Huge Core Dominates The Interior

Mercury is so small that the planet’s iron core should have cooled into a solid lump long ago. NASA’s MESSENGER probe has discovered that the core is not only huge, it is also still partly liquid.

takes up up to 85 % of the planet’s radius. That is much more than Earth’s core, which only makes up half. MESSENGER’s measurements of Mercury’s magnetic and gravitational fields have shown that the core is partly liquid.

between the core and the crust is much thinner than Earth’s. The explanation could be that at some point, Mercury was struck by another planet and that the violent collision tore off a large bite of the mantle.