The International Astronomical Union has spoken, and Pluto is no longer to be classified as a "planet." It is, however, still considered a "dwarf planet." Don't be fooled by any preconceptions you might have about English hyponymy: a dwarf planet is not, in fact, a planet. A proposal to encompass "classical planets" and "dwarf planets" under the same "planet" umbrella failed, so Pluto has been definitively cast out of the planetary club.
Yet another resolution was confirmed supporting the creation of "a new category of trans-Neptunian objects" of which Pluto is the prototype. Even though this gesture to assuage Plutophiles passed, we'll have to wait to find out what to call members of the new category. There was no clear majority in favor of the leading candidate, "plutonian objects," so it will take a longer procedure by the IAU to establish how to refer to this anonymous family of Pluto-ish thingamajigs.
(The text of the resolutions, as well as up-to-date coverage from Prague, can be found at Rob Britt's LiveScience blog.)
[Update: See here for backlash against the confusing planet vs. dwarf planet distinction.]
Posted by Benjamin Zimmer at August 24, 2006 10:17 AM