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Emily LakdawallaSeptember 23, 2010

Venus: Not so neat and tidy as we thought

When Pioneer Venus visited our sister planet in 1979, it found an atmospheric feature called a "dipole" near Venus' north pole -- a pair of eddies swirling and rotating around each other as Venus rotated. When ESA's Venus Express arrived in 2006, it observed the same sort of thing at Venus' south pole, and scientists wrote a lot about how Venus was symmetric from north to south and how the polar dipoles were atmospheric features that were stable over decades. Here's one of those photos from 2006:

Venus' south pole


Venus' south pole
A view of Venus in the thermal infrared, at a wavelength of 5 microns. The brightest part of the image is the uppermost atmosphere reflecting solar radiation on the dayside of Venus. On the nightside, subtle cloud features are visible, especially near the south pole, as thermal radiation is emitted from Venus' upper atmosphere at an altitude of around 60 kilometers. This image was captured on April 12, 2006 from a distance of 210,000 kilometers.

Except that it turns out it's not stable! Venus Express has been there for more than four years now, and as it's kept watching Venus' swirling atmospheric patterns, that "stable" southern dipole turned out not to be stable. At all. In a press release issued today, Venus scientist Giuseppi Piccioni remarks that the original observation of the southern dipole by Venus Express was "just a coincidence...the dipole in reality is not a stable feature on Venus, but just one shape among others."

The many faces of Venus' south polar vortex


The many faces of Venus' south polar vortex
Venus' south polar vortex changes over time in complicated patterns. These are just four snapshots from Venus Express' observations of the strange feature. They were taken by the VIRTIS camera at a near-infrared wavelength of at 3.8 microns. The images show the temperature of the cloud top at an altitude of about 65 kilometers. Darker regions correspond to higher temperatures and thus lower altitudes. The center of the vortex, at a temperature of about 250 Kelvins (-25 C / 20 F), is the deepest zone, exhibiting the highest temperatures.

The press release included several other cool images and animations. This one was my favorite.


Venus' southern vortex
A movie of the complicated swirling motions of Venus' south polar vortex as seen at a near-infrared wavelength of 3.8 microns, acquired by the Venus Express VIRTIS camera. The set of images show the temperature of the clouds' top. Darker regions correspond to higher temperature and thus lower altitude. The temperature contrast leads to an apparent three-dimensional effect of the images.

Because I just can't get enough of animations, here is one more. These are cool because in each of them the frames have been rotated to take out the overall rotational motion of the vortex. What's left is the dynamics of clouds within the vortex, which are mesmerizing.

Venus' southern swirling clouds

ESA / VIRTIS / INAF-IASF / Obs. de Paris-LESIA / Univ. of Oxford

Venus' southern swirling clouds
A 10-frame animation of the Venus' south polar vortex seen by Venus Express' VIRTIS at a near-infrared wavelength of 3.8 microns. The set of images has been reprojected to compensate for the overall rotation of the vortex, making the dynamics of atmospheric flow within the vortex more easy to spot.

This release is just one of many coming out of the European Planetary Science Congress (EPSC) meeting this week, and I do not have time to get to them all. All of the press releases are rounded up here, including news about Mercury's comet-like tail, Martian methane, water on the Moon, and Phobos' possible impact origin. Of course, there are huge numbers of scientific presentations going on that are not being announced via press releases, but you can browse the program and all the associated abstracts yourself on the EPSC website.

Read more: pretty pictures, atmospheres, Venus Express, Venus, explaining science

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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Emily Lakdwalla
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