement affords little comfort to would-be lunar colonists. The sample originated many kilometers below the surface, and the inclusions are so difficult to access that it took 39 years to detect them with a state-of-the-art ion microprobe instrument.

==Possible water cycle==

===Production===
Lunar water has two potential origins: water-bearing [[comet]]s (and other bodies) striking the Moon, and ''in&nbsp;situ'' production. It has been theorized that the latter may occur when hydrogen ions ([[protons]]) in the [[solar wind]] chemically combine with the [[oxygen]] atoms present in the lunar minerals ([[oxide]]s, [[silicate]]s etc.) to produce small amounts of water trapped in the minerals' crystal lattices or as [[hydroxyl]] groups, potential water precursors.<ref>{{Cite journal|title=Lunar Hydrogen Distribution after KAGUYA(SELENE)|journal=2009 Annual Meeting of LEAG (2009)|author=L.F.A. Teodoro |author2=V.R. Eke |author3=R. Elphic |last-author-amp=yes |volume=|issue=|pages=|id= |url=http://www.lpi.usra.edu/meetings/leag2009/pdf/2053.pdf|format=PDF|accessdate=2009-11-18 }}</ref> (This mineral-bound water, or hydroxylated mineral surface, must not be confused with water ice.)

The [[hydroxyl]] surface groups (S–OH) formed by the reaction of protons (H<sup>+</sup>) with [[oxygen]] atoms accessible at oxide surface (S=O) could further be converted in water molecules (H<sub>2</sub>O) adsorbed onto the oxide mineral's surface. The mass balance of a chemical rearrangement supposed at the oxide surface could be schematically written as follows:

:<big>2 S-OH —> S=O + S + H<sub>2</sub>O</big>
or, <br />
:<big>2 S-OH —> S–O–S + H<sub>2</sub>O</big>
<br />
where S represents the oxide surface.

The formation of one water molecule requires the presence of two adjacent hydroxyl groups, or a cascade of successive reactions of one oxygen atom with two protons. This could constitute a limiting factor and decreases the probability of water production, if the proton density per surface unit is too low.

===Trapping===
[[Solar radiation]] would normally strip any free water or water ice from the lunar surface, splitting it into its constituent elements, [[hydrogen]] and [[oxygen]], which then escape to space. However, because of the only very slight axial tilt of the Moon's spin axis to the [[Ecliptic|ecliptic plane]] (1.5&nbsp;°), some deep craters near the poles never receive any sunlight, and are permanently shadowed (see, for example, [[Shackleton (crater)|Shackleton crater]], and [[Whipple (crater)|Whipple crater]]). The temperature in these regions never rises above about 100&nbsp;[[Kelvin|K]] (about −170&nbsp;°&nbsp;Celsius),<ref>[http://nssdc.gsfc.nasa.gov/planetary/ice/ice_moon.html Ice on the Moon], NASA</ref> and any water that eventually ended up in these craters could remain frozen and stable for extremely long periods of time — perhaps billions of years, depending on the stability of the orientation of the Moon's axis.<ref name="sciam 9-Jul-08"/><ref name=Clementine />

===Transport===
Although free water cannot persist in illuminated regions of the Moon, any such water produced there by the action of the solar wind on lunar minerals might, through a process of evaporation and condensation<!--Caution such an assertion is still dubious and unproved-->, migrate to permanently cold polar areas and accumulate there as ice, perhaps in addition to any ice brought by comet impacts.<ref name="space.com"/>

The hypothetical mechanism of water transport / trapping (if any) remains unknown: indeed lunar surfaces directly exposed to the solar wind where water production occurs are too hot to allow trapping by water condensation (and solar radiation also continuously decomposes water), while no (or much less) water production is expected in the cold areas not directly exposed to the Sun. Given the expected short lifetime of water molecules in illuminated regions, a short transport distance would in principle increase the probability of trapping. In other words, water molecules produced close to a cold, dark polar crater should have the highest probability of surviving and being trapped.

To what extent, and at what spatial scale, direct proton exchange (protolysis) and proton [[surface diffusion]] directly occurring at the naked surface of [[wikt:oxyhydroxide|oxyhydroxide]] minerals exposed to space vacuum (see [[surface diffusion]] and [[self-ionization of water]]) could also play a role in the mechanism of the water transfer towards the coldest point is presently unknown and remains a conjecture.

==Uses==
The presence of large quantities of water on the Moon would be an important factor in rendering [[lunar habitation]] cost-effective, since transporting water (or hydrogen and oxygen) from Earth would be prohibitively expensive. If future investigations find the quantities to be particularly large, water ice could be mined to provide liquid water for drinking and plant propagation, and the water could also be split into hydrogen and oxygen by solar panel-equipped electric power stations or a nuclear generator, providing breathable oxygen as well as the components of rocket fuel. The hydrogen component of the water ice could also be used to draw out the [[oxides]] in the lunar soil and harvest even more oxygen.

Analysis of lunar ice would also provide scientific information about the impact history of the Moon and the abundance of comets and asteroids in the early [[Inner Solar System]].

==Ownership==
The hypothetical discovery of usable quantities of water on the Moon may raise legal questions about who owns the water and who has the right to exploit it. The United Nations [[Outer Space Treaty]] does not prevent the exploitation of lunar resources, but does prevent the appropriation of the Moon by individual nations and is generally interpreted as barring countries from claiming ownership of [[in-situ]] resources.<ref>[http://www.unoosa.org/oosa/SpaceLaw/outerspt.html Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies ("Outer Space Treaty")] {{webarchive|url=https://www.webcitation.org/5whITsteH?url=http://www.unoosa.org/oosa/SpaceLaw/outerspt.html |date=2011-02-22 }}, UN Office for Outer Space Affairs</ref><ref>[http://www.space.com/scienceastronomy/060306_lunar_ice.html "Moon Water: A Trickle of Data and a Flood of Questions"], space.com, March 6, 2006</ref> However most legal experts agree that the ultimate test of the question will arise through precedents of national or private activity. Some private companies such as [[Shackleton Energy Company]] are already asserting their right to own whatever resources they remove and/or benefit from the Moon or asteroids through their own effort, risk and investment. The [[Moon Treaty]] specifically stipulates that exploitation of lunar resources is to be governed by an "international regime", but this treaty has not been ratified by any of the major space-faring nations.<ref>[http://www.unoosa.org/oosa/SpaceLaw/gares/html/gares_34_0068.html Agreement Governing the Activities of States on the Moon and Other Celestial Bodies ("Moon Treaty")] {{webarchive|url=https://web.archive.org/web/20080514053326/http://www.unoosa.org/oosa/SpaceLaw/gares/html/gares_34_0068.html |date=2008-05-14 }}, UN Office for Outer Space Affairs</ref>

==See also==
{{portal|Moon}}
* [[In situ resource utilization]]
* [[Shackleton Energy Company]]
* [[Water on Mars]]
;Missions
* [[24 Themis]] (detection of water on an asteroid)
* [[Chandrayaan-1]] lunar orbiter
* [[Chandrayaan-2]] lunar orbiter and rovers
* [[Lunar Flashlight]] solar sail orbiter
* [[Lunar Reconnaissance Orbiter]]

==References==
{{Reflist|2}}

==External links==
* [http://nssdc.gsfc.nasa.gov/planetary/ice/ice_moon.html Ice on the Moon] — NASA Goddard Space Flight Center
* [http://www.sciencemag.org/cgi/content/full/281/5382/1496 Fluxes of fast and epithermal neutrons from Lunar Prospector: Evidence for water ice at the lunar poles] — Science
* [http://www.timesonline.co.uk/tol/news/science/space/article6847457.ece#cid=OTC-RSS&attr=797093 Moon has a litre of water for every tonne of soil] — Times Online
* [http://science.slashdot.org/story/09/09/24/0212221/Unambiguous-Evidence-of-Water-On-the-Moon Unambiguous evidence of water on the Moon] — Slashdot Science Story
* [http://spie.org/newsroom/technical-articles/6241-cubesat-for-investigating-ice-on-the-moon?highlight=x2418&ArticleID=x117007 CubeSat for investigating ice on the Moon] — SPIE Newsroom

{{The Moon}}

{{DEFAULTSORT:Lunar Water}}
[[Category:Articles containing video clips]]
[[Category:Exploration of the Moon|Water]]
[[Category:Extraterrestrial water|Moon]]
[[Category:Lunar science|Water]]

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