Wrong way planets screw up our perfectly good theories

By Phil Plait | April 13, 2010 11:00 am

Stupid reality, always mucking about with our ideas. How dare it!

In this case, reality is interfering with how we think planets form around stars. And the monkey in the wrench belongs to a handful of newly discovered planets that go around their stars the wrong way.

wrongwayplanet

That’s an artist’s illustration of one of these planets. As you can see in the diagram, the star rotates left-to-right, but the planet orbits right-to-left. That’s a bit of a puzzler, and here’s why.

First, how do we think planets form? If you look at my last post, you’ll see a giant cloud of gas and dust collapsing in places to form stars. The stars form from little knots of overdense regions in the cloud. As the material collapses, any slight amount of rotation it has — from eddies and vortices in the gas, say — get amplified (think ice skater as she draws her arms in and spins faster). Random collisions of particles inside the cloud tend to drop more of the matter toward the center, along the equator of the spin, forming a flat disk there.

The disk spins, rotating around its center like a DVD (though stuff toward the center goes around faster than stuff near the outer edge). The middle of the disk is where the star forms. Farther out, local eddies and vortices can form planets. But the important thing to note is that in this scenario, everything spins in the same way. If the disk appears to be spinning clockwise, say, then the star will spin that same way, the planets will orbit that same way, and the planets will spin that same way. We’re pretty sure this is how things work because that’s pretty much what’s happening in our own solar system.

This theory has been tested by observation and by increasingly complex modeling. Sometimes there are problems with it, but in general new ideas have been added that fix those problems, and over time we’ve been pretty happy overall with the idea that stars and planets form this way.

However, a bunch of newly discovered planets have messed this nice idea up. They orbit their stars the wrong way!

How do we know? That part is pretty cool. First, these are transiting planets. As the illustration above shows, from our point of view the planets pass directly in front of their stars every time they make an orbit. When that happens, they block a fraction (usually around 1%) of the star, and we see that as a slight dip in the light detected from the star. A lot of planets have been found this way, and it’s a pretty good method of finding planets.

Now picture the star in the image above. It’s spinning, so the left side of the star in the diagram appears to be headed toward us, and the right side moving away from us. But that means there’s a Doppler shift, a slight change in the color of the light from the star. Just like a car roaring past you makes that "EEEEEEeoooooooow!" sound, light changes pitch if the source is moving toward or away from us, and that change in pitch is seen as a shift in color.

The light from the part of the star rotating toward us shifts a bit to the blue, and the side moving away shifts a bit to the red. That shift is very small, but measurable.

But the planet messes that up. As it transits (moves in front of) the star, it blocks first one side, and then the other. If it orbits the star in the same direction as the star spins, it will first block the blueshifted side, and then a bit later the redshifted side. That change in the starlight can be seen and measured.

But for some of these planets just discovered, it’s all backwards! The redshifted side gets blocked first, and then the blueshifted side. That means the planet is going around the star the wrong way. The press release about this discovery has a nice video which makes this a bit more clear.

Does this mean our theory is wrong? Well, not exactly. It probably means that overall the theory is solid, but that there are exceptions, modifications, we don’t understand. Most likely the planets that form around other stars start off revolving around the star the same way, but then some sort of gravitational interaction with other forming planets knocks them off course. Some of these newly discovered systems do appear to have outer planets that could do the trick; the tug-of-war resulting from a close encounter could slingshot one of the planets into a retrograde (backwards) orbit.

This would play hell with the system. The planet knocked backwards would migrate in close to the star, tossing other smaller planets either into the star or out of the system entirely. If that’s true, then it means these weird planet systems won’t have many planets, just the one backwards-revolving one and one or two outer planets. That’s a nice prediction, in fact, and one that can be confirmed or falsified with more observations.

And it’s not like this is a rare event: fully 6 out of 27 systems appear to have these backwards-moving planets! That means that however these planets get knocked about, it has to happen fairly often. Obviously, we need to observe a lot more of these systems so we can get better statistics, and be able to see what similarities and differences they have with each other. That’s the best way to figure out what the heck is going on.

What does all this mean? Well, it means, as usual, that Nature is a bit more clever than we are, thinking up all sorts of ways of forming planets and systems of planets that didn’t initially occur to us. But that’s how science works. Things get complicated, so the first thing to do is simplify. Make your idea general. Then start adding complexity to it to explain what you actually see. As observation techniques get better, the idea has to get modified to account for new data.

In this case, it’s a pretty big modification, but that’s not surprising: we’re new at this planet finding thing. We’re bound to get plenty of surprises for a while, until we have a better grasp of the situation. Surprises are good: they help us test the theory, they help us understand reality a little better, and they help us learn a little bit more.

But they’re also fun. Who wants a Universe we understand completely and utterly? How boring that would be! Science is all about peeking around the next corner and seeing what’s there. And there are always more corners. Always.

ESO/L. Calçada

Comments (77)

  1. Spikey Pisarris

    THANK YOU GOD!! Another anomaly that I can use to inject some doubt into evolution…er I mean the science of astronomy!
    Obviously the planet rotates contrariwise because GOD DID IT! CHECK MATE SCIENTISTS!!!!!

  2. Ryan Smith

    Spikey, that is exactly what I was thinking. Just wait till Dinesh gets ahold of this nugget! ;)

  3. New rule, Phil: when describing multi-body gravitational interactions like this, you have to include a link to that simulation tool (linked from my name) that you posted about on March 1, along with the parameters needed to simulate the interaction you are describing.

    This would actually add 2-3 points of awesome to Bad Astronomy. I’m just sayin’.

  4. wright1

    Cue creationists quote-mining Phil’s “Well, it means, as usual, that Nature is a bit more clever than we are, thinking up all sorts of ways…” in 1, 2, 3…

    But seriously, that is fascinating. And in a significant fraction of local planetary systems (well, significant pending further investigation)? Amazing.

    Hmm, here’s a scenario for the sci-fi writers out there: assuming a life-bearing planet in a retrograde orbit with an intelligent species, what would be the effect on that people’s religious and philosophical thinking? Imagine the conflicts between astronomy and astrology on such a world!

  5. Richard Wolford

    Reality is so much cooler than superstition :)

  6. Mapnut

    All right, if we can’t think of a way a planet gets an orbit opposite its sun’s rotation, we have to apply Occam’s Razor. The obvious explanation is that it’s not a planet but a giant spaceship.

  7. So, how long could a planet maintain such an orbit before it either falls in to its sun or goes flying off into space?

  8. andy

    Chalk one up for the Kozai+tidal migration scenario? (Basic principle is that where systems have orbits that are misaligned to each other by more than 40 degrees, you can trade orbital inclination for eccentricity, then use tidal effects at perihelion to shut off the Kozai mechanism while shrinking and circularising the orbit, resulting in a misaligned hot Jupiter)

    Whether a significant fraction of hot Jupiter systems showing misalignment implies that a significant fraction of planetary systems are misaligned is another matter though. Hot Jupiters appear to be pretty rare: we find lots of them because they are easy to find, but apparently the proportion of stars that have them is about 1/300. This contrasts markedly with results from microlensing surveys that suggest systems with long period “cold Jupiters” like the one in our solar system have about 15% occurrence rate.

  9. Yoweigh

    “Does this mean our theory is wrong? Well, not exactly. It probably means that overall the theory is solid, but that there are exceptions, modifications, we don’t understand. Most likely the planets that form around other stars start off revolving around the star the same way, but then some sort of gravitational interaction with other forming planets knocks them off course.”

    How do we know this? i.e. what makes us hold onto the old theory instead of trying to develop a new one?

  10. HumanisticJones

    Awaiting creationists grabbing the top of this article and failing to read the rest of it. Amazing stuff though, now I want astronomers to find one of those interactions in action so we can see the kind of thing it takes to hurl a planet back the wrong way.

  11. The count of the color-shift is off by one. Change that and the color shifts in the right order again. Man, math is simple!

  12. Brian

    But you’re a scientists; aren’t you’re supposed to get all angry at having your theories proved wrong and insist that you’re right despite the evidence? That’s what always happens in the movies….

  13. XMark

    Captured rogue planets? Though I would think that those should be more rare than 6 out of 27 systems.

  14. Theron

    @Yoweigh:

    Any new theory would have to account for the data we already have. The current model does that, and wrong-way planets are plausible in the current model. Any new theory would have to account for why the older theory looks reasonably correct given current data. This puts some real limitations on where theorists can take their ideas. The simplest explanation is that the “final answer” would be a variation on the present model, or would contain the present model.

    As always, the best way forward is more data! What do we want? Next-gen telescopes! When do we want ‘em? Now!

  15. Chris

    Could there be another explanation for this? I think the problem science has sometimes is that it deals in absolutes. If A happens and B happens then C is the result, always. Unfortunately nothing in the universe is absolute. There are too many variables and things we do not yet understand that can throw a wrench into our scientific truths.

    In this case, the planet’s formation and orbit around it’s star seem to defy the rules of science. A rule that was based on the observation of exactly ONE solar system. Our own. Now that we have the capability to identify other planetary systems, we may find that our system is one of a variety of different types of solar system. Similar to the variety of different Galaxy’s and how they are formed. Not all are spiral galaxy’s. Some are clusters, others are eliptical, and still others are ringed or lenticular.

    Each type depends on a number of different factors so Solar Systems are mini microcosm’s of galaxies and thus have different variables on their creation and composition and orbital rotations.

  16. Captn Tommy

    So, let me throw a stone. I am standing on my roof a mile (1.6 kicks) away from Interstate 95 and I see a 1950 Plymouth Super Delux, black four door, flat head six, maxed out at 60 mph (100 KPH approx) when a Peterbuilt tractor hauling a Mayflower furnature van passes the Plymouth at 120mph (200kph approx), which vehicle is traveling backwards? It is all in the mind of the beholder. distance, time, speed… someone said it’s all Relative.

    Irregardless…..:)

  17. Richard

    Once again, Kara Thrace is right.

  18. @XMark Says The captured planet was my first thought as well, and I agree it would be pretty unlikely to have happened in so many cases. There’s a lot of space out there, and only a tiny bit of it is near enough to stars to create a situation in which the capture could happen.

    It’s interesting thinking about how this might happen though: what could put enough force on a planet to change the direction of its velocity entirely?

  19. Daniel

    #8: I think the answer why it shouldn’t be just abandoned is that it’s most likely almost complete. You seem to have stumbled upon the same blind alley that many others have, and that is in seeing things in black and white.

    the earth wasn’t flat, but it looked flat. The sun doesn’t go around the earth, but it did look like it. Then we thought the earth was a sphere – but it’s not. *almost* a sphere, yes – which makes the “the earth is a sphere” theory keepable most of the time, but it’s a refinement that was needed, not a whole new theory.

  20. andy

    In fact the paper available on the SuperWASP website states this is perfectly compatible with the Kozai migration scenario I mentioned in my earlier comment. This distribution of alignments was predicted by an existing model of planet migration, one that has a solid history of theoretical study.

  21. Oli

    Could it have been reversed by a passing star? Or even be a different star’s planet, which was captured by this one during a close encounter, like some people think is the cause of Sedna’s weird orbit?

  22. TravisM

    I make dinky point particle simulations of gravity using XNA and can get any combination of odd retrograde orbits depending on a given set of initial conditions. All proto-planets orbit the same direction. some get kicked out and a few that do get kicked out have a second encounter with a larger outer proto-planet and dive toward the star. A fraction of those actually settle into nearly circular orbits… eventually. (They do seem to spiral in, drawing outer planets with them, disrupting inner ones…)
    however, in my scenario, these proto-planets generally spin the same direction as the system as a whole… i.e.: the year is backward, not the day.

  23. potterbro

    Maybe I am missing something but don’t they have to make an assumption about the direction of the planets rotation if they use that logic? Wouldn’t they see the same effect if the planet was orbiting in the expected direction but rotating in the opposite direction?

  24. jcm

    By planets orbiting the “wrong” way about the star, don’t you mean that these planets have retrogade (counterclockwise) motion?

  25. MoonShark

    @jcm: Retrograde doesn’t necessarily mean counterclockwise. It means opposed to the direction we’d expect. As seen from above, we’d expect that if a star rotates clockwise, then its planets will orbit clockwise too, because they usually form together from the same spinning disk of matter.

    These “wrong way” planets either didn’t form together with the star (captured from outside) or there’s some other mechanism that changed their direction after forming (gravitational interplay with other planets we can’t yet detect, perhaps). And given that 6/27 of the observed planets do this, they’re unlikely to be captures.

    @potterbro: I don’t think the planet rotation matters much. E.g. Uranus’ axial tilt is very high, so it almost “rolls” along its orbit. Other planets in our system have fast (Saturn) or slow (Mercury) rotations. The solar system itself is tilted more than 85 degrees relative to the galactic center. *shrug*

  26. James

    @potterbro: The rotation of the planet doesn’t have a significant affect on what part of the star it’s blocking light from.

  27. ASFalcon13

    “If the disk appears to be spinning clockwise, say, then the star will spin that same way, the planets will orbit that same way, and the planets will spin that same way. We’re pretty sure this is how things work because that’s pretty much what’s happening in our own solar system.”

    Ok, I’m an aerospace engineer, not an astronomer, so feel free to correct me here…

    I’m calling shenanigans on your logic. Disk spinning clockwise will result in a star spinning clockwise, and the planets orbiting clockwise…cool, I’ll buy that. You lost me at spin though, and the whole “that’s pretty much what’s happening in our own solar system” bit. We’ve already got a nice counterexample in said solar system in Uranus, what with its ~98 degree axial tilt and all.

  28. andy

    ASFalcon13 – Uranus spins pretty much sideways. An even better counterexample to the assertion that the planets spin the same way as their orbits is Venus, whose axis is nearly perpendicular to its orbit and spins retrograde.

    Indeed, simulations of terrestrial planet formation indicate that the final rotation state gets randomised by giant impacts during the late stages of planet formation, at least in the case where the planets are formed far enough from the star that tides don’t lock them. As for the giant planets (Saturn, Uranus and Neptune all have significant obliquities), this is another matter. As far as I am aware, there isn’t a particularly satisfactory answer to the question of why these massive planets are tilted.

  29. potterbro

    Oh wait… i read it wrong. I thought I read that they were looking at some sort of doppler shift in the planet, not the star… I get what they are saying now.

  30. ASFalcon13

    andy – D’oh! I’d forgotten about Venus!

    Either way, thanks for the answer!

  31. The Mad LOLScientist, FCD

    Ceiling Cat loves a good practical joke. =^..^=

  32. whomever1

    On the idea that the retrograde planets might have come from outside the system–isn’t it possible that during stellar formation new stars and planets were being created close enough to each other that exchanges between them could have happened occasionally?

  33. > Science is all about peeking around the next corner and seeing
    > what’s there. And there are always more corners. Always.

    The above, of course, does not apply to Climate Science…

  34. Douglas Troy

    It’s obviously a machine threaded orbit.

    *sheese* Do I have to think of everything for you guys?!?!
    :P

  35. Jeffersonian

    It reminds me of how, when you release a baseball, you can make it spin differently depending on the release. If I was more knowledgeable, I’d make an analogy to these rogue planets, gas fingertips, etc.

  36. Jove

    Generally speaking does anyone know when these artist rendering are done, are these dont Astronomers who are also artists or does an Astronomer give them an idea?

  37. Gary Ansorge

    33. whomever1

    Depending on the nebula density in which the stars form, there could be significant interaction with other massive bodies. These ARE all super Jupiters, so the implication is that the stellar disk was quite dense and other massive bodies in this type of system could well flip the orbit of an incoming planet as it spirals toward its parent star.

    I like to think of it as gravitational billiards.

    Gary 7

  38. Chet Twarog

    Firstly, there aren’t any gods. So, stop that nonsense!
    Secondly, in our very own solar system we have a captured Kuiper Belt object orbiting Neptune in a retrograde orbit: “Triton orbits Neptune in what is known as a retrograde orbit. This means that it orbits Neptune a direction opposite the planet’s rotation. It is the only large moon in the Solar System to do this. Astronomers are not quite sure of the reason for this retrograde orbit. Some believe that it condensed this way from the original material of the early solar system. Others think that Triton may have been formed elsewhere and then captured by Neptune’s gravity. In fact, many astronomers have noticed that the surface features of Triton, as well as its size, are very similar to what they believe the planet Pluto to look like. Some even wonder if there is some connection between Triton’s features and the fact that Pluto actually crosses Neptune’s orbit from time to time. Just what that connection might be is anyone’s guess at this point.”
    http://www.seasky.org/solar-system/neptune-triton.html

  39. Messier Tidy Upper

    @ ^ Chet Twarog : Also on the outer solar system is “Dracula” or 2008 KV 42 which was the first backwards orbiting Centaur which has a weird highly inclined (104 degrees), retrograde orbit taking it from 20 to 70 AU. The odd orbit suggests that 2008 KV42 may have been pulled into our solar system from the Oort cloud. Thus “Drac”’s discovery may finally show how such objects transition from the Oort cloud to become comets. It was found on May 31st 2008.

    Yes there’s also Venus and Ouranos* and Triton in retrograde (“backwards”) orbits our own solar system too as pointed out here by Chet (39.), andy (29.) and ASFalcon13 (28.) respectively.

    So these objects aren’t totally unknown or unexplainable by any means – although this is still an awesome finding & another great write-up by the BA – Thankyou again Dr Plait! :-)

    ——————————————————–

    * Ouranos? Yes that’s no typo see :

    http://www.facebook.com/group.php?gid=189939051777&ref=ts

    Ouranos the correct name facebook group : All the planets except one are named after Roman gods, and Ouranos is the one exception. Unfortunately it has become the brunt of joke after joke due to a Latinization of the original Greek name, Ouranos. We do not call Poseidon Posidon, so why make Ouranos the exception? Ouranos is a magnificent planet that has been subject to a bromidic and stale joke for far too long.

    That’s why I for one always spell it that “correct” (IMHON) way &, yes, I’m a member of that group myself.

  40. Plutonium being from Pluto

    @ 7. andy Says:

    Chalk one up for the Kozai+tidal migration scenario? (Basic principle is that where systems have orbits that are misaligned to each other by more than 40 degrees, you can trade orbital inclination for eccentricity, then use tidal effects at perihelion to shut off the Kozai mechanism while shrinking and circularising the orbit, resulting in a misaligned hot Jupiter)

    @ 12. XMark Says:

    Captured rogue planets? Though I would think that those should be more rare than 6 out of 27 systems.

    @21. Oli Says:

    Could it have been reversed by a passing star? Or even be a different star’s planet, which was captured by this one during a close encounter, like some people think is the cause of Sedna’s weird orbit?

    @ 23. TravisM Says:

    I make dinky point particle simulations of gravity using XNA and can get any combination of odd retrograde orbits depending on a given set of initial conditions. All proto-planets orbit the same direction. some get kicked out and a few that do get kicked out have a second encounter with a larger outer proto-planet and dive toward the star. A fraction of those actually settle into nearly circular orbits… eventually. (They do seem to spiral in, drawing outer planets with them, disrupting inner ones…) However, in my scenario, these proto-planets generally spin the same direction as the system as a whole… i.e.: the year is backward, not the day.

    @ 33. whomever1 Says:

    On the idea that the retrograde planets might have come from outside the system–isn’t it possible that during stellar formation new stars and planets were being created close enough to each other that exchanges between them could have happened occasionally?

    All those comments seem to me like good explanations for the phenomena here & I would suggest that – quite probably – all these processes could be at work in different specific cases :

    Eg. one “backwards” system could be the result of a captured “rogue” exoplanet, another two or three could be from encounters during planetary formation from world’s outside or inside their own solar system another from the clsoe passage of another star through the system disturbing an outer SuperJovian exoplanet and others from the Kozai + tidal migration process.

    Thanks y’all for those great ideas & comments. :-)

    However, the range of possibile explanations above here does raise the following major question :

    Is there any way of telling the difference between these possible “retrograde” formation mechanisms in the specific systems we see these exoplanets in today I wonder?

    Anyhow that’s awesome news in the OP there – I love it! If I could put in a request to the BA then, y’know, more exoplanet news is always welcome by me; I just can’t hear enough about the marvellous exoplanets! :-D

  41. Pi-needles

    @16. Richard Says:

    Once again, Kara Thrace is right.

    I know that’s a reference to “Starbuck” in the new BattleStar Galactica but what’s the specific reference to here? Can you or anybody else please elaborate on that comment?

    (Unfortunately , I haven’t been able to watch the series myself for years – saw first season or two & that’s all & can’t recall any specific ref. to retrograde planets in it.)

    @ 1. Spikey Pisarris Says:

    THANK YOU GOD!! Another anomaly that I can use to inject some doubt into evolution…er I mean the science of astronomy! Obviously the planet rotates contrariwise because GOD DID IT! CHECK MATE SCIENTISTS!!!!!

    I’m guessing your NOT a real Creationist posting there! ;-)

    However, the name does seem very vaguely familiar in Creationist terms – is that the name (or parody on the name?) of a real ID-iot or Creationist and, if so, again, would you (or anyone else) mind elaborating for us who don’t know about it please?

  42. Joseph

    Rogue planets being captured on the counter-rotating side of the star.

    not a scientist, but a thinker.

  43. Messier Tidy Upper

    Did I remember to add the wiki-link for “Dracula” (2008 KV 42) here that I’d meant to put in my earlier comment (#40 ) here? Oops, no I didn’t. Oh well here it is now :

    http://en.wikipedia.org/wiki/2008_KV42

    Of course there’s quite a difference in scale between the very large comet-nucleus sized “Dracula” & the Superjovian or Hot Jupiter exoplanets but I guess it shows that the process can happen.

    I think there’s also a couple more retrograde Centaur / Trans-Neptunian Objects and many “backwards” orbiting comets known in our solar system so remarkable as these discoveries are such orbits are not unknown or unexplainable to science – as the number of theories suggested here demonstrates!

    Finally an additional explanation :

    Could a collision by one exoplanet into another result in such orbits?

    After all, collisions seem likely to have caused the sideways rotation of Ouranos and the backwards roatations of Venus albeit on a “daily” rather than “yearly” basis.

  44. Bruno Domingues

    Once we find a planet in a polar orbit, it will make more sense.

    Like comets migrate between stars, some planets might also take some wild rides.

    Is it that strange to believe that planets we see today have been trough a lot?

  45. Plutonium being from Pluto

    @ ^ Bruno Domingues :

    Like comets migrate between stars, some planets might also take some wild rides.

    Very true. Like fr’instance this one (HD 80606b) :

    http://blogs.discovermagazine.com/badastronomy/2009/01/28/weather-sizzles-on-a-planet-that-kisses-its-star/

    that the BA blogged about last year?

    “The planet’s orbit is incredibly elliptical, with a whopping eccentricity value of 0.927 — meaning the orbit is elongated like a rubber band being fought over by jealous children. It’s posited that gravitational interaction over time with a distant binary stellar companion to the star may have forced the orbit into this shape; it peaks at a distance of 125 million kilometers (75 million miles) from the star, but the planet’s 111 day orbit drops it to a mere 4 million kilometers (2.4 million miles) from the star’s surface. In the 55 days it takes to drop, it sees the disc of the star swell to 30 times its previous size, flooding the planet with nearly 800 times the amount of heat it felt at greatest distance.”
    - Dr Phil Plait from the post linked above.

    Is it that strange to believe that planets we see today have been through a lot?

    Not at all just look at the impact craters on our Moon, Mercury and Mimas (Saturn’s “Death Star” moon : http://en.wikipedia.org/wiki/File:Mimas_moon.jpg ) for example! ;-)

  46. Alex

    The planet which rotates in the ‘wrong direction’ would slow down rather quickly and fall into the star, so I don’t think this has been going on for a while.

    I suspect that the star may have been in a binary system, and rotated on its axis after it merged or lost its neighbor. Flipping the star would reverse its rotation, meanwhile the planets would continue in the same direction. If the star is rotating on two axes in this manner, then the planets would not slow down, nor would the star. Less likely, but also possible, is that the observed planet’s orbit flipped in a similar manner after a collision. Isn’t it feasible that a star or planet rotates on two axes? Who knows? I think that the planet formation theory is pretty solid.

  47. If you look at my last post, you’ll see a giant cloud of gas

    Your modesty does you credit, Phil.

  48. fernando

    that planete is female, she said was going one way, and then changed her mind… typical

  49. iDamir

    This is a clear case of temporary orbit. There is no way this planet could have originated with the star because of this anomaly. Can i please use this opportunity to say that creationists suck!!

  50. @Messier Tidy Upper: good luck with that.

  51. Larry

    I haven’t looked at the models mentioned but… What prevents the local dust from ‘swirling’? That is, the inner portion (that forms the star) having a moment of rotation in one direction while the outer portion (that becomes the accretion disk from which the planets are formed) rotates in the opposite direction. As each coalesces angular momentum is conserved and you wind up with a planetary system orbiting in the opposite direction as ‘conventional wisdom’ would have it.
    Stuff like this is observed to happen on other scales–stars and galaxies have different axes of rotation, even in local groups…planets in a system rotate on different axes (for example, Uranus or ‘Ouranus’) ['yours' or 'ours'...that will be the butt of a whole new series of jokes...] ;-)

  52. rob

    reality is for people who can’t handle planetary formation simulations.

  53. Pi-needles

    @48. vagueofgodalming Says:

    “If you look at my last post, you’ll see a giant cloud of gas.”
    Your modesty does you credit, Phil.

    LOL – classic. :-D

  54. johno

    No problem. Just call them dark orbits and move on hoping that someone, someday will figure out an explanation.

    johno

  55. mike burkhart

    Yes this is strange but so munch of the universe is one things for sure we will find the answer to this we just need to keep looking

  56. Chris Winter

    For any James H. Schmitz fans who may be about:

    We’ve found Karres! ;-)

    http://en.wikipedia.org/wiki/The_Witches_of_Karres

    That summary doesn’t reveal the fact that Karres (location a closely held secret) is found by Captain Pausert, when the witches lead him there, to travel in a retrograde orbit relative to the other planets of the system it then occupies.

    “Well, it would,” the Captain thinks.

  57. Boris S

    I think thet a star have a core wich runs oposit of a surfes.And it is probebly a metal core and magnetic force leads a planet in oposit direction…

  58. Chris Winter

    This article (and the Web site that carries it) may be of interest:

    http://www.centauri-dreams.org/?p=12065

  59. Robert Carnegie

    I don’t know about “cold” gas giants being more common, is that correct? The last I recall hearing on planet formation theories and computer models, your Jupiters form in outer orbits and then migrate in, usually – the Sun’s didn’t, so much. Otherwise we wouldn’t be here, because Jupiter would have also swallowed the Earth. So maybe you can also calculate that a wrong-way orbiting gas giant, arising from some crazy encounter with one or more partners, also would eat the small planets?

  60. Bill Nettles

    Another interesting property would be the rotational direction of the planet. It is the same as the star or opposite? Is the angular momentum of the rotation aligned with or opposite the revolution?

    Phil, could a measurement be made of the red/blue shift of the starlight coming across the edge of the planet’s atmosphere, or is that unresolvable with current instrumentation? Could Kepler (satellite) measure it?

    Finally, do we have a good model for why Venus rotates retrograde?

  61. JJ McGee

    Thank you Phil for the quick lesson and links in star formation. I have been watching the incredible Wonders of the Solar System and realized I know nothing of how stars and planets form. Now I know a little bit more conceptually and it’s nice.

    I like your posts because you always explain a little something.

  62. Jonas

    lol, my creationist friend JUST used this as an argument with me, and I hadn’t seen this yet! It was pretty much what Spikey said in comment #1. I was amused =)

  63. Some Aki

    Let me get it strait: the planet should by definition revolve around the star in the same direction the star rotates, because they both came from the same rotating disk. Is it not more logical and possible that the planet just continued to rotate the right way around its parent star as in the begining and that the star itself JUST FLIPPED ON ITS HEAD without changing its rotation or even the speed of rotation? Is there any possibility for the star to do such a thing? (Uranus rotates on its side, so I guess this is more than possible solution). My theory could be confirmed if the scientist find more planets in that system which revolve in the same “retrograde” direction. Sometimes simpler solutions are the right ones.

  64. Some Aki (67): Simpler isn’t always better. How do you get something the size and mass of a star to flip over? It’s far easier in reality to get a planet revolving the wrong way than a star rotating the wrong way.

  65. Some Aki

    That’s the beauty of science. I wouldn’t have beleived that some stars rotate as fast as they do, but they do, and this has pretty nice physical theories that explain this. But as far as I know there is no 100% good explanation on the Uranus rotation, which is, I would say, a pretty big planet far from its central star. And it does rotate on its side. :) ) Earth and Mars have also changed their rotation axis throughout their history. And not their revolution direction.

  66. Jon

    As we have a huge bias towards being able to detect systems with huge gas giants orbiting very close to the star, which can be one of the results of this process, you can’t really infer that retrograde planets are common, from the available data. It could be that less than 0.1% of all planetary systems have retrograde planets, for all we know.

    Also I think most reporters do a disservice to the accurate representation of the field by exaggerating the extent to which each new discovery overturns old stuff. They love to play up conflict whether or not it’s really there. Discovering 6 retrograde planets, out of the extremely lucky minority of planetary systems that we are capable of detecting, doesn’t overturn or add doubt to any theory of planetary formation.

  67. Jon

    To formalize it:

    Premise 1: Existing theory of planetary formation implies that retrograde planets are rare
    Premise 2: New observation implies that retrograde planets are not rare
    Conclusion: New observation conflicts with old theory.

    I don’t think either one of the premises really holds up under scrutiny.

  68. Ed

    Which way does our Sun rotates? I know Earth rotates clockways and revolves around the Sun clockways too, what about the rest of the planets?

  69. Ed

    Which way does our Sun rotate? I know Earth rotates clockways and revolves around the Sun clockways too, what about the rest of the planets?

  70. Motor Daddy

    Sooner or later you will all come to realize that the Earth came from the Sun, as did all the planets in our solar system. Mass evolves to space!

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