Mercury is thought to be the densest of all the planets, which makes sense when you consider the theory that during the early phases of the solar system’s formation, the lightest materials were sent farthest into space.
For a planet so small to be so dense, it may be mostly solid metal.
Scientists believe that Mercury’s core, which is 2,100 miles (3,500 km) in diameter, makes up 60 percent of its mass.
Because the planet also has a magnetic field, at least some of its metal must be liquid or molten.
Rocky silicate material makes up both the crust and mantle, the mantle is a denser form of the crust, which together are about 400 miles (700 km) in depth.