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This question already has an answer here:

If, say, there was a double planet system (not a planet + satellite, but two planets circling each other with the barycenter outside either of the planets, of a relatively high mass ratio), what would determine the speed of their rotations and revolutions?

How close or far could they conceivably be, and would this affect their speed?

Would they be tidally locked?

And, of course, could they support life? (Either one supporting life and the other be barren, or the event that caused the system to form i.e. a meteor induced planetary split resulting in two smaller planets with already established life?)

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marked as duplicate by Aify, Hohmannfan, Frostfyre, bilbo_pingouin, JDługosz Aug 23 '16 at 11:54

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ Do you not mean a low mass ratio? A high mass ratio is when one of the planets is much larger than the other. $\endgroup$ – Hohmannfan Aug 23 '16 at 6:02
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    $\begingroup$ Hi, Kay, welcome to Worldbuilding. You are asking all the right questions about a double planet system. May I suggest that you do a search of previous questions about double planets. They will go a long way to answering your question. Go the top right hand of the webpage where there is a search query box. Use that to look up "double planet". Hope to see more questions from you. Have fun here. $\endgroup$ – a4android Aug 23 '16 at 7:23
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    $\begingroup$ Why hello there, you seem to be asking about all the physics in the double planet system, and your question body contains 4 separate questions itself. This places your question into the "too broad" category, and I am voting to close as such. As a4android has mentioned, this site already has a ton of questions relating to double planet systems, many of which may help answer your question(s). Enjoy your search! $\endgroup$ – Aify Aug 23 '16 at 7:47
  • $\begingroup$ See Rocheworld. Forward describes the science in some detail. $\endgroup$ – JDługosz Aug 23 '16 at 11:54
  • $\begingroup$ Thanks everyone, I'll look through the other questions :) $\endgroup$ – Kay Aug 23 '16 at 13:33