Alain wrote:
> Jérôme M. Berger nous illumina en ce 2009-01-07 15:13 -->
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>> 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?
>>>
>>     It is: look at the Pluto-Charo pair of planets (planetoids?) in the
>> solar system.
>>
>>         Jerome
>>
>> PS: Of course, Pluto and Charo aren't 20 ligth-years away from their
>> sun, but that's probably just me being obtuse ;)
>>
>>
> It's 20 lightyears away from HERE.
> 
> A planet orbiting it's sun at a 20 lightyears radius would need to have 
> an extra-galactic sun, or get snatched away by nearby stars. Such a 
> planet would also be frozen solid, with, maybe, sone seas of liguid 
> hydrogen and helium. It's "year" would last several 100's of millenias.
> 
> 


Um, yea :-).

The star (Delta Pavonis) is about 20 lightyears from our Sun.  I don't 
think a planet could orbit a star at a distance of 20 light years.  The 
planets orbit their sun at a distance of 93.5 million km and the two 
planets are about 47,000 km apart from each other and rotating 19.7 
degrees off the ecliptic.  The Roche Limit is about 5900 km so they 
won't tear each other apart.   The binary planets have a 33.6 hour day 
and a year of 182 Earth days or 130 planet days.  Acceleration due to 
gravity is 7.2 m/s^2 (compared to 9.8 m/s^2 on Earth).  If you're on one 
planet, the other appears fixed permanently in the sky and is just over 
13.6 times the size of the Earth's moon in the sky. Every year, there 
are two periods (one in the spring and one in the fall) when the two 
planets eclipse each other for several days in a row.

(Ok, I'm a geek :-)  )

Back to the IRTC software.

David Buck

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