Analysis of the lunar surface by three different spacecraft has provided "unambiguous evidence" of water on the Moon, Space.com reports.
India's Chandrayaan-1, NASA's Cassini spacecraft, and the agency's Deep Impact probe have all detected the presence of either water or hydroxyl - one hydrogen atom and one oxygen atom linked by a single bond.
The NASA-built Moon Mineralogy Mapper (M3) aboard Chandrayaan-1 "detected wavelengths of light reflected off the surface that indicated the chemical bond between hydrogen and oxygen".
The M3 suggested water/hydroxyl in the top few millimetres of the lunar surface - the limit of its penetrative capability - and detected a water signal which "got stronger toward the polar regions".
Cassini passed by the Moon in 1999, en route to Saturn, and also noted a globally-distributed water/hydroxyl signal, once again stronger towards the poles.
Deep Impact, meanwhile, detected the same signal at all latitudes above 10 degrees N, and confirmed the poles showed the strongest signals. The probe made multiple passes of the Moon on its way to a planned rendezvous flyby of comet 103P/Hartley 2 in November 2010.
Commenting on the trio of studies, Paul Lacey of the University of Hawaii said the findings "provide unambiguous evidence for the presence of hydroxyl or water" - data which "prompts a critical re-examination of the notion that the moon is dry".
There are two possible sources for lunar water - from water-bearing comets hitting the surface, or an "endogenic" process. Space.com explains that since the material which makes up the lunar surface is roughly 45 per cent oxygen, "combined with other elements as mostly silicate minerals", it could interact with the solar wind to produce water.
According to the M3 team, if the solar wind's positively-charged hydrogen atoms impact against the Moon's surface with sufficient force they can "break apart oxygen bonds in soil materials", and "where free oxygen and hydrogen exist, there is a high chance that trace amounts of water will form".
Regarding just why there appears to be more water/hydroxyl at the poles, Deep Impact was able to "observe the same regions at different times of the lunar day", and found that "when the sun's rays were strongest, the water feature was lowest, while in the morning, the feature was stronger".
This leads the researchers to suggest "the daily dehydration and rehydration of the trace water across the surface could lead to the migration of hydroxyl and hydrogen towards the poles where it can accumulate in the cold traps of the permanently shadowed regions".
Carle Pieters of Brown University in Rhode Island, who led one of the three studies, said: "If the water molecules are as mobile as we think they are - even a fraction of them - they provide a mechanism for getting water to those permanently shadowed craters.
"This opens a whole new avenue [of lunar research], but we have to understand the physics of it to utilize it."
Quite what benefit the lunar water will be to future manned Moon missions remains to be seen. The resolutely imperial researchers note that one ton of the top layer of the lunar surface would yield just 32 ounces of water.
The three studies are published in tomorrow's issue of Science. ®