Why Doesn't Ceres Have Any Really Big Craters?

Ceres is the largest object in the asteroid belt, a world more than 900 kilometers in diameter. It's so big that planetary scientists tend to refer to it as a protoplanet rather than an asteroid. The latter group consists of pulverized rubble left over from the planetary formation process billions of years ago, but Ceres is different. It got big enough that it was well on its way to being a planet before it ran out of material to build with. When we look at objects in the asteroid belt (and many...