Recent images with Saturn's polar vortex may solve a piece in the puzzle of how that planet's atmosphere works. Since 1981, astronomers have known of a similar vortex on Venus North Pole.

ESA's Venus Express has been studying for six months this enigmatic atmospheric structure. The puzzling vortex is unique because it has two 'eyes'. A second double vortex was found by Venus Express in April 2006 on the South pole. Polar vortexes are not hurricanes. "Hurricanes are caused by moist air rising into the atmosphere," says Pierre Drossart, Observatoire de Paris, France.

They are provoked by Coriolis force, the interplay between the circulation of the atmosphere and the rotation of the planet, to drive them. But the Coriolis force is inefficient at the poles and on Venus it is virtually non-existent. A polar vortex is created by an area of low air pressure at the rotation pole of a planet, provoking air to spiral down from higher in the atmosphere. Polar vortexes are found at the poles of any planet with an atmosphere, Earth included. What's odd on Venus are the double-lobed vortexes.

Venus Express specifically targets polar regions. Scientists want to monitor the vortexes to see through their behavior the way the whole atmosphere circulates. Data on the Saturn polar vortex will continue to be collected by Cassini's Visual Infrared Mapping Spectrometer (VIMS), which, by using infrared wavelengths, will peer through the clouds. "We will see down to more than 100 km below the visible cloud tops," says Drossart.

The scientists will make a three-dimensional model of each polar vortex, in order to see differences between the various planetary atmospheres throughout our Solar System, for a better understanding of the Earth.

Photo credit: NASA