I guess we need a new mnemonic...
August 16, 2006 6:58 AM Subscribe
Ceres, Charon, and 2003 UB313 (a.k.a. Xena) may join the 9 planets we already know (and strive to remember) if a resolution by the International Astronomical Union is passed next week. So what makes a planet, according to the IAU? Having sufficient mass to achieve hydrostatic equilibrium (i.e. be round enough...welcome former asteroid Ceres) and being in orbit around a star without being a star itself or a satellite of another planet (apparently Charon and Pluto are actually a double planet.) Mike Brown, discoverer of "10th planet" Sedna and alleged "Pluto-hater", doesn't really like the idea.
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