Yeah, but is that really a fair criteria for not being a planet? Theoretically, the further out you go, the bigger the orbit, the harder it is to clean out your orbit? Or was it down sized from a planet so that those competing for space on a rocket and funding for their research project to get preference over the Pluto project because it's suddenly not a 'planet.' It was the last object found by hard work and persistent observation, knowing the math said it should be there.

But that's neither here nor there. The asteroid belt is likely the result of two planets colliding. A Mars size object hitting the earth resulted in the moon. There are lots of collisions and object capable of colliding, and it seems unreasonably speculative to be so precise that two Pluto size objects resulted in this. We don't have enough info. All I am saying is, there are lots of unexplored possibilities here. The two Pluto planetoid collision theory isn't the only, the most likely, and probably won't even be the last. I am sure someone else will push another theory, eventually.