Smithsonian.com

This is definitely one of our solar system’s weirder features: a hexagon that circles the north pole of Saturn (image credit: NASA/JPL/University of Arizona). The shape isn’t carved into the planet’s surface; it’s a constant feature in the atmosphere. It has puzzled scientists since it was first spotted in the 1980s.

But now physicists from the University of Oxford may have an explanation (their study appears in the journal Icarus); the hexagon may be a result of fluid dynamics. Adam Mann explains in Science NOW how the Oxford scientists were able to produce something similar in the lab:

They placed a 30-liter cylinder of water on a slowly spinning table; the water represented Saturn’s atmosphere spinning with the planet’s rotation. Inside this tank, they placed a small ring that whirled more rapidly than the cylinder. This created a miniature artificial “jet stream” that the researchers tracked with a green dye.

The faster the ring rotated, the less circular the green jet stream became. Small eddies formed along its edges, which slowly became larger and stronger and forced the fluid within the ring into the shape of a polygon. By altering the rate at which the ring spun, the scientists could generate various shapes. “We could create ovals, triangles, squares, almost anything you like,” says [Oxford physicist Peter] Read. The bigger the difference in the rotation between the planet and the jet steam—that is the cylinder and the ring—the more sides the polygon had.

The scientists say that Saturn’s jet stream may be spinning at just the right speed to form a hexagonal shape.

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