Volcanology of Venus
The surface of Venus is dominated by volcanic features and has more volcanoes than any other planet in the Solar System. It has a surface that is 90% basalt, and about 65% of the planet consists of a mosaic of volcanic lava plains, indicating that volcanism played a major role in shaping its surface. There are more than 1,000 volcanic structures and possible periodic resurfacing of Venus by floods of lava. The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Venus has an atmosphere rich in carbon dioxide, with a density that is 90 times greater than Earth's atmosphere.
Pioneer Venus Multiprobe
Below the altitude of 50 km the temperatures measured by the four probes are identical to within a few degrees. They are between 448 °C and 459 °C (838 °F and 858 °F) on the surface. The ground pressure is between 86.2 bar and 94.5 bar. Nephelometers identified three cloud layers with different characteristics. The most remarkable discovery was that the ratio of argon / argon isotopes much higher than in the atmosphere which seems to indicate that the genesis of the Venusian atmosphere is very different from that of Earth. The reconstituted trajectory of atmospheric probes was determined that the wind averaged a speed of 200 m/s in the middle cloud layer at 50 m/s at the base of these clouds and just 1 m/s at the ground. Overall data from airborne sensors confirmed, while specifying the data obtained by the Soviet space probe Venera program that preceded this mission.