Unexpected bright spots discovered on the surface of the dwarf planet Ceres may be plumes of ice blasting out into space.
NASA's Dawn spacecraft arrived at Ceres, the largest object in the asteroid belt, earlier this month and is in the process of positioning itself for a 14-month study.
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Early analysis of pictures taken as Dawn approached Ceres shows a pair of bright spots inside a crater.
The angle of the reflection changes as the mini-planet rotates and the spots are visible even when the crater's rim would block the spacecraft's view of the crater floor. That suggests that whatever is reflecting rises relatively high above Ceres' surface, scientists said at the Lunar and Planetary Science Conference in Houston this week.
"We believe we could be seeing outgassing, but we need higher resolution (images) to confirm this," said Andreas Nathues, with the Max Planck Institute for Solar System and the lead researcher for Dawn's framing camera.
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"The big question is whether Ceres has an active surface region - or more than one," he said.
Scientists suspect the interior of Ceres is rocky and wet, with a layer of water and/or ice. With its low density, Ceres has a high potential for ice volcanoes. Another option is that ice is sublimating, or transitioning from solid to gas, similar to what happens on comets.
"It could be quite interesting," said Dawn lead scientist Christopher Russell, with the University of California, Los Angeles.
"I believe we'll show Ceres is every bit a planet as its terrestrial neighbors Mars, Earth, Venus and Mercury," Russell said.