Pluto should never have been defined as a planet in the first place, it was mistaken for a bigger planet which doesn't actually exist because the calculations were based on faulty Newtonian physics. When we eventually learned its actual size, when we learned about its eccentric orbit, and when we learned about its binary relationship with Charon, the IAU should have admitted the mistake and moved on. But no, they spent 30 years looking for a bigger object than Pluto, and once they found one they finally had the sense to act.They didn't rename Pluto, they redefined what it is, which is not the same.
Pluto's characteristics are significantly different than those of the 8 known planets in the solar system, as such it deserves a seperate definition.
Anyway, here's some pictures:


