Much of the Venusian surface appears to have been shaped by volcanic activity. Venus has several times as many volcanoes as Earth, and it possesses 167 large volcanoes that are over 100 km across. The only volcanic complex of this size on Earth is the Big Island of Hawaii.[24] This is not because Venus is more volcanically active than Earth, but because its crust is older. Earth's oceanic crust is continually recycled by subduction at the boundaries of tectonic plates, and has an average age of about 100 million years,[30] while the Venusian surface is estimated to be 300–600 million years old.[22][24]
Several lines of evidence point to ongoing volcanic activity on Venus. During the Soviet Venera program, the Venera 11 and Venera 12 probes detected a constant stream of lightning, and Venera 12 recorded a powerful clap of thunder soon after it landed. The European Space Agency's Venus Express recorded abundant lightning in the high atmosphere.[31] While rainfall drives thunderstorms on Earth, there is no rainfall on the surface of Venus (though sulfuric acid rain falls in the upper atmosphere, then evaporates around 25 km above the surface). One possibility is that ash from a volcanic eruption was generating the lightning. Another piece of evidence comes from measurements of sulfur dioxide concentrations in the atmosphere, which dropped by a factor of 10 between 1978 and 1986. This may imply the levels had earlier been boosted by a large volcanic eruption.[32]
Impact craters on the surface of Venus (image reconstructed from radar data)
Almost a thousand impact craters on Venus are evenly distributed across its surface. On other cratered bodies, such as the Earth and the Moon, craters show a range of states of degradation. On the Moon, degradation is caused by subsequent impacts, while on Earth, it is caused by wind and rain erosion. On Venus, about 85% of the craters are in pristine condition. The number of craters, together with their well-preserved condition, indicates the planet underwent a global resurfacing event about 300–600 million years ago,[22][23] followed by a decay in volcanism.[33] Whereas Earth's crust is in continuous motion, Venus is thought to be unable to sustain such a process. Without plate tectonics to dissipate heat from its mantle, Venus instead undergoes a cyclical process in which mantle temperatures rise until they reach a critical level that weakens the crust. Then, over a period of about 100 million years, subduction occurs on an enormous scale, completely recycling the crust.[24]
Venusian craters range from 3 km to 280 km in diameter. No craters are smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed down so much by the atmosphere that they do not create an impact crater.[34] Incoming projectiles less than 50 metres in diameter will fragment and burn up in the atmosphere before reaching the ground
Several lines of evidence point to ongoing volcanic activity on Venus. During the Soviet Venera program, the Venera 11 and Venera 12 probes detected a constant stream of lightning, and Venera 12 recorded a powerful clap of thunder soon after it landed. The European Space Agency's Venus Express recorded abundant lightning in the high atmosphere.[31] While rainfall drives thunderstorms on Earth, there is no rainfall on the surface of Venus (though sulfuric acid rain falls in the upper atmosphere, then evaporates around 25 km above the surface). One possibility is that ash from a volcanic eruption was generating the lightning. Another piece of evidence comes from measurements of sulfur dioxide concentrations in the atmosphere, which dropped by a factor of 10 between 1978 and 1986. This may imply the levels had earlier been boosted by a large volcanic eruption.[32]
Impact craters on the surface of Venus (image reconstructed from radar data)
Almost a thousand impact craters on Venus are evenly distributed across its surface. On other cratered bodies, such as the Earth and the Moon, craters show a range of states of degradation. On the Moon, degradation is caused by subsequent impacts, while on Earth, it is caused by wind and rain erosion. On Venus, about 85% of the craters are in pristine condition. The number of craters, together with their well-preserved condition, indicates the planet underwent a global resurfacing event about 300–600 million years ago,[22][23] followed by a decay in volcanism.[33] Whereas Earth's crust is in continuous motion, Venus is thought to be unable to sustain such a process. Without plate tectonics to dissipate heat from its mantle, Venus instead undergoes a cyclical process in which mantle temperatures rise until they reach a critical level that weakens the crust. Then, over a period of about 100 million years, subduction occurs on an enormous scale, completely recycling the crust.[24]
Venusian craters range from 3 km to 280 km in diameter. No craters are smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed down so much by the atmosphere that they do not create an impact crater.[34] Incoming projectiles less than 50 metres in diameter will fragment and burn up in the atmosphere before reaching the ground
