During the early years of planetary space research Venus was regarded as a prime target, because it did not seem to be really hostile – probably more welcoming than Mars. Without going back 80 years to the ideas of Svante Arrhenius, who believed Venus to be in a state similar to that of the Earth during the Carboniferous Period, when the coal measures were being laid down and the lands were covered with lush tropical vegetation, there seemed no reason to doubt that there might be oceans, and that the climate was no more than tolerably hot. The probes of the 1960s and 1970s showed that this attractive picture was very far from the truth; the atmosphere was made up chiefly of carbon dioxide, the surface pressure was around 100 times that of the Earth’s air at sea-level, and the temperature was far too high for advanced life-forms of our kind. Moreover, the clouds were rich in sulphuric acid. The U.S. Magellan orbiter surveyed the whole surface in detail, and as a potential colony, Venus was ruled out; the main attention swung back to Mars.