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The many faces of Venus

Pictures from Europe’s Venus Express orbiter are providing new insights - and raising new questions - about Venusian weather systems that are fueled not by water, as on Earth, but by sulfuric acid.

For almost two years, the probe has been documenting what's going on within and beneath Venus' globe-girdling clouds. In visible light, the planet is a nearly featureless marble - but in ultraviolet light, the clouds and hazes swirl in fast-moving patterns. So fast-moving, in fact, that scientists wonder how Venus' atmosphere can do what it does.

This ultraviolet view from Venus Express shows

atmospheric patterns in Venus' southern hemisphere.

Click on the image for a larger version.

A series of ultraviolet images captured last July and released on Thursday shows how a high-altitude veil of haze can brighten and dim in a matter of days, moving from the southern polar region to equatorial latitudes and back again.

The scientists behind the $226 million mission speculate that the process is driven by the production of sulfuric acid particles at upper altitudes.

"This bright haze layer is made of sulfuric acid," Dmitri Titov of Germany's Max Planck Institute for Solar System Research said in Thursday's image advisory from the European Space Agency. Titov is science coordinator for the Venus Express mission as well as co-investigator for the Venus Monitoring Camera, which took the images.

At lower altitudes, the planet's atmosphere is predominantly carbon dioxide, with small amounts of water vapor and sulfur dioxide gas. If some atmospheric process lifts those molecules above Venus' cloud tops, they are exposed to the sun's ultraviolet rays and become highly reactive. That's what is thought to create the sulfuric-acid haze.

"The process is a bit similar to what happens with urban smog over cities," Titov said.

Scientists don't yet know exactly what atmospheric process is at work, and the European Space Agency says there's yet another mystery to be solved: The composition of the dark clouds seen on the Venus Monitoring Camera's ultraviolet images is still unknown. To figure out the answer, scientists plan to enlist yet another instrument on Venus Express, known as the Visible and Infrared Thermal Imaging Spectrometer.

While the Venus Express team works on that puzzler, you can check out the latest findings streaming in from other interplanetary probes, such as the Cassini spacecraft's study of Saturn's "mingling moons," Mars Reconnaissance Orbiter's look at the Red Planet's highest mountain (plus a belated Valentine) and a glimpse of Mars' grandest canyon from Europe's Mars Express, which is Venus Express' older brother.

And if that's not enough to keep you busy over the weekend, take a spin through our latest space slide shows, "Space Shots" and "Earth as Art."