18:20 27 March 2008
NewScientist.com news service
David Shiga


A false-color movie of a whirling vortex at Saturn's south pole has been released. The storm may be driven by updrafts of warm, moist air – just like hurricanes on Earth.

The vortex was discovered, space.newscientist.com/articl...le.html , in images taken by the Cassini spacecraft when it flew over Saturn's south pole in October 2006. It is about 8000 kilometers across and rotates in the same direction as the planet's overall rotation, but about 550 kilometers per hour faster. A video, www.nasa.gov/mov/172386main_pia09187.mov , pieced together from infrared images was released at the time, giving a black and white view of the whirling storm.

Scientists have now released false-color images and a false-color video of the storm, made from the 2006 infrared observations. The images are described in a paper in the journal Science, written by Ulyana Dyudina of Caltech in Pasadena, US, and her colleagues.

In the colour images, red shows deep clouds while bluish-green reveals high-floating haze. The inner eye of the storm appears red because its clouds are about twice as deep as the clouds covering most of the rest of the planet.

Outside the 4000-kilometre-wide eye is a ring of bluish-green haze, suggesting that gas rich in water vapor is rising in this area from deeper within the planet's atmosphere.

Hurricane force

The orange spots outside the eye are smaller, rotating storms that are hundreds of kilometres wide. Their bright appearance is thought to be due to the presence of cumulus clouds, which form when water vapour condenses from rising flows of moisture-rich gas.

Overall, the images fit the idea that the vortex's rotation is powered in a similar way to hurricanes on Earth, which form from warm, moisture-rich air rising above the ocean. "For Saturn, this might tell us that underneath the clouds, there's a moist atmosphere and that might be driving this whole circulation [of the vortex]," Dyudina told New Scientist.

The poles of Jupiter, Uranus and Neptune might sport similar vortices, Dyudina says. Ground-based observations of Neptune have shown that its atmosphere is warmer towards its poles, suggesting something similar might be present there, since Saturn's south polar vortex is several degrees warmer than its surroundings.

In Saturn's northern hemisphere there is a huge hexagon-shaped, space.newscientist.com/articl...le.html , structure about 25,000 kilometres across centered on the north pole.

Scientists are not sure if that structure boasts a vortex similar to the one at the south pole because it has been shrouded in darkness during the northern hemisphere winter. That means it is not lit up at the short infrared wavelengths used to discover the south polar vortex. But scientists hope to find out after mid-2009, when spring will dawn in the planet's northern hemisphere.

Journal reference: Science, sciencemag.org/ (DOI: 10.1126/science.1153633)


Original Publication (w/ video): space.newscientist.com/articl...ed.html

Video (directly): www.youtube.com/watch