How thick is Earth's inner core?

Seismological studies have measured the Earth's inner core at approximately 760 miles in diameter. The presence of the solid nickel-iron alloy inner core was extrapolated in 1936 by Inge Lehmann from reflections of seismic waves off the boundary area between the outer and inner cores, known as the Lehmann discontinuity.

The inner core of the planet is thought to be roughly the same temperature as the surface of the Sun, approximately 9,800 degrees Fahrenheit. The tremendous pressure of the outer core, mantle and crust, however, prevents the inner core from transitioning to a liquid or gas at that temperature. The rotation of the inner core acts as a dynamo, creating the Earth's magnetic field that protects it from the effects of the solar wind.