From the outside, the moon seems to be as dry as a bone. But in addition to frozen water molecules, scientists have found that our satellite hides tiny bits of liquid water inside its volcanic rocks — enough to fill 4 billion Olympic-size swimming pools, by some estimates. A new study, published Tuesday in Nature Communications, suggests that asteroids may have delivered this water to the moon back when it was a wobbly ball of magma.
Comets — bodies made mostly of ice — were once tentatively credited with delivering the first water to Earth. But the Rosetta orbiter’s analysis of the comet 67P/Churyumov-Gerasimenko revealed water of the wrong molecular composition, leaving asteroids — bodies that orbit closer to the heat of the sun, leaving them mostly composed of rock and metal — as the most likely water bearers.