Scientists discovered magmatic water, or water that originates from deep within the Moon's interior, on the surface of the Moon.
Published in the journal Nature Geoscience, the findings mark the first remote detection of this kind of lunar water and are based in data derived from NASA'a Moon Mineralogy Mapper (M3).
In addition to representing another step in the growing understanding of lunar water, the discovery, according to Rachel Kilma, a planetary geologist at Johns Hopkins University and the lead author of the paper, marks a significant advancement in the deciphering the Moon's volcanic processes and internal composition.
"Understanding this internal composition helps us address questions about how the Moon formed, and how magmatic processes changed as it cooled," she said in a statement. "There have been some measurements of internal water in lunar samples, but until now this form of native lunar water has not been detected from orbit."
Not long ago, the Moon was believed to be completely void of water with scientists assuming any trace detected in the samples brought back during the Apollo missions represented contamination from Earth.
Starting roughly five years ago, however, scientists began to rethink this theory as new laboratory techniques began to suggest the interior of the Moon is not as dry as once believed.
"Around the same time," Kilma explained, "data from orbital spacecraft detected water on the lunar surface, which is thought to be a thin layer formed from solar wind hitting the lunar surface."
According to co-author Justin Hagerty, of the US Geological Survey, what this surficial water did not reveal was any information on the magmatic water found deeper within the lunar crust and mantle. Though, he says, they were able to identify rock types around Bullialdus crater that they believed may hold secret to this and other questions.
"It's within 25 degrees latitude of the equator and so not in a favorable location for the solar wind to produce significant surface water," Klima said of Bullialdus crater, adding that the rocks found in its central peak are "of a type called norite that usually crystallizes when magma ascends but gets trapped underground instead of erupting at the surface as lava."
When the M3 fully imaged the crater in 2009, Kilma and her colleagues used the resulting data to discover that the crater contains a much higher rate of hydroxyl, or a molecule consisting of one oxygen atom and one hydrogen atom, compared to surrounding areas.
"Bullialdus crater is not the only location where this rock type is found, but the exposure of these rocks combined with a generally low regional water abundance enabled us to quantify the amount of internal water in these rocks," Kilma said.
With this step complete, the researchers say they plan on looking elsewhere on the Moon to test thier findings regarding the relationship between incompatible trace elements, such as thorium and uranium, and the hydroxyl signature.
"In some cases this will involve accounting for the surface water that is likely produced by interactions with the solar wind," Kilma said, "so it will require integration of data from many orbital missions."