Cassini snaps hexagon around Saturn's north pole

Stephen Withers
Wednesday, 28 March 2007 07:30

Science - Space

Images from Cassini have shone fresh light on a hexagonal structure in Saturn's atmosphere first seen 26 years ago.

Although Voyager 1 and 2 previously sent back images of the feature that encircles Saturn's north pole, Cassini's visual and infrared mapping spectrometer (VIMS) is the first instrument that's been able to capture the entire 25,000 kilometre wide hexagon in one shot.

"We've never seen anything like this on any other planet," said Kevin Baines, atmospheric expert and member of the Cassini VIMS team at NASA's Jet Propulsion Laboratory in California. "Saturn's thick atmosphere... is perhaps the last place you’d expect to see such a six-sided geometric figure, yet there it is."

The new images show the structure extends around 100 kilometres below the cloud tops, leading scientists to discount theories that it is related to Saturn's radio emissions or the planets northern aurora which lies overhead. A satisfactory explanation has yet to be developed.

"It's amazing to see such striking differences on opposite ends of Saturn's poles," said Bob Brown, team leader of the Cassini VIMS instrument, University of Arizona, Tucson. "At the south pole we have what appears to be a hurricane with a giant eye, and at the north pole of Saturn we have this geometric feature, which is completely different."

The hexagon could help scientists determine Saturn's rate of rotation: "Once we understand its dynamical nature, this long-lived, deep-seated polar hexagon may give us a clue to the true rotation rate of the deep atmosphere and perhaps the interior," said Baines.

Cassini is a cooperative project of NASA, ESA and the Italian Space Agency.