Two US spacecraft were crashed into a lunar crater today but scientists said it was too early to say whether the mission to search for supplies of water had been a success.
Nasa, which is hoping to find sufficient quantities of water to use as fuel for space exploration, said it could take two months to make a conclusive assessment of what was found.
A two-ton empty rocket stage slammed into the eternally dark Cabeus crater near the moon's south pole at 4.31am PDT (1131 GMT), intended to throw up a plume of spray from any ice that was there.
Instruments on a second craft, that flew through the plume and hit close to the same spot four minutes later, as well as a lunar orbiter and telescopes on Earth captured data that could show whether there was ice there.
Video transmitted back from the trailing craft did not show, as hoped, the eruption of debris, but infrared devices showed a hot flash that indicated a crater about 18 to 20 yards (metres) wide.
"We didn't see a big splashy plume like we wanted to see," said Michael Bicay, director of science at the National Aeronautics and Space Administration's Ames Research Center.
Scientists did not know whether there had been no plume or if it could not be seen in the Internet-quality video shown as the craft crashed.
The $79 million program, a bargain by space exploration standards, could help change views of the moon.
Recent signs of water have upended ideas of the lunar surface as barren and unchanging, and evidence of ice would also suggest new possibilities for space travel.
"Water is essentially energy," scientist Victoria Friedensen said on Nasa TV. "It can be used to make fuel."
Three studies released last month found clear evidence of water on the moon, but the skein of water bound with dust that was disclosed then was extremely thin.
"It's not enough to be of any economic importance," said Nasa Lunar Science Institute director David Morrison.
Hidden in the Cabeus crater near the pole, out of sunlight, could be soil concentrations of 2 per cent to 3 per cent ice that would be usable. "You're going into a place where the sun hasn't shined for a billion years," Morrison said.
Video from the trailing spacecraft gave the sense of the fast approaching crash as craters edged with light grew larger and larger.
"I was blown away by how long this little spacecraft lasted," Tony Colaprete, the mission's principal investigator, told a news conference. He said it got good spectroscopic data which would show what elements were in the crater and how they were changed by the heat of the first impact.
"The fact that we flew in, saw the crater and it was still glowing hot means that if there was ice there or a pool of water or whatever else, it was subliming (turning to vapor)," he said. "We got the data we need."
Hundreds of space enthusiasts in parkas and sleeping bags gathered in the early morning to watch the impact on a big outdoor screen at the Ames Research Center, housed on an old dirigible field in Silicon Valley.
When the video signal abruptly stopped, the sign the trailing spacecraft had also hit the surface, cheers erupted.
Reuters