Venus

Astronomers began to suspect that the surface of Venus was a decidedly inhospitable place when radio telescope measurements, made in the 1950s, indicated surface temperatures as high as 750K (891°F; 477°C). It is believed that a greenhouse effect is responsible for maintaining the high surface temperature on Venus.

A greenhouse effect occurs whenever incoming sunlight warms the planetary surface, but the atmospheric gases do not allow the infrared radiation emitted by the heated surface to escape back into space. The net result of the atmospheric trapping of infrared radiation is that the atmosphere heats up, and the surface temperature continues to rise.

An artist's impression of one of the three continent-sized highland regions of Venus, Beta Regio, which consists of two huge shield volcanoes rising above the plains. Both are about 2.5 mi (4 km) high, and appear to be on a north-south fault line connecting them with other possibly volcanic features in the south. They have smooth surfaces and are shaped like Hawiian volcanoes. The Russian spacecrafts Veneras 9 and 10 landed directly east of Beta Regio and determined that the surface rock was volcanic basalt. U.S. National Aeronautics and Space Administration (NASA).

That a strong greenhouse effect can operate at Venus is not surprising given that its primary atmospheric component is carbon dioxide. This gas has long been recognized as a problematic "greenhouse" gas on Earth.

Building a spacecraft to land on the Venusian surface has proved to be a major engineering challenge. Not only must a lander be able to operate at temperatures that exceed the melting point of lead, but it must also withstand an atmospheric pressure some 90 times greater than that experienced at sea level on Earth. The pressure exerted by the Venusian atmosphere, at the planet's surface, is equivalent to that exerted by a 0.6 mi (1 km) column of water in Earth's oceans. The first of only four spacecraft to soft-land, and successfully transmit images of the surface of Venus back to Earth, was the former Soviet Union-built spacecraft Venera 7. The lander, which set-down on August 17, 1970, managed to transmit data for 23 minutes.