Putting the spin on Saturn's hex

By Phil Plait | November 4, 2010 7:00 am

I get the odd (and I do mean odd) email every now and again from someone whose grasp of science is somewhat, um, tenuous. They tend to have unusual explanations for phenomena ranging from THEIR MIND-BLOWING THEORY THAT PROVES EINSTEIN WAS AN IDIOT to aliens visiting them and planting solutions for world peace in their brains.

cassini_saturnhexA lot of these emails are motivated by weird observations that on the surface don’t make sense. A great example of this is the bizarre hexagonal cloud feature at Saturn’s north pole. Seen here using images taken from Cassini, the storm is definitely freaky: how do you get a hexagonal shape on a spinning round planet?

Via Boing Boing, I found this really cool video that shows that this is actually expected under some circumstances! Scientists used a slowly spinning cylinder of water and created a much faster "jet stream" by using a more rapidly spinning ring inside the cylinder. What they got is, well, Saturn’s hex:

[I'll note that my pal Emily wrote about this a few months ago at The Planetary Society blog, too, but I somehow missed it.]

Pretty cool. It forms a hexagon! And you don’t need aliens, the electric Universe, plasma physics*, or anything like that. Just plain old fluid dynamics and a rotating plate.

I never would have thought that could happen. It goes to show you that our common sense fails us pretty miserably when we try to change from our relative stationary frame of reference to a spinning one, or vice-versa. After all, it’s not exactly intuitive that we’re standing on a vast spinning ball of mud flying through space, but there you go.



* Note: by mentioning plasma physics, I don’t mean to be lumping legitimate plasma physics in with the abuse of it by the Electric Universe folks. I was in fact referring to those people when I listed it. I hope no actual scientists took offense.


Related posts:

- A hex on Saturn
- A hex on Saturn (again)!
- Science wins at SMBC


CATEGORIZED UNDER: Antiscience, Astronomy, Cool stuff
MORE ABOUT: hexagon, Saturn

Comments (43)

Links to this Post

  1. Planetside Hexagon – The Stray World | November 4, 2010
  1. Dunc

    What I really love about these sorts of experiments is just how much you can learn about really big, complex phenomena with simple physical simulations. My favourite is probably still modelling whole-mantle convection using Lyle’s Golden Syrup…

  2. Pete Jackson

    Clearly the hexagon at the pole is the primary means for disassembling Saturn when needed for repairs. Somewhere to be found is an asteroid, shall we name it ‘allenwrenchicus’, which has the male hexagonal piece to fit.

    And my grasp of science is not at all tenuous!

  3. Zetetic

    It is very cool.

    So let’s see….
    Natural/scientific explanations for an unknown phenomena that others had previously assumed was supernatural/extraterrestrial in origin= ~10,000,000 (aka “a whole bunch”) ;)

    Phenomena that has been conclusively demonstrated to be supernatural/extraterritorial= 0

    Is it any wonder why Argument from Ignorance is a logical fallacy?

  4. Chris

    Cool, so there is a giant spinning ring inside Saturn.
    But fascinating why does it happen on Saturn but not the other gas giants?

  5. Maria

    I do have a rather tenuous grasp of science but I’d guess it has something to do with fluid density / temp variations? speed of rotation? .. The aliens told me so. ;)

  6. ScottDogg

    Well, I have to say, it’s great that we finally know what the hex going on with Saturn. :P

  7. Jason

    I am guessing the hexagon only forms if there are specific conditions met. Probably the ratio of the speeds of the inner and outer cylinders has to be just right, or with in a certain parameter. On the other Gas giants their size helps determine the wind speeds in that region and Saturn’s happen to match up. Things like the Cloud band thickness also undoubtedly play a role as well and conditions aren’t right on the other planets for formation.
    Edited to add
    @5 I had forgotten about the density having an effect. That is likely too. Though I would bet that if the speeds are correct it will occur with almost any fluid density, but that ratio is affected by the density of the fluid in question. Especially since the atmosphere of Saturn is likely less dense than whatever fluid was used (water, oil, etc..) in the lab experiment.

  8. Jim Shaver

    Yep, this is awesome on several levels.

    Pete Jackson (#2), you forgot to mention the hole in the middle of allenwrenchicus to accommodate the round “security” pin sticking up from Saturn’s pole. It sucks when you can’t find the right driver (and you’re half a billion miles from home)!

  9. Gary Ansorge

    Arguments from ignorance abound because there are SO many who are ignorant. Fortunately, lack of information is a curable condition but only if we have the patience to continue our arguments,,, one programmer figured out a way to enhance our patience, by automating it.

    http://www.technologyreview.com/blog/mimssbits/25964/?nlid=3722

    His ‘bot references links to real data about global warming to educate tweeters who have no idea what they’re actually arguing about,,,and it has infinite patience,,,COOL!

    Gary 7

  10. Jeff

    Just because it’s on YouTube you think it’s true? Where’s the skeptecism, Phil? WHAT laboratory did this? WHERE are the published results? How do we know this is any different than baking soda and mountain dew equalling the contents of a glow stick?

  11. John

    @ Chris – Did you notice the equation at the beginning of the video? It is about the rates of spin in relation to one another. Not all gaseous planets spin at the same rate.

  12. Jeff (11): If you read carefully, you may note the link I put in to Emily’s website. Also, had you bothered to actually click the link to the YouTube video, you’ll see that it’s referenced as well.

    Next time, please do some due diligence before insulting me.

    [UPDATE: as zzamboni says in comment 16 below, Jeff's comment may have been satirical, and if so, I am a victim of Poe's law. The thing is, this blog does get comments just like that all the time with no sense of irony whatsoever, and Poe rules supreme in such matters. If so, I apologize, and move on, chuckling ironically at myself.]

  13. Jason

    @13 Phil..
    I would hope he was just trying to be snarky and utterly failed.

  14. These hexagonal formations can also be seen encompassing the eye of terrestrial hurricanes – so they aren’t unique to Saturn (though perhaps the huge scale is).

    You can sort-of see it in this photo of Hurricane Isabel – though I do recall seeing better ones (just can’t remember their names – which makes ‘em harder to find)

  15. Phil, you should share some of those odd emails you get. They should make for some nice entertainment.

    (ps. I also think Jeff(11)’s comment was meant to be tongue-in-cheek)

  16. Ever since I began to really study science, I’ve found it fascinating that people can buy into the weird conspiracy theories and woo woo, because real science is weird enough without adding extra weird.

  17. Andrew W

    It’s like the surface of the ocean, complete with waves, bent around on itself.

  18. amphiox

    I am amazed as well with the vortices that form outside each side of the hexagon. The symmetry of the pattern recalls something one might expect to see in a work of abstract art.*

    You look at it and your first impulse is to think ‘ah, this must be design’. And of course you’d be wrong.

    *Or something a human being might have dreamed up as a sacred symbol.

  19. IBY

    Oh yeah, I wrote about this in my blog a while ago. Really cool stuff.

  20. Keith Bowden

    Phil, is it just me or have your recent posts been particularly rich in information, new revelations and kick-ass awesome sights? Thanks for all of this!

    I think maybe I’ll reread Contact on Saturday, to celebrate Carl’s birthday.

  21. What I always said: pi = 3!
    :)

  22. Bioth

    Since when is Plasma Physics allowed to be used in the same list as aliens and the electric Universe???

  23. Tim

    @amphiox, #19: I think you have that backwards. The hexagon is formed by the vortices. With the different rotation rates, vortices will inevitably be formed, the key for the hexagon is that the size of the vortices means exactly six can fit on the exterior of it. These six vortices then form the hexagon. I imagine that a slightly different setup would create a stable formation of seven or eight, and then you’d have a septagon or octagon.

  24. Matt

    I really find it interesting that the hexagon shape doesn’t travel at the same rate as the material, like ocean waves rolling along faster than the water.

  25. Phil, I’m feeling slightly time-shifted here. I seem to recall all this information being presented at the time of the initial release of pictures of the Big Hexagon a few years back, including the cylinder-within-a-cylinder demonstration. And since your site is the most likely place I would have seen this information, I’m guessing it was all presented here.

    …well, yeah, there it is, in the original post that you conveniently linked here and the original link to Emily Lakdawalla, three and a half years ago. It’s still super super cool and everything, and I guess there are lots of people who hadn’t read about this way back then.

  26. JohnW

    @5 Chris – I don’t think it’s necessarily that the other gas giants don’t have hexes, but that we haven’t sent a Cassini style probe to the other gas giants to take close up pictures of their poles.

    I’m assuming the hex photos were taken by Cassini?

  27. Egad

    Tim said,

    >I imagine that a slightly different setup would create a stable formation of seven or eight, and then you’d have a septagon or octagon.

    Yes indeed. Why a hexagon rather than an [N]agon? I’d guess rotation speed and effective viscosity and stuff like that. But some theory and experimental work need to be done.

    If it turns out that the hexagon in such situations is the One True Gon, that would be very interesting in itself.

  28. t-storm

    Way to put a spin on it. Ha!

    So if Bill O’Reilly were on Saturn he would kill the hexagon?

  29. Chris L.

    I was going to make some wise-ass comment about how this is “stunning confirmation” of Richard Hoagland’s HD physics thesis (yes, he does believe it is proof of his nonsense), but I’m afraid some here might not have gotten the joke. In any case, finding the real cause of the hexagon is a lot cooler than make believe physics.

  30. me

    DO NOT QUESTION THE MIGHTY HEXAGON!

    as it doesn’t know very much and gets upset easily

  31. Awe. This phenomenon was my go to example of something weird in the solar system that I knew of absolutely no explanation for. Next time I write some pro-materialism boilerplate I’ll need something different that doesn’t make a lick of sense.

    Anybody got a good list of things we are clueless about. I need to keep a few examples, but they only work for a couple years before scientists explain them. And while this isn’t an absolute explanation of exactly why, it certainly suffices to show that there’s no deep mystery here.

  32. For anyone who is interested, this is the journal article about the experiment:

    Aguiar, A.C.B., Read, P.L., Wordsworth, R.D., Salter, T. & Yamazaki, Y.H., “A laboratory model of Saturn’s North Polar Hexagon”, Icarus, volume 206, issue 2, April 2010, pages 755-763. http://dx.doi.org/10.1016/j.icarus.2009.10.022 (paywall for full article)

    and some similar work on other planetary polar vortices, from a conference proceedings:

    Montabone, L. , Wordsworth, R. Aguiar, A., Jacoby, T., Read, P.L., McClimans, T. & Ellingsen, I., “Barotropic instability of planetary polar vortices: concept, experimental set-up and parameter space analysis”, Proc. Hydralab III Joint User Meeting, Hannover, February 2010. http://www.hydralab.eu/hydralabIII/proceedings/NTNU-16_Montabone.pdf (this one is freely available I think)

  33. Here are some more examples, from hurricanes on Earth:

    http://www.atmos.ucla.edu/~kristen/wrf/wrf.html

    in particular, there is a triangle (simulated, hurricane Rita)

    http://www.atmos.ucla.edu/~kristen/wrf/pw_rita_24_03_talk.png

    and a pentagon (satellite photo, hurricane Isabel):

    http://www.atmos.ucla.edu/~kristen/wrf/isabel_dmsp.gif

  34. Kapriel

    @Phil-
    Are the equations describing fluid-mechanics identical to those describing gas-mechanics?
    Sorry, I don’t know what gas-mechanics are really called. I hope you get what I’m asking without my knowing the necessary science-speak. You said we’re standing on a spinning plate of mud, but our planet has no hex. What did you mean by that?

    Also, I think you were referring to Wal Thornhill’s Electric Universe website (?), which has an article explaining how electrified plasma also forms the hexagon shape. In fact I think, if I remember right, that he quotes the plasma physicist Anthony Peratt on that one. But anyhow, since we know plasma and gas, both, are present at the south pole of Saturn (I don’t know if liquids/muds are present there), can’t this hex be a combined effort of some kind? Saturn is really quite “electrical”, much more so than the Earth, for instance. What do you think?
    Just questioning and learning… Thanks.

    -Kap

  35. MG

    So, in what ways, specifically, is this any different from the OLD fluid dynamics “explanation” forwarded in 2007 (http://www.planetary.org/blog/article/00000927/), based on a 2006 physics paper (http://arxiv.org/abs/physics/0511251) on a quirky fluid dynamics behavior? This looks suspicious similar… And in the older experiment, they quite specifically said:

    “This study is probably not directly applicable to Saturn. They continue to say, ‘We speculate that the instability is caused by the strong azimuthal shear due to the stationary walls and that it is triggered by minute wobbling of the rotating plate. The slight asymmetry induces a tendency for mode-locking between the plate and the polygon, where the polygon rotates by one corner for each complete rotation of the plate.’ In other words, the polygons form as a result of interaction between the rotating fluid and the edges of the container. Saturn has no edges.”

    Does the same caveat apply to the new experiment, which seems to duplicate the old experiment to some extent? Are they more certain this time around that “this is it”? Or is there still some margin of error, whereby it’s a nifty experiment but may be inapplicable if the conditions at Saturn don’t match the conditions of the experiment (there are no cylindrical physical barriers @ Saturn, it’s just a gas giant’s atmosphere)? Also, does the new experiment at all cite the old somewhat similar experiment?

    Would the same results be achieved in a setup with NO container, or at least a container where there could be no direct and/or significant interaction with physical barriers (i.e., the walls of the container)? Say, for instance a similar device were used in the middle of the ocean or the center of an olympic-sized swimming pool.

    Also, what is the significance of the rotating table. Would the same results be achieved with a stationary table (only the ring allowed to move freely), or is the rotating table required? If so, why?

    The only difference I can think of off hand is that there might be centrifugal / centripetal forces exerted on the contained water by the rotation of the table/setup and the walls of the container respectively, depending on how quickly the table is rotating. If there is no “container” on Saturn, would the same be true there, or would the analogy break down?

    Just wondering. Some food for thought… Hopefully nobody’s already asked this in the page or three of comments. Sorry if it’s a duplicate… Hopefully not!

    In any event, it’s certainly an interesting experiment. Seems plausible enough, assuming it can be shown to actually APPLY to Saturn’s circumstances.

    One should note the last line of the description of the video on YouTube (all things with a grain of salt):
    “It is still unknown what exactly would generate such a jet stream and especially one at just the right angular velocity to produce a hexagon.”

    More study required?

  36. Brutus

    The video of the hexagon in water shows six distinct eddies/vortices all around the outside of the hexagon. Saturn’s hexagon shows nothing like that, just a clean hexagon. I think I need more to be convinced than this partial similarity.
    Weren’t those electric Universers the ones with the “looks like” arguments? Phil, you aren’t switching sides, are you?

  37. Tim Erney

    Consider the following statement from a paper, “Experiments on two-dimensional vortex patterns”:

    http://socrates.berkeley.edu/~fajans/pub/pdffiles/2DVortexPatternsPoF.PDF

    “The evolution of a strongly magnetized electron system is identical to that of an ideal
    two-dimensional (2-D) fluid; an electron column is equivalent to a fluid vortex. We have studied the stability of 2-D vortex patterns with electron columns confined in a Malmberg–Penning trap. The following cases are presented: the stability of N vortices arranged in a ring; the stability of N
    vortices arranged in a ring with a central vortex; the stability of more complicated vortex patterns.”
    [..]
    “The initial state in Fig. 10(b) exhibits a curious breathing motion around the stable N=6 hexagon. The patterns oscillate between near-triangular and near-hexagonal states in the reference frame rotating with the pattern…”

    From this paper, “Influence of profile shape on the diocotron instability in a non-neutral plasma column”, we have equations relating to a plasma column confined along an axial magnetic field.

    http://nonneutral.pppl.gov/pdfpapers/PP.1998.5.3497.RD.pdf

    “In this paper we examine theoretically the influence of density profile shape on the diocotron
    instability in a cylindrical, low-density non-neutral electron plasma column confined radially by a uniform axial magnetic field”

    ———————

    It should be noted that the hexagon fits neatly inside the auroral ring at Saturn’s North pole, encircling the magnetic axis, as if defining a “low-density non-neutral electron plasma column confined radially by a uniform axial magnetic field”. I recall seeing some images or animations where it seems the hexagon pattern morphs into something like a semi-triangular form as well.

    Which is a more realistic analog to the environment at Saturn’s north pole hexagon? A liquid spinning on a plate in a jar… or a plasma column (ionized gas) confined by a magnetic field?

    It seems that plasma physics is quite applicable in the case of Saturn’s hexagon.

  38. Kapriel

    There are also those hot-spots in the Saturnian Hex. Fluid mechanics doesn’t really explain that. That’s why I suggested a combination of effects here.

    Plasma physics isn’t voodoo science, so it’s certain that just about anything we see as “space weather” will have it’s plasma component. I wasn’t sure why Phil was so upset with the electric universe people specifically, but maybe there’s some “history” there we aren’t privy to, who knows. There’s a lot of brawling that goes on between scientific genres, despite the civilized lab-coats and so on. People are still people, and they seldom agree on all specifics. I guess that’s what keeps it interesting!

  39. Plasma dude

    It is very poor reasoning to suggest that just because something can be recreated in a test tube, then it precludes other options.

    Which is quite funny as the plasma physics people say the hexagonal shapes can be produced by Beltrami-type vortex filaments. This seems more likely as auroral phenomena are influenced by plasma physics. Guess we don’t need plain old fluid dynamics after all.

    In this case, there are similarities to and auroral curls, which are likely due to the Diocotron instability. See:

    http://www.plasma-universe.com/Diocotron_instability

  40. Tim Erney

    Here’s a paper confirming the similarities between hydrodynamic and magnetohydrodynamic vortices in a direct comparison of the spinning fluid experiment and the plasma experiments with the Malmberg-Penning trap.

    ‘The dynamic similarity between polygonal satellite vortices and electron columns in a Malmberg–Penning trap’

    http://iopscience.iop.org/0741-3335/50/12/124047;jsessionid=CADE74E2926EF8B60149839F2DD4B11B.c3

    “The formation of polygonal satellite vortices due to the rotation of the fluid by a bottom disk is studied. The results obtained for a normal fluid (water) are compared with that observed for pure electron plasma in Malmberg–Penning traps. The comparison shows similar patterns of vortices produced in two completely different systems, providing the experimental evidence of the direct analogy between the polygonal satellite vortices observed in a normal fluid and the vortices in pure electron plasma.”

    So now we seem to be at least on the level of the spinning fluid demonstration. With theoretical, mathematical, laboratory and comparative analysis to support the hypothesis that the hexagon at Saturn’s north pole is likely due to a column of charged particles (plasma) aligned with Saturn’s magnetic axis.

    Is there evidence of a correlation between the charged particle environment, magnetic field and the hexagon at Saturn’s north pole?

    Saturn has a strong magnetic field. Is there evidence that charged particles are “field aligned” around the magnetic axis at the north pole? Yes, the aurora occurs in a ring directly above the outer edge of the hexagon. In fact, the aurora is more hexagonal than circular with the brightest bands preferring the space between the corners of the well defined hexagon in the atmosphere below, as seen in the following three images at different times and angles.

    http://photojournal.jpl.nasa.gov/jpeg/PIA09185.jpg

    http://apod.nasa.gov/apod/image/0811/saturnhexaurora_cassini_big.jpg

    http://wwwvims.lpl.arizona.edu/three_aur.jpg

    Even though this is in no way definitive proof, the correlations appear worthy of further investigation and should bring into question whether the explanation supported by the spinning fluid experiment should be the end of the story.

    Regards

  41. Eric LaFlamme

    Dear Author….you don’t mean to disrespect to any real plasma scientists….just throwing juvenile potshots at those “Electric Universe” folks eh. The funny thing is a real scientist is not so confused by the dogma of accepted belief as you are. I think you should give up writing science articles and join the seminary. I coin your religion Lemaitreism. “Crackball” science is proffering an explanation for something that can not be observed or interacted with(DM, DE), just because your theory will not work without it.
    Electric currents exists everywhere in space; they are responsible for galactic, stellar, and planetary formation; they power the stars and the galaxies. Saturn’s polar hexagon is an electromagnetic artifact, as is the entire observable universe. Sorry to burst your bubble author, but it is you and your ilk who ride the short bus of life(my potshot at the Eddingtonites.)

    Cheers

  42. Islandguy

    Well, Phil, apart from ‘hiding’ the actual science behind a link that doesn’t read “look for science here”, this experiment has nothing to do with the situation on Saturn. If you’d actually followed your own link to Emily you would have noticed the little sequence of images obtained by my favorite space probe Cassini. Just look at that short clip and then look at the experiment again. There is no similarity other than that both feature a hexgonal geometry. The flow behavior is dinstinctly different, which of course is to be expected as the hexagon on Saturn is obviously a plasma/electrical phenomenon. You can scream and shout, ridicule actual scientists in your shallow propagandist mode as much as you like, it won’t make the facts go away. You are electrically illiterate and your publications are not concerned with science, but rather with propaganda. The “bad astronomer” is giving science a bad name.

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