Venus is our nearest planetary neighbour and orbits closer around the sun than the Earth. The mean mass densities and radii of Earth and Venus are very similar and therefore Venus is often regarded as Earth′s “sister planet”. However, the near-surface conditions on both planets differ considerably; while Earth′s mean surface temperature is 15°C and the main constituents of the Atmosphere are nitrogen (78%) and oxygen (21%), the mean temperature on Venus is 477°C and its atmosphere is almost exclusively composed of carbon dioxide (95%). The geological and geophysical exploration of Venus began in the 1960s and since then a large number of missions (flybys, orbiter and lander) built and operated by the Soviet Union and the United States have investigated the surface structure, the composition and dynamics of the atmosphere as well as the physics of the plasma environment surrounding Venus. Venus Express is the first European mission to the planet Venus and surveys the dynamics and chemistry of the Venusian atmosphere, the interaction processes between the atmosphere and the surface as well as the interaction of the interplanetary medium (solar wind) with Venus′ upper atmosphere.
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