A bizarre double vortex whirls in the atmosphere above Venus's south pole, images from Europe's Venus Express spacecraft reveal. But it is not clear what causes the "double eye" pattern.
Previous missions to Venus have spotted a similar structure over its north pole and glimpsed stormy atmospheric behaviour at the south pole. But the double vortex has never before been seen at the south pole.
The feature was not even clear in the first image released by the Venus Express team in April, just after the spacecraft entered into orbit around the planet (see First images of Venus’s south pole revealed). But images taken over the course of about a week during that first orbit do reveal two vortices above the south pole. The vortices are formed by winds of super-hurricane force.
The winds on Venus spin westwards at hundreds of kilometres per hour, taking only four days to rotate around the planet, which is slightly smaller than the Earth. This "super-rotation", combined with the natural recycling of hot air in the atmosphere, would logically induce a vortex over each pole. But the mystery is why there are two vortices.
"We still know very little about the mechanisms by which the super-rotation and the polar vortices are linked," said Håkan Svedhem, the mission's project scientist.
"Also, we are still not able to explain why the global atmospheric circulation of the planet results in a double vortex and not a single vortex," he says. "Atmospheric vortices are very complex structures that are very different to model, even on Earth."
Venus Express is Europe's first dedicated mission to Earth's nearest planetary neighbour. It went into a distant, elongated orbit around Venus on April 11 and entered into its final 24-hour orbit on 7 May.
It will study the planet's atmosphere to shed light on what drives the runaway global warming on Venus. The planet's mean surface temperature is 457 Celsius – hot enough to melt lead and even hotter than Mercury, the closest planet to the Sun. Its atmosphere is 96% carbon dioxide, with roiling, yellowish clouds of sulphur and sulphuric acid droplets.
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17:45 21 August 2008
11:17 21 August 2008
