Water in Moon Rocks Challenges Lunar Formation Theory

MOUNTAIN VIEW, Calif. — Scientists have recently discovered small traces of water from samples brought back from the moon by the Apollo 15 mission that took place in the 1970′s.

The research was published on Sunday in the journal Nature Geoscience that there is “native” water on the moon based on new analysis of lunar samples.

Prevailing theories hold that the moon was created when a Mars-sized body crashed into the young Earth and broke off debris that eventually coalesced into a new entity. In the process, much of the water would have evaporated into space, leaving Earth’s satellite very dry.

“It’s thought that the moon’s formation involved the materials getting very hot,” said Paul Warren, a UCLA cosmochemist who was not involved in the new study. “It’s usually assumed that little water would have survived through that.”

But the new study, lead by Hejiu Hui, an engineering researcher at the University of Notre Dame, has found that the Moon may have once had a watery landscape, turning older theories about the moon upside down.

Hui and his team found traces of water within the crystalline structure of mineral samples from the lunar highland upper crust. As the lunar highlands are thought to represent the original crust, crystallized from a magma ocean, the findings indicate that the early moon was wet and that the water there wasn’t lost as it formed.

“Because these are some of the oldest rocks from the moon, the water is inferred to have been in the moon when it formed,” said the study’s co-author Youxue Zhang.

The team used Fourier-transform infrared spectroscopy to analyze the water content in grains of plagioclase feldspar from lunar anorthosites – highland rocks composed of more than 90 percent plagioclase. These are thought to have formed early in the moon’s history when plagioclase crystallized from a magma ocean and floated to the surface.

The team found about six parts per million of water in moon rocks collected from the lunar surface in the early 1970s during the Apollo 15, 16 and 17 missions. By “water,” the researchers don’t mean liquid water, but hydroxyl, a chemical that includes the hydrogen and oxygen ingredients of water.

“The surprise discovery of this work is that in lunar rocks, even in nominally water-free minerals such as plagioclase feldspar, the water content can be detected,” says Zhang.

The hydroxyl groups are evidence that the lunar interior contained significant water during the moon’s early molten state, before the crust solidified, and may have played a key role in the development of lunar basalts.

“The presence of water could imply a more prolonged solidification of the lunar magma ocean than the once-popular anhydrous moon scenario suggests,” said Hui.

If you are interested in learning more, Space.com has an excellent article on the subject.

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