Not everyone agrees that this is a good way to decide, though. Andy Cheng, a planetary scientist at Johns Hopkins University, says that the new rules aren't clear enough and asks the question "how round is round? ...I'll still continue to maintain that Pluto is a planet," he said.

Owen Gingerich is an astronomer and historian at Harvard University in Cambridge, Massachusetts, and head of the IAU committee proposing the definition. He favored a special distinction for Pluto. Gingerich supported a proposal to call the big eight planets classical planets-as opposed to just plain "planets" and Pluto and the others dwarf planets, so there would be two classes of planets. He believes that reclassifying Pluto as a dwarf planet is not "sensitive to the historical and cultural role that Pluto has played."

The argument continues. In the meantime, however, many people are correct-new textbooks will list Pluto as being a dwarf planet. What do you think it is?