Geology Of Venus
Venus is a planet with striking surface characteristics. Most of what is known about its surface stems from radar observations, mainly images sent by the Magellan probe between August 16, 1990 and the end of its sixth orbital cycle in September 1994. Ninety-eight percent of the planet's surface was mapped, 22% of it in three-dimensional stereoscopic images.
The surface of Venus is covered by a dense atmosphere and presents clear evidence of former violent volcanic activity. It has shield and composite volcanoes similar to those found on Earth.
Relative to the Moon, Mars or Mercury, Venus has few small impact craters. This is likely a result of the planet's dense atmosphere, which burns up smaller meteors. Venus does have more medium-to-large-size craters, but still not as many as the Moon or Mercury.
Some other unusual characteristics of the planet include features called coronae (Latin for crowns, based on their appearance), tesserae (large regions of highly deformed terrain, folded and fractured in two or three dimensions), and arachnoids (for those features resembling a spider's web). Long rivers of lava have been discovered, as well as evidence of Aeolian erosion and tectonic shifts which have played an essential role in making the surface of Venus as complex as it is today.
Although Venus is the planet closest to Earth (some 40 million kilometres at inferior conjunction), and is similar in size, the resemblance is superficial: no probe has been able to survive more than one hour on its surface because the atmospheric pressure is some 90 times that of Earth's. The temperature on the surface is around 450°C (842°F). This is mostly caused by the greenhouse effect created by an atmosphere composed mainly of carbon dioxide (96.5%).
Ultraviolet surveys of Venus show a Y-shaped pattern of cloud formation near the equator indicating that the upper layers of the atmosphere circulate around the planet once every four days, suggesting the presence of winds of up to 500 km/h (311 mph). These winds exist at high altitudes, but the atmosphere at the surface is relatively calm, and most images from the surface reveal little evidence of wind erosion.
Read more about Geology Of Venus: Knowledge of The Surface of Venus Before Magellan, Magellan Studies The Geology of Venus, Topography, Impact Craters, Global Resurfacing Event, Volcanoes, Tectonic Activity, Magnetic Field and Structure, Lava Flows and Channels, Surface Processes
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