Researchers from Arizona State University (ASU) measured water content and hydrogen isotopic composition of samples of the asteroid Itokawa, returned to Earth by the Hayabusa spacecraft. This study, led by Ziliang Jin and Maitrayee Bose, shows that the particles of the mineral pyroxene are relatively rich in water — averaging 0.08 percent water by weight — more than in most pyroxenes on Earth. This analysis suggests that Itokawa (and its original parent asteroid) contained 0.016–0.05 percent water. The hydrogen isotopic compositions of these samples are indistinguishable from Earth. Based on their new findings, the ASU researchers suspect that S-type asteroids like Itokawa could have delivered up to half of Earth’s water supply early in our planet’s formation history.
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