Quote:
Originally Posted by jamesqf
Why should the moon not be considered to be the same as a planet in most practical ways? It's big enough to be round, is internally differentiated, has a bit of geology going on...
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Many have pointed out in the past (and present, I guess) that you could call the Earth-Luna system a binary planet, given the size of the moon in relation to its primary.
Well, not quite a binary system, as the center of the orbital system lies somewhere in the Earth's mantle. Give the moon a few million (a few ten million? hundred million? a billion?) years to wander further away and the center will be outside of Earth... at which point you will now have two planets (or one planet and one dwarf) orbiting a common point that is orbiting around the sun.