Introductory Astronomy: The Planet VENUS

Basic Facts:
Average distance from Sun: 0.72 AU
Period of revolution about Sun: 225 days
Period of rotation: 243 days
Radius: 0.95 Earth radii
Mass: 0.82 Earth masses
Average Density: 5.3 g/cm^3
Magnetic Field: none detected
Surface features: 75% rolling lava plains, 25% raised plateaus, shield volcanoes, rift valley, impact craters
Atmosphere: 96.5% CO2, 3.5% N2, traces of sulfuric acid in the clouds, 90 atm surface pressure
Temperature: 890 degrees Fahrenheit

Venus has often been called the Earth's twin: it is almost the same size as the Earth and has a cloudy atmosphere, as Earth does. However, scientists now know that the atmosphere of Venus is nothing like the Earth's. About 96% of the Venusian atmosphere is carbon dioxide, 3.5% is nitrogen, and the only the remaining 0.5% contains water (among other, more harmful gases).

Venus is 30% closer to the Sun than the Earth; it thus receives twice as much solar energy. This means Venus had a higher surface temperature from the beginning, which, in turn prevented oceans from forming on its surface. Without the presence of oceans, carbon dioxide stayed in the Venusian atmosphere. (Oceans on Earth allow carbon dioxide to become trapped in rocks and shells.) Volcanic activity on Venus' surface only added to the excess of carbon dioxide. Carbon dioxide is opaque to infrared radiation. This means that sunlight can reach the planet's surface, but cannot escape easily, causing the surface of the planet to be very hot.

Venus' thick atmosphere protects it from cratering by meteoroids. Its surface features are formed by craters which formed before the atmosphere and volcanic activity, such as lava flows. A computer generated view of the Venusian surface has been derived from data from Magellan. An actual view of Venus' surface taken by the Soviet Venera 13 spacecraft (you can see the leg of the spacecraft in the picture) is shown here.

To learn more about Venus, clickhere.