"I thought they'd see traces at the edges of craters near the poles," he said. "They're seeing this all over a huge area."
Some proponents of human space travel suggest that once extracted, the water could be made into fuel to propel rockets to Mars and beyond.
Scientists are still debating the form this lunar water is taking - whether it's incorporated into rocks or produced through a reaction between solar wind and oxygen in the soil. They expect to learn more after Oct. 9, when a spacecraft is scheduled to crash into a frigid crater while an accompanying orbiter measures what's kicked up.
Scientists first detected hints of ice on the moon in the 1990s, but many considered the data ambiguous.
The latest findings were beamed back from a NASA instrument flying aboard an Indian satellite called Chandrayaan 1. The instrument measured infrared light from the sun that was reflected off the lunar surface. Water and other molecules will absorb light at characteristic wavelengths called absorption lines.
"This is probably the next most reliable way to do it without going to the surface and tasting it," said James Green, director of the planetary science division at NASA.
They got their first indication of water five months ago, said team member Larry Taylor of the University of Tennessee, Knoxville. "We argued about it - and we didn't really believe it," he said.
Luckily, the Cassini mission had taken similar measurements of the moon while en route to Saturn. When they looked at that data, "lo and behold we saw the same damn thing," Taylor said. They also checked flyby data from another mission called Epoxi and got a second confirmation.
All three found the same water signature, said Taylor, but it was ephemeral. "It seems to come and go as a function of temperature." The water is concentrated at the poles, while at lower latitudes it becomes more concentrated in the mornings and evenings, much of it disappearing at noon.
Taylor's theory: The water is being continuously created by hydrogen from the solar wind bombarding oxygen in the soil. The daytime heat then drives it off. Spudis says the water could be created or liberated from rocks and then transported to the poles, or it could be that comets and asteroid impacts long ago supplied the poles with water and it's being periodically transported to the equator.
What's exciting to him is the pervasiveness of the water.
Taylor, who was involved in the collection of samples from Apollo missions, said they detected water in lunar soil and rocks back then but thought it was contamination.
"I thought it was mainly due to the fact that the rocks had come in contact with . . . Houston air." Now, he says, it's possible some of that water was really from the moon.
Spudis says that if the water is concentrated enough, astronauts could extract it and use it to supply a moon base. They could also separate it into hydrogen and oxygen for rocket fuel. That's an expensive prospect, but Spudis said it might save money because it costs so much to launch fuel from Earth.
Also announced yesterday was a detection of Martian water in the form of ice sheets buried beneath the planet's surface.
"The solar system is getting to be a soggy place," NASA's Green said.
Contact staff writer Faye Flam at 215-854-4977 or firstname.lastname@example.org.
See lunar images from NASA's Web site via http://go.philly.com/nasa