Why is Pluto not considered a planet because it’s too small, but some planets are made entirely of gas and considered planets?

Question

Edit: I know I sound like an idiot in the replies, but I’m really asking genuine questions so thank you all for being patient and answering

In: Physics

Answer 1

They are large, and size matters. If you are big enough to clear your orbit, you are a planet. If not, you’re not.