Animation: Virtual flight over asteroid Vesta (Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

Animation: Virtual flight over asteroid Vesta (Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)
Even though it doesn't quite qualify as a 'proper planet, the second most massive asteroid in the Solar System, Vesta - which has a diameter of approximately 530 kilometres - exhibits numerous planetary characteristics.
Credit:

NASA/JPL-Caltech/UCLA/MPS/DLR/IDA