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Comment by gewoonkris | Hacker News Reader

For those who are also wondering about the briefly mentioned hexagon-shaped jet stream:

One hypothesis, developed at Oxford University, is that the hexagon forms where there is a steep latitudinal gradient in the speed of the atmospheric winds in Saturn's atmosphere. Similar regular shapes were created in the laboratory when a circular tank of liquid was rotated at different speeds at its centre and periphery. The most common shape was six sided, but shapes from three to eight sided were also produced. The shapes form in an area of turbulent flow between the two different rotating fluid bodies with dissimilar speeds

Source: https://en.wikipedia.org/wiki/Saturn's_hexagon

Paper (paywalled): http://www.sciencedirect.com/science/article/pii/S0019103509...

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I like this work and the presentation by Tianlu Yuan (2013) about how our knowledge about the subject progressed -- the first photos were made by Voyager (1981-82):

http://www-hep.colorado.edu/~tianlu/public/saturnHex_paper.p...

http://www-hep.colorado.edu/~tianlu/public/saturnHex_present...

"In the 1980s images of Saturn taken by Voyager led to Godfrey's surprising discovery of a hexagonal structure on the planet's north pole [9]. Now, over three decades later, Saturn's north polar hexagon remains, superficially unchanged and not entirely understood. Voyager's iconic images proved a challenge to explain theoretically, but with additional data from ground based observations and the HST in the early 90s, and images from the Cassini mission more recently, our knowledge of many physical parameters forming the hexagon has increased. Along with observation, laboratory experiments and numerical simulations have helped foster greater understanding of the possible causes of the jet's six-sided shape."

The more recent pictures (2016) are also interesting, as the color has changed(!):

http://www.forbes.com/sites/startswithabang/2016/10/31/satur...

And for completeness, the comics from 2010:

http://www.smbc-comics.com/comic/2010-07-06

I read the article and thought I must research into the hexagonal madness. Turned to comments, HN's transcendent consciousness wins again! Cheers gewoonkris.

Thanks for providing these references. The hexagonal cloud formation was the first thing I noticed and was hoping someone would have already provided references in the comments. One of the great aspects of the HN community!

I think it's a sphere packing thing. [0] Equally sized circles touching on edges "like" to pack into a six-up orientation, not unlike a revolver pistol.

My hunch is that it's an artifact of pi, somehow. Six being easily factored to three, which has close proximity to pi.

[0] https://en.m.wikipedia.org/wiki/Sphere_packing

> Saturn's south pole does not have a hexagon, according to Hubble observations; however, it does have a vortex, and there is also a vortex inside the northern hexagon. (o)

could the fact that there is only one hexagon imply a consequence of the 'hairy ball theorem'?(i)

(o) https://en.wikipedia.org/wiki/Saturn's_hexagon

(i) https://en.wikipedia.org/wiki/Hairy_ball_theorem

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