Recent images from ESA's planetary orbiter
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.
Mars, Earth and Venus are immersed in a flow of plasma, an ionised and highly variable gas originating from the Sun, called the solar wind.
While Earth has a planetary magnetic field, which can deviate the flow of solar wind, Venus (and Mars) don’t. Gases in the upper atmospheres of
these planets are ionised, and can thus interact with the solar wind.
Venus is as large as Earth and it is difficult for its atmosphere to escape due to the planet’s gravity. The solar wind is the best source of energy to
accelerate the upper atmosphere’s charged particles, giving them enough energy to escape. This is why Venus loses its atmosphere due to interaction
with the solar wind.
To understand this phenomenon, the key questions that the instruments studying plasma on Venus Express must answer are: what and how much of
the atmosphere is lost, and where is it lost?
Right now, solar activity is at its minimum in the 11-year cycle, making the solar wind weaker than average. The critical question now is how solar
wind interacts with Venus when solar activity is low.
This is a false-colour image taken with the Venus Monitoring Camera (VMC) on board ESA’s Venus Express. It shows the full view of the southern hemisphere from equator (right) to the pole. The south pole is surrounded by a dark oval feature. Moving to the right, away from the pole and towards the equator, we see streaky clouds, a bright mid-latitude band and mottled clouds in the convective sub-solar region.
This image was taken in the ultraviolet at 365 nanometres on 23 July 2007 as Venus Express was 35 000 km from the surface of the planet.
The magnetometer (MAG) on board ESA’s Venus Express detected wave signals that show evidence of lightning in the atmosphere.
This false-colour view was obtained on 26 August 2006 by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) onboard ESA’s Venus Express, at a distance of 65 000 kilometres from Venus’ surface, from the south. The horizon seen at the bottom-right in both panels is about Venus’ equator. The top left of the images is located at about 60 degrees south latitude; the images centre is at 130 degrees west longitude.
Both panels show the oxygen airglow in the night-side atmosphere of Venus, fully detectable only at specific infrared wavelengths. The images are built by a combination of colours: the airglow is blue, corresponding to 1.27 micrometres; yellow corresponds to 1.7 micrometres, and its modulation is due to the different cloud thickness in different areas.
On the right panel the airglow appears in atmospheric structures similar to ‘clouds’. In the left image a slightly different colour scale has been used to emphasize the brightening of the limb (side view of the atmosphere) due to the airglow itself.
The fluorescence of the airglow is produced when oxygen atoms, ‘migrating’ from the day-side to the night-side of the atmosphere of Venus under the push of the so-called sub-solar and anti-solar atmospheric circulation, recombine into molecular oxygen (or ‘O2’) emitting light.
The false-colour view is the composite of three infrared images acquired by the Ultraviolet, Visible and Near-Infrared Mapping Spectrometer (VIRTIS) on board ESA's Venus Express on 22 July 2006, at a time interval of about 30 minutes from each other and from a distance of about 65 000 kilometres over the planet's surface. Venus was in the night side.
The image, taken at a wavelength of 1.7-micrometre, shows the thermal radiation emitted from about 15-20 kilometres altitude. The brighter the colour (towards white), the more radiation comes from the surface, so the less cloudy the region in the line of sight between the view and the spacecraft is.
This global view of the southern hemisphere of Venus is a mosaic of images obtained by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board ESA’s Venus Express on 16 May 2006.
The night-side hemisphere (in red at the top) is made of infrared images taken at 1.74 micrometres, showing the lower layers of the cloud deck surrounding the planet at about 45-km altitude.
The day-side hemisphere (in blue at the bottom) is made of ultraviolet images taken at 480 nanometres. It shows the cloud top layer at about 65-km altitude.
The red part of the central panel was taken at 3.8 micrometres, and shows the double vortex at the south pole, at an altitude of about 60 km, surrounded by a collar of ‘cold’ air.