New details on venusian clouds revealed


Southern hemisphere of Venus in the ultraviolet
 
This beautiful, false-colour ultraviolet image of the Southern hemisphere of Venus was obtained by the Venus Monitoring Camera (VMC) on board ESA’s Venus Express on 27 July 2007. It was taken from a distance of 30 000 km from the planet’s surface at a wavelength of 365 nanometres. The planet is seen from the southern hemisphere: the south pole is at the bottom, while equator is at the top.

The shape of the clouds changes dramatically from the equator to the pole. At low latitudes, the cloud shape is spotty and fragmented, a consequence of a vigorous convective movement powered by the radiation of the sun heating the atmosphere itself. The bright lace visible on top of the darker cloud deck is made of freshly formed droplets of sulphuric acid.

At mid latitudes, the convective clouds make way for more streaky shapes indicating that the flow is basically laminar in this portion of the atmosphere.

At high latitudes, the cloud structure appears as a dense, almost featureless haze forming some a ‘polar cap’ on Venus. The dark, circular feature visible at the rightmost edge of the image is one of the dark streaks usually present in the polar region, indicating atmospheric parcels spiralling towards the pole.

Cloud structures at Venus’ low latitudes
 
This false-colour ultraviolet image of the equatorial region of Venus was obtained by the Venus Monitoring Camera (VMC) on board ESA’s Venus Express on 22 July 2007 from a distance of about 20 000 km, at a wavelength of 365 nanometres. The octagonal shape of the image is due to the VMC field of view.

It shows, in unprecedented detail, the cloud top over Venus’s equator. What appears as a bright lace is due high concentration of sulphuric acid.

Another view of Cloud structures at Venus’s low latitudes
 
This false-colour ultraviolet image of the equatorial region of Venus was obtained by the Venus Monitoring Camera (VMC) on board ESA’s Venus Express on 22 August 2007 from a distance of about 15 000 km, at a wavelength of 365 nanometres. The octagonal shape of the image is due to the VMC field of view.

It shows, in unprecedented details, the cloud top over Venus’s equator. What appears as a bright lace is due high concentration of sulphuric acid.

Close-up on venusian clouds at mid-latitudes
 
This false-colour ultraviolet image of the atmopshere of Venus was obtained by the Venus Monitoring Camera (VMC) on board ESA’s Venus Express on 27 July 2007 from a distance of about 15 000 km, at a wavelength of 365 nanometres. The edge of the southern polar hood is seen at the bottom. The octagonal shape of the image is due to the VMC field of view.

This image shows the transition between the equatorial area dominated by convection and the mid-latitude area populated by streaky clouds. This region is located at about 40-50 degrees latitude. The way the transition between structures and dynamics so different from each other occurs, is one of the outstanding enigmas in our understanding Venus.

Close-up on venusian cloud structures at the south pole
 
This false-colour ultraviolet image of the south pole of Venus was obtained by the Venus Monitoring Camera (VMC) on board ESA’s Venus Express on 25 February 2008 from a distance of about 20 000 km, at a wavelength of 365 nanometres. The octagonal shape of the image is due to the VMC field of view.

It is a zoom-in on the south polar ‘cap’, located inside a 60-degree-latitude circle. It shows a very bright and uniform appearance and lacks small-scale markings. However several dark streaks usually encircle the polar regions and seem to indicate strong jet-stream-like winds in the atmosphere around the pole.

Cloud structures along the northern hemisphere of Venus
 
This mosaic is composed of more than 40 single ultraviolet images obtained by the Venus Monitoring Camera (VMC) on board ESA’s Venus Express when the spacecraft was around the closest point of its orbit to the planet over the northern polar region. The images, taken at 365 nanometres on 23 April 2007 were obtained from decreasing distances ranging between 5000 and 1000 km, which resulted in a shrinking of the VMC field of view from 1500 to 300 km.

The mosaic covers latitudes from the equator (bottom) to the northern polar regions (top). The transition from mottled clouds at low latitudes to streaky patterns at mid-latitudes is quite similar to that observed in the southern hemisphere. This suggests a global north-south symmetry of the overall cloud structure at Venus



Release date: 17 July 2008