This composite image, with Vesta at the center, shows the relative size of nine asteroids that astronomers have been watching. "Up until now, Lutetia, with a diameter of 81 miles (130 kilometers), was the largest asteroid visited by a spacecraft, which occurred during a flyby," NASA explained. "Vesta dwarfs all other small bodies in this image." And we'll soon know more about Vesta, which is so large that it's also considered a protoplanet; at a diameter of about 330 meters, the asteroid came very close to moving into a new level of classification.
The Dawn probe, managed by NASA's Jet Propulsion Laboratory but part of an international cooperative, reached Vesta in mid-July and will remain there, orbiting the planet and studying it, until 2012. At that point, it will leave Vesta's orbit and head to Ceres, another protoplanet.
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