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.
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