科学美国人60秒:Earth and Moon Had Same Water Source

It’s sad but true: the moon is not made of cheese. But it still holds some fascinating surprises. Because a recent study finds that the moon harbors more water than was previously thought, and that this lunar H2O appears to hail from the same source as the water on Earth. That’s according to work published online, in the journal Science Express. [Alberto E. Saal et al., Hydrogen Isotopes in Lunar Volcanic Glasses and Melt Inclusions Reveal a Carbonaceous Chondrite Heritage]

The moon is thought to have formed by a violent collision between a spacefaring rocky body and the proto-planet Earth. It was also assumed that the heat of this impact would have caused any water, or its constituent elements, to boil off into space, leaving the baby moon high and dry.

But recent studies have found that samples of volcanic glass, brought back from the moon on the Apollo missions, contain as much water as magma found here on Earth. Now, by examining the isotopic composition of that water, researchers have found that it matches that of meteorites, the likes of which also delivered Earth its first drink.

The simplest explanation is that our planet was all wet before the impact that gave rise to its satellite. Next mystery to unravel: how did the moon manage to maintain that moisture?

—Karen Hopkin