As most people are aware of now, the International Astronomical Union (IAU) is about to decide to "add" 3 planets to our Solar System by (re)defining what a planet is. It will not stop at 3, since there are many objects beyond Pluto that likely fit this definition and will be found in the coming decades.
"Bad Astronomy" has an excellent article on the news: Congratulations! It's a planet!
I think he hits the nail on the head when he describes the problem as being unscientific: the IAU is trying to construct a scientific definition to a cultural term which already seems to have its own meaning. The results aren't pretty, especially since one of our new "planets" is a moon (Charon)! However, a truly satisfying solution is hard to imagine. It hilights another related point that he makes in the article, the term "planet" has no real use in science anymore because it does not explain anything. Terrestrial, Jovian, and Pluton planets do not share the same explanation for how they were formed, not to mention that their physical and orbital properties are widely different (adding the asteroid Ceres makes a fourth category). It's one thing to add planets to the "back" of the Solar System, but sticking Ceres there in the middle really messes me up!
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