# Can a planet have a figure-8 type of orbit around two separate stars?

Could a planet have an orbit in the shape of a figure 8 around twin (possibly binary) stars?

Mostly curious about the physical possibility of such an orbital arrangement; is it stable over a long time scale? Could both stars be different sizes (masses) and still maintain this 8-like planet orbit?

Ideally I'm going for a planet that orbits a red star and a small bluish/white star; it would have effectively three seasons:

• Orbit around the red star: the "Red Season" - Hot summer like weather over the entire planet
• Crossing between the starts in the center of the figure 8: the "Transition" - the weather is cooler since the orbit is drifting away from the red star, however the planet is almost constantly bathed in light (just not as much heat)
• Orbit around the blue/white star: the "Blue (or White) Season" - effectively winter as a small dwarf type star would not have the same out put as the larger red one.

Is this at all feasible?

• I was under the impression that red stars were cooler than blue/white stars. Oct 16, 2014 at 15:42
• @DannyReagan I'm fairly sure you are right on that. Oct 16, 2014 at 15:43
• Cooler but also larger my intent was that the orbit around both stars would be (relatively) equal in distance to the center; so the red stars surface is closer to the planet then the smaller white star. Other wise I can flip the "seasons" as well depending on what the reality check portion the answers are. Oct 16, 2014 at 16:07
• @Culyx - comments are right, red is significantly cooler than a little white star...has everything to do with what stage of fusion the star has reached. Very possible that the size of the red giant might be larger, but the white/blue star can be more massive. A brown dwarf + yellow star like our sun might be more feasible for what you are going for here. Heh, need some physics peeps in here for the figure 8 orbit Oct 16, 2014 at 16:18
• I don't have the data to make a proper answer but a few years ago I ran some simple orbital simulations exactly as you describe (I thought it would make an interesting final section) but I found that while these figure 8 orbits were "possible" they were highly chaotic. That meaning that even slight peterbations caused large changes in the orbit. In other words these orbits exist "on a knifes edge" and any tiny push (such as other planets gravity) will wildly effect the orbit (often crashing the planet into a sun or ejecting it from the solar system) Oct 16, 2014 at 22:00

The question was already asked on the physic stack exchange: https://physics.stackexchange.com/questions/31201/might-a-planet-perform-figure-8-orbits-around-two-stars

I can add that the difference in mass between the stars is not important as long as the planet moves on the ridge as explained in the example.

About red stars: Red is just a color, they can be small: red dwarf or large : red giant. red giant are at the end of their life. This state is only temporary so I would not recommend it. Red dwarfs are stars with a long life expectancy. Some of them are also flare stars that haver large variations in brightness but some are more stable.

Blue/white: It's the same about the blue and white stars. They can either be dying stars or normal stars. Keep in mind that stars of that color are usually very hot when they are in their main sequence (adulthood for stars). They are large and massive but have a short life.

White dwarfs, These are old dying stars. When small to medium sized stars arrive at the end of their normal life, they become a red giant. Then, it will contract and become a white dwarf. They are very hot at the start but cool down very quickly. The temperature never stabilize but with time it will become almost stable.

You can find more about the stellar classification of colors here: http://en.wikipedia.org/wiki/Stellar_classification

and other informations about star here : What kind of star should I use for my world?

Possible combinations using the Wikipedia table:

If you want the planet to develop life, you can't have a really big star. O and B stars are out and A stars are really at the limit. They live for 1 or 2 billion years if I remember correctly. This is a very short period of time for life to evolve but it's possible.

Most likely combination: Red dwarf (M star) and white dwarf. Similar mass.

This is a stable couple. Not very hot or very bright, the planet will need to orbit relatively close to them to have enough heat. It's hard to tell the influence on the temperature since I don't have the parameters of each star but don't put the planet too far. It is probable for the red star to be the hottest star. The white star is hotter but smaller and this usually mean that it will be a dim star.

Possible problem: natural satellites are likely to break the balance of force toward one or the other star when the planet is between the two stars.

• Thinking about the orbital dynamics involved in a system like this makes my head hurt... But now I'm thinking that a really neat possibly-stable setup for a binary system might have a planet in a "horseshoe orbit" that is co-orbital to the secondary star (which itself would have to be in the habitable zone of the primary star). (en.wikipedia.org/wiki/Horseshoe_orbit) Oct 16, 2014 at 20:14
• @CalebHines Looked over that article, that would make for some extremely interesting sunrises and seasonal shifts =D Oct 16, 2014 at 20:53
• Note that the development of life requiring billions of years depends entirely on how that life is getting there and how complex you want it to be. If your original lifeform is being imported it can be somewhat shorter, and if you have a supernatural origin for life (like a life-imbung Æther or some such) it can be extremely short. Furthermore, the origin of life is still extremely poorly understood and we basically just know if took billions of years here. We don't really know that it has to happen that way or even really what other ways it might look. Don't worry bout timescale too much. Aug 14, 2015 at 16:37

I'm but a hobbist. I believe the reference you need are

The press coverage (Physicists Discover a Whopping 13 New Solutions to Three-Body Problem)
The paper by Dr. M. Šuvakov and V. Dmitrašinović (A guide to hunting periodic three-body orbits)
The resource website (Three-Body Gallery)

I'm concerned about the 8-figure orbit in that its net angular momentum is 0, which may suggest some very special origin / genesis mechanism / artificiality.

• Welcome to the site. References are great to have but the meat of your answer should be posted not supplied by links. This is mostly done to avoid link rot. If you could post the answer itself and the keep the links for reference that would be the best way to go. Oct 16, 2014 at 18:04
• That's not one small object in a figure 8 around two larger ones. It's three equal sized objects in a mutual figure 8 with no other significant masses. Jun 12, 2015 at 5:40

(I might have to check on meta if this is a valid answer)

I think the figure 8 orbit is possible, my only issue is how the two stars interact (orbit each other) and the impacts that might have on a planet trying to go between them. A more physics inclined person should be able to answer that.

But the reason I wanted to post an answer, is even if there is gravitational forces at work here, don't neglect the effects 2 magnetic fields will have on a planet.

• Recent research appears to be able to link our magnetic interactions between our Sun and Earth influence storms here on earth.
• the magnetic interactions of two stars orbitting one another (or even existing close to each other) is something we have little to no knowledge on.

Lets assume that the weather to solar magnetism link is there...traversing the area between these two stars where the magnetic interactions are taking place could cause some of the most destructive weather this planet has ever seen. Sorta adds another element of extreme weather phenomenon (maybe some amazing 'northern lights' as well) during that phase.

If such an orbit was possible on paper, it would not be stable.

Having a planet that chaoticly switches stars rather than evey time is better, but still won't last. You would need some waymto contrive it to stay in such an arrangement, such as other bodies sculpting the gravitational gradients (like a Lagrange point but more complicated).

It appears to me that a planet in a binary star system could have an orbit around one of the stars, perpendicular to the mutual orbit of the stars around each other. The first star would keep the planet in orbit, but it would not be an orbit around the center of the star, because the gravity of the second star would pull it off-center. The first star would rise and set on the planet, but the second star would probably be seen constantly in one hemisphere of the planet, and never seen at all in the other hemisphere. Strange!

Most probably this can exist, but will be stable for only a very short time. If the planet had really small mass or maybe was just a comet, it could be stable. Here's an animation (I know it's not much - made by eye) showing how this idea would look like - it seems insane to me:

(Planets and stars are not scaled right)

This animation is a bit hard to get, so I made another one which shows the same, just without the stars rotating:

(Planets and stars are not scaled right)

So, for me, this is not possible long-term, with a normal-sized planet, and this would be even more unstable, if one of he stars had a much bigger mass.

Edit conducted by the flags: this answer adds perspective - shows through an animation how chaotic this concept is. But the animation isn't the main part - The text (answer) part is. The answer is no, this is not possible long-term.

• How does showing how it looks answer the question of whether it's possible? Did you just make up a path or do the math and animate the findings? What dies this add over the other answers and pointer to Physics.SE? Sep 13, 2016 at 22:04
• I agree with the commenters above; I don't think this answers the question. Appearances can be deceiving; planetary systems I thought could never work have turned out to be quite stable. Sep 13, 2016 at 23:00
• This answer is the subject of a Worldbuilding Meta discussion: Looking for some constructive criticism
– user
Sep 16, 2016 at 18:43