The moon’s interior may harbor water at concentrations higher than found on Earth. That’s the implication of measurements scientists have made on beads of volcanic glass in rocks that astronauts brought back during the Apollo moon missions.
The results, the team says, represent the first evidence that the moon had – and may still have – significant amounts of water in its mantle. No one is saying it was in well-defined deposits, but rather was diffused throughout the rock. Others have scrutinized moon-rock samples and have detected carbon dioxide, sulfur, fluorine, and chlorine. But only recently have devices become sensitive enough to sniff out the very low concentrations where water appears to lurk.
The team, led by Brown University geochemist Alberto Saal, found water, associated with tiny beads of lunar volcanic glass. The evidence indicates that glasses held may have contained contain at least 260 parts per million (p.p.m.) of water, and perhaps as much as 745 p.p.m of water before they were ejected during volcanic eruptions. That suggests, the the team says, that the moon's mantle today might hold from a third as much to as much water as Earth's upper mantle. One possible explanation for its presence: When Earth got smacked with a Mars-size object 4.5 billion years ago, some of the highly evaporative chemicals here, including water, got caught up in the turbulence and ended up on the moon.
The results appear in today’s issue of the journal Nature.
[Editor’s note: In the original version of this article, the water concentrations attributed to the moon's mantle today should have been attributed to the water present in the glass beads just before they were ejected during volcanic eruptions. Water present in the lunar mantle today may be as high as the water concentrations present in Earth's upper mantle today.]