Here’s a Mercury diagram, showing the interior of planet Mercury.
Mercury is the closest planet to the Sun, orbiting at an average distance of 57.9 million km from the Sun. It’s also the second densest planet in the Solar System, with an average distance of 5.427 grams per cubic centimeter. Based on this density, astronomers have some estimates about the interior structure of Mercury.
The center of Mercury is its metal core, similar to the Earth’s core. But in the case of Mercury, the core occupies 42% of the volume of Mercury, while the core of Earth is only 17%. And for some reason, the metal core of Mercury doesn’t create a magnetic field with the same intensity of Earth’s magnetic field. Mercury’s magnetosphere is only 1% as strong as Earth’s field.
Surrounding the core is Mercury’s mantle. This is a 500-700 km thick layer of rock, composed of silicates. And surrounding the mantle is Mercury’s crust. Based on observations made by Mariner 10 and Earth-based telescopes, astronomers think that Mercury’s crust is 100 – 300 kilometers thick. There are many large depressions in Mercury’s crust, and scientists think these formed as Mercury slowly cooled and contracted.
We’ve also recorded an episode of Astronomy Cast about Mercury. Listen here, Episode 49: Mercury.