Discovery Hints At Water Hidden In Moon's Interior

 Credit: NASA/GSFC/Arizona State University

The findings, published Aug. 25 in Nature Geoscience, represent the first detection of this form of water from lunar orbit. Earlier studies had shown the existence of magmatic water in lunar samples returned during the Apollo program.

M3 imaged the lunar impact crater Bullialdus, which lies near the lunar equator. Scientists were interested in studying this area because they could better quantify the amount of water inside the rocks due to the crater’s location and the type of rocks it held. The central peak of the crater is made up of a type of rock that forms deep within the lunar crust and mantle when magma is trapped underground.

“This rock, which normally resides deep beneath the surface, was excavated from the lunar depths by the impact that formed Bullialdus crater,” said Rachel Klima, a planetary geologist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.

“Compared to its surroundings, we found that the central portion of this crater contains a significant amount of hydroxyl – a molecule consisting of one oxygen atom and one hydrogen atom — which is evidence that the rocks in this crater contain water that originated beneath the lunar surface,” Klima said.

In 2009, M3 provided the first mineralogical map of the lunar surface and discovered water molecules in the polar regions of the moon. This water is thought to be a thin layer formed from solar wind hitting the moon’s surface. Bullialdus crater is in a region with an unfavorable environment for solar wind to produce significant amounts of water on the surface.

“NASA missions like Lunar Prospector and the Lunar Crater Observation and Sensing Satellite and instruments like M3 have gathered crucial data that fundamentally changed our understanding of whether water exists on the surface of the moon,” said S. Pete Worden, center director at NASA’s Ames Research Center in Moffett Field, Calif. “Similarly, we hope that upcoming NASA missions such as the Lunar Atmosphere and Dust Environment Explorer, or LADEE, will change our understanding of the lunar sky.”

The detection of internal water from orbit means scientists can begin to test some of the findings from sample studies in a broader context, including in regions that are far from where the Apollo sites are clustered on the near side of the moon. For many years, researchers believed that the rocks from the moon were bone-dry and any water detected in the Apollo samples had to be contamination from Earth.

“Now that we have detected water that is likely from the interior of the moon, we can start to compare this water with other characteristics of the lunar surface,” said Klima. “This internal magmatic water also provides clues about the moon’s volcanic processes and internal composition, which helps us address questions about how the moon formed, and how magmatic processes changed as it cooled.”

APL is a not-for-profit division of Johns Hopkins University. Joshua Cahill and David Lawrence of APL and Justin Hagerty of the U.S. Geological Survey’s Astrogeology Science Center in Flagstaff, Ariz., co-authored the paper. NASA’s Lunar Advanced Science and Engineering Program, the NASA Lunar Science Institute (NLSI) at Ames and the NASA Planetary Mission Data Analysis Program supported the research. NLSI is a virtual organization jointly funded by NASA’s Science Mission Directorate and NASA’s Human Exploration and Operations Mission Directorate in Washington, to enable collaborative, interdisciplinary research in support of NASA lunar science programs.

Rachel Hoover
Ames Research Center, Moffett Field