Equations of Disturbed Movements of Structurally-Heterogeneous Planets

Equations of small movements of the non-rotating planet that consists of the gravitating spherical solid shell - mantle, self-gravitating liquid, and gravitating spherical solid core are deduced and analyzed. It is shown that the mechanical system under consideration having initially an infinite number of degrees of freedom may be reduced to an oscillating system with a finite number of degrees of freedom. Calculation results are compared to the known published data.