Quote:
Originally Posted by Snuffleupagus
Our moon is only the 5th largest in the solar system, if Ganymede and Titan weren't in orbit around Jupitar and Saturn they would be planets, both are larger Mercury
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Sorry I wrote that poorly, long winded, and a lot of assumptions
The moon is a large object that has become spherical under the force of it's own gravity.
It's orbital pathway is generally clear
The thing that prevents it from being considered a planet is that it's primary orbit is not around the sun but around another body.
The orbital center of gravity between the earth and moon is about 1/4 way to the center of earth.
The moon is roughly half the density of earth.
If the moon had similar density to earth the orbital center of the system would be outside of the earth. and rather than the earth orbiting the sun and the moon orbiting the earth, than the earth moon system would be orbiting the sun and the earth/moon would be orbiting a gravitational center.
because of all of these things the earth/moon system very closely resembles a binary planet system, and if you remove yourself from the frame of reference created by a culture originating under that big light in the night sky, and put yourself into the mindset of some with a more typical planet to moon scale, you might consider the earth/moon system a binary planet, which appears to be pretty unusual. There is definitely something unique about the size of the moon when compared to the earth, but any reasons to think that is meaningful in anyway are pure speculation at best.
Saturn and Jupitars moons orbital pathways are full of objects, and there is no question that they are not comparable objects to the gas giants they orbit.