[Geza Gyuk] said that changing the classification of Pluto is the easy part; it's harder to change the definition of the word "planet" and get it to stick. "The IAU has absolute authority to classify objects, but I'm not sure they have the authority to define 'planet' as such," Gyuk said in a telephone interview. (The IAU added the criterion that a "planet" must "clear the neighborhood around its orbit"; Pluto swings into Neptune's orbit, and so it's disqualified.)