Finding water in the moon's crust, the scientists say, implies that the moon's rocks could have taken longer to crystallize than previously thought. The exact amounts of water present in these rocks, however, could vary in future measurements, depending on how they are calibrated.
Past moon water finds
Hui decided to analyze the Apollo rocks again following a suite of research results in recent years suggesting the moon is much wetter than previously thought, he said.
NASA's Clementine spacecraft found evidence of water ice after scanning the surface with radar in 1996, but follow-up observations with the Arecibo radio telescope in Puerto Rico suggested the spots where it found ice were in areas with too much sun for ice to survive. Instead of ice, later researchers chalked up the observations to piles of rubble.
NASA's Lunar Prospector found possible water in 1998 at both of the moon's poles, but the instrument was only able to detect the presence of hydrogen, not other elements.
Then in 2008, new lab work on Apollo lunar samples found hydrogen in lunar volcanic glasses.
Starting in September 2009, however, three spacecraft orbiting the moon found "unambiguous evidence" of water on the lunar surface. India's Chandrayaan-1 and NASA's Cassini and Deep Impact missions detected a hydrogen-oxygen chemical link — an indication of water or hydroxyl — through wavelengths of light reflected off the moon.
These findings were believed to represent only small amounts of water. Just two months later, in November 2009, however, scientists for the Lunar CRater Observation and Sensing Satellite (LCROSS) mission announced the spacecraft had found large deposits of ice at the moon's south pole.
Scientists then discovered a trove of ice in the south pole's Shackleton Crater in 2012. Based on the results, some groups say long-term human missions could live off the moon's water reserves while performing science, mining and other tasks on the moon.
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