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Some of my characters travel to a planet orbiting two suns. They don't spend long there and it's implied some other species lived there before but don't anymore.

Is this possible? Would two suns affect gravity, temperature, etc. making it impossible for life to exist at all?

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    $\begingroup$ Hello Ambient. I try not to vote to close new user questions, but this question is far to vague to answer. When it comes to life, we have one and only one data point: Earth. Period. Any answer your receive that suggests the possibility of life in any other solar system is a best guess until we find proof. It appears that most single-star systems won't support life, which makes Earth uncommon if not rare. You can expect similar statistics for any other star system not incorporating a wacko star (like a pulsar). (*Continued*) $\endgroup$
    – JBH
    Commented Nov 11, 2022 at 1:13
  • $\begingroup$ ... Further, please remember that while we'll help people to build worlds that are as realistic as possible, the root of our efforts as stated in the help center is that we help people build imaginary worlds. The likelihood of a life-supporting binary star system among the bazillions of star systems in the galaxy is good enough that if you want one, you can have one and no one will complain. Thus, "can you have?" really isn't a valuable question. "What configuration of stars and planets will believably support life?" Now that's an interesting question. And it's likely already answered. $\endgroup$
    – JBH
    Commented Nov 11, 2022 at 1:15
  • $\begingroup$ binary star are extremally common, some have even proposed they are more common than lone stars. $\endgroup$
    – John
    Commented Nov 11, 2022 at 2:50
  • $\begingroup$ en.wikipedia.org/wiki/The_Three-Body_Problem_(novel) $\endgroup$ Commented Nov 11, 2022 at 3:30
  • $\begingroup$ duplicate ocmment. $\endgroup$ Commented Nov 13, 2022 at 7:48

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Survivability would be very poor. The best condition I could imagine would be a binary star system where the stars are much closer to each other than the planet, and even that wouldn't be stable long-term. If it were somewhere in the goldilocks zone, it would still shift between freezing and boiling as the larger of the two stars shifted closer and further.

If it were out in the icy depths, then life might survive by tolerating frozen conditions while occasionally thawing out for more active behaviors. Such stability wouldn't be persistent, however, and the planet would still be in danger of either being roasted or flung into deep space.

This is what's called "The three body problem," and it's notoriously unsolvable. In his book of that name, Cixin Liu suggests a lifeform that can release all of its water and go into hibernation when things get too hot or too cold. Humans could probably survive underground long-term if they had to, but there's no way we could evolve there.

For a short-term visit, there probably wouldn't be a problem. You could still have life forms, like plants, but they would need some extreme survival strategies. Such inhospitality would be obvious for anybody approaching it. Anybody who writes "the planet/star snuck up on them" should be soundly thumped.

There would be no noticeable effect on gravity. From the perspective of the stars, planets are always in free-fall, so nobody on the surface would notice the gravity shifts as the planet moved closer and further.

There would likely not be a meaningful atmosphere. The stars would have boiled and blown it off a long time ago.

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  • $\begingroup$ Thank you, that's extremely helpful. Would it be possible for another life form– non-human– to exist for a short amount of time, before being wiped out? $\endgroup$ Commented Nov 11, 2022 at 1:09
  • $\begingroup$ If you're talking about a space faring race temporarily setting a base up, sure. With a pile of imagination, you could even have life evolving there, but you'd have to go way beyond the normal alien architypes. $\endgroup$ Commented Nov 11, 2022 at 1:12
  • $\begingroup$ I think that yu are exaggerating hte difficulties of a planet in a circumbinary or P-type orbit around a binary star. en.wikipedia.org/wiki/Habitability_of_binary_star_systems With the right astronomical set up a planet in a circumbinary orbit could have along term stable orbit and relatively constant temperatures. $\endgroup$ Commented Nov 13, 2022 at 7:44
  • $\begingroup$ @M.A.Golding, A little exaggeration, sure, but we're talking stability over a period of, say, five billion years. For P-type, you need to have the stars close enough together that you don't move the planet in and out of the habitable zone as they orbit, but far enough apart that they don't share material and eventually merge. The folks at Kepler have determined that orbital stability is possible, but the jury is still out on whether you can keep a planet in a water-bearing zone for long enough for evolution. Still, close enough for sci-fi. $\endgroup$ Commented Nov 14, 2022 at 17:35

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