Identify the force that caused stars and planets in the universe to become layered according to density differences in their composition

Planetary differentiation is the separation of elements of the planets according their physical characteristics. The heavy elements sank to the center while the lighter ones rose to the top. Iron, nickel and other heavy metals mostly settled to the core; lighter elements remained in the mantle around the core.This separation produces a layered structure of the stars and planets in the universe. Several forces cause this separation: the gravity , thermal diffusion, melting and crystallization..