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Vesta Is a Baby Planet, Not an Asteroid
astroengine writes "Vesta, the second largest object in the main asteroid belt, has an iron core, a varied surface, layers of rock and possibly a magnetic field — all signs of a planet in the making, not an asteroid (abstract). This is the conclusion of an international team of scientists treated to a virtual front row seat at Vesta for the past 10 months, courtesy of NASA's Dawn robotic probe. Their findings were presented during a NASA press conference on Thursday. As to why Vesta never made it to full planethood, scientists point to Jupiter. When the giant gas planet formed, nearby bodies such as Vesta found their orbits perturbed. 'Jupiter started to act like a spoon in a pot, stirring up the asteroid belt and the asteroids started bumping into one another,' said Dawn lead scientist Christopher Russell. 'If they're just out there gently orbiting and everything is going smoothly, then without Jupiter in the picture, they would gather mass and get bigger and bigger and bigger. But with Jupiter there, stirring the pot, then the asteroids start bumping into one another and breaking apart, so nothing grew in that region, but started to shrink.'"
That was the old theory. The problem with studying the cosmology of star systems is that until recently we only had a sample of one. When they started finding planets orbiting other stars, they tended to be gas giants because of the methods used (orbit perturbations, light falloff due to occultations). But a surprising number of these gas giants orbit closely around their parent star. IIRC one has an orbit whose period is a few Earth-weeks. At this point, I think you can say all bets are off.