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Old 08-09-2020, 11:00 AM   #1
Dr. Beckenstein
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Join Date: Sep 2013
Default First In - Planets for companion stars?

Out of sheer boredom (thanks, Corona!), I pulled out my old copy of First In and fiddled with the star / world generation. As I worked up a double star system (2 MV stars), I stumbled upon something.

Do I understand it right that the rules for "forbidden zones" (p. 54) prevent that companion stars can have their own planets?
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Old 08-09-2020, 11:38 AM   #2
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Join Date: Aug 2004
Location: traveller
Default Re: First In - Planets for companion stars?

No, they just preclude planets in certain ranges of orbits, based on the separation between the primary and companion star. This is due to orbital instability: a planet in the "forbidden zone" is likely to be kicked out of the star system on a time-frame much less than the lifetime of the system.

So, for example: A Cen A and B orbit their common barycenter, with eccentricity ~ 0.5 but never getting closer than 11.2 AU (making A Cen B a Moderate or Wide companion, in GT:FI terms). Either star of the pair could have planets with stable orbits at less than 1/3 this distance, or <3.7 AU. This would encompass the entire inner Solar system, out to the edge of the Main Belt.

Note, however, that GT: First In (published in 1999) pre-dates most of the work on planetary migration and hot Jupiters that have come since, so some of its other assertions about where planets can wind up (e.g., inner limits and snow lines) have been rendered obsolete by more recent research.
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