Space scientists have found the strongest evidence yet that water exists on the moon, a discovery that helps complete a picture of a water-rich solar system and that could make colonizing our nearest neighbor in space much easier than previously thought.
Using data from three spacecraft that have made close flybys of the moon in recent years, research teams in the United States say they have found proof that a thin film of water coats the surface of the soil in at least some places on the moon.
"Within the context of lunar science, this is a major discovery," said Paul G. Lucey, a planetary scientist with the University of Hawaii, who was not involved in the current research. "There was zero accepted evidence that there was any water at the lunar surface, [but] now it is shown to be easily detectable, though by extremely sensitive methods. As a lunar scientist, when I read about this I was completely blown away."
The discovery "will forever change how we look at the moon," added Roger Clark, a scientist with the U.S. Geological Survey in Denver and the author of one of three papers -- each dealing with data from a different spacecraft -- appearing in this week's edition of Science magazine.
For decades, the moon had been considered a dead and uninteresting world by scientists. The Apollo missions of the 1960s and '70s brought back some rocks that contained tiny amounts of trapped water, but scientists at the time decided they had been contaminated by water from Earth.
Proponents of human space travel hope this discovery could put pressure on the White House to follow through with the George W. Bush administration's plans to return to the moon by 2020 and to construct Earth's first off-world colony there.
At the very least, the discovery lends weight to a new view of a friendlier solar system, where water, the lifeblood of biology on Earth, suddenly seems to be everywhere. Last year's Phoenix mission to Mars' polar region found ice just beneath the lander's struts. Ice has been found on Saturn's moon Titan and it covers Jupiter's moon Europa.
Research teams from Brown University, the University of Maryland and the U.S. Geological Survey used spectroscopic measurements taken of the lunar surface by NASA's Cassini and Deep Impact spacecraft, as well as India's Chandrayaan 1 satellite. The instruments on all three spacecraft detected the signature of the OH chemical bond (oxygen and hydrogen) at many places on the lunar surface, including areas subject to daytime temperatures that reach the boiling point of water. The greatest concentrations, however, were found in the coldest regions near the two poles.
Detecting the OH bond is not a sure indicator of water. The instruments could be picking up hydroxyl, which is composed of one oxygen and one hydrogen atom. Water has two hydrogen atoms and one oxygen.
But one of the papers, by research scientists Lori Feaga and Jessica Sunshine of the University of Maryland, found clear evidence for both hydroxyl and water in measurements taken by the Deep Impact spectrometer on June 2 and June 9. "We saw both species," Feaga said.
The amount of water in any one place is tiny. Clark estimated it at about a quart per ton of soil.
The moon "is almost as wet as a bone," Lucey said in an e-mail interview with The Times. "It is in the form of an imperceptible film on soil grains, perhaps several molecules thick."
Unless science makes some technological breakthrough, it would be extremely difficult for future moon colonists to harvest such tiny amounts of water. The research indicates, however, that the water migrates toward the poles -- by literally lifting off the soil particles and drifting north and south -- when the temperature rises during the lunar day.
When the water molecules land in a colder area near the poles, they are trapped there in higher concentrations, "perhaps high enough to use," Lucey said.
The question of how much water might have accumulated at the poles could be answered on Oct. 9, when NASA's Lunar Crater Observation and Sensing Satellite, known as LCROSS, is set to steer a rocket into a south pole crater called Cabeus A.
The resulting collision, which will send up a dust cloud two miles above the surface of the moon, will be observed and sampled by satellites and observatories on Earth for evidence of water. Cabeus A was chosen because it is in a perpetual shadow, so any water stored there in the form of ice would not melt.
"The results of the present studies lend credence to the lunar polar water hypothesis by providing a proven source of water on the surface of the moon," Lucey said.
If there is water on the moon, where did it come from? One possibility, according to the research teams, is that the water was deposited by one or more comets colliding with the moon. Another is that meteorites colliding with the moon might have unearthed underground sources of water.