Washington, Sep 25 - Discovery of water on the moon by India's first lunar mission Chandrayaan-1 with a thin layer of surface 'dew' appearing to form and then dissipating each day has set the scientific community agog.

'Finding water on the Moon in daylight is a huge surprise, even if it is only a small amount of water and only in the form of molecules stuck to soil,' writes University of Maryland astronomer Jessica Sunshine.

New data from the Deep Impact spacecraft and the Moon Mineralogy Mapper (M3), an instrument aboard Chandrayaan-1 spacecraft, provide, for the first time, clear evidence that water exists on the surface of the Moon, she said.

'The Deep Impact observations of the Moon not only unequivocally confirm the presence of OH/H2O on the lunar surface, but also reveal that the entire lunar surface is hydrated during at least some portions of the lunar day,' write Sunshine and co-authors in a paper on the Deep Impact data published online in the journal Science.

Prevailing scientific opinion for long has been that there probably is no water on the Moon and that, even if it does exist, it would be only in permanently cold, shadowed craters at the lunar poles.

'In the Deep Impact data we're essentially watching water molecules form and then dissipate right in front of our eyes,' said Sunshine, who said her first reaction to the M3 data was scepticism.

'We aren't certain yet how this happens,' she said, 'but our findings suggest a solar driven cycle in which layers of water only a few molecules thick form, dissipate and reform on the surface each lunar day.