Our solar system may have at least twelve planets, including Charon, Ceres, and 2003 UB313 (AKA Xena). That's based on an official definition of planet now being debated at the International Astronomical Union meeting in Prague. According to the definition, Pluto, Charon, and certain other small objects with tilted orbits would be deemed planets but part of a separate class called "Plutons." Astronomers will vote on the proposed definition next week. From National Geographic:
The IAU proposal says that a planet is an object large enough to have become rounded due to the force of its own gravity.
But it's not that simple. What counts as a planet also depends on what it's orbiting around.
A planet has to orbit a star, so rounded objects floating freely through space won't make the cut.
But if an object is orbiting another, much larger object that's not a star, it wouldn't count as a planet either.
Astrophysicist Alan Boss of the Carnegie Institution in Washington, D.C., is… critical of the proposed definition.
"It doesn't have the elegance I was hoping for," Boss said. "It looks like it was written by a committee of lawyers rather than scientists."
