By KENNETH CHANG
Published: March 8, 2010
Water Found on Moon, Researchers Say (November 14, 2009)
In Test of Water on Moon, Craft Hits Bull’s-Eye (October 10, 2009)
In Surprise, Moon Shows Signs of Water (September 24, 2009) Over the past year, scientists have found more and more convincing evidence that the moon, once thought desert dry, holds significant amounts of water ice within the deep, eternally dark craters near the south pole. The evidence turned conclusive with the deliberate crash of a NASA spacecraft into one of the craters last October, kicking up about 26 gallons of water.
The effort focused on the south pole, with its larger and deeper craters, but last week, scientists reported there is also ice in craters near the north pole.
And not just a dusting of frost. Within 40 small craters, one to nine miles wide, they estimated 600 million metric tons of water. Perhaps most notably, “It has to be relatively pure,” said Paul Spudis, the principal investigator for the instrument that made the discovery.
That is significant, because the ice in these craters could be easily tapped by future lunar explorers — not just for drinking water, but also broken apart into oxygen for breathing and hydrogen for fuel. In the previous findings, scientists could not rule out the possibility that the water was sparse or locked up within rocks and difficult to extract.
In this case, the evidence comes from radar signals bounced off the moon’s surface by a NASA-built instrument that flew aboard India’s Chandrayaan-1 moon probe, which was launched in 2008 and operated until last August. The reflections contain a telltale signature when they pass through transparent ice. If too much dirt and rocks are mixed in, the signature vanishes, and even permafrost, which typically contains 10 to 50 percent water, does not exhibit signs of water in the radar reflections.
Dr. Spudis, a scientist at the Lunar and Planetary Institute in Houston, said he guessed the water ice in the north polar craters might be 90 percent pure. He said the team was currently analyzing data covering the south pole craters.
The findings were reported at the Lunar and Planetary Science conference last week and will appear in the journal Geophysical Research Letters.
A similar experiment in 1994 aboard the Clementine probe, a joint effort between NASA and the Department of Defense, first revealed hints of water ice near the south pole, but the interpretation of the data remained controversial. The newer instrument is much more sensitive, and another copy of the experiment is currently operating aboard NASA’s Lunar Reconnaissance Orbiter.
In addition to the water near the poles, scientists also reported that a very thin layer of water covers much of the lunar surface. Water, it appears, not only exists, but is also moving around. “The moon is working in a way you didn’t expect,” Dr. Spudis said.
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