Water on the moon: Historical Evidence

Called the "Genesis Rock," this lunar sample of unbrecciated anorthosite collected during the Apollo 15 mission was thought to be a piece of the moon's primordial crust.

In a paper published online Feb. 17 in Nature Geoscience, a University of Michigan researcher and his colleagues report that traces of water were found in the rock. 

Credit: NASA/Johnson Space Center

Traces of water have been detected within the crystalline structure of mineral samples from the lunar highland upper crust obtained during the Apollo missions, according to a University of Michigan researcher and his colleagues.

The lunar highlands are thought to represent the original crust, crystallized from a magma ocean on a mostly molten early moon.

The new findings indicate that the early moon was wet and that water there was not substantially lost during the moon's formation.

The results seem to contradict the predominant lunar formation theory—that the moon was formed from debris generated during a giant impact between Earth and another planetary body, approximately the size of Mars, according to U-M's Youxue Zhang and his colleagues.

"Because these are some of the oldest rocks from the moon, the water is inferred to have been in the moon when it formed," Zhang said.

"That is somewhat difficult to explain with the current popular moon-formation model, in which the moon formed by collecting the hot ejecta as the result of a super-giant impact of a martian-size body with the proto-Earth.

"Under that model, the hot ejecta should have been degassed almost completely, eliminating all water," Zhang said.

A paper titled "Water in lunar anorthosites and evidence for a wet early moon" was published online Feb. 17 in the journal Nature Geoscience.

The first author is Hejiu Hui, postdoctoral research associate of civil and environmental engineering and earth sciences at the University of Notre Dame.

Hui received his doctorate at U-M under Zhang, a professor in the Department of Earth and Environmental Sciences and one of three co-authors of the Nature Geoscience paper.

Over the last five years, spacecraft observations and new lab measurements of Apollo lunar samples have overturned the long-held belief that the moon is bone-dry.