A hex on Saturn (again)!

By Phil Plait | December 9, 2009 1:46 pm

Either Saturn likes playing role-playing games, or it has really weird weather patterns… and we know it has weird weather patterns.

Behold, Saturn’s northern hexagon!


This odd six-sided pattern — which is over 20,000 kilometers across — was first seen in Voyager images back in the 1970s. When Cassini arrived at Saturn it was winter in the planet’s northern hemisphere, so the hexagon was shrouded in darkness. Cassini’s infrared cameras were able to get some images, and while they did reveal needed info on the feature, astronomers really wanted higher-res visible light images.

Finally, earlier this year the Sun started peeking over into Saturn’s arctic regions as the Equinox approached. When dawn broke over the north pole, astronomers pointed Cassini’s higher-resolution visible light cameras there. This new image, taken in January, is a mosaic from those observations. It reveals quite a bit about the hexagon. You can easily see that the clouds are darker inside the hex than outside, for example. The borders of the hexagon have multiple walls of clouds, too, and the feature extends all the way to the top of Saturn’s atmosphere (the earlier IR imagery showed the hex goes deep into the atmosphere as well).

Cassini scientists took 55 of the images and created this nifty mosaicked animation, showing the jet stream feature in motion. It moves at about 100 meters per second as it circles Saturn at 77 degrees north latitude.

This planetary stop sign is long-lived; it’s been around at least 30 years, and who knows how long it existed before that. Earth has atmospheric features that can stick around; our jet stream is a good example. But most terrestrial weather patterns come and go quickly, of course, like storms and hurricanes. But on the giant outer planets they can last decades or, in the case of Jupiter’s Great Red Spot, even centuries. At least part of that is because the planets spin rapidly, and the Coriolis effect helps power these behemoth storms. The heat source for these storms is different than on Earth, too: it comes partly from the Sun, but also from the interior of the planets themselves, and that plays a role.

But the weird shape of this jet stream is likely to puzzle and delight scientists for some time to come. These new images will give them critical clues to figure it out… and after all, isn’t that why we explore in the first place?

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: Cassini, Saturn

Comments (54)

  1. Aerimus

    The silhouette of my d20 fits nicely over the image…

    In a related note, I’m teaching my 3.5 year old about planets off and on since she first spotted Jupiter in the sky a few months back. Saturn, Mars, Jupiter and Earth she recognizes in images! One of her Christmas gifts is a Galileoscope that we bought for her earlier this year. Can’t wait to spend sometime sky watching with our scopes (I’ve got a 3.5″ Maksutov) – we just need to work on the whole “afraid of the dark” thing first…

  2. Levi in NY

    Planetary stop sign? Uhh, Phil, you do know that stop signs are octagonal, right? 😉

  3. Saturn rolls a Will saving throw and fails. Saturn takes 100,000D6 damage. Saturn is barely scratched.

  4. Paul Clapham

    It’s obviously a message from aliens. We’re supposed to bring a hex (Allen) key and wrench on it. But it doesn’t appear to be one of our standard sizes… we should get NASA working on that. I wonder if the aliens use clockwise or anti-clockwise screw threads?

  5. Mike Hall

    I’m confused where exactly this is on Saturn. Is it centered on the North Pole?

  6. Nick

    How in the name of the Flying Spaghetti Monster does that even do that?!?!?

    Is there even a hypothesis that attempts to explain hexagonal clouds that doesn’t involve noodly appendages?

  7. Richard

    Clearly, aliens on Saturn are just prepping for a giant game of Settlers of Catan.

  8. Doc

    I remember seeing a video of someone generating a similar hexagonal shape in a vortex with liquid, but I can’t find the link anymore.

  9. Benny

    #5 Yeah, that’s exactly what I was wondering. I was hoping to see a hypothesis here.

  10. Saturn’s core is actually a truncated rhombic dodecahedron. The atmosphere just makes it look roundish.

  11. Adrian Lopez

    “Planetary stop sign? Uhh, Phil, you do know that stop signs are octagonal, right?”

    In Phil’s defense, six-sided stop signs are the standard on Saturn.

  12. Folks,

    No explanations yet for how a vigorous jet stream makes a left hand turn.

    But it’s good, isn’t it, having some things left to ponder? You don’t want us figuring everything out, do you?!

  13. David

    Star Trek, The Doomsday Machine.

  14. Adrian Lopez

    Offtopic, but:


    Can anybody else see Jamie’s face on Adam’s left knee? I even see a beret. Pareidolia FTW.

  15. Bill

    What REALLY blew the astronomer’s mind was when he stared at the image and asked “How does this happen?”…and a bluish-colored triangle appeared in the center reading “Ask again later”.

  16. I’d really like to see close-ups. It looks like there are many hundreds (thousands?) of mega-hurricanes. My eyeball estimate is that they’re each maybe a minimum of as big as Katrina (over 650 km).

  17. tacitus

    Come on Phil, you know the reason for hexagonal shapes on Saturn — Richard Hoagland’s been telling you for years….

    Hyperdimensional Physics!!

    (Just don’t ask him how he knows)

  18. Paul

    My bet is on a resonance of a Rossby wave…

  19. Regner Trampedach

    What our eyes/brains interpret as a hexagon, is obviously just a standing transverse wave, very sinusoidal and fitting 6 periods into the given space. The terrestrial jet streams typically meander in latitude, but not with a fixed period. Isn’t it likely that the featureless Saturn (no continents) and the higher rotation rate makes conditions more homogeneous and therefore makes it possible for there to be a standing Rossby wave.
    Carolyn; good to see you here. I’m a big fan of your work.
    Cheers, Regner Trampedach

  20. ruidh

    Is this really that weird? It’s a standing wave with six peaks. Stretch it around a sphere and it looks sort of like a hexagon. We have a similar standing wave on Earth. We call it “The Jet Stream” except that Earth’s continents distort it. Saturn doesn’t have continents and the clouds make it visible while Earth’s Jet Stream isn’t.

  21. Just more purposeless matter hovering in the dark. Move along. Nothing to see here.

  22. Slade Jokela

    I suspect that Regner Trampedach’s post works into this as well. I can’t tell from the images captured, but my initial thought is that this could be caused by tidal forces from multiple moons that have harmonic orbits. If this were true, I think you would also see the hexagon precess at a harmonic as well. Of course, I suspect you would also see the planet bulge around the equator along the same longitude. (EDIT: Of course changing latitude is easier than changing elevation)

    So, two things I’d like to see… does the hexagon precess and does the speed of gas flowing along the border decrease as you approach a vertex.

  23. RMH

    Right away I thought Standing wave. My studio suffers from one and a friend mentioned building a round room to solve it and when I explained to him how that wouldn’t help, I drew it out and got this pattern. Funny coincidence.
    This is still cool tho. I’m assuming the scientists have already hypothesized this…
    I’m imagining this is still ultra strange considering its in the atmosphere.

  24. Chris A.

    I’m with Regner (#19) and ruidh (#20) on this one: Isn’t the immediate assumption that the hexagon occurs at a latitude circle whose circumference is six times some sort of characteristic atmospheric oscillation’s wavelength? I find myself then asking, why don’t we see a pentagon or square or triangle at higher latitudes, respectively? (And/or heptagon, octagon, etc. at lower latitudes?) Guess I need to do some reading about Rossby waves…

    The “twisted rope” appearance of the hexagon also makes me really curious about what’s happening in the “z” (radial) direction, too.

  25. awesomekip

    Earth’s jet stream also looks like a hexagon when view from above the North pole.


  26. psuedonymous

    A great big Bénard cell maybe?

  27. photosphere

    I often see this at work. It happens when mixing our proprietary fluids with a straight edged propeller, relatively close to the surface, on a shaft sunk vertically into the proprietary fluids. Different depths/speeds can also produce a circle of mini-vortexes.
    Thanks to this blog I get to think about astronomy while enduring my soul-crushing labors. Keep up the good work BA!

  28. CR

    Doc beat me to it in post #8… I, too, recall seeing pics of the liquid tube vortex creating hexes.

    As for the hexagonal stop sign mistake, I used to proof printed copies of books, and one was a children’s activity book about math tricks. That book specifically asked “Can you picture a hexagon? It’s the shape of a stop sign.”
    I let the customer service rep in our company know about the error, suggesting that the word ‘hexagon’ be changed to ‘octagon’ (which might render the whole math trick moot), or change the words ‘stop sign’ to ‘honeycomb.’ The CSR passed the info on to the customers (publisher and/or author), who later said that they were very appreciative of my attention to detail.
    I hoped that my supervisor would be that appreciative during my next performance review, and looked forward to the revision of the math book when we reprinted it.
    The performance review went OK, but a year later, when we reprinted the book, the error was unchanged.

  29. Jeremy Henderson

    It looks like a photo of Saturn’s colonoscopy…

  30. Kaleberg

    Regner and ruidh are right. We have the same pattern on earth. Look at the isobars on a north polar projection. You’ll see a similar pattern. I noticed it some years ago doing flight planning for a polar route.

  31. Huh?

    10. Todd W. Says: “Saturn’s core is actually a truncated rhombic dodecahedron.

    Rhombus or dodecahedron?

    Maybe I’m making a geometry FAIL here* but aren’t they two separate shapes? Can you have something that is both a rhombic and a dodecahedron? (Puzzled.)

    * Been a very long time since I studied any geometry (way back in high school?) and I was rubbish at it even then. So forgive me please if what I’ve just said is utterly dumb.

  32. Proctological Nazi

    30. Jeremy Henderson Says:

    It looks like a photo of Saturn’s colonoscopy…

    Ewww! That’s a planet-load of s***t! 😉

    I guess that explains why Saturn is within the rings. 😉

    Could be worse though. Could be giving Uranus an enema .. 😉

  33. As mentioned, these kind of polygons are known to form when you stir water in a bucket using a rotating bottom plate. It’s cool to see them on such a large scale. The link below has some details and a link to videos.


  34. StevoR

    @ 10. Todd W. Says:

    Saturn’s core is actually a truncated rhombic dodecahedron. The atmosphere just makes it look roundish.

    Wouldn’t gravity compress Saturn’s core into a sphere? Assuming its massive (Ceres- size upwards) which seems a safe assumption to make.

    I’m not sure whether Todd W. is joking there or not – think he probably is posting in jest but you never quite know.

    Could Saturn’s core crystalise at the immense pressures and temperatures at the bottom of the planet? Could Saturn’s core be like a giant diamond as was famously suggested for some gas giants? (Originally Ouranos and Neptune but Arthur C. Clarke was inspired to use that idea for Jupiter in fictional form in his Space Odyssey novels.)

    How massive is Saturn btw? Anyone know?

    I think Jupiter is 318 Earth-masses & I remember from reading one of Patrick Moore’s books (The Sky at Night Norton, 1985.) that Ouranos has 14 earth mases and Neptune 17 earth masses but I’m really not sure how Saturn compares. I think its significantly less massive than Jupiter – its definitely a lot less dense as its the least dense planet in the solar systemand would float on a big enough ocean. So my guess is maybe 30-50 earth mass for Saturn? Alas, I’ve no idea if that’s anything even close to the right number. Still that’s a lot of mass and thus internal gravity and pressure.

    I have read something somewhere about possible core erosian in the gas giants and gather that their cores are still very mysterious. I don’t know if there’s any chance Todd W’s idea is right but I think it very unlikely.

    Great image though BA although a colour shot would be even better. Looks cool & fascinating! :-)

  35. StevoR

    Having asked : How massive is Saturn btw? Anyone know?

    I’ve now just checked & answered – answer is that Wikipedia makes Saturn 95 earth masses.

    See : http://en.wikipedia.org/wiki/Saturn

    Saturn is only 95 Earth masses, compared to Jupiter, which is 318 times the mass of the Earth but only about 20% larger than Saturn.

    They’ve also got an animation of the hexagon storm here :


  36. FrankZA

    This paper applies to this story: http://arxiv.org/abs/physics/0511251

    Jansson et al., 2007, Polygons on a rotating surface


    We report a novel and spectacular instability of a fluid surface in a rotating system. In a flow driven by rotating the bottom plate of a partially filled, stationary cylindrical container, the shape of the free surface can spontaneously break the axial symmetry and assume the form of a polygon rotating rigidly with a speed different from that of the plate. With water we have observed polygons with up to 6 corners. It has been known for many years that such flows are prone to symmetry breaking, but apparently the polygonal surface shapes have never been observed. The creation of rotating internal waves in a similar setup was observed for much lower rotation rates, where the free surface remains essentially flat [1]-[3]. 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.

  37. Nigel Depledge

    The BA said:

    The heat source for these storms is different than on Earth, too: it comes partly from the Sun, but also from the interior of the planets themselves, and that plays a role.

    I think also that the Kelvin-Heimholtz mechanism is relevant, which is an atmospheric phenomenon.

  38. Michel

    Looks like broth to me.

  39. ZERO

    Those storms are quite beautiful indeed!

  40. Richie

    Kinda reminded me of the “Well of Souls” series by Jack L Chalker. The Markovians were nutty on the number six, and made everything in hexagonal shapes – including their teleport gates. I think we just found the Sol gate….

  41. shawmutt

    OK…am I the only one who can make out hands on either side of that vortex?

  42. Sili

    and who knows how long it existed before that.

    And this is exactly why the current inch-by-inch exploration of the Solar system has to end.

    We need permanent observations of all the planets. The next orbiter needs to be in place before the first one conks out. Just look at how much more effective our exploration of Mars has become after we established a permanent presence.

    Make Science! Not war!

  43. Robert

    Of course permanent observation of all planets is to be desired, but we don’t have the resources for this. If I had to make a choice between a continual observation of only Mars, or a sporadic observation of each of the planets/moons I think I’d choose the latter option.

  44. CR

    shawmutt asked if anyone else saw hands around the hex. Nope, I don’t see any hands. But if they ARE there, I wonder if a banana would fit perfectly into the shape? (Ha, ha! 😉 )

  45. Damon

    If I had to venture a guess I’d say there’s something “off” about Saturn’s electromagnetic field.

  46. huh? sez:
    >0. Todd W. Says:
    >>Saturn’s core is actually a truncated rhombic dodecahedron.
    >Rhombus or dodecahedron?
    >Maybe I’m making a geometry FAIL here* but aren’t they two
    >separate shapes? Can you have something that is both a rhombic
    >and a dodecahedron?
    huh?, there’s a difference between “RhomBUS” (noun) and “rhomBIC” (adjective)…
    Wikipedia page on ‘rhombic dodecahedron’: en.wikipedia.org/wiki/Rhombic_dodecahedron

  47. Huh?

    ^ Thanks for that Cubist. :-)

  48. Christian Treczoks

    It’s too dark and too far away, I can’t see the monolith in the center!

  49. kk

    i read somewhere that cassini mission have a backdoor in software and hardware and this might be product of a group of hackers.

    the images are well photoshoped to look more dramatic.

    they would call this the joke of the millenium.

  50. @41: Yeah, and he also said that the surface of the entire (spherical) planet was covered in a network consisting only of hexagons. You would need /some/ pentagons or triangles. Non-Euclidean geometry fail.

  51. Pongsun Anurat

    Long time ago, it was a Alien military base which has six giant walls.

    And the aliens think like bee because “Hexagons are the stablest structures that use the least material and have the most space. That is why bees build their hives with hexagonal cells out of bees wax.” (Dannon Oneironaut, http://www.dreamviews.com).

    If some life forms built it, they possibly do know some mathematical proof 55.

  52. Hakko

    A stop sign is an octagon…not a hexagon… -_-;


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