Polar Region of Venus
© ESA/VIRTIS-VenusX/INAF-IASF/LESIA-Obs. Paris/ Univ. Lisbon/Univ. Evora
This image shows the polar region of Venus, at a wavelength of 3.8 microns. The arrows denote the motion of the atmosphere around a center of rotation (marked with a white dot). The center of rotation is found to be displaced on average by about 300 km from the geographic south pole.

A giant vortex at the south pole of Venus is actually a shape-shifter that changes form at least once a day, at times bizarrely taking on the appearance of a giant letter "S" or the number "8," a new study reveals.

Venus, the second closest planet to the sun, possesses giant, hot and essentially permanent vortexes of clouds whirling fast at its poles. These result from how Venus' atmosphere circulates much faster than any other rocky planet's in the solar system - the cloud-level atmosphere of Venus on average spins 60 times faster than the planet's surface.

The vortexes cannot really be called storms, as scientists have seen neither rain nor lightning in them.

Past images suggested the roughly 1,200-mile-wide (2,000-kilometer) southern polar vortex was only a spinning oval shape. However, new infrared pictures from the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on the European Space Agency's Venus Express mission revealed far more detail than past images, showing that the vortex's internal structure changes shape at least every 24 hours.

Polar Region of Venus_1
© ESA/VIRTIS-VenusX/INAF-IASF/LESIA-Obs. Paris/ Univ. Lisbon/Univ. Evora (D. Luz, Univ. Lisbon & D. Berry, U. Evora)
This image shows thermal infrared radiation (at a wavelength of 5 microns) emitted by the cloud tops at the southern polar region of Venus on Jan. 20, 2008, as viewed by the VIRTIS imaging spectrometer on Venus Express. The white arrows show the atmospheric winds, measured by tracking the movement of cloud features.
"Filaments swirl around one or two bright - that is, warmer - centers," researcher David Luz, a planetary scientist at the University of Lisbon, told SPACE.com. "Sometimes the shape looks like an S or an 8, sometimes it shows three bright centers, but mostly it's irregular."

The vortex is not poised directly over the south pole, but instead its center is consistently located approximately three degrees of latitude away, and it drifts around the pole, completing a circuit every five to 10 days.

These findings suggest the atmospheric dynamics at Venus' southern pole are more complex than scientists thought. They suspect the vortexes are fed by air descending from currents circulating along the meridians over the poles, and the fact the southern vortex drifts suggest the point of maximum downwelling is also wandering.

"This is a change in our understanding that general circulation models of Venus will need to take into account," Luz said.

The researchers suspect the vortex at Venus' north pole acts similarly, "but for the moment we don't know, because Venus Express' highly elliptical orbit brings it too close to the north pole, making it impossible to do similar imaging studies," Luz said. "We can see only a very small region."

Europe's Venus Express orbiter has been studying Venus since it arrived in 2006.

The scientists detailed their findings online today (April 7) in the journal Science.