VENUS IS A ROCKY PLANET and the second planet from the Sun. Venus spins slowly backward as it orbits the Sun, causing its rotational period to be the longest in the solar system, at about 243 Earth days. It is slightly smaller than Earth and probably has a similar internal structure, consisting of semisolid metalcore, surrounded by a rocky mantle and crust.
Venus is the brightest object in the sky after the Sun and Moon because its clouds reflect sunlight strongly. The main component of the atmosphere is carbon dioxide, which traps heat in a greenhouse effect far stronger than that on Earth. As a result, Venus is the hottest planet, with a maximum surface temperature of about 900°F (480°C). The thick cloud layers contain droplets of sulfuric acid and are driven around the planet by winds at speeds of up to 220 miles (360 km) per hour. Although the planet takes 243 Earth days to rotate once, the high-speed winds cause the clouds to circle the planet in only four Earth days. The high temperature, acidic clouds, and enormous atmospheric pressure (about 90 times greater at the surface than that on Earth) make the environment extremely hostile. However, space probes have managed to land on Venus and photograph its dry, dusty surface. The Venusian surface has also been mapped by probes with radar equipment that can “see” through the cloud layers. Such radar maps reveal a terrain with craters, mountains, volcanoes, and areas where craters have been covered by plains of solidified volcanic lava. There are two large highland regions called Aphrodite Terra and Ishtar Terra.
