An orbiting spacecraft has detected water on the moon - and scientists believe that it came from a mystery source deep beneath the lunar surface.
It’s the first time “magmatic” water - water from deep inside the moon - has been detected from orbit.
Samples of water had been found on the moon by the Apollo missions, but scientists believed for decades that they must have been contamination carried from Earth.
The new find, by NASA's Moon Mineralogy Mapper (M3) instrument aboard the Indian Space Research Organization's Chandrayaan-1 spacecraft, is the first evidence of water coming from inside the moon.
The finding could throw light on the origins of the moon - and on what lies underneath the surface.
The scientists imaged a crater, Bullialdus, near the lunar equator - where debris from deep beneath the surface had been blasted out by an ancient impact.
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The central peak of the crater is made up of a type of rock that forms deep within the lunar crust and mantle from trapped magma.
"This rock, which normally resides deep beneath the surface, was excavated from the lunar depths by the impact that formed Bullialdus crater," said Rachel Klima, a planetary geologist at the Johns Hopkins University Applied Physics Laboratory (APL).
"Compared to its surroundings, we found that the central portion of this crater contains a significant amount of hydroxyl - a molecule consisting of one oxygen atom and one hydrogen atom -- which is evidence that the rocks in this crater contain water that originated beneath the lunar surface," Klima said.
For many years, researchers believed that the rocks from the moon were bone-dry and any water detected in the Apollo samples had to be contamination from Earth.
"Now that we have detected water that is likely from the interior of the moon, we can start to compare this water with other characteristics of the lunar surface," said Klima. "This internal magmatic water also provides clues about the moon's volcanic processes and internal composition, which helps us address questions about how the moon formed, and how magmatic processes changed as it cooled.
Further research will help scientists pinpoint where the water comes from - and where it might still exist in the moon’s rocks, NASA says.
"This impressive research confirms earlier lab analyses of Apollo samples, and will help broaden our understanding of how this water originated and where it might exist in the lunar mantle," said NASA Lunar Science Institute Director Yvonne Pendleton.