You are right, that number is incorrect. The radius of the Earth (surface crust to the center of the core) is about 3,954 miles long. The interior of the planet is basically divided into four major sections: the inner core, the outer core, the mantle, and the crust. The asthenosphere is part of the upper portion of the mantle; it is the liquid that the crustal plates of the Earth "float" on. The mantle runs from about 22 miles in depth to about 1,790 miles. The asthenosphere in particular sits at about 62 to 125 miles in depth from the surface of the Earth.