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

So, the three criteria of the IAU for a full-sized planet are:

1. It is in orbit around The Sun.
2. It has sufficient mass to assume hydrostatic equilibrium (a nearly round shape).
3. It has “cleared the neighborhood” around its orbit.

Pluto is in orbit around the Sun, and it is round. However there are still asteroids in Pluto’s orbit, disqualifying it from being a planet.