Genuine moon water has been found for the first time in rocks that were brought back to Earth during NASA's historic Apollo missions 40 years ago. The water is similar to that detected in comets, suggesting that the moon's scarce supply got there through the impacts of these icy bodies.

To determine where this moon water came from, researchers studied thin slices of rocks collected by astronauts in the 1970s using several kinds of microscopes. Under examination was the ratio of hydrogen – two atoms of which bind with oxygen to make a water molecule – to a rare version of hydrogen called deuterium.