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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.'"
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A Planet That Orbits Its Star the Wrong Way

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

    Maybe the sun reversed its spin.

  • by Anonymous Coward on Thursday August 13, 2009 @08:17PM (#29060167)

    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)
    " 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 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:Captured object? (Score:3, Interesting)

    by russotto ( 537200 ) on Thursday August 13, 2009 @09:13PM (#29060631) Journal

    The odds are pretty slim for a planet to be stripped from one star and then captured again by another star.

    How about a direct capture, from an near-encounter with another star? That is, similar to the explanation in TFA, except that the planet originally belonged to the other star.

  • by Anonymous Coward on Thursday August 13, 2009 @09:33PM (#29060791)

    I was looking at the stars one evening and the thought occurred to me that every star harbors a hideous mess; an immense collection of orbiting debris ranging from bloated gas giants with dozens of exotic moons to mangled chunks of gold weighing billions of tons. Those nice neat little points of light are actually solar systems, every bit as rich and complex as our own. Life, at least in primitive forms, is probably a common afterthought.

    Think about the planet you're on now. Everything beyond iron is the shrapnel of stellar detonations coalesced and melted into a ball of metal orbiting the sun. Staggering quantities of baryons mushed together in weird configurations, colliding, erupting and aging for billions of years. Somewhere there is a near perfect sphere of nickel weighing five Earths and orbiting a black hole. It will be destroyed next week when it collides with and vanishes forever into the guts of an 9 billion year old brown dwarf. It will have never been observed by anything more sentient than a dusty comet.

    When you really think about it the universe is creepy.

    Extrasolar astronomy requires extraordinary equipment. We need to build more of it and figure out what the universe looks like below cosmological scales because we haven't got the first clue what's really out there. Humans were simply not endowed by nature with sufficient imagination to anticipate more than a small fraction of all the crazy shit we're going to find.

  • 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.

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