Four planets?

[redbird]

I don't care much whether Pluto is called a planet, though it's nice seeing people actually talk about the Solar System.

But any definition of a planet that excludes Earth and Jupiter is worthless. "Sweeps out its orbit" is a kludgy phrasing to deal with the Neptune:Pluto 3:2 resonance, but no matter how you phrase it, Pluto is still there, crossing Neptune's orbit, and half the planets in the system have associated asteroids.

Comments

[lysana.livejournal.com]

Pluto is not bound to Neptune. It has an eccentric solar orbit that crosses Neptune's path, but that is not the same thing.

[drplokta]

It's in a 3:2 orbital resonance with Neptune, as are most of the other Neptune-crossing plutinos. Pluto's orbit is absolutely controlled by Neptune's gravitation. It's a similar relationship to that between Cruithne and Earth.