Could Two Planets Form A Binary System?
For my current purposes, assume we have two planets identical to earth. So, could two of these planets form a stable binary system, and still be close enough to see the green foliage on the surface of the other planet? They would ideally not be tidal locked. If this is possible, how would it affect the day/night cycle and seasons? (If you don't mind taking it into account, I intended for these planets to rotate a binary star system, in which both stars are nearly identical.)
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The way the moon formed was that something big collided with early Earth when things were still pretty gooey, and knocked a big chunk out, which then fell into orbit instead of drifting away or falling back to earth.
If you had a planetary mass that was somewhere between 2 and 3 earths, and hit it with a big rock so that it split fairly equally, then sure, why not.
As JDÅ‚ugosz says, you'd have to get the orbit distance right, and there are some formulas to determine the Hill Sphere.
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