The Planet Definition Commitee of the IAU has proposed a new definition of what a planet is: it is an object orbiting a star (but is not itself a star) that has a strong enough gravity that it will be shaped like a sphere. A moon is an object orbiting a planet, and the center of gravity must lie inside the host planet. Today we know 12 planets in our solar system that agree with the new definition. They are Mercury, Venus, Mars, Earth, Ceres (located in the asteroid belt), Jupiter, Saturn, Uranus, Neptune, Pluto+Charon (a double planet system), and "2003 UB313" (found in the Kuiper belt). More planets in the Kuiper belt surrounding our solar system are likely to be discovered in the coming years.

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