Riding with Robots sends us to a NASA page with photos of a little-understood hexagonal shape surrounding Saturn's north pole. "This is a very strange feature, lying in a precise geometric fashion with six nearly equally straight sides," said Kevin Baines, member of Cassini's visual and infrared mapping spectrometer team. "We've never seen anything like this on any other planet." This structure was discovered by the Voyager probes over 20 years ago (here's an 18-year-old note on the mystery). The fact that it's still in place means it is stable and long-lived. Scientists have no idea what causes the hexagon. It's nearly big enough to fit four earths inside — comfortably larger than Jupiter's Great Red Spot. The article has an animation of clouds moving within the hexagon captured in infrared light.