This thread is such epic self-pwnage on a scale legendary even for The Ceej. I can't help but stick my nose in.

Quote Originally Posted by The Ceej View Post
Well, mass and size are two different entities.

I doubt they're going to judge whether a rock is a planet or not on solely mass. I know I won't. Besides, Pluto has a moon.
No, they don't do that. The IAU defines a planet thusly;

The IAU members gathered at the 2006 General Assembly agreed that a "planet" is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
Pluto hasn't cleared the neighbourhood around its orbit, and thus is considered a dwarf planet.

And now, don't go doing what my college science instructor did, once he learned and informed us that Pluto was no longer a planet, and claim I saying every planet that doesn't have a moon isn't a planet.
If we're going to get technical, Pluto and Charon are a binary system - neither is really a moon (Although the IAU hasn't got around to giving a specific definition for dwarf planet binary systems, so it's not entirely unreasonable to call Charon a moon of Pluto.)

But yeah long story short the presence of orbital bodies does not qualify something as a planet cf. The Sun.