Ask any kid how many planets are in our solar system, and you'll get a firm answer: nine. But knock on a few doors in Berkeley's astronomy department, and you'll hear, amid the hemming and hawing, a whole range of numbers. Professor Gibor Basri, who plans soon to propose a formal definition of a planet to the international body that names astronomical objects, argues that there are at least 14 planets, and perhaps as many as 20. To the well-known list of nine he adds several large asteroids and more distant objects from the rocky swarm called the Kuiper Belt circling beyond the orbit of Neptune.
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Someday kids may be stumping their parents with planet names such as Vesta, Quaoar and Varuna, if not Ixion or Radamanthus. They'll be around for a while -- at least a few billion years -- so you might as well get used to them.