There are many Sci-Fi stories that feature planets with two or more suns. But is it possible? Are there any planets like this?
Yes, it is possible.
Dual stars are very common.
However, the planet would almost certainly have to be much closer to one of the suns (the one it orbits). If it was not, it would likely have an unstable orbit, and would soon crash into one of the suns.
I don’t know if such a planet has ever been discovered, but it is unlikely. The number of planets discovered is very small (astronomically speaking) and I would guess we have only looked for planets in the best places to look, which would not be close to two stars (it would be too bright to easily see the shadow of the planet, and more complex to isolate the results).
I have seen simulations of binary star systems where a planet does a figure-of-eight between the two stars and the stars themselves do a kind of dance using eachother’s gravity. but weither this happens for real I have no idea. I would be interested to see real examples posted in this thread.
As I understand it - and IANAAstronomer- binary star systems are not rare. CNN 10/29/02
The question is - would these systems provide an environment suitable for life.
There are now three known binary star planets.
There are animations of the motion of the planet around Gamma Cephei here. Note that the planet and the companion star both orbit the main star.
It’s believed that a planet couldn’t orbit both stars in binary system in a stable orbit, AFAIK.
I found that CNN article, too.
Most sources seem to suggest that you are only going to get planets orbiting one of the partners - shared orbits like “figure eight’s” are unstable or at least highly unlikely. Given this, another question might be whether the secondary would be bright enough in the planet’s sky to be seen as a “second sun”, or would it just be a very bright star?
Speculating again,
Such systems could contain planets capable of sustaining human life. It mostly depends on the amount of light the planet receives. Since the light is inversely proportional to the square of the distance, there are plenty of circumstances where the total light from two stars would be about the same as it is on Earth. In most situations, the second star would hardly matter.
About the figure-8 orbit: I suspect that, though it is possible to set up a stable 3-body orbit in a simulation, they are very rare in nature, and when they do occur, they likely degenerate relatively quickly due to outside influence. Not to say that it never happens – I would guess that just about every possible orbital configuration exists somewhere in the universe.
The question should be rephrased as “Do multiple star systems have planets?”
Enjoy.
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- There are double, triple and at least one quadruple star system within view of small telescopes. You cannot visually tell these systems are orbiting each other; it was deduced with redshifting, scientific methods and so on. They lie very close together (in astronomical terms) and one is moving slightly towards Earth, and the other is moving slightly away–therefore, they are orbiting.
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- Could you live on a planet orbiting one of these stars? Yes–but these star systems are spaced fairly far apart, and they don’t rotate once a day or once every few weeks; their orbital periods tend to run in the hundreds-of-thousands of Earth-years, or longer. So you could live on your planet, but you wouldn’t see “two suns” when you looked up in the sky, you’d see one normal-looking sun and one (or more) rather bright star(s).
- It is not possible to have an Earth-like planet orbiting a pair of suns, with the suns orbiting each other (as in Star Wars/Tattooine). The ratio of distances required means that one of the three (sun1, sun2 and planet) would have to be vastly farther away from the other two.
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Another possible stable orbital configuration, is the two suns orbiting each other at an extremely close distance and the planet orbiting the center of gravity at a safe distance.
This is probably very rare. I read that colliding stars are very rare even in colliding galaxies, and two suns orbiting each other at close distance is almost as rare as them colliding. It would probably be even more rare for such a system to have any planets.
There are three possible stable configurations: You can have the two stars very far apart, with the planet orbiting around one of the stars, or you could have the stars very close together, with the planet orbitting around both stars as if they were a single object, as mentioned by others. You could also have a Trojan orbit, with the planet and the two stars forming a roughly equilateral triangle. Tatooine is presumably the second case: Both suns appear to be the same angular size, brightness, and color, which suggests that they’re at the same distance, and they’re much closer together in the sky than 60 degrees. On the other hand, the situation in Asimov’s “Nightfall”, with a half a dozen stars in irregular orbits, would not be stable for long times, probably not long enough for a planet to develop life. This may be the one case where Lucas did a better job on the science than Asimov did.
because otherwise, the answer is “Yes, actually, all planets have more than one sun, but most of the suns are light-years away…”
I lent my copy of ‘Nightfall’ to a friend long ago, and never got it back, but I’m pretty sure that it was moons, not suns, that the planet had in overabundance.
If Jupiter were just massive enough to have ignited, would Earth’s orbit still be stable? How bright would it appear in various orbital configurations? Would it be enough to destroy life as we know it?
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- Such a situation is not possible for an Earth-like climate: to orbit the combined mass of two suns, the planet would have to be orbiting them both at a much farther distance than if it had only one sun–and then the amount of heat it received would be far lower than normal. A larger planet can hold in more heat, but a planet can only get so big before it begins to have a liquid-covered surface (Earth’s surface is already mostly-liquid covered!)
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-So then, if we had a very large-diameter planet that had a very light core–Berylium, or–maybe a planet with a hollow core, orbiting a pair of suns…
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- Such a situation is not possible for an Earth-like climate: to orbit the combined mass of two suns, the planet would have to be orbiting them both at a much farther distance than if it had only one sun–and then the amount of heat it received would be far lower than normal. A larger planet can hold in more heat, but a planet can only get so big before it begins to have a liquid-covered surface (Earth’s surface is already mostly-liquid covered!)
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It’s rare for stars to collide, but not the other. There are stars that orbit so close we can’t separate them with our best telescopes. Some of them have orbital periods of just a few days. We know they are there two ways: 1) they eclipse each other or 2) doppler shifts as they periodically approach and receed from Earth.
In fact, these are also the two ways we know there are planets out there, since no one has directly observed a non-Solar System planet. Most are found via doppler shifts, but for one or two we’ve seen the dip in light when the planet eclipses the star.
This is an aside, but Huh!?
From the site, Gamma Cephei A has a mass “a mass of 1.5 times that of the Sun”, and Gamma Cephei B is a “low-mass star”, presumably with less mass than Gamma Cephei A. But the planet has “a mass of at least 1.8 times that of the Sun”, larger than either of the stars. Color me purple… 
Nope, suns. What’s more, there were at least two stable planetary orbits in the system (the civilization’s home planet and the occulting planet.)
I suspect they screwed up and really meant the planet has 1.8 times the mass of Jupiter.
Hmm. I could swear it was moons. Maybe that was one thing reworked in the novel version with Silverberg? I’ve never read the short story, just the novel.