clipka wrote:
> David Buck <dav### [at] simberoncom> wrote:
>>   It was for a science fiction story I was working on that takes place
>> on a planet that orbits a star 20 lightyears away.  This is actually a
>> binary planet where two approximately equal mass planets orbit each
>> other (or around the center of mass of the two planets) and both orbit
>> the star.  The two planets are tidally locked to each other.  I wanted
>> to discover the dynamics of this world.
> 
> Out of curiosity: Would such a system actually be stable in reality?
> 
> 
> 

You need to have the two planets separated more than the Roche Limit 
otherwise the tidal forces will tear them apart.  In this case, they are 
about 10x the Roche Limit.  Within that range, it should be fine over 
long periods of time (billions of years) but I haven't done the 
simulations to verify that.

David Buck

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