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NASA Space Science

NASA's Kepler Discovers Multiple Planets Orbiting a Pair of Stars 121

DevotedSkeptic writes "Kepler has continued its stellar (pun intended) discovery spree, this time locating multiple planets orbiting a binary star system. This is especially interesting because it proves that more than one planet can form under the stresses of a binary star system. The system is known as a circumbinary planetary system, a mechanism where a planet orbits two stars. Prior to this discovery, having multiple planets in a circumbinary system was unproven. Named Kepler-47, the system consists of a pair of orbiting stars that eclipse each other every 7.5 days. One star is similar in size to our Sol, however it only provides approximately 84% of Sol's light, the other is smaller, measuring one third of the size of Sol and emits less than 1% of Sol's light. Kepler-47b is the closer planet to its two suns, orbiting in 50 Earth days. Kepler-47c is further out and orbits every 303 days, within the Goldilocks zone. 'Unlike our sun, many stars are part of multiple-star systems where two or more stars orbit one another. The question always has been — do they have planets and planetary systems? This Kepler discovery proves that they do,' said William Borucki, Kepler mission principal investigator at NASA's Ames Research Center in Moffett Field, Calif. 'In our search for habitable planets, we have found more opportunities for life to exist.'"
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NASA's Kepler Discovers Multiple Planets Orbiting a Pair of Stars

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  • well ... (Score:5, Funny)

    by therealkevinkretz ( 1585825 ) * on Wednesday August 29, 2012 @09:56AM (#41167001)

    I just wanted to have the first Tattoine reference

    • You win for now...nerd
      • Re:well ... (Score:5, Interesting)

        by mcgrew ( 92797 ) * on Wednesday August 29, 2012 @10:27AM (#41167489) Homepage Journal

        You win for now...nerd

        That's a compliment. Of course, even the mainstream news sites are saying this is "like Tatooine". Of course it isn't Tatooine itself, since Tatooine is long ago in a galaxy far, far away. This is in our own galaxy only 5000 light years away; the Mayans and Egyptians were still building pyramids when the light we're measuring left those stars.

        What's exciting about this isn't that it's like Tatooine (or a lot of other science fiction star systems) but that it exists at all. It was formerly thought impossible for a binary star system to have planets. TFA I read earlier this morning said one of them was the size of Neptune and in the goldilocks zone, and wondered if the Neptune-sized planet had moons, and how strange it would be to be standing on one of those moons.

        It seems likely that the outer, Neptune sized planet would have moons, since all the gas giants in our system do. Imagine, two suns, a HUGE GIANT moon (the planet) taking half the sky, and other moons visible as well.

        Too bad it's impossible to get 5k light years away, I'd love to see the place.

        • Imagine, two suns, a HUGE GIANT moon (the planet) taking half the sky, and other moons visible as well.

          Several classic fanatasy & sci-fi novel covers come to mind with your description.

        • Re:well ... (Score:4, Funny)

          by Quiet_Desperation ( 858215 ) on Wednesday August 29, 2012 @11:06AM (#41168043)

          Of course it isn't Tatooine itself

          Yeah, we figured that bit out.

        • Re: (Score:2, Interesting)

          by wganz ( 113345 )

          You win for now...nerd

          Too bad it's impossible to get 5k light years away, I'd love to see the place.

          Always remember that The Royal Astronomical Society definitively proved that it was impossible for a passenger train to travel >= 32 mph lest all the oxygen would be sucked out of the rail car. It has to be true since it was proved with science!

          Once the branch of mathematics is discovered that will solve such limits problems as division by zero and the speed of light; we could very well make that trip in a matter of minutes.

          Yet another reason that we need to support pure basic fundamental research. (repe

          • >

            Once the branch of mathematics is discovered that will solve such limits problems as division by zero and the speed of light; we could very well make that trip in a matter of minutes.

            I keep telling people those problems are one in the same but no one believes me. We need to divide by zero to travel faster than the speed of light!

          • by mcgrew ( 92797 ) *

            I have an answer for the divide by zero problem, but mathematicians say I'm wrong.

            When a divisor is less than 1 and greater than zero, the smaller the divisor the larger the answer. De one by one and you get one.
            1 / .5 =2
            1 / .05 = 20
            1 / .005 = 200
            1 / .0005 = 2000 ...
            1 / 0 = infinity

            But again, people who know what they're talking about tell me I'm full of shit.

        • Re:well ... (Score:4, Interesting)

          by tnk1 ( 899206 ) on Wednesday August 29, 2012 @01:25PM (#41169869)

          I know they said that the planets formed around the system, but I was wondering if they could also have been later captures of planets expelled from other systems by gravitational interaction. In other words, planets can certainly orbit multi-star systems, but they may still be unable to form under those conditions. My reading of the article doesn't seem to exclude that as a possibility although they appear to be very clear on the fact they think the planets were formed in that system.

          Of course, you'd have to presume that it is possible for multiple objects to form in a system that is already multi-stellar, but the idea was never that they couldn't form, but that extreme gravitational conditions would eject extra matter as soon as the stellar objects formed, leaving only the most massive objects to be stable over long periods of time.

        • It was formerly thought impossible for a binary star system to have planets.

          How is that much different than a system with a large gas giant?

        • Re: (Score:2, Interesting)

          by Anonymous Coward

          It was formerly thought impossible for a binary star system to have planets.

          It wasn't thought that to be impossible for binary systems to have planets, only thought that it is impossible for some situations. Orbits can quickly become unstable when you have a planet trying to navigate its way closely around two stars. However, orbits are just fine if the two stars are much closer together than the planet's orbit in which case the two stars almost act like a single central body (e.g. like this discovery), or if one of the stars is very far away, at which point the second start is l

        • by jc42 ( 318812 )

          It was formerly thought impossible for a binary star system to have planets.

          Well, on seeing the diagram of the system, my immediate thought was that with the two star s so close together, it doesn't seem likely that any planets in the "habitable" zone would be able to tell that there are two suns. Even the closer-in planet would just think that it's orbiting a single big mass down at the center. Could a pair of stars so close together (and one of them so small) actually have any effects that are measurably different from a single star with the sum of their masses?

          Of course, Ne

        • by mcvos ( 645701 )

          From what I understand, planets around binary stars weren't considered impossible, but for their orbit to be stable, they had to orbit so far away from the binary that they'd always be far outside the Goldilocks zone. But this, with a period of 303 days inside the Goldilocks zone, that's really amazing. Too bad they're gas giants.

          • by mcgrew ( 92797 ) *

            Too bad they're gas giants.

            They could have habitable moons; all our gas giants have satellites. Imagine standing on an earth-sized moon orbiting a gas giant orbiting a binary star!

            • by mcvos ( 645701 )

              True, that would be awesome. But if I understand correctly, this one is Neptune sized. Does Neptune have large moons? And are even the large Jovian moons big enough to hold on to a breathable atmosphere?

              • by mcgrew ( 92797 ) *

                Well, Triton is similar in mass and size to Pluto and has a tenuous atmosphere. Jupiter's Ganymede's atmosphere isn't well understood but is thought to be thin. But looking at the size of our own moon's size in comparison to Earth's size, and Earth compared to Neptune, I don't see any reason why a Neptune-sized planet couldn't have an Earth-sized moon.

                • by mcvos ( 645701 )

                  I'm not so sure our moon's origin is the same as those of other moons in the solar system. Our moon was apparently born out of a collision with another planet, which would explain why it's so big. But I hope you're right.

    • Fox News beat you to it— they titled this story "Alien planets found with twin suns like Luke Skywalker's homeworld []."
      • And the BBC site article of about 8 hours ago used the headline 'Tatooine-like' double-star systems can host planets [].
    • Yeah, well I have the first Twinsen reference.
    • by mcspoo ( 933106 )
      No one has mentioned 2010 and Jupiter turning into a sun, so I'll throw that one out there too.
  • Never say (Score:5, Insightful)

    by geekoid ( 135745 ) <> on Wednesday August 29, 2012 @10:02AM (#41167095) Homepage Journal

    "Pun Intended". Either people get it, or they don't. It's not clever if you have to point it out.

    • by Trepidity ( 597 )

      Similarly, "no pun intended" has only quite limited uses, since by its nature it calls attention to the pun.

      • by Anonymous Coward
        Yet it can be entertaining to append "no pun intended" to something that does not contain anything that could be a pun. Some people will spend hours wondering where that pun is.
      • Similarly, "no pun intended" has only quite limited uses, since by its nature it calls attention to the pun.

        Sometimes the most accurate way to describe something sounds like a joke. You're not saying it isn't funny, you're saying it's accurate.

      • Yeah, I've always questioned that phrase, since while the pun might not have been intentional, your decision to call attention to it rather than changing your wording to avoid the pun certainly was.

    • Never say puns, period. They aren't funny and neither are you. (not you geekoid, punsters)

    • You forgot to include your "~" at the end of your comment.

    • by Nyder ( 754090 )

      "Pun Intended". Either people get it, or they don't. It's not clever if you have to point it out.

      Thanks Pun Intended Nazi.

  • "this time locating a multiple planets orbiting a Binary Stars"

  • by Anonymous Coward

    Finds like this and the expansion of human knowledge continues to amaze me. Every. Single. Time.

    More funding for science!

  • From TFA:
    "The outer planet, Kepler-47c, orbits its host pair every 303 days, placing it in the so-called "habitable zone," the region in a planetary system where liquid water might exist on the surface of a planet. While not a world hospitable for life, Kepler-47c is thought to be a gaseous giant slightly larger than Neptune, where an atmosphere of thick bright water-vapor clouds might exist."

    Wouldn't this cause some bizarre tidal forces too? IANAP, but seems that the relative masses of these bodies might

    • Re:Liquid water? (Score:5, Interesting)

      by dpilot ( 134227 ) on Wednesday August 29, 2012 @10:33AM (#41167567) Homepage Journal

      There are those who think that tidal forces are part of the reason complex and even intelligent life arose on Earth, and that without our highly-unlikely over-sized moon, we wouldn't be here to talk about it. We have temperature variations on the order of 20% (absolute) and call it "seasonal".

      With that thought in mind, I've wondered if looking for a small rocky planet in the Goldilocks zone is the best way to look for life. I've wondered if a small rocky moon orbiting a gas giant might be a more likely place to find complex life. On the other hand it was disappointing to hear that there would never be colonies on Ganymede because of radiation near Jupiter, though I know nothing of the intensity, or whether a planetary magnetic field and atmosphere would shield it, etc.

    • by mr1911 ( 1942298 )

      IANAP, but seems that the relative masses of these bodies might lead to a excentric orbit that would push Kepler-47c into and out of the habitable zone.

      Or you could RTFA. Actually you don't even have to RTFA since there is a graphic clearly showing one of the planets maintains an orbit well inside the habitable zone.

      • Sorry, was text only from work, I do see the graphic your
        referencing. And low and behold it seems to vary pretty much fromVenus to Mars, so I feel vindicated all the same.

    • Unless I'm much mistaken, Earth's tides are mostly a result of the Earth-Moon gravitational interactions, not Earth-Sun. Obviously there will be some effects, but not major ones.

      If there were liquid water on a moon orbiting a giant planet orbiting two stars (one of which is tiny), I'd assume the gravitational pull of the planet would more or less completely overwhelm the gravity from the two stars.

    • At those distances tides would be extremely minor. The Sun does have tidal effects on the Earth, but they are quite minor. The tidal effects of a binary star would be about the same (they would vary according to the orbit more than it does on Earth, but not enough to be an issue).

      The much bigger problem would be the fact that the planet would vary in distance from a star according to it's orbit, much more so than the Earth does, even if the orbit isn't eccentric, simply because the suns are orbiting each o

  • a [sic] multiple planets orbiting a [sic] B[sic]inary S[sic]tars.

    Really? I'll give the submitter the benefit of the doubt because English may not be their first language, but isn't this what we have editors for?

    Kepler-47b is closer to its two suns orbiting in 50 Earth days.

    Err, closer than what? Kepler-47a, I'm going to assume. No, I'm not going to RTFA. We are Slashdotters!

    • Yes that was very poor proofreading on my part, and the editor missed it as well. Things happen we all make mistakes however I was not mistaken on the identity of the the two planets Kepler-47a and Kepler-47b. []
      • Erm, b and c - not sure why there isn't an a. And I see it now - when I read

        Kepler-47b is closer to its two suns

        It wasn't immediately clear that it simply meant "closer of the two planets" - I thought some other piece of text, perhaps referring to 47a, had been cut out.

  • Ok, this writer clearly isn't a scientist. They say that 84% of the light of the system comes from the brighter star, and 1% from the dimmer. That's all the light, right?...84 + 1 != 100 If you read the original NASA article, they said the brighter star is 84% as bright as our Sun and the dimmer one 1% as bright as our Sun. *sigh*
    • It could have been phrased better, I admit, but the way it's phrased is pretty common. I also don't see how you possibly got '84% of the system's light output' in a section where they were clearly comparing it to our Sun. The use of the word 'however' is a pretty clear indicator that they're continuing the current comparison, not jumping off to something completely different.

      If I said to you 'my car is just as big as John's but only needs half the gas' would you think I mean half of the entire world's suppl

    • 84% of Sol's light, and likewise 1%. Combined, they still have 15% less light than Sol at the same distance.

    • by mark-t ( 151149 )
      You've misread it. Permit me to quote...

      One star is similar in size to our Sol however it only provides approximately 84% of the light, the other is smaller measuring one third of the size of our Sol and emits less than 1% the light.

      This isn't saying that one star provides 84% of the light in the system, it's saying that one star provides 84% of the light as our own sun. The other 1%. Obviously, the total amount of light is only 85% of our own sun.

      Nowhere do the percentages read as being relative t

  • by Rich0 ( 548339 ) on Wednesday August 29, 2012 @10:47AM (#41167751) Homepage

    Seems like a bit of a degenerate case to me. The two stars orbit each other each 7.5 days. I wouldn't be surprised if their atmospheres practically overlapped with that kind of distance. The planets essentially would be orbiting the center of mass of the two stars as a result. I wonder if they'd eventually merge, and what would happen then.

    I think that this situation is likely to be a lot more stable than having another star orbiting further out than the planets.

    • Re:7.5 days? (Score:5, Informative)

      by creelbm ( 2718189 ) on Wednesday August 29, 2012 @10:58AM (#41167939)
      Using Kepler's 3rd Law, a^3 = p^2, with a = average orbital separation in AU (Earth to Sun distance), and p the orbital period in years: a = (7/365)^(2/3) = 0.07 AU. 1 solar radius is about 0.0046 AU. Go to the original paper here: [] and you see the larger star is about the size of our Sun, the smaller star 1/3 the size. 0.07 AU/0.0046(AU per radius) = 15.2 Solar radius separation between the stars. So, close but not close to overlapping.
    • This is the simplest case, but its conceivable to have stability with a star orbiting farther out as well. In the case like this one, you could maintain accretion disk formation with much larger star separations as long as the separations weren't so large that they cleared all the material, or introduced significant eddies / disturbances in the disk. To a point, simulations have actually shown that a little bit of this stirring helps. Solar orbit distances are also often vast compared to planetary orbit
    • by Hentes ( 2461350 )

      Not really, planets [] orbiting one member [] of a multiple-star system are fairly common.

  • With a period of just 7 days, you have to wonder how fast the little bugger is moving. Could be a significant fraction of C...?

    • Re:Velocity? (Score:5, Informative)

      by creelbm ( 2718189 ) on Wednesday August 29, 2012 @11:05AM (#41168037)
      Looks like I'm fielding the astronomy numbers today. Ok, look at my response to the 7.5 days question. The stars are separated by 0.07 AU (distance Earth to Sun in our system). The center of gravity's closer to the more massive star, so let's say the center of mass is 1/4(0.07 AU) from the larger star. Assume a circular orbit (not a bad assumption). Then, v = 1/4*2PiR/(t) = 2*Pi*(1/4*0.07AU*1.15x10^11 m/AU)/4*(7 days*24*60*60) = 390,000 m/s = 3.9*10^5 m/s, a tiny fraction of c, which is 3*10^8 m/s. Fast, not that fast. 0.001 c
      • true, not a significant fraction of c.
        but take into account that relativistic effects are noticeable (on the scale of 100 years) for Mercury, which orbits between 0.3 and 0.4 AU from the Sun. also take into account that these are heavy objects, and we might find that a satellite moving between these two stars could be used to study relativistic effects. I'm not gonna try to compute anything, but relativistic effects are noticeable for GPS satellites, so what I said must make sense.

        obviously, the interesting

  • binary star is not a proper noun unless you're talking about the old school hip hop group []
    • "old school" huh? You 7-digit posters...

      Love the group btw

      • =) i say old school cuz they came out in something like '97 or '98 and it's already almost '13. but you're right, old school is more like '91 and before. organized konfusion sounds a lot like binary star too, they're awesome.
  • ... on Kleper-47c? 47c maybe is a gas giant, but may have many rocky or ocean moons.
  • by zerosomething ( 1353609 ) on Wednesday August 29, 2012 @11:24AM (#41168323) Homepage
    We only have one known planet where life has occurred and is sustained. There is no prof, yet, that life ever occurred on Mars or any other planet in our system. At this point with what we actually know about life I think the "habitable zone" graphics on some of these press releases are overly optimistic. I hope we can find evidence of life on Mars so we can actually expand our "known" habitable zone.
    • by Hentes ( 2461350 )

      The point of the habitable zone is not that it proves that life exists on the planetas (Mars and Venus are also in the zone). It's quite the opposite, if a planet isn't within the zone we can exclude the possibility of life. Still, it's pointless to check for that when we are talking about a gas giant.

    • by tnk1 ( 899206 )

      I don't think the habitable zone requires Mars to have had life, although that would certainly confirm it.

      A lot of the reason that Mars (or Venus for that matter) does not currently harbor life appears to be due to things like atmospheric volume, as well as the ability of the planet to undergo plate tectonics as opposed to complete crustal inversion to release core heat. That and core/mantle makeup which determines if there is a magnetic dynamo which can create a magnetic field.

      You could have an otherwise

  • by catmistake ( 814204 ) on Wednesday August 29, 2012 @11:49AM (#41168637) Journal

    Unlike our sun, many stars are part of multiple-star systems

    IIRC from my star fighter days, most stars, the vast majority of them, are part of multiple-star systems. Sol is very weird and a rare counter-example in that regard.

    • According to this [], most stars (2/3rds in the Milky Way) are actually single. Assuming other galaxies are similar in that respect to ours (which is safe, logical, and pretty much required given the difficulty involved in observing stars in other galaxies), most are probably single everywhere.

      • by Anonymous Coward

        New science... it's not most stars, just that most bright stars that have stellar companions. Most dim stars are solo. Sol is still an odd one... a bright solo star.

  • Time to start looking for Smoke Rings []
  • >Prior to this discovery, having multiple planets in a circumbinary system was unproven
    Ok when movies like Star Wars come out with visible advanced knowledge that such things do exist, either it leads me to believe that many humans on this earth are really aliens mascarading as us and enjoying lives of financial freedom due to the use of knowledge that no one else would know... George....I know u r really an alien and actually just brought your story from another galaxy where you came from as a regular s

    • by tnk1 ( 899206 )

      It was never far-fetched or advanced to accept planets around a multiple star system. You could look at multi-moon systems around planets and just assume you could do that with stars too. It was merely a case in which the director's ignorance of current scientific thought was an advantage when the status quo was overturned.

      It's just like those people who believe that it is only "a matter of time" before we break the speed of light. Currently, there's no way to even approach light speed in a spacecraft ma

  • A sparse multiple system with planets orbiting at least two of the stars. That would make for some good scifi for it would allow practical interstellar travel between the planets.

  • Sounds like the Seefra system - I wonder if one of the suns is artificial?
  • Wake me up when they find habitable planets with six suns [].

  • Instead of writing "Sol" all the time, how about . . . the sun? Do we really need to be so ashamed of the Germanic heritage of the English language that we won't even call the sun "the sun" in a scientific context? I can understand using the word "solar," since we have no other common adjectival version of the word "sun" . . . but "Sol"?

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