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...but then I think the notion of a planet as a discrete object is flawed. Celestial objects exist on a spectrum, starting (arguably) with stars and passing through brown dwarfs to gas giants to rocky planets down to major asteroids and then minor objects like comets. Some formed from the original accretion disk of the solar system and some are the product of later collisions or dissolutions. Some orbit the gravitational center of the solar system and some belong to gravitational subsystems formed around high-mass objects. There are lots of objects that inhabit the fuzzy borders between these categories, and trying to create a distinct line between them is like trying to argue whether purple is bluish-red or reddish-blue.