I am creating a solar system that has a binary star system. The system has 3 planets. The closest being like Mercury. The next being the planet that supports life and being slightly larger then earth. And after that an ice giant similar to Neptune. My biggest interest is in the 2 moons around the 2nd planet. I want the race on the planet to use the moons and the 2 suns for religious purposes. The closest moon is mars-like in color and geography but not in size, while the further moon is similar to our moon. I would like to know if a situation like this is possible and stable, as well as the needed distances between planets, as well as the times between solar eclipses and lunar eclipses, and any other info. I will show an image of the system as well as the stats of all the objects.

Yellow star:


Sol mass: 1.12

Star like are sun

Red star:


Sol mass: 0.42

Red dwarf

Orbital Period: 38.28 days(time tacks for stars to go around each other)

Grey planet:

2750km radius

Orbital period: 21.81 earth days

Blue Planet:

Ice giant

Radius: 275000km

Green planet:

Radius: 8500km

Year length: 419.91 earth days (234.58 days on the planet)

Day length: 1.79 earth days

Closest moon:

Radius: 1900km


Orbital Period: 21.92 earth days

Other moon:

Radius: 1650km


Orbital Period: 41.72 earth days

enter image description here

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    $\begingroup$ Slight correction; it's planet, not planit. $\endgroup$ – Sach Dec 6 '19 at 22:48
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    $\begingroup$ One problem: the blue planet is huge, in fact it's more the size of a very small star or brown dwarf. The calculations you ask for would take a lot of effort and would need more information. Key is the mass of the planets. $\endgroup$ – Slarty Dec 6 '19 at 23:05
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    $\begingroup$ @Sach - I have corrected this for Vexxen $\endgroup$ – Slarty Dec 6 '19 at 23:06
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    $\begingroup$ Oh dear, I didn't notice the size of Blue Planet. It's radius is like 4-5 times that of Jupiter I believe? That is pretty massive. $\endgroup$ – Sach Dec 6 '19 at 23:09
  • $\begingroup$ And it is also considered impossible, since a planet's radius should only get a little larger than Jupiter's no matter how massive it gets. $\endgroup$ – M. A. Golding Dec 7 '19 at 18:58

This is possible, but you need some conditions met.

Typically, there are two types of orbits that planets around a binary star system can have.

  1. P-type (circumbinary)

    • Planet orbits is around both stars. This is what all your planets do.
  2. S-type (non-circumbinary)

    • A planet orbits only one of the two stars.

This picture illustrates the difference better:

enter image description here

Since all your planets are P-type, let's focus on them. For a circumbinary planet, orbital stability is guaranteed only if the planet's distance from the stars is significantly greater than star-to-star distance.

Reading on,

The minimum stable star to circumbinary planet separation is about 2–4 times the binary star separation, or orbital period about 3–8 times the binary period. The innermost planets in all the Kepler circumbinary systems have been found orbiting close to this radius. The planets have semi-major axes that lie between 1.09 and 1.46 times this critical radius. The reason could be that migration might become inefficient near the critical radius, leaving planets just outside this radius.

So if you can satisfy these conditions, then you're good to go.

  • $\begingroup$ Any other types of orbit possible, how about an S type orbit that periodically switches out to the other sun? $\endgroup$ – Pelinore Dec 7 '19 at 2:19
  • $\begingroup$ @Pelinore. In my opinion such an orbit would be either totally impossible or else extremely improbable. There might be questions about that on this site but I couldn't find one just now. So maybe you should ask a question about it. $\endgroup$ – M. A. Golding Dec 7 '19 at 19:00
  • $\begingroup$ @M.A.Golding : likelihood aside I was just wondering if a 'stable' (in the sense of infinitely repeating) was possible according to math & orbital mechanics, imagine the massive changes in climate hopping from a sun like ours to a red dwarf every once in a while ;) a regular extinction level event most likely .. I might ask it, but perhaps in Astronomy SE or Space Exploration SE rather than here for that one. $\endgroup$ – Pelinore Dec 7 '19 at 19:09
  • $\begingroup$ @M.A.Golding : I've already got one (probably) silly question currently exercising my interest so probably not right now though :) $\endgroup$ – Pelinore Dec 7 '19 at 19:20
  • $\begingroup$ Thanks for the answer. It is appreciated. $\endgroup$ – Vexxen Dec 9 '19 at 19:50

http://astro.twam.info/hz/ This is the site I usually usr for this kind of stuff.


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