Space scientists are intrigued by a honeycomb feature at Saturn’s north pole that is shaped like a perfect hexagon. Unlike the usual swirling, circular storms and hurricanes in the giant planets’ clouds, the oddity has six straight sides.

Nasa’s Cassini spaceprobe, in orbit around the ringed planet, has taken a movie of the hexagon rotating about the entire north pole.

Scientists first noted the oddity in photos from the Voyager missions into deep space in the early 1980s and then a Hubble picture in 1991. Now Cassini has shown its geometrical structure in detail and indicates that it is a long-lasting rather than temporary phenomenon.

The orbiter’s visual and infrared mapping spectrometer – a thermal camera – is the first instrument to capture the entire hexagon feature in one image. Saturn’s north pole is currently tilted away from the Sun and is in darkness.

Atmospheric expert Kevin Baines, of Nasa’s Jet Propulsion Laboratory, in California, said: “This is a very strange feature, lying in a precise geometric fashion with six nearly equally straight sides. We’ve never seen anything like this on any other planet.”

The hexagon is nearly 25,000 kilometers (15,000 miles) across – enough to contain the Earth nearly four times. The hexagon appears to be unlike the feature that dominates Saturn’s south pole – a hurricane resembling a giant eye.

Scientists hope that understanding the hexagon’s structure will help them pin down a precise figure for the length of Daturn’s day – the rate at which the planet rotates beneath the clouds. Photo: Nasa.