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Space Science

First Exoplanet Discovered Orbiting Two Stars 88

Posted by timothy
from the good-to-visit-not-to-live dept.
astroengine writes "For the first time, astronomers have discovered an exoplanet orbiting binary stars. Kepler-16b, a Saturn-sized world approximately 200 light-years away, orbits Kepler-16, two stars locked in a mutual dance. Although other exoplanets are known to exist in binary systems, they have only been known to be orbiting one star of the binary pair; Kepler-16b orbits both. No doubt Kepler-16b will excite memories of Tatooine, Luke Skywalker's homeworld, but the double sunset is where the similarities end. Kepler-16b would be anything but a desert world; it is the approximate size of Saturn, it is extremely cold, and its average density is that of water."
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First Exoplanet Discovered Orbiting Two Stars

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  • The first planet orbiting two stars?

    The exoplanet part being redundant.

  • by 0racle (667029) on Thursday September 15, 2011 @02:55PM (#37412654)
    A desert doesn't have to be hot and covered in sand.
    • But it does have to be on land...

      • by blair1q (305137)

        Who said this planet wasn't land? Maybe it's half rock and half air.

        • by MightyMartian (840721) on Thursday September 15, 2011 @03:11PM (#37412840) Journal

          It's Saturn sized with density of water. It's a friggin' gas giant. It has no surface, unless you count the super-dense core that's probably hydrogen in a metallic state.

          • I watched the press conference, and they suggested it likely had about half of it's mass as a solid rocky core, the other half as gas.
          • It's Saturn sized with density of water. It's a friggin' gas giant. It has no surface, unless you count the super-dense core that's probably hydrogen in a metallic state.

            Of course if it's Saturn sized, it might have large moons with a rocky surface, water, and possibly life. And while the sunsets on such a moon are likely spectacular, the eclipses would be even more amazing.

            • by Agripa (139780)

              Of course if it's Saturn sized, it might have large moons with a rocky surface, water, and possibly life. And while the sunsets on such a moon are likely spectacular, the eclipses would be even more amazing.

              The eclipses would only be amazing until the nocturnal predators come out and start hunting down the crew and passengers one at a time.

            • by Maritz (1829006)
              There are certainly all kinds of possibilities, especially when you consider the stars wouldn't have to be the only heat source on such theoretical moons. Tidal flexing could generate plenty of heat, and then you might have a heat retentive atmosphere. Something like an atmosphere of the density of Titan's, but composed of a better greenhouse gas like carbon dioxide could certainly retain ample heat to be at water's triple point. Or of course it could shoot way over that and be a boiling oven like Venus. Ob
        • Wouldn't rock be land?

      • by 0racle (667029)
        That's one definition, another is -

        a lifeless and unpleasant place, esp. one consisting of or covered with a specified substance.

        A gas giant would be a place covered with specified substance, the gas. Being really pedantic now, but, take that.
        • The problem with a gas giant being that the whole thing is just transitional phases all the way down. There's no real point that one can declare the divide between lithosphere and atmosphere. It's turtles all the way down...

          Well, that's probably not true. The sub-giants like Neptune probably do have a surface of some sort, but I still don't buy that anything Saturn sized does.

    • Just outside Mexico City we have "Desierto de los Leones" (the lions' desert). It is a beautiful forest with a 400 year old convent in it.

      Why?

      Because it used to belong to the "de León" family, and it was far enough from the city that it became a perfect spiritual retirement place - A desert.

  • Wrong sci-fi planet? (Score:4, Interesting)

    by muecksteiner (102093) on Thursday September 15, 2011 @02:59PM (#37412686)

    Tatooine? Would that thing not be much more like Solaris [wikipedia.org] (the planet from the novel, not the OS), especially since it's density is that of water?

  • This is not the planet you're looking for. Move along.
  • by Hatta (162192) on Thursday September 15, 2011 @03:06PM (#37412768) Journal

    How do they calculate the density of these things? I get that they can detect the mass from the wobble of the star. How do they calculate the volume?

    • If it passes in front of the star (resp. one of them), then it can be determined how much light it blocks, and thus how large it is. I don't know if this applies here, though.

    • Re:Density? (Score:4, Informative)

      by cnettel (836611) on Thursday September 15, 2011 @04:02PM (#37413400)
      Kepler is observing the dimming of the light of the star (basically a part of the star disc is shadowed by the planet), when the planet transits directly in the line of sight between Kepler/Earth and the star. Hence, you can get a cross-section area, and by assuming the planet to be reasonably spherical (a fair assumption), you get the volume.
    • by Anonymous Coward

      We get the radius from the size of the star, the depth of the transit, and the semi-major axis. As you noted, we can get the mass by measuring the radial velocity (RV, Doppler-effect, or red shift) but for small planets, or large planets that are too far away from the star, this method doesn't work. For smaller planets in multi-planetary systems, we can measure the mass with transit timing variations (TTVs).

      We always get the radius with our transit photometry, but we can't always get the mass.

  • So, can anybody who understand this explain a little more.

    Is the orbit of the planet around both stars, making it like the orbit is eccentric around some center of mass common to the two stars?

    If it's that, then I think I get this. If it's anything beyond that, then I'm afraid my meager understanding of Kepplers laws falls apart.

    Most importantly, I love this part:

    Computer models show that in early 2018, the planetary transits across the larger star will disappear from Kepler' view until around 2042. The pa

    • by BergZ (1680594)
      I wonder if, in 30 years, we'll be talking about the discovery of exomoons.
      • That's not a moon. It's a space station!
      • by gstoddart (321705)

        I wonder if, in 30 years, we'll be talking about the discovery of exomoons.

        It wouldn't surprise me.

        I seem to recall in the early-mid 90's, some of my astronomy geek friends ... at the time detecting an exo-planet was an exciting prospect, gravitational lensing was something to hope for, and possibly that black holes hadn't been confirmed by observation but were widely accepted.

        Now exoplanets get discovered almost daily, we've confirmed through observation a bunch of black holes, and the universe continues t

        • I'm hoping they find signs of life somewhere. Alternatively, and less cool, that they find some reason why life is exceedingly rare.

          • by fisted (2295862)
            And who said life was exceedingly rare? Bear in mind that distances in our universe are exceedingly large.
            • I didn't. But I suppose it might be, and if that's the case, it would be good to know. Of course it would be more interesting to find a universe teeming with life. But whatever the truth is, it would be nice to know.

    • Kepler's laws only apply for the 1 planet + 1 star case. They're really just some consequences of the more general Newton's laws, applied to that simple scenario. If the two stars are much closer together than their distance from the planet, then Kepler's laws will probably be a fine approximation for the short term, just using the center of mass of the stars and their average mass. Eventually (or soon, if the stars aren't so close to each other), deviations from the simple elliptical orbit from Kepler'

    • Like with with multiple star systems, it pretty much has to be structured with the planet orbiting the binary stars much further then the stars orbit each other. Otherwise the system would not be stable.

      As for catching this star system in the short window of discoverability, on the one hand we could be a little lucky. But on the other hand there are probably many other systems out there that will be just entering a window of discoverability as this system exits it. So while the odds of us catching this par

    • by Maritz (1829006)
      About a minute into this [space.com] video, after all the fair-use Star Wars guff, there's an animation which will make it pretty clear to you. Put very simply, the smaller star goes around the bigger one (or rather they both revolve around their barycentre) and the planet describes a larger ellipse around both.
  • Fantastic, now all we need is a Placet (from Fredric Brown's Placet is a crazy place).
  • by peter303 (12292) on Thursday September 15, 2011 @03:46PM (#37413176)
    This planet had an orbit of 229 days. Kepler ideally desires three transits with two equal intervals to call it planet candidate. Kepler's observing duration is approaching the length where it could start detecting Earth-year planets now. The alternative experiments havent had enough sensitivity or duration to detect many Earth-year planets. Earth-year planets are likely to be in the habitable zone of G-type stars like the Sun.

    I thought the next big Kepler data dump would be September 23 2011, after many of the preliminary papers had been published.
    • This is when things will get really exciting. Even though I have become jaded about space travel over the last three decades, I am still excited about the prospect of being able to observe the galaxy. Once we've cataloged a few hundred planets very similar to our own, we will finally get some good statastical support around how common life is in the universe. The first step is obviously finding them. The next is analyzing them.

      If we can keep our society from falling apart and at least somewhat focused on sc

      • by instagib (879544)

        Also, after finding them, maybe SETI analysis could be focused on these areas for some time.

    • In this case they could cheat -- the two stars are orbitting each other fairly rapidly compared to the planets orbital period. They could see them alternately passing behind the planet. You would be able to see the phase shift in the light dip and from that you can deduce the orbital speed of the planet. Other clues from ground based observation would confirm the planet and allow its mass to be determined.
      • by peter303 (12292)
        Thats kind of why the Kepler Consortium suggests hundreds of "candidate" planets to be verfied by further study. Its estimated there may be alternative hypotheses explaining the light curves of 5% - 20% of the candidates.
  • I *might* be able to get excited about these sorts of discoveries if once.... just once... they found a rocky planet in the habitable zone of a star having between roughly .75g and 2g... and I'd especially get excited if they could determine that it has a breathable atmosphere and presence of water.

    We already know that we can detect gas giants around other stars. We've been doing it for years now and considering that binary stars are not that uncommon in our galaxy, it should come as no surprise that th

    • The larger gas giants are much easier to detect. And frankly with a UID as low as yours, I am surprised at your jaded view of exoplanet discovery. These are amazing times we live in and as Keppler's observation time goes up, it will detect planets further from its host star. By this time next year, we should start to get confirmations of planets with the same orbital period as our Earth. We may not find hundreds of them with the g's you are looking for in 2012, but statistically we will almost certainly fin

      • by oPless (63249)

        That's not a low UID, whippersnappers - get off my lawn! :^)

      • by mark-t (151149)

        I'm jaded because it's always the same thing. I can't count how many times it's been headline news that we've discovered yet another jupiter or larger sized gas giant moving around another star. The first few are somewhat impressive, because they establish that exoplanets actually do exist, and that we have the technology to detect some of them. After that, however, it's just the same old story, as far as I'm concerned.

        As for needing an orbital period that is exactly the as Earth, that isn't really

    • by Jeng (926980)

      I am not the most well versed in these topics, but I think it is surprising that they have detected a planet that orbits two stars.

      With a regular star system planets orbit a single point, extremely easy to figure out and therefor rather obvious, with a binary system how do the planets maintain their orbits with the gravity fluctuating as the stars orbit each other?

      • If the distance between stars is very much smaller than the distance of the planet from the stars then you can grossly approximate the system as two bodies. The mass of the two stars is placed at their centre of mass and the virtual star and planet then orbit their centre of mass. In the real world there will be perturbations from the dual stars and the other bodies in orbit that we have yet to see.

        The "obvious" nature of "regular" solar systems is far from simple. The barycentre [wikipedia.org] of a multi-planet solar

    • And not just one of them. Kepler has previously found 5 Earth-sized planets, in the habitable zones around their stars. And quite a few that are either Earth sized, or in the habitable zone, but not both. Including things like super-Earth sized ones in the habitable zone. :) http://www.nasa.gov/mission_pages/kepler/news/kepler_data_release.html [nasa.gov]

      The findings increase the number of planet candidates identified by Kepler to-date to 1,235. Of these, 68 are approximately Earth-size; 288 are super-Earth-size; 662 are Neptune-size; 165 are the size of Jupiter and 19 are larger than Jupiter. Of the 54 new planet candidates found in the habitable zone, five are near Earth-sized. The remaining 49 habitable zone candidates range from super-Earth size -- up to twice the size of Earth -- to larger than Jupiter. The findings are based on the results of observations conducted May 12 to Sept. 17, 2009 of more than 156,000 stars in Kepler’s field of view, which covers approximately 1/400 of the sky.

    • by Maritz (1829006)

      Why is this news?

      As far as I'm aware this is the first detection of a planet around a binary star. That alone makes it newsworthy even if not of interest to you. Not the most earth-shattering discovery ever but you have to at least note the first of a new batch.

  • by Anonymous Coward

    Looks like the human race is run.

  • It was my understanding that a planet made entirely of water [wikipedia.org] would not have enough mass to hold together, and would eventually disapate. Thus... wouldn't a planet made of something equal to the density of water also have trouble forming and maintaining coherence?
    • Re:saw this episode (Score:4, Interesting)

      by sunspot42 (455706) on Thursday September 15, 2011 @07:30PM (#37415416)

      Not sure if that's true or not, but if the planet had a dense, large, rocky core, it could hold on to a thick, massive atmosphere that's far less dense than liquid water, at least for much of its overall volume.

      Saturn is a good example in our own solar system - it has an overall density less than the density of water. If you had a big enough bathtub, you could float Saturn in it.

      It would leave a ring, though...

      • by Nyder (754090)

        Not sure if that's true or not, but if the planet had a dense, large, rocky core, it could hold on to a thick, massive atmosphere that's far less dense than liquid water, at least for much of its overall volume.

        Saturn is a good example in our own solar system - it has an overall density less than the density of water. If you had a big enough bathtub, you could float Saturn in it.

        It would leave a ring, though...

        The ring would still be better then what Uranus would leave...

    • um... nope. It's a little complicated, but it has to do with gravitational acceleration overcoming centripetal force to hold a body together. Same reason why the air on this planet, which is 1/1200 the density of liquid water, and 1/6000 the average density of the planet as a whole, doesn't just float off into space.

    • by Maritz (1829006)
      The average density might be that of water, i.e. when you add the gaseous layers to the solid rocky/metallic hydrogen core. The centre would still be very dense though.
  • Poincare would be so excited about this... Poincare and the three-body problem [wikipedia.org]
  • ...According to the BBC this morning Kepler-16 is only 20 LY away... of course, the BBC have it completely wrong; from the NASA initial press release:

    "The distance from Kepler-16 to Earth has not been measured, but is probably about 200 light years, judging from the apparent brightness of star A and theoretical models of stellar structure that give a crude estimate of its intrinsic luminosity."

    http://kepler.nasa.gov/Mission/discoveries/kepler16b/ [nasa.gov]

  • To calculate density they need both mass and volume. Mass is in principle calculated by the wobble of the source star, and assumes that you have an accurate measure of it's mass. However circling a binary, the wobble is that of the pair. The uncertainty of this is substantial.

    To calculate the volume, you need the diameter. This would require having a reasonable curve of light drop as the disk of the planet transits one of the stars. Is Kepler sensitive enough to pick out the effect of the shadow of a si

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