A Mystery Aurora above Saturn’s Mysterious North Pole Hexagon

The aurora above Saturn's North Pole hexagon (NASA)

Not only does Saturn have a mysterious hexagonal shape etched into the bands of cloud above its north pole, it also has a unique magnetic structure. This is suggested by recent results recorded by the NASA Cassini probe that passed over the pole to see a huge active auroral region, much larger and more dynamic than expected. Interestingly, the NASA press release has not linked the strange aurora with the long-lived hexagonal shape in the gas giant’s atmosphere. Could the hexagon be formed by a unique magnetic structure above Saturn? Or could both phenomena be connected in some other way?

Tom Stallard, a scientist working with Cassini data at the University of Leicester, describes the new Cassini infrared observations above the north pole of Saturn:

We’ve never seen an aurora like this elsewhere. It’s not just a ring of auroras like those we’ve seen at Jupiter or Earth. This aurora covers an enormous area across the pole. Our current ideas on what forms Saturn’s aurora predict that this region should be empty, so finding such a bright aurora here is a fantastic surprise.” – Tom Stallard, NASA press release

So, it would appear we have another piece in the puzzle that is Saturn’s north pole. Recently, Cassini returned high resolution images of the magnificent pattern etched into the clouds around the pole. The (almost) perfect hexagon has been observed since 1980 when the Voyager 1 probe journeyed past the planet, and the same pattern exists 28 years later. So, we are dealing with a long-lived, stable pattern, that remains unaltered even when vast and powerful cyclones buffet its hexagonal boundary.

Infrared observations of the north pole of Saturn as taken by the Cassini mission in 2007 and 2008 (NASA)
Infrared observations of the north pole of Saturn as taken by the Cassini mission in 2007 and 2008 (NASA)

Last month I investigated what could be causing the pattern, and the only explanation I had was the possibility of some kind of standing wave (a Rossby-like process). As the atmosphere of Saturn is more dense than the Earth’s, perhaps a global wave could endure for decades, possibly longer. However, over at the Universe Today, some readers commented that a pattern like this had been seen before during Danish experiments on spinning fluids. Occasionally a fluid being spun inside a smooth-sided beaker will spontaneously snap into a geometric formation. An explanation for this fluid behaviour has, so far, not been found.

So we already have two possibly explanations for the near-perfect hexagon in Saturn’s atmosphere, one that dominates weather processes here on Earth (Rossby waves) and one that has been observed in the dynamics of spinning fluids in the laboratory.

Now there is another, attractive possibility.

Aurorae are generated when charged solar wind particles interact with the magnetospheres of planets. Ions are channelled to the polar regions where the magnetic field feeds down into the planet’s atmosphere. As the energetic ions interact with the atmospheric gases, light is generated. Depending on the density of the atmospheric elements, light will be emitted when the gases are excited through particle collisions. For example, in the Earth’s atmosphere green and red light in optical wavelengths can be observed when molecular oxygen is excited.

The structure of the Earth's magnetic field. Energetic particles enter the atmosphere via the polar cusp, thereby allowing plasma from the magnetosheath in (NASA)
The structure of the Earth's magnetic field. Energetic particles enter the atmosphere via the polar cusp, thereby allowing plasma from the magnetosheath in (NASA)

It is unclear what component of Saturn’s atmosphere is glowing in the infrared part of the spectrum, but the interesting thing is that the auroral oval appears to be located directly above the atmospheric hexagonal shape. The auroral oval above Earth’s poles sketch the location of the point at which magnetosheath plasma (i.e. the outer “edge” of the magnetosphere) can access the Earth’s upper atmosphere (the ionosphere). This is basically where energetic particles (originally from the solar wind) trapped inside the layers of the Earth’s magnetic field are “funnelled” downward via the “polar cusp”, so auroral interactions can occur (refer to the diagram above). A similar magnetic configuration is assumed for Saturn.

It seems that scientists working with the Cassini data are surprised by the size of Saturn’s auroral oval, suggesting we do not fully understand the configuration of Saturn’s magnetosphere. The infrared auroral oval is the point at which Saturn’s own polar cusp is located, magnetic fieldlines feeding into Saturn’s atmosphere, blasting solar wind ions into Saturn’s atmospheric gases. Could there be a connection between solar wind processes and the enduring “Saturn hexagon”? This doesn’t really explain why it should be hexagonal in shape, but the coincidence of the mystery auroral oval located directly over the mystery hexagon is too stark to ignore.

NASA details about the aurora image (top):

This image of the northern polar region of Saturn shows both the aurora and underlying atmosphere, seen at two different wavelengths of infrared light as captured by NASA’s Cassini spacecraft.

Energetic particles, crashing into the upper atmosphere cause the aurora, shown in blue, to glow brightly at 4 microns (six times the wavelength visible to the human eye). The image shows both a bright ring, as seen from Earth, as well as an example of bright auroral emission within the polar cap that had been undetected until the advent of Cassini. This aurora, which defies past predictions of what was expected, has been observed to grow even brighter than is shown here. Silhouetted by the glow (cast here to the color red) of the hot interior of Saturn (clearly seen at a wavelength of 5 microns, or seven times the wavelength visible to the human eye) are the clouds and haze that underlie this auroral region. For a similar view of the region beneath the aurora see http://photojournal.jpl.nasa.gov/catalog/PIA09185 .

This image is a composite captured with Cassini’s visual and infrared mapping spectrometer. The aurora image was taken in the near-infrared on Nov. 10, 2006, from a distance of 1,061,000 kilometers (659,000 miles), with a phase angle of 157 degrees and a sub-spacecraft planetocentric latitude of 52 degrees north. The image of the clouds was obtained by Cassini on June 15, 2008, from a distance of 602,000 kilometers (374,000 miles) and a sub-spacecraft planetocentric latitude of 73 degrees north.

Source: NASA

12 thoughts on “A Mystery Aurora above Saturn’s Mysterious North Pole Hexagon”

  1. Dear Ian O’neill,

    I came here to thank you for the article on, shall we say, the shortened version of Mars Direct. I am a believer, and have written numerous times, of not returning the first explorers. Your article and interview with Mr. Aldrin was a breath of fresh air.

    Thank you.

    As to your hexagonal feature. It is most likely the same balancing act of rotational energy (momentum) vs. the draw of a low pressure central gradient. My prediction, based upon works of the National Hurricane Center, Dr. Gray (? I’m terrible with remembering names.) of the University of Colorado, and the fine researchers of eyewall replacement. Those people are with the University of Wisconsin. All of this is from memory, please forgive the likely errors.

    My prediction then is that: The temperature at the pole, the outflow, will be warmer, check the infrared spectrums.

    The eye of a hurricane is NOT naturally round, it will quite normally exhibit a pentagonal or hexagonal like sidedness. Particularly just before an eyewall replacement cycle. Check for photos at NOAA. A further investigation may reveal subtle structures at the cloud tops linking the verticies with the center. Again a charateristic sometimes seen in NOAA photos.

    It is a storm.

    Dean Unick


  2. They’re probably not all that connected. I say probably, because who knows what makes the hexagon shape in the lower atmosphere – but it’s unlikely to be correlated. DOesn’t make either any less mysterious though.

  3. Hello Tom S., (Stallard?)

    The eye wall of an Earthside hurricane, typhoon,,, etc. IS the fastest moving air of the storm. I would expect, like in any good thunderstorm, the motion of the air to be more than sufficient to create one heck of an electrical field. If you were talking a static feature, denser atmosphere, different gas composition, You would be talking potentially (a little humour) more than enough energy to guide or create a magnetic field. But the soft sided polygon to me is a dead give away.

    Talk to the hurricane guys in Florida at NOAA. I studied a bit of this a couple of years ago. (I reinvented the wheel. Maybe I should explain. I intuited, posited, that an eyewall should not be round. Emailed the guy’s at the hurricane center and got a rousing ‘Duh!” and they sent me some pretty special photos of exactly this polygonal shape.)

    They can certainly lead you to Gray at Colorado and ? at Wisconsin. Look for eyewall replacement cycles. And another idea that just occurred to me, likely another , “Duh”, how much of that atmosphere is a metal on the periodic table? (hydrogen?) You could be talking one heck of a generating capacity. (capacitance? More lame humour)

    Offer me a job when I turn out correct, if I am way off I’ll buy the beer.


  4. Bear with me guys…

    I think the answer lies in electrodynamics, per Thornhill and may be given impetus for investigation by a recent submitted paper by Hultqvist on auroral processes’ importance in the universe (specifically the consideration of electric fields and field aligned currents; his emphasis was on the electron-cyclotron maser effect/instability, but may just apply to other circumstances).

    I was working on something else (gathering notes for a series of non-mainstream in the works), and seeing the various references put all in one place suddenly crossed the right synapses.

    So, okay, here’s hultqvist’s paper:

    (On the Importance of Auroral Processes in the Universe)

    Here are Thornhill’s thoughts (feel free to ignore all but the part on Saturn’s polar hexagon, if you like, it’s the only bit I’m interested in at this moment).


    Thornhill implies that a diocotron instability may be responsible for the polar hexagon, where field-aligned currents (Birkeland currents) impinge on Saturn’s pole. Part of the process of the diocotron instability is the filamentation of the larger current into individual filaments. Those may adopt a hexagonal shape.

    Hultqvist’s paper analyzes new results from the study of terrestrial auroras here at Earth, and concludes that electrical interactions (electric fields and magnetic-field-aligned currents) and the electron-cyclotron maser are responsible for the Auroral Kilometric Radio waves. He also suggests that this new understanding may be applicable to other astrophysical bodies.

    In the process he sets the stage for a re-examination of fundamental assumptions with respect to electric fields and currents in space.

    The wider implications aside, Birkeland’s work from the early 1900’s were some the earliest rigorous investigations into field aligned currents and how they might interact with a magnetized body. From his investigations, he concluded that the sun was the source of field aligned currents impinging upon the atmosphere of the Earth. His view was opposed strongly by Chapman and others, who argued for a local source of currents in the auroras. In the end, Triad satellites confirmed Birkeland’s view that the Earth was involved in a circuit fed by the sun along field-aligned currents. This fact was re-discovered in late 2007 by the THEMIS satellite(s), probing substorms. Granted they chose to couch their results in the language of “magnetic reconnection,” but nonetheless, their own multimedia betrayed them and they noted the “flux ropes” carried a current of some 650,000 Amps.

    That in mind, Hultqvist’s paper implies that processes good here on Earth may well be good on other bodies locally and in the cosmos at large. I submit that further investigation from this new vantage point is required at Saturn.

    If, indeed, both the auroras and the polar hexagon can be explained in terms of an impinging field-aligned current, it may be ABSOLUTELY NO COINCIDENCE that the hexagon and the aurora appear to be coincident, one with the other.

    (Saturn’s North Pole Hexagon and Aurora)

    In other news, Thornhill was (as far as I know) the only one to predict experimentum crucis that BOTH poles should be expected to be warm due to impinging currents, in contrast with the view of Keck researchers who thought one pole (sunward) should be anomalously warm (on account of “seasonal variation,” which admittedly didn’t account for the STRUCTURE of the warm pole observed in 2005) while the other (antisunward) should be anomalously cold (since it was in Saturnian winter).

    In any event, thee seems to be growing anecdotal evidence that Thornhill may have hit the nail square on the head on both counts. If the warm poles, the hexagon AND the auroras can all be explained through a single mechanism, a new look at the data with a fresh eye might be strongly indicated!


  5. I received a message in regards to this today saying it was the star of david and pointing towards the bowels of the earth and it basically represents earthquakes and Gods judgement on earth and things will get much worse, something on that order. I think they were also talking as if this is something recently discovered but then I thought it sounded familiar since I love to watch the science channels. so I did a search and sure enough , this is what they were referring to. it does resemble the star of david and very unusual but very cool too.

    1. I was working on something else (gathering notes for a series of non-mainstream in the works), and seeing the various references put all in one place suddenly crossed the right synapses.

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