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SYFY WIRE Bad Astronomy

Ceres Spins Under Dawn

By Phil Plait

The Dawn spacecraft recently slid ever so gently into the embrace of Ceres, the largest asteroid in the main belt between Mars and Jupiter. It actually flew past Ceres, slowing itself with its ion engine in a long, looping trajectory that kept it over the tiny world’s unilluminated half.

But then, a few days ago, it got close enough and in the right geometry to begin observations of some sunlit real estate on Ceres. It did this by peeking over the north pole of the asteroid, and the result was an amazing animation of Ceres rotating:

That’s phenomenal! These images were taken on April 10 from a distance of 33,000 kilometers and are the highest resolution images we’ve seen so far.

Ceres is a mess. It’s heavily battered, as you might expect for the largest airless body in its neighborhood surrounded by a few billion smaller ones. As I wrote about before, a lot of the craters look to have flat floors, which is what you expect on a world where there’s lots of ice under the surface; that stuff can flood in and fill the crater after an impact (materials with lower tensile strength tend to leave flatter floors, but the ice could also melt and flow in as well).

Some of the craters have central peaks, which is also common in larger impacts as material pushed out by the huge energy of the impact rushes back into the center (like a drop of milk or water that splashes up from the center when you pour the liquid into a glass—this is called isostatic rebound).

Soon enough there will be a lot less guesswork, once Dawn settles into its mapping orbit. We’ll see much better images then and get a much better understanding of this weird little world.

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