(See description below)
Asteroid Vesta's South Pole
The bottom of asteroid Vesta, the second largest object in the asteroid belt, was imaged for the first time by the robotic Dawn satellite. A close inspection of the 260-meter resolution image shows not only hills and craters and cliffs and more craters, but ragged circular features that cover most of the lower right of the 500-kilometer sized object. What created the circular structure around the south pole of Vesta? Early speculation posits that the structure might have been created by a collision and coalescence with a smaller asteroid. Alternatively, the features might have originated in an internal process soon after the asteroid formed.
Here's a movie of Vesta rotating.