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

The center of Mass of Pluto’s dual system with Charon is outside of Pluto’s physical body. A planet orbits the sun directly and other things orbit it. Pluto isn’t massive enough to be making this happen so it lost planet status. “Other” planets, while made entirely of gas, are bigger and because they have enough mass to have independent solar orbits, they are planets.