Ignore the bright spots, and what do I notice next? The craters. There are lots of them, as there are lots on all the icy moons. Many of the smaller craters on Ceres are bowl-shaped, but the bigger ones have noticeably flat floors, like the ones on Tethys and Rhea. In the picture above, the two craters on the left, (e) and (f), look a lot like those on Rhea or Dione: they have steep rims, but flat floors, a hint of a central peak, and a hint, also, that the craters aren't perfectly round. On Rhea and Dione, we think that the non-roundness of the craters is caused by the existence of fractures in the crust; those fractures were zones of weakness, and the rupturing of the impact crater followed those weaknesses, making straight rim segments.

But there's one crater on Ceres that made my jaw drop: it's the big one at the center of the view above, (g). It's incredibly flat. You can barely see its rim. Its interior is very smooth and lacks any mid-sized craters, though there are many small ones. On the Max Planck website, they go so far as to say that the large crater is relatively recent, because it contains no middle-sized craters, only small ones.

The main question about such a flat crater, other than its age, is: was it born that way, or did it become flatter over time? On icy worlds, initially deeper craters become shallower when, over geologic time, the warmer ice in the world's interior flows from high places to low places, raising crater floors. But a layer of ice at the surface is so stiff that it still preserves the pre-impact topography. That's how Tethys' huge Odysseus basin still has a rim, a peak ring, and a central peak, even though its floor has risen over time so that it is now convex, continuing the curvature of Tethys' globe rather than concave, like the original bowl shape of an impact crater: