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Venus Express Spies Double Vortex

Venus Express captured a peculiar double-eye vortex structure around the Venusian south pole. Image credit: ESA/VIRTIS/INAD-IASF/Obs. de Paris-LESIA
by Staff Writers
Paris, France (SPX) Jun 28, 2006
ESA scientists said Tuesday that analysis of Venus Express data from the spacecraft's first orbit around the planet confirm the presence of a huge double-eye atmospheric vortex at the planet's south pole. Last April 11, Venus Express was captured into a first elongated orbit around Venus lasting nine days and ranging from 350,000 kilometers to 400 kilometers (217,000 miles to 248 miles) from the surface.

The initial orbit made possible the ability to obtain the first clues about the Venusian atmospheric dynamics on a global scale, before the spacecraft got closer and started observing the planet in greater detail.

During the spacecraft's orbital adjustment process, mission controllers used some of its instruments to perform the first observations at different distances from Venus - a few hours at a time from six different positions between April 12 and April 19.

Those observations produced images of a huge, double-eye atmospheric vortex over the south pole, not dissimilar from the equivalent structure present at the north pole - the only one previously studied in some detail.

Only glimpses of the stormy atmospheric behavior at the south pole were obtained by the Pioneer Venus and Mariner 10 missions, but such a double-eye structure never has been seen clearly before now.

High-velocity winds are known to spin westwards around the planet, and to take only four days to complete a rotation. This super-rotation, combined with the natural recycling of hot air in the atmosphere, would induce the formation of a vortex structure over each pole.

The question is why Venus is exhibiting two vortices.

"We still know very little about the mechanisms by which the super-rotation and the polar vortexes are linked," said Hakan Svedhem, ESA's Venus Express project scientist.

"Also, we are still not able to explain why the global atmospheric circulation of the planet results in a double and not single vortex formation at the poles," Svedhem added. "However the mission is just at the beginning and it's doing fine; we expect this and many other long-standing mysteries to be addressed and possibly solved by Venus Express."

Atmospheric vortexes are very complex structures that are very difficult to model, even on Earth. Thanks to these first pictures, it has also been possible to observe the presence of a collar of cold air around the vortex structure, possibly due to the recycling of cold air downwards.

Views of the Venusian southern hemisphere, taken in visible and ultraviolet light, show interesting atmospheric stripe-like structures. Spotted for the first time by Mariner 10 in the 1970s, they may be due to the presence of dust and aerosols in the atmosphere, but their true nature remains unexplained.

"Venus Express has the tools to investigate these structures in detail," Svedhem said. "Studies have already begun to dig into the properties of the complex wind fields on Venus, to understand the atmospheric dynamics on local and global scales."

Venus Express also made use for the first time ever from orbit of the so-called infrared windows present in the atmosphere of Venus - if observed at certain wavelengths, it is possible to detect thermal radiation leaking from the deepest atmospheric layers, revealing what lies beneath the dense cloud curtain situated at about 60 kilometers altitude.

The first infrared images making use of these windows show complex cloud structures, all revealed by the thermal radiation coming up from different atmospheric depths.

Venus Express also has compiled preliminary data about the chemical composition of the atmosphere. The planet's atmosphere is composed mainly of carbon dioxide. The incoming solar radiation dissociates this molecule into carbon monoxide (and oxygen in the upper atmospheric layers.

Venus Express already has spotted the presence of an oxygen airglow high in the atmosphere. However, the spacecraft's instruments have revealed the presence of carbon monoxide as low as the cloud-layer top.

Scientists will continue the data analysis and retrieval to understand the phenomenon, which is very important to clarify the complex chemical processes and cycles at work in the atmosphere of Venus under the influence of solar radiation.

Since May 7, Venus Express has been circling the planet in its final 24-hour orbit, ranging between 66,000 kilometers and 250 kilometers (40,920 miles and 155 miles), so it is now closer to the planet that during its capture orbits.

Venus Express scientists are now analyzing the new data, which already show what seem to be exciting new features. "We have never seen Venus in such great detail so far, Svedhem said. "We are eagerly waiting for these new data to be available."

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Venus Express Commissioning Phase Completed
Paris, France (SPX) Jun 12, 2006
After 207 days of flight, 43 orbits around Venus and many test activities, Venus Express formally completed its commissioning phase June 3 and entered the routine science phase, ESA announced last week.







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