Geologists vs. Astronomers: Round I

According to an article in Nature, as quoted here for those without access to a subscription, the most recent meeting of the International Astronomical Union has decided to steal adopt the term 'pluton' to describe "a round object orbiting the sun with a period more than 200 years."

Why?

Well, when they were typing up their document, the word didn't show up on Microsoft Word's spellcheck, so they just assumed it was up for grabs.