Dual Solar System

Discussion in 'Astronomy, Exobiology, & Cosmology' started by LostInThought7, Nov 8, 2009.

  1. LostInThought7 Registered Senior Member

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    Is it possible for one planet to orbit two separate stars, and in any way, be habitable?
     
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  3. Ophiolite Valued Senior Member

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    If you mean orbit the two stars in a complex figure of eight pattern the answer is almost certainly no, though you would have to run a series of Monte Carlo simulations to determine for sure.

    If you are envisaging a close binary where the planet 'circles' their barycentre (the centreof mass of the two stars) then it is perhaps just possible. In this situation the Goldilock's zone would be perilously small and its change over time would be complicated by different evolutionary rates of the stars if they are not the same mass. Also this situation would make for some complex and highly variable seasons, though I imagine life would find an interesting way around that problem. Finally I still have doubts the planetary orbit would be stable over the necessary billions of years.
     
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  5. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Blue text is later by edit
    I do not know (and am sure the answer is well known) but strongly suspect that such an "orbit" is highly unstable.

    Assume the planet is initially in circular orbit about the Barycenter. My argument here was un-necessarily assuming that planet's orbit is in the plane swept out by the rotating line between the two stars. An orbit perpendicular to the line between the stars can have the force always towards that line, and probably constantly towards the barycenter. Half of orbit period it is attracted more strongly towards one star than the other. This modifies its orbit (makes it more "eliptical" or something sort of like an elipse) I think that now in this modified orbit it would spend approximately the same time with stronger attraction to the other star and make a second modification to the now non circular orbit. It is very improbable that that "second modification" can exactly cancell out the first and return the planet to a circular orbit.

    All the above sort of goes along with your implied suggestion that there is a net force towards the barycenter. I think that is very false, except briefly twice each orbit. If the two stars were of equal mass, then the attraction towards the barycenter would briefly occurr only when the planet is equally distant from the two stars.

    I can more easily imagine that some stable open "figure eight" orbit might exist, IFF the planet mass is very much less than the smaller star's mass, but doubt any does. I say "open" as of course the 8 would not close because the axis between the two stars is rotating about the barycenter.

    Both the "in plane" and "inclined to plane" potential orbits would need to be considered. If any is stable, I am reasonable sure there would need to be a "resonance" between the figure eight period and the stellar rotation periods. I.e. after some relatively small interger number of planet orbits the orbit must retrace itself (in the rotating frame of the two stars).

    PS I think that most stars are part of a dual star system. - I.e. when a great gas cloud is condensing and forming star(s) I believe that the total angular moment is "easier" to conserve with two separate stars. Our sun probably formed from a cloud with relativley little angular momentum, so could get by with only one star and a couple of large planets.
     
    Last edited by a moderator: Nov 8, 2009
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  7. Ophiolite Valued Senior Member

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    BillyT,
    I recall reading some research on this a few years ago and my recollection is that with close binaries a stable orbit was possible for the order of hundreds of millions of years. We only need to step up an order of magnitude. The same research, if I am remembering correctly, showed a figure eight orbit would be unstable and would rapidly (order of tens of millions of years) lead to ejection of the planet from the system.
    If I can I'll track down the research, but I'm not too optimistic. I'll just have to search the NASA-ADS site with suitable words.

    Equally, later research may have identified parameters that allow, or absolutely exclude stable orbits for such a scenario.
     
  8. The Esotericist Getting the message to Garcia Valued Senior Member

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    One word. . . Tatooine.

    lol. Seriously though, I think your question is vague at best. You really need to redefine what you mean. For certainly, with our technology, we can make just about ANYWHERE, "habitable." Look at the ISS. . . If that is habitable, then sure, we could make a planet that is orbiting two stars habitable, as I'm sure any advanced civilization could.
     
  9. Ophiolite Valued Senior Member

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    Of course another point to consider is the impact of a binary pair on planetary formation. Not only would this, surely, have a large effect upon the collapse of the nebula to form an accretion disc, but the relative time at which the binary stars entered their T-Tauri phase.
     
  10. D H Some other guy Valued Senior Member

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    There are two stable configurations. One is a planet in a 'P-type' orbit in which the distance between the two stars is much greater than the distance between either star and the planet. This is the close binary pair + planet configuration that Ophiolite mentioned in post #2. The other is a planet in an 'S-type' orbit in which the planet is essentially orbiting one of the two stars; the distant binary pair essentially acts as a giant Jupiter that perturbs the planet's orbit about its primary. This arXiv article (http://arxiv.org/abs/0705.3444) suggests that such orbits are common.


    Lastly, a figure-8 orbit is another possible configuration. However, the three objects must have fairly close to the same mass. See http://www.santafe.edu/~moore/gallery.html.

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  11. superstring01 Moderator

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    No. It´s gravitationally impossible.

    For starters, it would require that the two starts remain still, totally unmoving, un-shifting in order to keep the figure eight pattern. Just isn't possible.

    ~String
     
  12. D H Some other guy Valued Senior Member

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    Read post number 8, string. There are two configurations that are habitable: The planet orbiting some distance away from both stars, and the planet orbiting just one of the two stars.
     
  13. superstring01 Moderator

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    Ahh. Sorry. But, really? Can it happen? What are the odds?

    ~String
     
  14. D H Some other guy Valued Senior Member

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    According to the paper at arXiv cited in post #8, about 3/10 of the binary stars should be able to have planets of some sort. Note well: That article is talking about planets in either a P-type or S-type orbit. I am interpreting the OP's question to be about the odds of a habitable planet in a binary system rather than a question about a specific configuration.

    Regarding the figure-8 orbit, the odds are zero for a planet and two stars. That figure 8 configuration is not stable if one of the masses is much smaller than the other two masses. The three objects must all have roughly the same mass. Three stars could orbit each other in a figure 8, but even then the odds are very slim.
     
  15. Michael 歌舞伎 Valued Senior Member

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    That'd be really pretty cool to see. Could these stars have planets circling them too?
     
  16. LostInThought7 Registered Senior Member

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    Hm. So if the odds are against it....hm. And even then, I'd probably have to have quite a bit more knowledge about such things to be able to write a story about it. I'll just have this be the only planet in the solar system.

    I'm sorry, I'm writing a story.

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  17. D H Some other guy Valued Senior Member

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    LostinThought7, were you specifically asking about a figure-8 orbit, or were you asking more generally whether a hospitable planet can exist in a binary system? While the figure-8 orbit is pretty much ruled out, the more general issue is not.

    Then again, you are dealing with fiction rather than fact. You can make stuff up that contradicts science. Problems arise only if the contradiction is so egregious that your readers cannot suspend their disbelief.

    Three stars of nearly equal mass could be in a figure-8 configuration. One of those stars could have a planetary system. The other two stars might perturb the orbits in weird ways. Now suppose each of the three stars hosts a planetary system, each having a life-bearing planet. If one of those planets bears intelligent life they will have a very solid reason to extensively develop space travel. If two bear intelligent life you have the potential for an interesting space war. All three bearing intelligent life? That seems a bit incredulous. I might have to suspend my disbelief.
     
  18. draqon Banned Banned

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  19. ElectricFetus Sanity going, going, gone Valued Senior Member

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    At present: we don't know. We may have to wait until after Kepler to get even a hint. I would think though the odds are good for an so called S-type orbit in which the habitable planet is not perturbed enough to cause serious deviations in climate , this would easily exist in binaries in which the stars are always many AU apart. Take predictions of planets around Alpha Centarui for example:http://aether.lbl.gov/www/classes/p139/speed/Alpha-Centauri.html

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    In that cause the stars in their loopy orbit never get closer then 11 AU and allow for roughly 2 AU stable "S-type" orbiting planets around either A or B centari, completely encompassing their "Goldilocks zones".

    Now a P-Type orbit supporting a habitable planets is less likely, the stars would need to be orbiting very tightly for the planet to always or often be in a habitable zone. Again in Alpha Centaurus case a P-type planet would always be as cold or colder than Neptune.

    In short assuming the OP questions it is unlikely but far from impossible for planet in a P-Type orbit to be habitable, the star system must have very close orbiting stars (from the paper </=.2 AU!) and/or the planet must have proper orbital resonance to get close enough to one or both stars to be warm for a reasonable amount of time.
     
    Last edited: Nov 9, 2009
  20. eburacum45 Valued Senior Member

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    Actually the article says that wide binaries should be separated by more than 7 AU for Earth-like planets to form. For close binaries they consider the limit to be about 0.1 AU.

    These estimates are slightly more restrictive than limits I've read in the past; previously the limits were about 3 AU and 0.28 AU respectively.

    Those are the limits I've used on this Orion's Arm page
    http://www.orionsarm.com/eg-article/460d90f53fb24
    (but I would remind everyone that OA is fiction, althoug we try to make it relatively feasible).
     
  21. ElectricFetus Sanity going, going, gone Valued Senior Member

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    There was an article while back about binary star systems disk formation, they show disk formations was limited for binarys >3Au and <50Au, so those mid range binnaries like alpha centary may not have much for planets.

    http://astroprofspage.com/archives/838

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  22. Scaramouche Registered Member

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