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. A team of researchers from University of Michigan now report that traces of water were found in the rock. Credit: NASA/Johnson Space Center
The lunar sample, known as “Genesis Rock,” was thought to be a piece of the moon’s primordial crust, and researchers writing in Nature Geoscience are now reporting they have found traces of water in the rock.
The traces of water were detected within the crystalline structure of mineral samples taken from Genesis Rock. These findings indicate that the early moon was wet, and that water there was not lost during the moon’s formation.
Researchers say that the findings contradict the predominant lunar formation theory, which is that the moon was formed from debris generated during a giant impact between Earth and another planetary body.
“Because these are some of the oldest rocks from the moon, the water is inferred to have been in the moon when it formed,” University of Michigan researcher Youxue Zhang said in a statement. “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.”
He said that under that model, hot ejecta should have been degassed almost completely, which would have eliminated all water.
For the study, the scientists used infrared spectroscopy to analyze the water content in grains of plagioclasefeldspar from lunar anorthosites, which are highland rocks composed of more than 90 percent plagioclase. These rocks are thought to have formed early in the moons history, when plagioclase crystallized from a magma ocean and floated to the surface.
The infrared spectroscopy helped to detect about 6 parts per million of water in the lunar anorthosites.
“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,” said Zhang, James R. O’Neil Collegiate Professor of Geological Sciences.