First clues in the cloud riddle of Venus

New recordings of the ESA probe Venus Express help with cause research

Cloud turbulence in the Venus atmosphere. © ESA
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At the moment she is standing in the sky every evening as a bright evening star in the sky: Venus. However, the processes in the atmosphere of the sister planet of the earth are not visible and are still enigmatic. New images of the ESA Venus Express probe have now provided new insights into the planet's cloud formations.

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The atmosphere of Venus is still a mystery to the scientists. Because the storms in their gas envelope are so fast and strong that they completely orbit the planet in only four earth days, and this, although the planet itself only extremely slowly turns: After all, the Venus needs 243 Earth days for only one turn around its own axis, At the poles, this dynamic becomes even more complicated, because here massive double vortexes additionally mix up the atmosphere. As if that were not enough, the whole thing is still covered with a thick layer of cloud, which makes it difficult to closely observe and explore the processes.

The more valuable are the data of the probe Venus Express. She can use her multi-wavelength camera eyes to see through the cloud layer, providing important insights into the processes in the atmosphere. What causes strong winds and turbulence in the atmosphere? And what role does the topography of the surface play for the complex dynamics of the gas envelope?

Solar radiation is causing a stir

At least part of these questions could now be answered by the data of the Venus Express. The probe investigated the cloud formations in their different layers not only on the day but also on the night side. It shows that the strong winds of the "superrrotation" at the equator are in constant battle with local turbulence and regional winds and thus create the complex, irregular-bubble cloud structures. display

It seems clear that at least one type of these regional winds is created by the strong sunlight on the daytime side of the planet. This radiation heats up the atmosphere and creates convection cells, localized areas where hot air rises quickly causing turbulence.

Landscapes responsible for turbulence?

Strangely, however, similar air currents and turbulence also occur on the night side - without the radiation could play a role here. In search of a possible mechanism, the scientists of the Venus Express team resorted to the data of the VIRTIS instrument aboard the probe. This uses the so-called infrared window of the Venus atmosphere, radiation of a certain wavelength, which is not absorbed by the clouds and therefore allows a clear view of the surface.

VIRTIS footage of Alpha Regio, an area near the equator of the planet, reveals a highly jagged terrain characterized by long trenches, gullies and ridges. The mountain ridges rise up to four kilometers high here. According to the Venus researchers, these forms of surface might possibly play a crucial role in the atmospheric turbulence as well. In what form this happens exactly and whether this also applies to other areas, must now show more shots and data.

(ESA, 04.04.2007 - NPO)