PROVIDENCE, R.I. [Brown University] — In a discovery that promises to reinvigorate studies of the moon and potentially upend thinking of how it originated, scientists at Brown University and other research institutions have found evidence of water molecules on the surface of the moon.
The molecules and hydroxyl — a molecule consisting of one oxygen atom and one hydrogen atom — were discovered across the entire surface of earth’s nearest celestial neighbor. While the abundances are not precisely known, as much as 1,000 water molecule parts-per-million could be in the lunar soil: harvesting one ton of the top layer of the moon’s surface would yield as much as 32 ounces of water, according to scientists involved in the discovery.
Carle Pieters, a planetary geologist at Brown, is the lead author of one paper this week in Science that reports evidence of water in the moon’s high latitudes — greatly expanding current thinking about where water in any form was presumed to be located.
“We’ve made a very important step with this discovery, and now there are some very important steps to follow up on,” Pieters said.
Pieters is the lead investigator on the Moon Mineralogy Mapper (M3), a NASA instrument that was carried into space on Oct. 22, 2008, aboard the Indian Space Research Organization’s Chandrayaan-1 spacecraft. She said the findings from M3 reveal interesting, new questions about where the water molecules come from and where they may be going. Scientists have speculated that water molecules may migrate from non-polar regions of the moon to the poles, where they are stored as ice in ultra-frigid pockets of craters that never receive sunlight.
“If the water molecules are as mobile as we think they are — even a fraction of them — they provide a mechanism for getting water to those permanently shadowed craters,” Pieters said.
She continued, “This opens a whole new avenue [of lunar research], but we have to understand the physics of it to ultilize it.”
The M3 team found water molecules and hydroxyl at diverse areas of the sunlit region of the moon’s surface, but the water signature appeared stronger at the moon’s higher latitudes. The M3 discovery was confirmed by data from two NASA spacecrafts — the Visual and Infrared Mapping Spectrometer (VIMS) on the Cassini spacecraft and the High-Resolution Infrared Imaging Spectrometer on the EPOXI spacecraft. Data from those missions also are being published in separate papers in Science.
Pieters credited the Indian space agency for its role in the findings. “If it weren’t for them, we wouldn't have been able to make this discovery,” she said.
Other Brown members listed as contributing authors to the M3 paper include Brown planetary geology faculty James Head III and John “Jack” Mustard; postdoctoral research associates Rachel Klima and Jeffrey Nettles; and graduate student Peter Isaacson.
Isaacson said the M3 results were a huge surprise. “There was no evidence that this was possible on such a broad scale,” he said. “This discovery turns a lot of the conventional thinking about the lunar surface on its head.”
Mustard, who has had major findings of water-bearing minerals on Mars, said the moon discovery is “intriguing, because it shows water on a planet that we weren’t anticipating, and it’s in a form that’s mysterious. The finding may have implications for other planets, such as Mars, but it is different.”
From its perch in lunar orbit, M3’s state-of-the-art spectrometer measured light reflecting off the moon’s surface at infrared wavelengths, splitting the spectral colors of the lunar surface into small enough bits to reveal a new level of detail in surface composition. When the M3 science team analyzed data from the instrument, they found the wavelengths of light being absorbed were consistent with the absorption patterns for water molecules and hydroxyl.
“For silicate bodies, such features are typically attributed to water and hydroxyl-bearing materials,” Pieters said. “When we say ‘water on the moon,’ we are not talking about lakes, oceans or even puddles. Water on the moon means molecules of water and hydroxyl that interact with molecules of rock and dust specifically in the top millimeters of the moon’s surface.”
The research was funded by NASA.