Mercury's dense iron core
Mercury is to a great extent denser than the Moon (5.43 gm/cm3 vs. 3.34). Mercury is the second densest mainly important body in the solar system, after Earth. Actually Earth's density is outstanding in part to gravitational density; if not for this, Mercury would be denser than Earth. This signifies that Mercury's dense iron core is reasonably larger than Earth, probably comprises the greater part of the planet. Mercury therefore has only a comparatively thin silicate mantle and crust.
Mercury's inner is under enemy control by a big iron core whose radius is 1800 to 1900 km. The silicate on the outside shell (analogous to Earth's mantle and crust) is just 500 to 600 km thick. At least several of the core is perhaps molten. Mercury truly has an enormously thin atmosphere consisting of atoms blasted off its surface by the solar wind. Because Mercury is so hot, these atoms speedily flee into space.