Moon May Have 100 Times More Water Than We Thought. How’d We Miss It?
1969: “We landed on the moon. It’s dry.”
2008: “Excellent, we were wrong: It’s not totally dry.”
2010: “Actually, we may have been very wrong about that: There could be even hundreds of times more water there than we thought.”
That last statement is the latest in a rising tide of announcements of water on the moon; DISCOVER covered when the news broke in March, and now the study is out in the Proceedings of the National Academy of Sciences. To sum up: After reanalyzing moon samples from the Apollo landings and meteorites of lunar origin, a team led by Francis McCubbin calculated a water content of 64 parts per billion to 5 parts per million. That’s paltry compared to even the driest places on Earth. But, they write, “This lower limit range of water contents is at least two orders of magnitude [100X] greater than the previously reported value for the bulk Moon, and the actual source region water contents could be significantly higher.”
As exciting as that is, it begs the question: How did we miss this for 41 years?
First, this water is not sloshing around in some subsurface ocean; it’s locked up in lunar minerals:
The team peered into the apatite crystals using a technique called secondary ion mass spectrometry—training a beam of ions on the rocks and then studying the ions that the beam dislodges from the material. In the process, the researchers stumbled onto something big: the telltale chemical signature of water, in the form of hydroxyl ions. “Until this study water had never been reported within minerals from the moon,” McCubbin said. Apatite naturally soaks up water as water-bearing magma cools, locking it up in the form of hydroxyl ions—pairs of bonded hydrogen and oxygen atoms [National Geographic].
When scientists found evidence of water in volcanic glass and ice deposits at the moon’s pole, McCubbin’s team had the motivation to reexamine those old Apollo samples. And, lunar scientist Bradley Jolliff from Washington University in St. Louis says, four decades after Apollo our imaging technology was ready for this find:
“The concentrations are very low and, accordingly, they have been until recently nearly impossible to detect. We can now finally begin to consider the implications—and the origin—of water in the interior of the Moon” [BBC News].
All this news of a more-watery moon could help answer questions as old as our planet and its only natural satellite: When the moon formed, probably after a Mars-sized body struck the early Earth, did the moon form just from the remains of the impactor? Or did pieces of the Earth carry some of its water to the coalescing moon?