Posted: 7/15/2012 2:52:35 PM EDT
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Charon, previously considered a moon of Pluto, is 12% of Pluto's mass, and the center of mass about which the two bodies orbit (the barycenter) is outside Pluto's radius (by contrast, the Moon has only 0.01% of the mass of the Earth, and the Earth and the Moon orbit a center of mass that is inside Earth's radius). Two stars with a barycenter outside the radius of either star would be called binary stars... so why not call Pluto and Charon binary planets? |
