Hexagon-shaped storms exist. There is a massive, persistent, hexagon-shaped jet stream on Saturn’s north pole — “the perfect six-sided hurricane, 60 miles deep, that could swallow four Earths…”
The New York Times‘ Storm Chasing on Saturn describes our first Voyager mission views of the phenomenon in 1981–82, as well as more recent Cassini images, like the NASA/JPL-Caltech/SSI/Hampton University images below.
How did this unusual hexagonal storm form? How long has it existed? What’s happening in those corners? Lab tests suggest some “how it’s made” answers — “friction with slower-moving atmosphere on either side of the jet stream would create eddies, miniature hurricanes, that would push the jet stream north and south as it went around the planet, resulting in a wave shape” — but the Cassini team is still looking into a huge list of unanswered questions as they prep to observe Saturn during its well-lit summer solstice in 2017.