The mysterious white spots of Ceres as seen by NASA's Dawn spacecraft from about 3,000 miles (4,400 km)
We profiled NASA's Dawn spacecraft
several months ago as it was closing in on the dwarf planet Ceres. Dawn has finally settled into its primary surveying orbit. For years the Hubble Space Telescope had spied what looked like a big bright spot on the little world, but the resolution was so low no one could definitively say it was even there, much less what it might be. Now, with hundreds of times sharper resolution thanks to Dawn's camera eyeballs,
we're still not sure:
These bright spots are unique; no other such high-contrast feature is seen on airless, rocky bodies. We know Ceres has a lot of water ice under the surface, so it’s not too far out to think that may be what we’re seeing. A recent impact could’ve dredged up ice (we’ve seen that on Mars, in far smaller craters), splashing it around the crater, and also caused that darker spray. But right in the exact center of that big crater (which is clearly much older)? That seems like a big coincidence. Could it be from some sort of vent?
But it would have to be a relatively recent impact. Water ice would sublimate away under unfiltered solar radiation where Ceres resides, in between Mars and Jupiter about 250 million miles away from the sun. Dawn will examine the spots in greater detail and spiral in closer over the next few months. We'll probably have a better idea what's going on with Ceres, soon.