Lunar and Planetary Institute
Lunar and Planetary Institute


500 Days at Venus, and the Surprises Keep Coming

September 7, 2007
Source: European Space Agency

These images were taken in eight orbits within 10 consecutive Earth days (between orbits 299 and 309) with VIRTIS, in February 2007.  The images were all taken on the night side, in the evening sector. The quarter that is observed is that which is experiencing late evening, or pre-midnight hours. Intense, bright colours show less cloudy areas, while darker, black areas, show more cloudy regions. Credit: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA.Venus Express has now orbited Earth’s twin for 500 Earth days, completing as many orbits. While the satellite maintains steady and excellent performance, the planet continues to surprise and amaze us. In spite of experiencing a challenging environment, Venus Express is in excellent condition. It receives four times the amount of solar radiation as compared to its sister spacecraft, Mars Express, but modifications to the spacecraft design have worked just as intended and operation has been very stable.

Many different activities transpire on board with each orbit:  instruments are switched on and off, they change modes and targets, and the spacecraft checks out and monitors its subsystems more or less continuously. The few anomalies that have occurred have been quickly resolved by vigilant spacecraft controllers.

On August 18, Venus was at the shortest distance from Earth. The planet was also aligned with Earth and the Sun. Given the short distance, all instruments worked at full speed and the communication system is at its maximum. Back on Earth, data was downloaded without difficulty. This situation is very different from when Venus is on the farside of the Sun. Due to the large distance, the rate at which data can be downloaded plummets to 22 kbps, a tenth of the maximum. At such times, competition between the instruments can be quite tough. Despite this, an impressive amount of data — about 1 Terabits, or one million million bits — has been transmitted to Earth over the first 500 days.

Hakan Svedhem, Venus Express Project Scientist, says, “The scientists analyzing the data have a challenging but exciting task ahead.” They will have to archive the data and extract the most important detail from this immense collection of images, spectra, and profiles of temperature, pressure, and chemical composition. Some of the first detailed analyses are now being completed and will soon be published in acclaimed scientific journals.

Among many other findings that have surprised scientists, Venus’ atmosphere seems extremely fickle. Recent observations with the Visible and Near-Infrared Mapping Spectrometer (VIRTIS) have shown that Venus’ atmospheric structure changes quite rapidly, from day to day.

According to Giuseppe Piccioni, co-Principal Investigator for VIRTIS on board Venus Express, "It seems that the mid latitudes form a sort of transition region with mostly laminar flow. Moving equatorward, there is more convective flow in the atmosphere, whereas the polar region is dominated by huge vortices.” The meteorology of the planet, including its deep atmosphere, is highly variable. “Although the configuration of the flow is similar, the intensity of turbulence changes significantly from one orbit to the next,” adds Pierre Drossart, co-Principal Investigator for VIRTIS.

The polar region (the “black hole” seen in the images) is where the polar dipole dominates. The polar dipole is the name given to a giant double-vortex, each of which is about 2000 km across, similar to the eye of a hurricane. The double-vortex has been seen at both the north and south poles, rotating in opposite directions (clockwise at the north pole and counter-clockwise at the south pole). Observations with Venus Express show that the vortex at the south pole also changes its shape rapidly from one orbit to the next.

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