When spacecraft dawn first beamed back pictures of an unusually bright spot on the asteroid Ceres (right), space fans began waiting to hear what it could possibly be-something exotic perhaps? (In addition to the big one, scientists have discovered up to 130 smaller bright spots around the rock.) Now a team from Max Planck Institute in Germany believes the bright spot is a kind of salt: hexahydrite, which is a magnesium sulfate. The theory suggests that Ceres used to have a subsurface layer of saltwater, which left the salt behind when the water turned to gas and escaped.
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