I'll admit, I did a double-take when I first saw the pictures of the hexagon at Saturn's north pole. We don't see too many regular polygons in astronomy. It makes me think of Ellie Arroway's (played by Jody Foster) ominous line in the movie Contact upon seeing the geometric patterns of light on a distant planet: "They're alive."
It also begs the question: Is it natural? And how can it be? To find out, physicists at the University of Oxford have recreated the hexagon in the lab. They've found that a regular, pointy shape is indeed a natural phenomenon in this case.
The hexagon was first detected by the Voyager missions in the 1980s. Infrared mapping of the strange shape by Cassini in 2006 showed that it had survived for at least 25 years.
The Oxford researchers made a model of Saturn's North Pole. A slowly-spinning cylinder of water represented Saturn's atmosphere, and a small, rapidly-spinning ring represented a jet stream. They added some fluorescent green dye, and got a pretty well-defined hexagon.
By playing with the speed of the ring, the researchers could make nearly any shape that they wanted. The greater the difference in speed between the water and the ring, the fewer sides the polygon had. The shape seems to be bound by eddies that slowly orbit and confine the inner ring into the polygon.
Apparently, these shapes are not uncommon in fluid dynamics and can even be seen in hurricanes. This seems to be an example of a well-known phenomenon in one field being relevant to another in a completely unexpected way. But it takes a while for each community to be aware of the other one's results.
Watch the video of the laboratory hexagon growing (credit: Anna Barbosa Agular):
Thanks to my friend and fellow grad student, Jarron, for bringing this story to our journal club this week!
Image credit (top): Anna Barbosa Agular; (inset) NASA/JPL/University of Arizona