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
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.
They estimate that lunar soil consists of 25% water. Two other probes equipped with M3-type instruments also detected the chemical signature for the presence of water. These include data gathered by the American spacecraft Cassini as it passed near the Moon a decade ago on its way to Saturn.
The third probe, NASA's Deep Impact, was launched toward the comet Tempel-1 in 2005 to pierce it with a projectile in order to test the dust cloud created by the impact. Deep Impact passed near the Moon to gather data with an instrument similar to M3.
"We were fooled"
Samples of lunar rock and soil brought back to Earth by Apollo astronauts in the 1960s also contained traces of water. But the containers in which they were transported were not hermetically sealed so researchers dismissed the presence of water as coming from the Earth.
"To some extent, we were fooled," said Taylor, who has studied the original Apollo missions. "Since the boxes leaked, we just assumed the water we found was from contamination with terrestrial air."
Indian scientists lost radio contact with the Chandrayaan-1 lunar satellite last month, but it had already collected enough data to provide the firmest evidence so far of water concentrated near the lunar poles.
"To find water on the moon was one of the main objectives," said mission director Mylswamy Annadurai in Bangalore. "The baby has done its job... It's a major milestone, although we still have to quantify the findings."
Future colonisation
"This is a major discovery that will have a significant impact on international plans for exploration of the Moon," commented Marc Norman a space and earth scientist at the Australian National University on Canberra. "China and the U.S. in particular will have significant interest in the distribution, size, and origin of this potential resource for human exploration."
However Norman said it is important to note that the water is bound up with minerals, rather than being in liquid form, "so we won't be able to pump it like groundwater, but will have to collect fairly large volumes of lunar soil, then extract and store it."
"This discovery will provide a huge boost to plans for devising robotic exploration and processing systems that work in the extremes of temperature, gravity, and dust found on the Moon," Norman said.
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with AFP.
