"Our goal was to find a scientific basis for a new definition of planet and we chose gravity as the determining factor," said Richard Binzel, an MIT planetary scientist who was part of a seven-member IAU committee that hashed out the proposal. "A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet." The definition, which basically says round objects orbiting stars will be called planets, is simple at first glance: Q&A on the Proposal / Gallery: The 12 "Planets" / Read the Draft Resolution IAU members will vote on the proposal Thursday, Aug. For example, Brown said, it does not make sense to consider Ceres and Charon planets and not call our Moon (which is bigger than both) a planet.
He applauded the committee's efforts but said the overall proposal is "a complete mess." By his count, the definition means there are already 53 known planets in our solar system with countless more to be discovered.īrown and other another expert said the proposal, to be put forth Wednesday at the IAU General Assembly meeting in Prague, is not logical. "It's flattering to be considered discoverer of the 12th planet," Brown said in a telephone interview.
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