The verdict is in — mostly. The bright spots on the dwarf planet Ceres are probably made of salt, NASA’s Dawn spacecraft has found.
Mixed with the salt are bits of rock and frozen water. When sunlight hits the blend, the ice sublimates into a misty haze above two of Ceres’s craters, researchers report in the 10 December issue of Nature.
But mission scientists are not sure how the salt, ice and haze are interlinked. “The whole picture we do not have yet,” says Andreas Nathues, a planetary scientist at the Max Planck Institute for Solar System Research in Goettingen, Germany, and the paper’s lead author1.
Dawn has also found ammonia-rich clays on Ceres, a second Nature paper reports2. Ammonia is more common in the frigid outer Solar System than in the asteroid belt where Ceres reigns. The discovery suggests that Ceres may have collected bits of outer Solar System material — or even that it was born near Neptune before migrating inward.
Both papers are the first major published results from Dawn. The spacecraft, which launched in 2007, visited the asteroid Vesta in 2011–12 and arrived at Ceres in March.