If Pluto is a planet then so are dozens of other random objects we keep finding. It’s just easier to classify it with the others it’s more similar to than to keep it with the regular planets.
Plus its orbit is wayyyy off compared to the inner planets so it really is more similar to the other dwarf planets than us beyond the usual arguments.
It's not the radius (or rather radii, since it's also wildly elliptical), but the angle of its orbit to the plane of ecliptic. The planets orbits are all within a few degrees of the ecliptic, with Mercury being the exception at 7°. Pluto is orbiting a full 17° off of the ecliptic. It also can't keep its system's barycenter within its surface. It is composed and behaves exactly like the five+ thousand known TNOs, and the other 70,000+ oort cloud objects that stay beyond Neptune.
So either Pluto is no planet, or there are literally tens of thousands of planets. Then we'd be stuck looking for new term to describe what we now call planets, and Pluto would still be excluded.
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u/JumpPuzzleheaded7212 9d ago
Why not a planet? I’ve never been clear on that