A surprising amount of water has been found to exist in the Moon's soil.
Data from three spacecraft, including India's Chandrayaan probe, shows that very fine films of H20 coat the particles that make up the lunar dirt.
The quantity is tiny but could become a useful resource for astronauts wishing to live on the Moon, scientists say.
"If you had a cubic metre of lunar soil, you could squeeze it and get out a litre of water," explained US researcher Larry Taylor.
The rock and soil samples returned by the Apollo missions were found to be ever so slightly "damp" when examined in the laboratory, but scientists could never rule out the possibility that the water in the samples got in only after they were hauled back to Earth.
Now a remote sensing instrument on Chandrayaan-1, India's first mission to lunar orbit, has confirmed that there is real H20 signal at the Moon.
Two other spacecraft to look at the Moon - Nasa's Deep Impact probe and the US-European Cassini satellite - back up Chandrayaan.
Both collected their Moon data long before Chandrayaan was launched (in the case of Cassini, 10 years ago), but the significance of what they saw is only now being realised.
The quantity of water is seen to increase the closer the observations are made to the poles.
Water ice
Scientists suspect the water is created in the soil in an interaction with the solar wind, the fast-moving stream of particles that constantly billows away from the Sun.
Harsh space radiation triggers a chemical reaction in which oxygen atoms already in the soil acquire hydrogen nuclei to make water molecules and the simpler hydrogen-oxygen (OH) molecule.
The amounts are small, say researchers, but boost the notion that astronauts based on the Moon could use it as a resource.
"If it is a little or a lot, it's easy enough to split into hydrogen and oxygen and then you have rocket fuel," said Professor Taylor, a University of Tennessee researcher working on Chandrayaan. read more
