Precession of the Nonrigid Earth: Effect of the Fluid Outer Core

Abstract

We show that, unlike commonly believed, the presence of a fluid core does affect the precessional motion of Earth by a nonnegligible amount, equivalent to a variation of several parts per million in the value of the precession constant or, correspondingly, the dynamical ellipticity of Earth. This contribution arises from the second-order terms of the averaged Hamiltonian after the application of perturbation methods to remove the periodic terms, some of the former being amplified as a consequence of resonance induced by the fluid core. Our evaluation corresponds to a simplified Earth model of the "Poincaré kind" (rigid mantle and liquid core). Under these assumptions, the effect of the fluid core is larger than -002 per century, which represents a significant contribution to the total amount of precession, since it is about two-thirds of the total planetary effect.