Ceres' bright spots have been a winking mystery for months, but NASA finally thinks it's solved the riddle: No, we're not looking at a giant alien ice rink. More likely, enormous piles of salt.
"We believe this is a huge salt deposit," principal investigator for the Dawn spacecraft Chris Russell told scientists on Monday at the European Planetary Science Congress. "We know it's not ice and we're pretty sure it's salt, but we don't know exactly what salt at the present time."
As NASA's Dawn spacecraft continues its spiral toward dwarf planet Ceres, we're discovering a world filled with geologic complexity and strange, glimmering spots. The largest of the spots — a roughly six-mile wide patch in the ominously-named Occator Crater — was visible from afar, but now, we're close enough to see that the brightness is everywhere. Even some of Ceres' mountains are smeared with shiny streaks.
A yet-to-be-named mountain also bears the mysterious brightness. Image Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Back in May, Russell speculated that the spots are caused by "the reflection of sunlight by highly reflective material on the surface, possibly ice." While the ice hypothesis fits with another theory — that Ceres might be hiding a subsurface ocean — Russell acknowledged that further studies were needed in order to verify the spots' composition.
Now, as Russell explained in his recent talk, data on the reflectivity of the bright spots has ruled out water ice. Based on the spots' albedo, we're pretty sure Ceres is encrusted in salt.
"[Salt] tells me that this is an active surface," Russell said. "Some comet or asteroid did not come in carrying salt, this is derived from the interior somehow."
As for how or why Ceres is oozing salt? That's another science mystery for you! For the next two months, Dawn will continue its descent, taking even closer shots of Ceres and continuing to collect scientific data in order to unravel the mystery of the now-probably-salt-piles. Sit tight Earthlings, the answers are coming!
Top : The Occator Crater, colour-coded to show differences in elevation, via NASA/JPL-Caltech/UCLA/MPS/DLR/IDA