Apparently, there is no exact definition of ‘planet’ among astronomers.
“‘It’s time we have a definition,’ said Alan Stern, who heads the Colorado-based space science division of the Southwest Research Institute of San Antonio. ‘It’s embarrassing to the public that we as astronomers don’t have one.’”
Yeah, that’s what the public keeps telling me. If I had a nickel for every e-mail I’ve gotten that complained of “chronic lack-of-planet-definition embarrassment syndrome”…