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Scientists announce evidence of water on Moon
Posted: September 24, 2009

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Data from the Indian Chandrayaan-1 Moon mission, supported with similar data collected during Deep Impact and Cassini flybys of the Moon, has provided unambiguous evidence of water locked up in the lunar soil, bringing dreams of a sustainable Moon base one step closer.

"The Moon continues to surprise us," says Carle Pieters of Brown University, lead author of one of three papers describing the new results and featuring in the journal Science this week. Pieters is the lead investigator of the M3 instrument. "Widespread water has been detected on the surface of the Moon. We need to think outside of the box, this is not what we expected a decade ago."

The new results follow in the wake of an announcement by the Lunar Reconnaissance Orbiter (LRO) team last week that detailed further evidence for water ice at the lunar poles (read our report here). This ahead of the planned impact of the Lunar Crater Observation Sensing Satellite (LCROSS) into a permanently shadowed crater on 9 October in a dramatic attempt to throw up icy debris for LRO and other ground- and space-based telescopes to analyse.

Water abundance is dependent on temperature in Deep Impact observations. Image: NASA/University of Maryland.

Now, new data from Chandrayaan-1's Moon Mineralogy Mapper, M3, suggest that water is still being formed on the Moon today, a finding that has exciting implications for the future of manned exploration of our nearest celestial neighbour, since astronauts could use water reserves to drink, extract oxygen to breathe and use hydrogen as fuel. Although the Moon is drier than any desert on Earth, the new results suggest that a cubic metre of soil could yield one litre of water.

Moreover, water molecules were found across the whole surface of the Moon, and not just at the frigid poles. “We’ve made a very important step with this discovery, and now there are some very important steps to follow up on,” says Pieters.

Scientists think that the stream of charged hydrogen ions carried from the Sun to the Moon by the solar wind might explain the possible presence of water on the Moon. Image: University of Maryland/F. Merlin/McREL.

An extremely sensitive imaging spectrometer, M3 detects the presence of water by soaking up the signature electromagnetic radiation emitted by minerals on or just below the surface. The M3 team found that the wavelengths of light detected by the instrument were consistent with the absorption patterns for water (H2O) and simple hydrogen-oxygen (OH) molecules. The data also suggests that water is created every day, cycling through a loss and gain process.

"At noon the absorption is weak but in the evening it is much stronger," says Jessica Sunshine, Deptuy Project Investigator for the Deep Impact mission which also observed signatures of water and hydroxyl on the Moon."We're seeing an entire cycle of loss and recovery of water features. In the daytime the solar wind, which includes hydrogen ions, interacts with oxygen in the lunar soil to form and accumulate hydroxyl and water molecules. Water is lost at noon when it is hotter, but when it cools down in the evening it can accumulate water again."

This proposed explanation has extremely important implications for the rest of the Solar System. "This cycle means that regardless of the location and terrain type, the entire surface of the Moon will be hydrated during at least part of the lunar day," says Sunshine. "If this is the explanation (which it may not be) the same process would cause similar hydrations effect on any oxygen rich environment that doesn't have an atmosphere, for example, Mercury."

The scientists also present hypotheses on the occurrence of the water bearing minerals. The data confirms that water exists in the top one or two millimetres of the lunar surface but that it could occur as single layer of molecules, it could be mixed in, or be in the form of altered minerals on the surface. Unravelling the nature and occurrence of the water will provide the focus for decades worth of research.

Altitude measurements from NASA's LRO mission show the location of Cabeus A, the target crater for the LCROSS impact scheduled for 9 October. Impact: NASA/GSFC.

Scientists have also speculated that water molecules migrate from high latitudes to the polar regions where it is colder, especially to the deep, dark traps of ancient craters where the water inventory there has likely been supplemented by deliveries from comet impacts that dominated the early years of the Moon's existence.

“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,” says Pieters. “This opens a whole new avenue [of lunar research], but we have to understand the physics of it to ultilise it.”