The interior of Venus. Click on image for full size version (43K GIF)

Venus is a slightly smaller than the Earth, with a radius 95% that of Earth (12,103 km) and a mass 81% that of Earth. If we could walk around on the surface of the planet (without being killed by the toxic blast furnace of an atmosphere), gravity would be close to that on the surface of Earth.

The interior of Venus is probably similar to Earth's interior. Venus, like Earth, is one of the terrestrial planets and is made of rock and metal. It probably has a partly molten metallic core, a rocky mantle, and a crust. The planet rotates very slowly, taking more than 243 Earth days to spin once on it's axis (even longer than the time it takes for Venus to orbit the Sun, about 225 Earth days). This may be the reason the planet doesn't have a magnetic field like many of the other planets, including Earth.

The varied terrain of Venus, including volcanoes, mountains, craters, and lava flows, suggests that the planet was once, and perhaps still is, geologically active. But basic questions about the interior of Venus remain, such as the thickness of the lithosphere.