Saturn's hexagon (a long-term storm near the North Pole) has been known to exist at least since 1988. See also TRF 2007.
NASA's Cassini mission has just revealed this picture of the six-sided jet stream.
Is the nonlinear mechanism behind this bizarre, seemingly artificial shape of the vortex/soliton theoretically understood? Is there some literature about it? Independently, do you have an explanation yourself? That's also a question I asked on Physics Stack Exchange now.
I can imagine an explanation in terms of the same mechanisms that would explain the circular shape – but with some extra terms that try to repel the extrinsic curvature of the boundary of the soliton from the value associated with the disk shape. Effectively, the curvature radius of the boundary could prefer to be either close to the huge curvature radius near the near-straight sides; or the much shorter radius near the vertices. Would it actually work? Can these terms be naturally generated by the dynamics?
Or do we have to postulate extraterrestrial aliens who built their U.S. Department of Defense plus 20% on their North Pole?
P.S.: Someone posted an answer that the shape was recreated in the lab. Nice. What about theorists, can they explain this easy-to-formulate pattern?