Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?
Space Science

A Planet That Orbits Its Star the Wrong Way 257

Smivs writes "BBC News is reporting that astronomers have discovered the first planet that orbits in the opposite direction to the spin of its star. Planets form out of the same swirling gas cloud that creates a star, so they are expected to orbit in the same direction that the star rotates. The new planet is thought to have been flung into its 'retrograde' orbit by a close encounter with either another planet or with a passing star. The work has been submitted to the Astrophysical Journal for publication. Co-author Coel Hellier, from Keele University in Staffordshire, UK, said planets with retrograde orbits were thought to be rare. 'With everything [in the star system] swirling around the same way and the star spinning the same way, you have to do quite a lot to it to make it go in the opposite direction.' Professor Hellier said a near-collision was probably responsible for this planet's unusual orbit. 'If you have a near-collision, then you'll have a large gravitational slingshot from that interaction,' he explained. 'This is the likeliest explanation. But it might be possible you can do it by gradually perturbing the orbit through the influence of a second planet. So far, we haven't found any evidence of a second planet there.'"
This discussion has been archived. No new comments can be posted.

A Planet That Orbits Its Star the Wrong Way

Comments Filter:
  • by Anonymous Coward on Thursday August 13, 2009 @08:02PM (#29060051)

    You know, he has this thing about spinning planets the other way around...

  • by flaming error ( 1041742 ) on Thursday August 13, 2009 @08:03PM (#29060057) Journal

    Maybe the sun reversed its spin.

    • by eebra82 ( 907996 ) on Thursday August 13, 2009 @08:14PM (#29060137) Homepage
      They don't blame the planet, they blame a planet or a big body that passed its orbit.

      The star is not a likely cause for its abnormal rotation, although that would make it far more interesting.
      • by srothroc ( 733160 ) on Thursday August 13, 2009 @08:17PM (#29060173) Homepage
        The way I read it is that the GP is not saying that the star CAUSED the retrograde orbit -- he's asking why everyone's asking how the PLANET's orbit changed rather than asking why the star's spin changed. For a car analogy.. it's like asking why the car pissed off the dog that's chasing it rather than why the dog is chasing the car.
        • How does this happen? TFA is an article about a planet that has retrograde motion and someone manages to whip out a car analogy. And it even sort of makes sense. Well played, sir. Well played.

    • I think it would be orders of magnitude harder to reverse the spin of a large star than it would be to reverse the orbit of a planet, but I don't really know anything about celestial mechanics.
      • Sorry, this is only semi-related to your post, but I'd rather not look for a better place to post this: I don't know why the summary even proposes the "gradually by another planet" explanation of reversing the orbit of a planet. If it's so gradual, eventually it won't be orbiting at all (before it starts to go the other way), and it'll fall straight into the star... right?
        • by ChromaticDragon ( 1034458 ) on Thursday August 13, 2009 @10:28PM (#29061171)

          Depends on what gets perturbed, I guess.

          Try not to think just in two dimensions. Imagine the orbit as a very large ring. Instead of thinking of it shrinking, imagine the ring pivoting out of the usual orbital plane. Imagine this ring slowly rotating. Eventually, it'll settle back to the plane yet the planet will be orbiting backwards relative the the original and the star's rotation.

          • Re: (Score:3, Insightful)

            Wow, what a free-your-mind moment I had reading that.

            A similar scenario could be that the sun somehow turned upside down. Maybe the sun spins in two dimensions: around the expected axis perpendicular to the orbital plane, and also an axis parallel to the orbital plane.

      • More likely the planet was captured in a drive-by of sorts from another star and didn't have enough velocity to escape the gravity of the local sun during the slingshot pass. It just happened to pass the sun on the wrong side and the slingshot effect grabbed it and forced it into the wrong direction.

        I'm curious if the gravity well of the new local sun will eventually slow it's backwards orbit down and reverse it at some point or if it will end up like our moon in a locked orbit that never changes the sid
    • by davester666 ( 731373 ) on Thursday August 13, 2009 @08:30PM (#29060275) Journal

      Sun's don't go both ways. They're all either straight or gay.

    • by jmv ( 93421 )

      I wonder if that would be possible if the planet's star collided with a second star, which could have inverted the original momentum.

      • Re: (Score:3, Insightful)

        by Fluffeh ( 1273756 )
        What if the sun was turned on it's axis 180 degrees (turning it upside down). It would appear that the planet is therefore orbiting in the wrong direction.

        Could this perhaps been the effect of another star passing nearby and changing the axis of the star rather than flipping the orbit of the planet?
    • I would suspect (without bothering with any math) that the energy required to reverse the spin on the star would be much larger than to set the planet orbiting backwards.

      Hence the planet changing orbits is more likely.

      • by bronney ( 638318 )

        How about the energy required for the big bang versus no big bang? Which is more likely then?

    • by Yvanhoe ( 564877 )
      Or maybe the planet was captured by the Sun without being created there. Is that possible ? A panet ejected by a supernovae for instance ?
    • Conservation of angular momentum.

  • by randy of the redwood ( 1565519 ) on Thursday August 13, 2009 @08:04PM (#29060071)
    Doesn't everything rotate backwards if its from down under?
  • which left? (Score:2, Funny)

    by lsdi ( 1585395 )
  • Poor Planet (Score:5, Funny)

    by russlar ( 1122455 ) on Thursday August 13, 2009 @08:12PM (#29060125)
    All the other planets keep pointing and saying "You're doing it wrong!"
  • by Anonymous Coward

    but wouldn't this type of retrograde orbit be possible if the planet had gone "rouge" from it's original system and was then captured in the gravity well of its current parent star?

  • by msauve ( 701917 ) on Thursday August 13, 2009 @08:34PM (#29060309)
    "...you can do it by gradually perturbing the orbit through the influence of a second planet" claims the article.

    But, if it were to happen slowly, doesn't that imply that at some point it has a minimal orbital speed (if that's the correct term), and would fall right in? Seems to me that if it reversed direction, it must have been a relatively quick event. Unless, perhaps, the planet ends up being sent away from the star, and is then recaptured in a retrograde orbit. But, that's still not a "gradual perturbation."
    • by DaveAtFraud ( 460127 ) on Thursday August 13, 2009 @08:39PM (#29060363) Homepage Journal

      Er, no. The idea is that the inclination of the orbit keeps getting larger until the planet is orbiting "backwards." The planet doesn't stop and reverse its orbit.


      • that this is the first planet found with such an orbit. Would it not require a lengthy sequence of "just right" nudges to produce that outcome? Statistically, wouldn't the second planet be just as likely to pull the first back toward an equatorial orbit on each encounter? Are the orbital mechanics such that retrograde planets coexisting with prograde planets is more stable than, say, having planets end up in polar or high inclination orbits?

        Finally, the article explains how they can tell which direction th
        • Re: (Score:2, Insightful)

          I would think that one side of the star would be blueshifted, the other side redshifted ever so slightly.
          I also wonder if the planet suffers more collisions than it would otherwise.
      • by Anonymous Coward on Thursday August 13, 2009 @09:09PM (#29060611)

        To put this in analogy form:
        Picture someone making a pizza, when they spin it and throw it up in the air it lands spinning the same way. But if the pizza flips over in mid-air the rotation will be reversed when it lands but it didn't have to stop and reverse direction to do it.

        Oh, and somehow a car is involved.

    • by FooAtWFU ( 699187 ) on Thursday August 13, 2009 @08:40PM (#29060385) Homepage
      No. Here's the ASCII art.





    • by gehrehmee ( 16338 ) on Thursday August 13, 2009 @08:42PM (#29060405) Homepage

      In this case, it's really the angle of the orbit that would be perturbed. Eventually it would be orbiting above and below the north and south poles of the star, and then perturbed even further until it was rotating the wrong direction. In that sense, it's actually orbiting in the correct direction, just offset 180degrees.

      A similar explanation is often used to describe the fact that Uranus rotates clockwise, whereas all the other planets in our solar system rotate counter-clockwise. (Note, rotation != revolution. Rotation == spin, revolution = orbit). Effectively, virtually all the angular momentum of any given solar system is in the same direction. The odd object's motion may be twisted into appearing the wrong way by some dramatic celestial event.

    • Re: (Score:2, Funny)

      "...you can do it by gradually perturbing the orbit through the influence of a second planet" claims the article.

      Even if I had a second planet, I could probably figure out waaay more productive things to do with it than piss off the orbit of my first planet. That kind of puerile use of a natural resource on such a massive scale would probably only serve to perpetuate the vicious cycle of interplanetary-domestic-violence that has ruined so many healthy, loving solar systems. On behalf of Solar Family Therapists everywhere I'm ashamed that this Prof. Hellier condones such a flagrant misuse of such a precious resource.

    • Re: (Score:3, Informative)

      But, if it were to happen slowly, doesn't that imply that at some point it has a minimal orbital speed (if that's the correct term), and would fall right in?

      In a 2 dimensional universe, yes. In this one? No. It implies that the plane of the orbit rotates through 180 degrees much like (here it comes everyone) a car tyre when you do a U-turn. It keeps rotating but eventually ends up going the other way.

    • by Minwee ( 522556 )

      If this were a movie then Mr. Spock would say that your pattern indicates two dimensional thinking.

      Then, Captain Kirk would pound you in the butt in a totally heterosexual way with photon torpedoes.

      I think it's a good thing that we aren't in a movie.

  • Oooh ooh, it's called a DoppelgÃnger [wikipedia.org]! And there are people there just like us.
  • IIRC, our solar system was not original part of the Milky Way, but was from some smaller dwarf galaxy that got absorbed into it. There could have been a parallel here which might be easier to explain it.

  • Opposite spin (Score:5, Informative)

    by StartCom ( 1018308 ) on Thursday August 13, 2009 @08:55PM (#29060509) Homepage
    Well, in our solar system at least one planet is spinning the other way around: http://wiki.answers.com/Q/Why_does_venus_spin_the_other_way [answers.com] It's not quite the same like orbiting into the opposite direction, but the Venus apparently received a nudge or two as well in order to spin the other way around. Such accidents appear to happen.
  • by LordNimon ( 85072 ) on Thursday August 13, 2009 @08:57PM (#29060521)
    planets with retrograde orbits were thought to be rare

    Since this is the only one that's been found, I'd say that planets with retrograde orbits are still thought to be rare.
  • by PPH ( 736903 ) on Thursday August 13, 2009 @09:17PM (#29060665)
    Why does everything different have to be labeled 'wrong'?
  • Axial Tilt? (Score:3, Insightful)

    by Ark42 ( 522144 ) <slashdot&morpheussoftware,net> on Thursday August 13, 2009 @09:18PM (#29060671) Homepage
    Instead of spinning the "wrong" way, couldn't the planet just have a 180 degree axial tilt, sort of like Uranus has a pretty steep 97 degree tilt. At 180 degrees, it would be right sight up by a different perspective, but spinning the opposite direction as the star.
  • the planet wasn't spawned by that particular star? Maybe it's a capture. I would imagine that a capture doesn't have to go with the spin, or against the spin - it could orbit from pole to pole.

    Phhhht. I should have been an astronomer, huh?

    • Maybe if I could think of a way for a fully-formed planet to escape its system intact. It'd take a damn heavy body and an incredibly unlikely interaction.

      (And by the way, I think if a planet's axis made a radical change, the poles would change as well. But I'm not sure.)
      • But - what if the planet weren't intact yet, when the capture was made? Two stars passing close together, one or both capture some of the matter swirling around the other star. It's still hot and gaseous, but orbiting in the opposite direction. Only later does it cool, coalesce, and eventually form a planet. I suppose it's more likely that an older star stole the matter from a young star - if they were both young stars, the captured matter would have been more likely to have met resistance, and eventual

  • by jameskojiro ( 705701 ) on Thursday August 13, 2009 @09:46PM (#29060897) Journal

    This evokes that scene from "Trains Planes and Automobiles"......

    • by JSBiff ( 87824 )

      Thanks for the laugh. That is one of my all-time favorite comedy scenes. I laugh every time I think of it.

  • But it might be possible you can do it by gradually perturbing the orbit through the influence of a second planet. So far, we haven't found any evidence of a second planet there.

    Wouldn't a slowly perturbed planet fall into it's star once it reached stand still or near to it? Or maybe it was perturbed while way out far from the star, and then managed to reverse and miss the star as it fell towards it, and somehow got a near circular orbit again. I'd like to see what the path for a theoretical gradual perturbation and orbit reversal would look like.

  • It is probably not a planet. It is a Death Star. Lord Vader is near!
  • I'm not entirely sure how, but I know global warming is involved in some way.

  • ... can't we send Superman to make it spin the other way to have normal time and not going back in time? :P

  • It's pretty obvious the planets backwards orbit is due to a drunk space bum playing pool with planets [youtube.com]
  • Did you feel that tremor? It was from millions of astrologist/astrology "practitioners" shuddering at the thought of a planet's permanent retrograde status!

  • Another possibility (Score:4, Interesting)

    by fireman sam ( 662213 ) on Friday August 14, 2009 @01:04AM (#29062171) Homepage Journal

    Another possibility is that the planet does not originate from the star it is orbiting. For example, the planet may have been in an unstable orbit around star 'A' and eventually escaped from star 'A' it traveled through space until it was caught in the gravitation of star 'B' and began to orbit. The orbit of the planet around star 'B' would be based more on the direction and angle it approached star 'B' as opposed to the spin of star 'B'

    Just my theory.

  • No matter how much proof of intelligence and competence we send, the earthlings just don't get it.
  • Yup, a pretty silly statement when the observation was of the first one discovered.

    Still a silly statement after the second one discovered, the very next day:

    http://www.newscientist.com/article/dn17613-second-backwards-planet-found-a-day-after-the-first.html [newscientist.com]

"I think trash is the most important manifestation of culture we have in my lifetime." - Johnny Legend