Mars' interior. Computer artwork showing the interior structure of the planet Mars. Current studies say its core consists primarily of iron with about 14-17% sulphur, and is about 1480 km in radius. The core is surrounded by a silicate mantle that formed many of the tectonic and volcanic features on the planet, but now appears to be inactive. The average thickness of the planet's crust is about 50 km, while the maximum thickness is about 125 km. In comparison, Earth's crust, averages 40 km, and is only one third as thick as Mars' crust.