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Cassini captures movie of Saturn's mysterious hexagon

Paul Sutherland, Feature writer
Dec 7, 2013, 8:00 UTC

Sen—NASA’s Cassini spacecraft has produced a remarkable new high-resolution movie of a peculiar hexagonal feature that surrounds Saturn’s north pole.

The unique feature is a six-sided wavy jet stream of winds blowing at around 320 kilometres per hour (200mph). At its heart is a huge rotating storm. Nothing similar to the hexagon has been seen on any other planet.

A series of images captured over a 10-hour period has given space scientists a chance to take a close look at the movements of clouds within the feature.

It may seem bizarre that such a geometrical structure can persist for so long. Yet planetary scientists say it might have been there for a very long time. The hexagon spans about 30,000 km (20,000 miles) and stretches from the pole to 70° latitude.

Andrew Ingersoll, a Cassini imaging team member at the California Institute of Technology, said: “The hexagon is just a current of air, and weather features out there that share similarities to this are notoriously turbulent and unstable.

“A hurricane on Earth typically lasts a week, but this has been here for decades - and who knows - maybe centuries.”

The reason why the hexagon can be so long-lasting is being put down to Saturn’s structure as basically just a giant gasball. Without any solid landforms, as might be found on Earth, to disrupt things, the feature has stayed stable.

Seasonal changes on Saturn are now giving planetary scientists better views of the hexagon. Spring in its northern hemisphere only began in August 2009 and the Sun began to illuminate its interior late in 2012.


An image of the hexagon taken in natural colours. Image credit: NASA/JPL/Space Science Institute

Cassini’s mission is due to end in September 2017, when the planet’s northern hemisphere reaches summer solstice. The scientists will make the most of their time until then to learn more about the hexagon.

Scott Edgington, Cassini deputy project scientist at NASA’s Jet Propulsion Laboratory in California, said: “As we approach Saturn’s summer solstice in 2017, lighting conditions over its north pole will improve, and we are excited to track the changes that occur both inside and outside the hexagon boundary.”

Observations by Cassini until now have shown the storm around the pole, as well as small vortices rotating in the opposite direction of the hexagon. Some of these vortices are swept along with the jet stream. The largest of these vortices spans about 3,500 km (2,200 miles), which is around twice the size of the largest hurricane recorded on Earth.

By analysing the images in false colour, scientists were able to distinguish different types of particles suspended in Saturn’s hazy atmosphere inside and outside the hexagon.


A movie made from the hi-res images. Credit: NASA/JPL/Space Science Institute

Kunio Sayanagi, a Cassini imaging team associate at Hampton University in Virginia, said: “Inside the hexagon, there are fewer large haze particles and a concentration of small haze particles, while outside the hexagon, the opposite is true. The hexagonal jet stream is acting like a barrier, which results in something like Earth’s Antarctic ozone hole.”

The Cassini-Huygens mission, which launched in 1997 and arrived at Saturn on July 1, 2004, is a joint project between NASA, the European Space Agency and the Italian Space Agency.