where C is the first principal moment of inertia of the body, M is the mass of the body, and R is the mean radius of the body. For a sphere with uniform density, C / M R 2 = 2 / 5 . For a differentiated planet or satellite, where there is an increase of density with depth, C / M R 2 < 2 / 5 . The quantity is a useful indicator of the presence and extent of a planetary core, because a greater departure from the uniform-density value of 2/5 conveys a greater degree of concentration of dense materials towards the center.