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Space Science

Two Planets Found Sharing One Orbit 175

dweezil-n0xad writes "Buried in the flood of data from the Kepler telescope is a planetary system unlike any seen before. Two of its apparent planets share the same orbit around their star. If the discovery is confirmed, it would bolster a theory that Earth once shared its orbit with a Mars-sized body that later crashed into it, resulting in the moon's formation."
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Two Planets Found Sharing One Orbit

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  • by edalytical ( 671270 ) on Sunday February 27, 2011 @02:58PM (#35332018)

    Quick, we need to redefine the meaning of "planet" yet again.

    • by painandgreed ( 692585 ) on Sunday February 27, 2011 @03:11PM (#35332104)

      Quick, we need to redefine the meaning of "planet" yet again.

      Possibly. As neither has "cleared its neighbourhood" [] of other masses in their neighborhood, they might be back to being called planetoids like Pluto. Both are to be considered "dwarf planets" until they collide and one becomes obviously dominant. There's already bits that cover things like this, but people are already arguing about the exampled in our own solar system. I be something like this would cause even more hub bub and another conference to further define the meaning of planet yet again.

      • Re: (Score:3, Funny)

        by Anonymous Coward

        There can only be one!

      • Moreover, at least outside exceptionally unlikely external forces, such a system is not stable, so the arrangement is temporary.

        • by Ambiguous Coward ( 205751 ) on Sunday February 27, 2011 @03:48PM (#35332360) Homepage

          Is an estimated minimum of 2 million more years not stable enough for you? With the two planets orbiting their star about every 10 earth days, that's over 70 million orbits, at minimum. What makes this an interesting find it that it IS unlikely, and it does NOT require external forces. Hence there's an article about it. :)

          As referenced by TFA: []

          Unless you're claiming that nothing is stable because y'know, entropy, man!

          • by rrohbeck ( 944847 ) on Sunday February 27, 2011 @04:52PM (#35332728)

            Nothing is stable. All orbits change chaotically in the long term.
            Corollary: There are no planets.

            • Other fun facts about the universe: The universe contains no population, no money, and no sex*.

              (*Actually there is quite a lot of this.)

              Corollary: sex is entropy.

              Corollary to the corollary: Slashdot is immune to entropy.

          • Even with the center of mass of each planet exactly in the L point of the other, then if the planet has a radius of 100km, parts of it will be 100kms away from the lagrange point --> inestability, whatever long it takes to become catastrophic.

            • The L4 and L5 points are actually stable equilibria, meaning that a body a very short distance away from the L-point will circle it. I would guess instability is more likely to come from effects like orbits being not perfectly planar and circular, and perturbations from other bodies in the system, rather than from being not quite on the L-point.
            • Even with the center of mass of each planet exactly in the L point of the other, then if the planet has a radius of 100km, parts of it will be 100kms away from the lagrange point --> inestability, whatever long it takes to become catastrophic.

              Actually, two earth sized masses on opposing sides of the sun will stabilise each other.

          • by sznupi ( 719324 )
            No reason to bring in stability, really. The orbit of Pluto - in an orbital resonance with Neptune, totally dominated by it (kinda similar deal with Lagrange points) - is quite stable...
      • Re: (Score:3, Interesting)

        by Jiro ( 131519 )

        That's not what "clearing the neighborhood" is defined as. "Clearing the neighborhood" contains an exemption for other objects under the first object's gravitational influence.

        If there are two objects in one orbit *and* the objects stay that way because of some complicated gravitational interaction, they are exempt from "clearing the neighborhood" and can still count as planets. In order to not count as planets you'd have to have two objects in the same orbit that just stay there because they happen to be

        • by sznupi ( 719324 )
          Almost the other way around?... If objects stay in ~one orbit (also) due to gravitational interaction between them, all except the dominating one don't count as planets.
        • Great, I foresee the birth of a new acronym, IANAAL - I am not an astronomical lawyer.

      • by Artifakt ( 700173 ) on Sunday February 27, 2011 @04:03PM (#35332460)

        The definition that makes Pluto a dwarf planet specifically apples only to our solar system, and the part that calls for clearing the orbit was inserted in case a Kuiper belt object actually bigger than Mercury was found later, so the IAU would not have to debate the subject again, not as a straight-forward rule based on any physical fact. Incidentally, the belt is named after Kuiper because he was a. the third major working astronomer to propose such as zone, and b. the first to be fundamentally wrong about its nature, as he claimed such a belt could not still exist.
              All the debate about how to define a an extra-solar planet will be driven by the very people who have totally screwed up any rational, scientific definitions when it comes to our own solar system. Expect a rule about how planets in the 'northern' part of the galaxy must have an eccentricity of less than 5.2%, and planets in the direction of Virgo are allowed 7.1%, but only if they move in square orbits on alternate St. Swithen'sdays.

      • Both are to be considered "dwarf planets"

        We prefer the term "little planets"... (you insensitive clod!)

      • by sznupi ( 719324 )
        Most importantly, the definition in question is only about the planets of Solar System. Somehow a lot of people manage to ignore it... (as well as how it is not set in stone; BTW, Ceres and Vesta were also "planets" for quite a time, and now hardly anybody remembers that... heck, Sun was, too)

        Also, those two extrasolar planets might very well be in a very strong gravitational interaction...
      • Imagine what the last close flybys would have been like as an observer. Tidal forces ripping up the ground, seeing something massive in the sky getting larger and larger, then whoosh, and fading away. Awesome.
        That'd probably get people's minds off of war and onto helping one another pretty quick.

    • Re: (Score:3, Insightful)

      by Anonymous Coward

      Quick, we need to redefine the meaning of "planet" yet again.

      Yeah... because it's been changed so many times, right? And for no good reason to boot, right?

      Truth is, the term "planet" has only really been defined once, a few years ago. before that, we had an intuitive idea of what a "planet" was; we included Pluto, as it appeared to be a comparatively unique object, but then we found that Pluto isn't unique and that there is no reason to believe that we wouldn't have millions (at least!) of planets, since there'll be that many objects that all share Pluto's characteri

      • Well, it pointless to start or maintain an argument because of this discover. what they are observing is the Death star beta production facility. It just took a long time for the light to eventually reach us. But then again, it all happened A long time ago in a galaxy far, far away.

    • as long as you don't define "planets" as "girls" and "orbit" as "cup".

    • by rossdee ( 243626 )

      Does the IAU have jurisdiction over extra-solar planets?
      It would be interesting to see them tell some advanced alien race 'sorry the world you live on is not a planet'

    • by Sabalon ( 1684 )

      In my best Jean Luc Picard: There....are...nine...planets!

  • by bunratty ( 545641 ) on Sunday February 27, 2011 @03:07PM (#35332082)
    This is more liberal lies. Bill O'Reilly told me that you can't explain that []!
  • I always assumed that Dantooine and Tatooine were twin planets like this. Or did that mean something else?

    • by ceoyoyo ( 59147 )

      I don't think they're even supposed to be in the same solar system.

      The classic twin planet arrangement is two planets orbiting each other though. Like the Earth and moon.

  • First? (Score:5, Informative)

    by jc42 ( 318812 ) on Sunday February 27, 2011 @03:21PM (#35332178) Homepage Journal

    It's not clear that this is anything new. A number of astronomers have suggested that we should treat the Earth/Luna and Pluto/Charon pairs as "double planets" sharing an orbit. And there's a pair of Saturn's moons that share an orbit. Of course, whether these are counterexamples depends on the picky, legalistic details of how you define the term "planet", which we've discussed to death here on /. already. Fun as such pseudo-arguments may be, the fact is that they're not terribly significant.

    Thus, for the Pluto/Charon pair, reclassifying Pluto as a "dwarf planet" make it especially an edge case, since it still includes the term "planet" in its classification. But they're both large, spherical bodies in a single orbit around the sun, while also orbiting each other.

    The Earth/Luna pair is a bit of a mathematical curiosity. One of the arguments supporting calling our moon a "planet" orbiting the sun is that its orbit is everywhere convex with respect to the sun. You'd expect a "moon" to have a much more wiggly orbit, parts of which are curved away from the sun, and this is true of the other objects in the solar system that we call moons. OTOH, the barycenter of the Earth/Luna pair is (slightly) inside the Earth, which can be used with some definitions to say that it's really a satellite of the Earth.

    And, of course, Saturn's two moons in a single orbit can be disqualified because they're obviously not "planets". They're not even big enough to be spheroidal, which is required by most definitions of a planet.

    But the fact remains that our solar system contains at least three example of paired bodies sharing an orbit about their primary, and periodically exchanging the lead position. The mechanics of such orbits have been long understood, and astrophysicists can tell you when such orbits are stable. So while this may be "news" in the sense that it's about such orbits around another star, it's hardly news in the astrophysics sense.

    What'll be interesting news is the discovery of three astronomical bodies in a "Scottish reel" orbit, which was proved possible several years ago, but to my knowledge hasn't actually been observed yet. Possible places to find them are in the asteroid belt, in Jupiter's "Trojan" asteroid clumps, and in the Kuiper Belt.

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

      by Ambiguous Coward ( 205751 ) on Sunday February 27, 2011 @03:55PM (#35332400) Homepage

      What'll be interesting news is the discovery of three astronomical bodies in a "Scottish reel" orbit, which was proved possible several years ago, but to my knowledge hasn't actually been observed yet. Possible places to find them are in the asteroid belt, in Jupiter's "Trojan" asteroid clumps, and in the Kuiper Belt.

      I googled "scottish reel orbit" and of course the first result was your own post. However, I did come across this, for those who are interested: []

    • I note that your post is the first I find to be on topic (and not +'Funny')

      TFA does not really say much. In addition, when I follow suggested links in its hosting webpage, "Read more:", as they put it, I am informed that I have not clearance enough, something that can be altered if I will part with my personal information and/or credit card number.

      And all that just to read insufficiently technical articles like this? Are the restricted articles more technical? I am puzzled- Is this a lifestyle tabloid?

    • These planets are at the stable lagrange points, not in orbit with each other.

      Which, by the way, is perfectly fine with regards to the IAU's definition. These planets have cleared their orbit nicely, and are gravitationally bound to each other.

    • Two planets orbiting the same star is arguably only possible with horseshoe orbits. If two objects are of similar size so on cannot say one orbits the other, it is described a a double body rather than primary and satellite.

      A Lagrangian moon will likely develop into a horseshoe orbit over time.

    • Saturn's two moons in a single orbit

      The moons distance from the Earth increases as angular momentum is transferred by tidal action. Makes me wonder if Earth and Luna will eventually co-orbit in that way. Doesn't sound very safe for us, but certainly spectacular.

    • by radtea ( 464814 )

      So while this may be "news" in the sense that it's about such orbits around another star, it's hardly news in the astrophysics sense.

      It's news in the sense that it provides more information about the dynamics of planetary formation, at least amongst hot Jupiters. While we know that the orbital dynamics of these bodies creates a stable situation, we did not know that they could actually form this way--the dynamics of early planetary formation is still much debated. There are a lot of things that happen, the initial conditions are not well-understood, the collision dynamics depend on the properties of the colliding bodies, etc. Ergo, th

  • by kenwd0elq ( 985465 ) <> on Sunday February 27, 2011 @03:50PM (#35332374)
    The problem with the planet detection methods used by the Kepler team is that it is all calculated based on occultations; the slight dimming of the star's light as a planet passes between that star and the Kepler satellite. This only works if the planet in question is 1) HUGE or 2) very close to the star or 3) the Earth just HAPPENS to be in the plane of the planet's orbit around the star. That's why we're discovering so many enormous planets with orbital periods in the range of only a few days. But the nice thing about the Kepler data seems to be that it's eliminating many of the "it could NEVER have happened that way!" explanations. With upwards of 500 billion stars in the Milky Way galaxy and we've looked only at a few thousand, it looks more and more that ANYTHING is possible when it comes to planetary formation.
    • The distance from the star doesn't matter much for occultation methods. The difference between the Earth orbital radius and the Jupiter orbital radius from tens or hundreds of light years is negligible. The place where the radius does make a difference is in the time to repeat an observation. To get the orbital period of a planet in an Earthlike orbit will take around a year, while a jupiterlike orbit would require 16 years. The "wobble" method that found the first planets is the one that is really sens

      • The distance between the planet and the star matters very much for the occultation method. That's because planets that are far away from their stars don't orbit very often. We are exceptionally unlikely to spot a planet that only orbits once a century with a telescope that has only been looking for a year.

      • by jgoemat ( 565882 )
        The distance does matter. At 1 AU the planet's orbit has to be within about 1/2 degree of the viewing angle for it to be seen. At .5 AU that doubles and at 2 AU it is cut in half.
        • by jgoemat ( 565882 )

          Imagine the sun (1.39E6 km) is as big as a square on a sheet of graph paper (1/4 inch). The Earth would be 100 squares away (about 2 1/4 sheets taped together the long way). The Earth is about 1/100th the size of the sun, so it would be much smaller than a period. What matters for Kepler is the angular size of the star. That is because on the scale with graph paper, Kepler would be 6,770 MILES away. Basically we could see any planets whose orbit takes them into that one square line of graph paper poin

    • by ceoyoyo ( 59147 )

      Kepler was specifically designed to find planets of an interesting size (like Earth, but it can certainly detect larger ones) in interesting orbits (like Earth's, but it can certainly detect ones closer in). We have other methods to identify giant planets further out.

  • by frisket ( 149522 ) <peter@[ ] ['sil' in gap]> on Sunday February 27, 2011 @03:59PM (#35332434) Homepage
    I googled "two planets one orbit" and was shocked by the sick porn it brought up.

    Oh, sorry, typed it wrong...

  • What two consenting planets do doesn't affect other planets' orbits.
  • by PolygamousRanchKid ( 1290638 ) on Sunday February 27, 2011 @04:14PM (#35332528)

    Captain Kirk beams down there, takes his shirt off, and gets the chick. Wait, two planets? Wait a second, we'll have to fly in a second, evil, Captain Kirk from a parallel universe. And how about a Spock with a beard? Does Ryanair fly there? Can we get a discount rate for two? Well, knowing them, they'll charge an extra exorbitant fee for Spock's beard. And the plane won't even land in the parallel universe, but in another universe, "Really close by!"

  • Kepler has identified 1200 planet candidates in its first four months of data operations, 19 which had been confirmed as of last week. Graphing the planets by various attributes starts to give a respectable idea of size, year, star-type, density and perhaps other attributes in solar systems. Kepler could find ten times as many planets as these in its 3.5 year nominal, 10-year extended, mission.
  • filing a few billion John Doe lawsuits against "Any and all current or potential occupants of said potentially planetary bodies..." for sharing an orbit.

    Sharing is bad

  • Planet...or space station?


  • In theory, matter in a disc of material around a newborn star could coalesce into so-called "co-orbiting" planets, but no one had spotted evidence of this before.

    Off course not. Even star turtles like a little privacy.

  • Doppelgänger [] (Journey To The Far Side Of The Sun).

  • No, not belts. You know. Like, rings, dude. You know that's what Kepler's *really* for, right?

%DCL-MEM-BAD, bad memory VMS-F-PDGERS, pudding between the ears