Asteroids Delivered Half of Earth's Water, New Sample Suggests

The Japanese Space Agency, JAXA, reached asteroid Itokawa in 2005 and returned a sample to Earth in 2010. (Credit: JAXA) In 2010, a Japanese mission called Hayabusa returned to Earth from a seven-year space journey. It brought back not only images and data from its adventure, but also actual samples, small grains of rock from its target, the asteroid Itokawa. Just a handful of space missions have ever returned to Earth at all, let alone brought back pieces of their destinations. So Hayabusa’s samples are highly prized, and have been studied by many teams across the world. Now, researchers from Arizona State University have analyzed a tiny subset of Hayabusa’s collection, and they've uncovered a surprising amount of water contained within the rock grains. The finding puts stony asteroids like Itokawa back in the spotlight, reigniting a long-standing debate among scientists over where Earth’s vast oceans come from. Did the water originate from comets, asteroids, or some other source altogether?