A team of researchers led by Dr. Shuai Li of the University of Hawaii and Brown University has directly observed definitive evidence of surface-exposed water ice in the lunar polar regions. The distribution and abundance of the lunar ice are distinct from those on other airless bodies in the inner Solar System such as Mercury and Ceres, which may be associated with the unique formation and evolution process of the Moon. These ice deposits might be utilized as a resource in future exploration of Earth’s only natural satellite.
If the Moon has enough water, and if it’s reasonably convenient to access, future explorers might be able to use it as drinking water or to convert it into hydrogen and oxygen for rocket fuel or oxygen to breathe. Image credit: NASA’s Goddard Space Flight Center.
Dr. Li and colleagues used data from NASA’s Moon Mineralogy Mapper (M3) instrument to identify three specific signatures that definitively prove there is water ice at the lunar surface.
The M3 mapper, aboard the Chandrayaan-1 spacecraft, launched in 2008 by the Indian Space Research Organization, was uniquely equipped to confirm the presence of solid ice on the Moon.
It collected data that not only picked up the reflective properties we’d expect from ice, but was able to directly measure the distinctive way its molecules absorb infrared light, so it can differentiate between liquid water or vapor and solid ice.
“Most of the newfound water ice lies in the shadows of craters near the poles, where the warmest temperatures never reach above minus 250 degrees Fahrenheit (minus 157 degrees Celsius),” the scientists said.
“Because of the very small tilt of the Moon’s rotation axis, sunlight never reaches these regions.”
This image shows the distribution of surface ice at the Moon’s south pole (left) and north pole (right), detected by NASA’s Moon Mineralogy Mapper instrument. Blue represents the ice locations, plotted over an image of the lunar surface, where the gray scale corresponds to surface temperature (darker representing colder areas and lighter shades indicating warmer zones). The ice is concentrated at the darkest and coldest locations, in the shadows of craters. This is the first time scientists have directly observed definitive evidence of water ice on the Moon’s surface. Image credit: NASA.
Previous observations indirectly found possible signs of surface ice at the lunar south pole, but these could have been explained by other phenomena, such as unusually reflective lunar soil.
“With enough ice sitting at the surface — within the top few millimeters — water would possibly be accessible as a resource for future expeditions to explore and even stay on the Moon, and potentially easier to access than the water detected beneath the lunar surface,” the researchers said.
“Learning more about this ice, how it got there, and how it interacts with the larger lunar environment will be a key mission focus for NASA and commercial partners, as we endeavor to return to and explore our closest neighbor, the Moon.”
The study was published in the Proceedings of the National Academy of Sciences.
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Shuai Li et al. Direct evidence of surface exposed water ice in the lunar polar regions. PNAS, published online August 20, 2018; doi: 10.1073/pnas.1802345115
