The moon’s magnificent desolation is far wetter than scientists imagined. A NASA spacecraft sent to study lunar dust and atmosphere also picked up signs of water being released from the moon as meteors collide with its surface. This unprecedented detection, reported today in the journal Nature Geoscience, shows that tiny impacts release up to 220 tons of water a year—much more than should be on the surface based on previously known delivery systems.

“There was so much that the instrument on the spacecraft acted like a sponge, soaking up the water that was moving through the atmosphere,” says study leader Mehdi Benna, a planetary scientist at NASA’s Goddard Space Flight Center. “When we turned the instrument on, what