Ever since man first landed on the moon, scientists have wondered whether it would be possible to live on the lunar surface for an extended period. They always thought the answer was a resounding no - as the moon lacked water.
But now, three different space probes have found the chemical signature of water all over the moon's surface.
The findings surprised the scientists who at first doubted the unexpected measurement until it was confirmed independently and repeatedly.
It is not enough moisture to foster homegrown life on the moon. But if processed in mass quantities, it might provide resources, drinking water and rocket fuel, for future moon-dwellers, scientists say.
The water comes and goes during the lunar day. It is not a lot of water.
In a two-litre soda bottle of lunar dirt, there probably would be a medicine dropper full of water, said one of the scientists who discovered the water, which was spotted by spacecraft that either circled the moon or flew by.
Another way to think of it is that a drink of water would require a 730 square meters of dirt to produce, said team leader Carle Pieters of Brown University during a news conference on Thursday.
The discovery, with three studies published in the journal Science on Thursday and a NASA briefing, could refocus interest in the moon. The appeal of the moon waned after astronauts visited it 40 years ago and called it "magnificent desolation."
The announcement comes two weeks before a NASA probe will be smashed near the moon's south pole to see whether it can kick up buried ice.
Over the last decade, astronomers have found some signs of underground ice on the moon's poles.
This latest discovery is quite different. It finds unexpected and pervasive water clinging to the surface of soil, not absorbed into it. The water was spotted by spacecraft that either circled the moon or flew by.
All three ships used the same type of instrument that looked at the absorption of a specific wavelength of light that is the chemical signature of only two molecules: water and hydroxyl.
Hydroxyl is one atom of hydrogen with one atom of oxygen, instead of two hydrogen atoms in water. Because of the timing during the daylight when some of that wavelength disappears and some does not, it shows that both hydroxyl and water are present, scientists said.
This light wavelength was discovered first by an instrument on the Indian lunar satellite Chandrayaan-1, which stopped operating last month.
Scientists initially figured something was wrong with the instrument because everyone knew the moon did not have a drop of water on the surface, said Carle Pieters, NASA's Principle Investigator on the project.
Scientists looked back at the records of NASA's Cassini probe, which is circling Saturn. It has the same type instrument and whizzed by the moon 10 years ago. Sure enough, it had found the same thing.
The chance that three different instruments malfunctioned in the same way on three different spaceships is almost zero, so this confirms that it is water and hydroxyl, scientists said. Scientists testing lunar samples returned to Earth by astronauts did find traces of water, but they had figured it was contamination from moisture in Earth air, according to Pieters.
Pieters explained three theories about the source of the water: it came from comets or asteroids that crashed into the moon, those crashes freed up trapped water from below the surface, or the solar wind carries hydrogen atoms that binds with oxygen in the dirt.
If it is the solar wind, that also means that other places without atmosphere in Earth's solar system, such as Mercury or asteroids, can also have bits of water. AP