Venus is often referred to as Earth’s twin planet (evil twin planet is more like it, when you consider the scorching temperatures). It’s almost the same size, mass, gravity and overall composition. The composition of Venus is pretty similar to Earth, with a core of metal, a mantle of liquid rock, and an outer crust of solid rock.
Unfortunately, scientists have no direct knowledge about Venus composition. Here on Earth, scientists use seismometers to study how seismic waves from earthquakes propagate through the planet. How these waves bounce and turn inside the Earth tell scientists about its composition. Since the surface of Venus is hot enough to melt lead, and no spacecraft have survived on the surface for longer than a few hours, there just isn’t the information about Venus’ internal composition.
Scientists can calculate the density of Venus, though. Since it’s similar to Earth, and the other terrestrial planets, scientists guess that the internal structure of Venus is similar to Earth. One of the big differences between our two planets, however, is the lack of plate tectonics on Venus. For some reason, plate tectonics on Venus shut down billions of years ago. This has prevented the interior of Venus from losing as much heat as the Earth does, and could be the reason Venus doesn’t have an internally generated magnetic field.
Before spacecraft missions were sent to Venus, scientists had no idea what the composition of Venus was. They could calculate the planet’s density, but the surface of Venus was obscured by dense clouds. Spacecraft equipped with radar were able to penetrate the thick clouds and map out features on the planet’s surface, showing that it has impact craters and ancient volcanoes. It’s believed that Venus went through some kind of global resurfacing event about 300-500 million years ago, which is the age of the planet’s surface (calculated by the number of impact craters).
The crust of Venus is thought to be about 50 km thick, and composed of silicious rocks. Beneath that is the mantle, which is thought to be about 3,000 km thick. The composition of the mantle is unknown. And then at the center of Venus is a solid or liquid core of iron or nickel. Since Venus doesn’t have a global magnetic field, scientists think that the planet doesn’t have convection in its core. The planet doesn’t have a large difference in temperature between the inner and outer core, and so the metal doesn’t flow around and generate a magnetic field.
We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.
We have recorded a whole episode of Astronomy Cast that’s only about planet Venus. Listen to it here, Episode 50: Venus.