In what will go down as a major milestone in space exploration, NASA has confirmed that frozen water has been found on Earth's Moon. The scientists who made the discovery don’t know how long the ice has been there, but they say it might be ancient.

It could be used by future lunar explorers, according to a NASA statement: “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 Moon’s surface.”

This is the first “direct and definitive evidence” of ice on the Moon’s surface, according to their findings, published in the Proceedings of the National Academy of Sciences. Prior evidence of lunar ice has been extensive but ambiguous, and some of the past evidence of ice turned out to be something else, like hydrogen-enriched minerals, reports Scientific American.

The ice, detected by NASA’s Moon Mineralogy Mapper (M3) instrument, is shown in blue in the below images. At left is the Moon’s south pole, and at right is the north pole.


Darker hues represent colder temperatures, and as you can tell from the image, the ice was found in the coldest, darkest areas of the Moon's poles—in most cases, the shadows of craters. Sunlight never reaches these areas, and the temperature remains at or below -250°F.

M3 has been aboard the Indian space agency's Chandrayaan-1 spacecraft since it launched in 2008. It has been used to collect data and find signature molecular absorption features in near-infrared light, allowing the device to tell liquid water apart from vapor and solid ice. It also confirmed previous findings.

Last year, researchers used satellite imagery to identify droplets of water preserved inside glass beads within the Moon’s volcanic deposits. NASA also reported in 2009—after intentionally slamming probes into a crater to create a plume of debris that could be studied—that the Moon’s south pole did in fact contain ice.

However, conclusions from that mission were indirect because they were based on modeling, according to the new study's lead author, Shuai Li of the University of Hawaii at Manoa.