On Pluto

[unnamed525]

I don't see why an object which has an atmosphere thick enough to obscure viewing the surface doesn't constitute a "planet".

Comments

[tosk]

Because the powers that believe they have some justification for labeling things said so

[duriyah]

Very true. I like that.

[tosk]

http://www.rawilson.com/whistlepiss.shtml

Robert Wilson to the rescue again!

[anivair]

I can't disagree with him. the jist of it is that pluto doesn't have a stable circular orbit and cannot perpetuate indefinately. it's an accident that it hasn't crashed into neptune yet.

[unnamed525]

Actually, Neptune and Pluto aren't going to collide, for a couple of reasons, the biggest being that Pluto's orbit has a much larger z-component than the eight planets; another reason is that Pluto and Neptune are in a 3:2 resonance which transfers angular momentum between the two. There's a better explanation than mine here ... he's got nice graphs and stuffs.

[catachrestic]

None of the planets have a 'circular' orbit. They are all ellipical.

The primary reason for Pluto being demoted was that its orbit crosses with Neptune's. Although, for the life of me, I'm not sure why that doesn't eliminate Neptune as a planet for the same reason.

[thesandsabrase]

Mainly because they've have to make Charon and other small bodies in the solar system planets.

[unnamed525]

It was alot simpler when the definition of "planet" was "heavenly body that obviously moves against the backdrop of the 'fixed' stars".

[fractaltime]

Titan.

[unnamed525]

Titan directly orbits Saturn, while the Pluto-Charon dual body directly orbits the Sun.

[fractaltime]

Mercury.

Doesn't have an atmosphere, so it shouldn't be a planet if atmosphere is a criterion.