Planetary science is subset of the branch of science known as astronomy, not a separate one. It includes planets as well as moons and other objects down to meteors. The term is from back when ‘planet’ was a more general term than today. Really there are few astronomers who engage in this silly argument about what a planet is—it’s mostly from those see it from an armchair perspective.
Yet it’s the armchair guys who have to point out how terrible a requirement it is that a planet has to clear its orbit.