Eleven years ago, a spacecraft changed our view of the moon forever. Data collected by the robotic travelers showed that Earth's only natural satellite was not the dry, dusty desert we had long believed. The spacecraft detected samples of water.
Scientists couldn't say for sure how much of the "molecular" water was. Discoveries in 2009 led scientists to suspect that much of the moon's "water" was hydroxyl, because it is more thermally stable than molecular water.
On Monday, two studies, published in the journal Nature Astronomy, give us even more information.
In the first study, scientists examined the moon in infrared with exceptional clarity. They determined that it is mainly H2O that is present on the lunar surface, rather than hydroxyl.
“The research results are unique,” says Shuai Li, a planetary scientist at the University of Hawaii and co-author on one of the new studies.
Shuai Li has been hunting for water on the lunar surface for years and was part of a team of scientists who detected water ice on the moon in 2018. The ice was trapped in permanently shaded areas of the lunar surface that never receive sunlight. In a second study, another team of researchers reported that the ice may be even more widespread and exist in other parts of the moon.
Studying water on the moon requires a huge telescope.
One of the keys to the discovery was the Stratospheric Observatory for Infrared Astronomy, or SOFIA, a custom-built Boeing 747 with a telescope mounted on its back. The aircraft, operated by NASA and DLR, the German Aerospace Center, flies at about 43,000 feet. During the flight, a door in the back opens, turning its telescope skyward and studying the world in infrared light.
Turning the SOFIA telescope on the moon in 2018, the research team selected two sunlit surfaces: one at high latitudes near the Clavius crater and one that was closer to the equator. Around the Clavius crater, the team detected water.
“It’s the same water we drink on Earth,” says Li. “But the abundance is extremely low. You would need to process a few thousand kilograms of lunar regolith to get 1 kilogram of water.”
