Wednesday, December 9, 2015
Tentative ID of the white spots on Ceres
Well, it's about time. After months of observing as the Dawn satellites spiraled in toward a closer orbit of asteroid aka dwarf planet Ceres, scientists think they know what the bright white spots are made of.
They think they are a salt, a form of magnesium sulfate called hexahydrite. Darn - back so far as April I thought they'd turn out to be ice. But apparently the data collected so far indicates that they are a salt, made of substances brought from a subsurface briny layer to the surface by an impact.
But ice is still part of the story, even if the brightly reflecting spots aren't made of it, primarily. What the astronomer asteroid geologists think happened is that the impact brought a brine to the surface, whereupon it froze, whereupon the water sublimated to space, whereupon leaving the magnesium sulfate bright salts behind.
One other aspect of this is that the crater haze seen near the spots is putatively ascribed to remnant bits of ice still in the ice sublimating quietly, and taking a little salt and dust with them as they do so.
So if this turns out to be what they say, then even though the spots are not mainly ice, there's ice involved in what Dawn is seeing now, and ice was involved in what made them. (Not like this is a surprise, as most of the big moons of Jupiter excepting Io are mixtures of rock and ice.) But the interesting part is that there's enough subsurface water, apparently, to help make the spots shine bright.
Astronomers have finally solved the mystery of those weird bright spots on Ceres
Salty source of Ceres' mysterious biight spots found
at 8:26 PM