There is much more water on the Moon than previously thought, according to scientists who have analysed data gathered by three different space missions. Data from one mission show that water is retained by the Moon through chemical reactions, suggesting that water may also be present below the lunar surface. Significant amounts of water on the Moon would make it much easier to sustain human colonies.

Ever since the Apollo missions brought back chunks of the Moon, scientists have been under the impression that there is very little (if any) water on our nearest neighbour. As well as being bone dry, these Moon rocks also showed no signs of ever interacting chemically with water. Later studies of the Moon's surface yielded tantalizing hints that water could be there, but these were not conclusive.

Most of what we know about the surface of the Moon is limited to its equatorial regions. That's where the Apollo missions landed, and it's also where subsequent Russian robotic missions gathered samples. Far less is known about the polar regions, where frozen water may be lurking – particularly in shady craters.

Damp days

New data from NASA's Deep Impact spacecraft reveals that water and hydroxyl (water less one hydrogen atom) molecules are present just about everywhere on the surface of the moon. What's more, the concentration of these molecules goes up and down in a daily cycle, suggesting that they are formed during the day by chemical reactions between protons in the solar wind and moon rocks. Deep Impact used its infrared spectrometer to survey the entire surface of the moon and also found that the concentrations of water and hydroxyl were highest at the north pole.

Similar evidence for such surface water has also just been found by Roger Clark of the US Geological Survey, who has analysed data gathered in 1999 by the Visual and Infrared Mapping Spectrometer (VIMS) aboard the Cassini mission.

According to lunar expert Ian Crawford of Birbeck College London, however, the most significant of the three findings was made by Moon Mineralogy Mapper (M3) on board India's Chandrayaan-1 satellite, which was launched 11 months ago. M3 maps the mineral content of the surface of the Moon using spectrometers covering the infrared to the ultraviolet.

Retaining water

"The M3 result shows that there are hydrated minerals on the Moon," explained Crawford. "This shows that the water is not just frozen on the surface, it requires some interaction between rocks and water". These interactions show that the Moon is retaining water that arrives on its surface via comets, meteorites and dust as well as the solar wind.

Crawford also believes that these three latest results suggest that there is enough water on the Moon to be useful to future lunar colonies.

We will learn even more about the Moon next week, when NASA's LCROSS probe will crash into a shady polar crater – and hopefully kick up ice and other debris that will then be analysed.

The next big challenge for Moon scientists, according to Crawford, will be to combine the results from all these missions to gain a better understanding of water on the Moon. In particular, he points out that ice on the Moon should contain a historical record of exactly what comets deliver to terrestrial planets. This could help us understand how Earth acquired its watery environment, which is crucial for life on this planet.

Results from the three missions will be published in Science later today.