Apollo Moon Rocks

Hints of water in moon samples first surfaced in a 2008 study in the journal Nature, in which scientists reported having detecting water molecules in lunar glasses from the Apollo missions.

That team, however, hadn't been able to prove the water hadn't been introduced to the moon rocks on Earth, perhaps through sloppy handling.

One way to determine a water sample's birthplace is to measure the amounts of different hydrogen isotopes inside the water—a technique unavailable to the Nature team, said James Greenwood, a professor of Earth and environmental sciences at Wesleyan University in Middletown, Connecticut.

Isotope measurements can serve as fingerprints. Water from Earth's mantle has a different isotope ratio than water from a comet, for example.

When the Nature study came out, Greenwood was pioneering a technique that allowed him to study the chemical makeups of Martian meteorites. He later applied his method to samples of the mineral apatite, culled from a variety of moon-rock types, to determine the fingerprint of the water molecules inside.

The work proves that the moon-rock water "is not from us," he said at a presentation of his findings at the 41st Lunar and Planetary Science Conference in Houston, Texas.