The interior of Venus.
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The Interior of Venus

Venus is a slightly smaller than the Earth, with a diameter 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.

Because Venus is so close to Earth in the solar system and is about the same size, we would expect that it would have been composed initially of somewhat similar materials, would have experienced a somewhat similar history, and would have a somewhat similar interior. We now know, however, that there are differences between Earth and Venus, not only in it's atmosphere but also on it's surface. The varied terrain of Venus, including volcanoes, mountains, craters, and lava flows, suggests that the planet was once, and perhaps still is, geologically active. Scientists are unsure whether volcanic activity continues on the planet, although we know it did in the past, and still have basic questions about the interior of Venus, such as the thickness of the lithosphere.

Nonetheless, the interior of Venus is probably similar to Earth's interior, with a partly molten metallic core, a rocky mantle, and a crust. The extremely slow rotation of the planet -- at 243 Earth days even longer than it's orbital period around the Sun, about 225 Earth days -- may explain the lack of a planetary magnetic field such as those exhibited by many of the other planets, including Earth.

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