Venus is one of the four terrestrial planets in the Solar System, meaning that, like Earth, it has a rocky composition and solid surface. The atmosphere of Venus is made of a thick layer of cloud that is mostly carbon dioxide. The surface pressure is 92 times that experienced on Earth. The thick clouds have helped to create a very strong Greenhouse Effect making Venus the hottest planet in the Solar System, even though Mercury is closer to the Sun! The temperature at the surface can get as high as 462 °C. Venus is also very unusual because it spins in a different direction to all the other planets.
Although the thick clouds stop us from seeing the surface of Venus it has been mapped using radar imaging. This has showed that there are lots of volcanoes and large craters on Venus. There are no craters smaller than 3 km on Venus because small meteors burn up in the thick clouds before reaching the surface.
The Soviet Union, United States, European Space Agency and Japan have all sent spacecraft to visit Venus. Since the first visit by Mariner 2 in 1962, over 25 other spacecraft have been to Venus. The first one to go into orbit around Venus, called Magellan, produced the radar images of the surface (see image on the left).