In the darkest and coldest parts of its polar regionsa team of scientists has directly observed definitive evidence of water ice on the Moon’s surface. These ice deposits are patchily distributed and could possibly be ancient. At the southern polemost of the ice is concentrated at lunar craterswhile the northern pole’s ice is more widelybut sparsely spread.

A team of scientistsled by Shuai Li of the University of Hawaii and Brown University and including Richard Elphic from NASA’s Ames Research Center in California’s Silicon Valleyused data from NASA’s Moon Mineralogy Mapper (M3) instrument to identify three specific signatures that definitively prove there is water ice at the surface of the Moon.

M3aboard the Chandrayaan-1 spacecraftlaunched in 2008 by the Indian Space Research Organizationwas 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 icebut was able to directly measure the distinctive way its molecules absorb infrared lightso 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 poleswhere the warmest temperatures never reach above -250 degrees Fahrenheit. Because of the very small tilt of the Moon’s rotation axissunlight never reaches these regions.

Previous observations indirectly found possible signs of surface ice at the lunar south polebut these could have been explained by other phenomenasuch 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 Moonand potentially easier to access than the water detected beneath the Moon’s surface.

Learning more about this icehow it got thereand how it interacts with the larger lunar environment will be a key mission focus for NASA and commercial partnersas we endeavor to return to and explore our closest neighborthe Moon.

The findings were published in the Proceedings of the National Academy of Sciences on August 202018.