>>6151967Do you know the definition of planet? Before 2006 it came from the Greek 'astēr planētēs' which means 'wandering star.' That's not a real scientific way to decide if a thing is a planet or not. So they had to define it, now to be a planet you have to make these criteria;
Massive enough to be rounded by its own gravity.
Not massive enough to cause thermonuclear fusion.
Has cleared its neighbouring region of planetesimals.
Pluto does not make that third onw, so it's not a planet.
TL;DR see
>>6151981 
