In the late 1990s, the probes Clementine and Lunar Prospector discovered what appeared to be water ice in craters that lie in perpetual shadow at the south pole of the moon.
The indications, by extension, raised the possibility that ice may lie in the shadowed regions of the north lunar pole, as well.
This week, a team of scientists said it has directly observed definitive evidence of water ice on the Moon’s surface.
According to the data released this week, these ice deposits are patchily distributed and could possibly be ancient.
At the southern pole, the findings are that most of the ice appears to be concentrated at lunar craters, while the northern pole’s ice is more widely, but sparsely spread.
The scientists say they used data from NASA’s Moon Mineralogy Mapper instrument to identify three specific signatures that definitively prove there is water ice at the surface of the Moon.
The 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.
According to a NASA release, 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 -250 degrees Fahrenheit.
Because of the very small tilt of the Moon’s rotation axis, sunlight never reaches these regions.
Scientists say 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, should government or commercial missions to the moon be in the future.
The findings were published in the Proceedings of the National Academy of Sciences on August 20.