Discovered in 1930, poor old Pluto got a pretty rough ride in the last decade or so. Once it was a fully fledged planet; now it's just puny "minor planet" in the newly designated Kuipier Belt -- astronomers just couldn't leave it alone. But I guess all this really depends on your definition of what a planet really is -- watch and learn.
Maybe it's time we change what we call all those massive lumps of rock we'd all like to go visit -- the word "planet" just doesn't really cut it anymore. [YouTube]