For the first time, evidence of water has been found in a stony type of asteroid once thought to be bone-dry.

Grains of dust from the asteroid Itokawa actually contain a surprising amount of water, two cosmochemists from Arizona State University in Tempe report May 1 in Science Advances.

“We didn’t really expect water to be there in Itokawa at all,” says study coauthor Maitrayee Bose. But if similar asteroids have similar amounts of water, the space rocks could have been a major source of water for the early Earth.

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