False colour infrared map of Venus, 1978.

This was taken by the Mount Hopkins Observatory in Arizona at the time when the probes from the Pioneer Venus Multi Probe spacecraft were entering the Venusian atmosphere. The red areas are 10 degrees Celsius hotter than the blue regions. Although similar in size and internal structure to Earth, Venus is a very different world. It has a thick atmosphere of mainly carbon dioxide with clouds of sulphuric acid, creating a runaway greenhouse effect with surface temperatures of 485 degrees Celsius and atmospheric presure 90 times that at sea level on Earth. The impenetrable clouds meant that nothing was known about the planet's surface until the Soviet Venera probe landed and was briefly able to transmit images in 1975.