Diagram showing the stream of charged hydrogen ions carried from the Sun by the solar wind. One possible scenario to explain hydration of the lunar surface is that hydrogen ions liberate oxygen from lunar minerals to form OH and H₂O, which are then weakly held to the surface.

Credit: University of Maryland/F. Merlin/McREL

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SYDNEY: Bound up with minerals, great quantities of water have been detected on the surface of the Moon. The discovery improves the prospects of future colonisation.

The evidence, disclosed today in separate papers in the U.S. journal Science, overturns the long accepted view that lunar soil is dry. It also comes just two weeks before a NASA probe is to crash into the surface near the Moon's southern pole to see if water can be detected in the dust and debris released by the impact.

Fresh surprise

"The Solar System has sprung another surprise on us. The Moon, until now thought to be drier than a bone, turns out to be covered in water," said Malcolm Walter, head of the Australian Centre for Astrobiology at the University of New South Wales in Sydney.

"It does not mean that there might be life on the Moon, but it might be a useful resource for future explorers," he said.

The new data was gathered by probes equipped with NASA instruments designed to map the Moon's mineral composition. The so-called Moon Mineralogy Mapper, or M3, uses the reflection of sunlight off the Moon's surface to determine soil composition.

In one of the three papers, researchers said they analysed light waves detected by an M3 instrument on board an Indian Moon satellite, Chandrayyan-1. The reflected light waves indicated a chemical bond between oxygen and hydrogen - proof, the researchers said, of the existence of water on the Moon's surface.

Solar wind

Larry Taylor of the University of Tennessee, one of the study's co-authors, said the instrument is capable of detecting the composition of the thin upper layer of the Moon's surface only to a depth of around five centimetres.

Until now, scientists had advanced the theory that there might be ice at the permanently dark bottom of craters at the Moon's poles but that the rest of the Moon was totally dry.

Lunar rocks and soil contain about 45% oxygen, but the source of the hydrogen observed by the instruments on the three probes remains to be determined. Taylor and his colleagues believe it may have come from a reaction with the solar wind, which consists mainly of streams of positively charged hydrogen atoms emitted as the sun undergoes nuclear fusion.