36
$\begingroup$

Several science fiction books I have read (including, IINM, Nightfall by Asimov) have featured planets with several suns. Some worlds where this happened wrought interesting effects on the inhabitants of said planet; for example, in a world that was perpetually experiencing daylight, people might be so afraid of the dark that their psychologists considered fear of the dark to be a primal, impossible-to-overcome condition of humanity.
Multiple suns on a planet makes things interesting.

Is it realistic for a planet to have multiple suns?

$\endgroup$
  • 11
    $\begingroup$ NASA seems to think so :) rt.com/news/circumbinary-planets-kepler-nasa-863 $\endgroup$ – MadPink Oct 15 '14 at 19:50
  • 1
    $\begingroup$ @Vincent Thanks for that edit.....from Pink's article: "NASA’s Kepler space laboratory has discovered a pair of planets orbiting a pair of suns." .....it may not be so simple after all. $\endgroup$ – Shokhet Oct 15 '14 at 19:55
  • 1
    $\begingroup$ @Vincent Fair points (both of them). Why not toss that out as an answer? $\endgroup$ – Shokhet Oct 15 '14 at 20:02
  • 2
    $\begingroup$ @Shokhet, you should have a look at this simulator (especially the "Binary Star, Planet" preset). $\endgroup$ – mccannf Oct 15 '14 at 21:20
  • 1
    $\begingroup$ Check this out iflscience.com/space/… $\endgroup$ – James Watkins Jul 9 '15 at 23:13
27
$\begingroup$

A planet can have multiple stars. You have 2 important conditions that you need to meet.

1-The system must be stable. With multiple stars, you will face the n-body problem. This problem arise when you have multiple celestial bodies that interact with each others. You can't place the bodies where you want and expect the system to be stable without taking in consideration how the will influence the other bodies.

  • n-body problem: This problem can be illustrated in our own solar system. The Sun is 1047 times the mass of Jupiter. But even with such huge difference, Jupiter is considered heavy. So heavy that the center of the system is not in the center of the Sun. Jupiter makes the Sun ''wobble'' toward her a little. Now imagine that Jupiter was a red dwarf and 100 times more massive.This would make the Sun move even more and also the other planets of the system.

    To get rid of the problem, you can move object away. it should make the system more stable. I don't have the numbers but I know there is a formula somewhere.

  • Hill sphere: One important thing I could say is that your planet orbit need to be located completely inside one of the star hill sphere. This sphere is where the gravity of a given body is stronger than the other bodies. The Sun has a hill sphere, Earth, the Moon, all celestial bodies have one. The size of the sphere depends on the mass of the body, the mass of the larger body and the distance between the large and smaller body. The more massive is the smaller body, the larger is the sphere. The closer the larger body is form the large one, the smaller is the sphere. Even if the planet stays inside the sphere, other forces can make the planet change course if she goes too close to the sphere's limit.
  • To have a multiple star system, you can either have the stars close to the center of the system. Or they can be far from each other: the planet orbit the smaller star and the smaller star also orbit a bigger star far away.

    When the stars are in the center, they need to be close to each other. Otherwise, it will make a larger difference of gravity pull depending which star is closer to the planet. This means that the planet cannot have a stable orbit unless she is very far aways form the center. This probably falls outside the habitable zone.

    When the stars are far away, it's simpler. Make sure your planet is comfortable inside the hill sphere of the closest star and don't worry about the rest.

And if the planet needs to be habitable by mankind.

2- The planet must not be too hot.

Multiple stars means multiple sources of heating. And you need to consider this as well.

To find the impact on temperature on the planet, check this out: http://www.cartographersguild.com/attachment.php?attachmentid=66387&d=1407439779

you need to make the calculation for each star in the system.

$\endgroup$
  • 2
    $\begingroup$ +1, thanks for the great answer! ....this is even better than my answer, as you have not one but two setups for multiple planet systems -- stars in the center + planet orbiting star orbiting star, as well as a pretty rigorous scientific explanation of possible problems. Thanks!! $\endgroup$ – Shokhet Oct 15 '14 at 20:50
  • 2
    $\begingroup$ Isn't there a stable solution where the planet and the two stars make an equilateral triangle? Such a planet is not in the hill sphere of either star. $\endgroup$ – Loren Pechtel Oct 15 '14 at 23:00
  • 2
    $\begingroup$ Maybe but all the elements will move with time and the triangle will change. Furthermore, to be outside both hill spheres means that the planet will be very cold. $\endgroup$ – Vincent Oct 15 '14 at 23:04
  • 2
    $\begingroup$ I would actually argue that the temperature change makes this unfeasible. Stars need to be a certain mass, and when the planet is between the two stars, it would be heated nearly twice as much as when it's farther away. If you're looking for Earth-like temperatures, you're unlikely to find them in this configuration. $\endgroup$ – Aza Oct 16 '14 at 6:12
  • 2
    $\begingroup$ If the stars are far enough apart it could work. $\endgroup$ – Tim B Oct 16 '14 at 8:11
24
$\begingroup$

This answer was started by Pink's comment on the question.

Kepler/NASA have discovered what they call "circumbinary" planets -- planets that orbit multiple suns (or "stars" or whatever you want to call them).
The way it works is that there is a planet that orbits two suns, both of which orbit each other.

That article did not discuss whether or not these planets are capable of supporting life, but I would imagine if there was enough of whatever else was needed for life, and your multiplicity of suns did not overheat the planet, your planet's inhabitants should be fine.

Here's a (very) crude illustration of how this system could work:

Illustration of a planet and binary stars orbiting the stars' center of mass

A million thanks to Tim for giving me a much clearer illustration for this answer! Here it is:

Tim's image

$\endgroup$
  • 16
    $\begingroup$ Very good answer. We'll hang it on the refrigerator right next to the school lunch menu. (Seriously though, well answered. +1) $\endgroup$ – Zibbobz Oct 15 '14 at 20:38
  • 1
    $\begingroup$ It's theoretically possible to have binary stars so close together that their photospheres merge. $\endgroup$ – Tim B Oct 16 '14 at 8:09
  • 1
    $\begingroup$ I'd seriously doubt any planet in an orbit out far enough to not be torn apart by the fluctuating gravitational field of those stars would be inside the habitable zone... For earth life that is of course. $\endgroup$ – jwenting Oct 16 '14 at 11:26
  • 1
    $\begingroup$ @Vincent That's possibly not a scale drawing. $\endgroup$ – Ant Oct 16 '14 at 12:02
  • 2
    $\begingroup$ @TimB - a danger when you get that close is the interaction of the two start adding instability to the output. Super strong flares when a big chunk of star A flops onto star B, cooking the planets. On the other hand, 2 stars in the middle move the habitable band out because of the increased emission from the two stars, reducing perturbation issues. $\endgroup$ – Oldcat Nov 14 '14 at 0:47
14
$\begingroup$

Stars come in all kinds of sizes. There are lots of known star systems with more than one sun. The north star, for example, happens to be a trinary system of one large sun orbited by two smaller ones:

Polaris star system

I see no good reason why a sun orbited by multiple other suns shouldn't also be orbited by one or more rocky planets. Also, one of the outer suns could itself have small, rocky planets, just like planets in our solar system have moons.

If you want to build a solar system with plausible masses and distances, then I'd recommend reading about the main sequence to learn which masses are plausible for stars and how stars' masses and ages affect their luminosity. You certainly want all of your suns to have enough apparent magnitude to create notable illumination, but not so much that they grill the planet.

Some numbers to get you started:

  • Jupiter: 317.8 Earth masses
  • Minimum mass for a star to maintain hydrogen fusion (red dwarf): ~30,000 Earth masses
  • Our sun: 332,946 Earth masses
  • Most massive star known (R136a1): ~88,000,000 Earth masses (but there might not be any reason to believe that even larger stars might not exist…)
$\endgroup$
  • $\begingroup$ +10, I joined this site to up-vote your answer. It would make a more stable planet, maybe the only stable option. Above answers are obvious in that it must have a stable orbit, but don't provide evidence it is realistic. This will work for sure. $\endgroup$ – user568109 Oct 16 '14 at 10:21
  • 1
    $\begingroup$ yah, a binary with a significant distance between the stars, with the planet circling one of them, would probably be your best bet. But not sure that'd technically be a planet with multiple stars... Starts me wondering whether the planet could have a weird orbit that circles both stars in some sort of convoluted figure 8 shape. $\endgroup$ – jwenting Oct 16 '14 at 11:30
  • 1
    $\begingroup$ @jwenting I doubt that such an orbit would be stable. There is an interesting solution for the three-body problem with 3 equally large masses following each other in a figure-8 pattern, but 1. a planet with the mass of a sun (even a small one) would have such a high surface gravity that life as we know it would be impossible on it and 2. such a configuration is very unlikely to occur naturally. $\endgroup$ – Philipp Oct 16 '14 at 11:50
  • 1
    $\begingroup$ @Philipp I doubt it'd be stable too. But given the number of scenarios we see in Sci Fi that are utterly bogus (like a planet stuck in a gravitational dead spot between multiple stats) it's at least somewhat plausible (and might make for an interesting environment, especially if the two stars are rather different, the climate and lighting conditions constantly shifting). $\endgroup$ – jwenting Oct 16 '14 at 11:53
  • 4
    $\begingroup$ @jewnting Sure, when you are willing to ignore any scientific laws when they get in your way, then nothing is impossible. But Shokhet tagged this question as science-based, so I believe the author wants a solution which is scientifically plausible in every aspect. $\endgroup$ – Philipp Oct 16 '14 at 12:06
4
$\begingroup$

Yes, as others have said it is possible for a planet to orbit a binary star system. However, in your question you seemed more interested in the psychological implications of having 24/7 light. So may I suggest a binary star system with a planet in the middle?

Binary star with centrally located planet.

This configuration, while technically possible, would be extremely rare. It requires both stars to be nearly the same mass, they would need to be far enough apart to keep the planet from burning up, and any interference from large fly-by's could easily upset the delicate balance. So don't expect it to survive long enough to support life.

Rare as it may be, don't dismiss it so easily unless you can truly comprehend how large the galaxy is, let alone the universe.

$\endgroup$
  • $\begingroup$ I like how this puts the planet in the center of the solar system, which has interesting theological implications. Another similar setup that this question made me think of would be to have a smaller star orbiting a big one, with a planet in one of the Lagrange points. $\endgroup$ – Dan Smolinske Mar 22 '15 at 17:44
  • 3
    $\begingroup$ I don't think there is any theoretical way it would actually work out that way. $\endgroup$ – Serban Tanasa Mar 22 '15 at 17:50
  • $\begingroup$ I didnt work out the math, but I think its possible if u add other bodies to the system to help balance things out. $\endgroup$ – James Watkins Mar 23 '15 at 0:35
  • $\begingroup$ It is possible to have a planet remain in the same location relative to both stars, even if they are not exactly the same mass, if it is at one of the LaGrange points. One of those is effectively in between the two objects it is "orbiting". $\endgroup$ – Nick Jun 3 '15 at 21:32
  • 4
    $\begingroup$ So unstable though. Like the planet is balanced on a razor's edge between the gravity wells of the two stars. It's hard to imagine it staying put long enough for life to develop, unless massive, artificial energy sources were used to keep it there. $\endgroup$ – Joanna Marietti Jul 13 '15 at 3:14
3
$\begingroup$

There have been theories that a hidden, dead star (named Nemesis) orbits our solar system far beyond the Oort cloud. Such hypotheses generally assume that Nemesis is now in the form of either a red or a brown dwarf due to the limiting constraint that we cannot see it. And, realistically, even if it were still burning, it would probably be too far away to look like a 'second sun' without being so massive that it would destabilize our main sun's planets' orbits. In all likelihood, Nemesis would be seen as a very bright star.
But such a star would, even then, have pretty bad implications for the stability of our solar system's planets' orbits as previously stated. That is, in fact, one of the things that led to the 'Nemesis' hypothesis; apparently, a periodicity has been been observed in the frequency extinction events, and this could be explained by periodic meteor bombardments caused by a distant massive object mucking with the orbits of comets and sending them spiraling in toward the inner planets.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.