Space

A deep, hexagon-shaped feature lies above Saturn's north pole, newly released images from the Cassini spacecraft reveal. The strange structure appears to be nearly stationary and may be a wave that stretches deep into the giant planet's atmosphere.

NASA's Voyager 1 and 2 spacecraft glimpsed parts of the feature nearly 30 years ago, but because of their viewing angle, they were not able to see the whole thing. Now, Cassini's visual and infrared mapping spectrometer has captured the entire hexagon for the first time, thanks to a series of infrared images it took as the spacecraft flew over the pole in October and November 2006 (see Cassini snaps Saturn from a dizzying height).

The hexagon spans nearly 25,000 kilometres - the width of two Earths - and appears to be a clearing in the clouds that extends at least 75 km below the planet's visible cloudtops. Watch a movie of clouds whipping around Saturn's strange hexagon (4.2 MB, gif).

"This is a very strange feature, lying in a precise geometric fashion with six nearly equally straight sides," says team member Kevin Baines of NASA's Jet Propulsion Laboratory in Pasadena, California, US. "We've never seen anything like this on any other planet."

Striking differences

In a statement, NASA says the feature may be "an unusually strong pole-encircling planetary wave that extends deep into the atmosphere".

Saturn's south pole also boasts a dramatic feature - a hurricane-like storm two-thirds as wide as the Earth (scroll down for image and see Spectacular storm rages on Saturn's south pole).

"It's amazing to see such striking differences on opposite ends of Saturn's poles," says Bob Brown, leader of the Cassini visual and infrared mapping spectrometer at the University of Arizona in Tucson, US. "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."

Currently, the hexagon can only be detected at infrared wavelengths because it is winter in the northern hemisphere - a 15-year-long season in which sunlight does not fall on the pole. As spring begins to dawn in the region over the next two years, astronomers will search for the feature at visible wavelengths.

If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.