The inner core is a solid and dense. It extends to the liquid outer core surrounding it, to the center of the Earth. It's about 6,380 km under Earth's surface and around 1,230 km wide. The inner core is very hot (9,000 to 13,000 degrees fahrenheit), but it doesn't melt from the heat of the liquid outer core because of the pressure of Earth's other layers on top of it. Since the inner core is made up of mostly iron, it is a metal, making the entire planet magnetic; the outer core controls the magnetism.