Mercury is a small, rocky planet. It is the most metal-rich body in the solar system. The core of the planet is made mostly of iron-nickel. Mercury's core has a radius of about 1,136 miles (1830 km), or about 75 percent of the planet's radius. Of all the planets, Mercury has the largest core compared to its total size. Mercury was thought to have a solid core. However, recent evidence indicates that it may be at least partially molten.
The core is surrounded by a mantle of silicate rock. The mantle is just about 380 miles (600 km) thick, or almost 25 percent of the radius. Above that is a very thin crust.
