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

[drplokta]

No, because objects that are gravitationally bound to the primary don't count. Earth's moon is bound to the Earth, the Trojan asteroids are bound to Jupiter and Pluto is bound to Neptune, so none of them stop Earth, Jupiter and Neptune from being planets.

[timill]

Pluto?

[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.