Vesta: Not Quite a Planet, Not Quite an Asteroid

As the second-largest object in the main asteroid belt, Vesta attracts a healthy amount of scientific interest. While smaller asteroids in the belt are considered fragments of collisions, scientists think Vesta and the other three large objects in the belt are likely primordial and have survived for billions of years. They believe that Vesta was on its way to becoming a planet and that the Solar System's rocky planets likely began as protoplanets just like it. But new research is casting doubt on that conclusion.