True Polar Wander on Dynamic Planets: Approximative Methods vs. Full Solution

Almost three decades ago, the problem of long term polar wander on a dynamic planet was formulated and simplified within framework normal mode theory. The underlying simplifications have been debated ever since, recently in series papers by Hu et al. 2017a, 2017b, 2019, who clarify role neglecting short-term relaxation modes body. However, authors still do not solve governing equations full, because they make approximations to Liouville equation (LE). In this paper I use time domain approach for previously studied test loads both body LE full. also compute energy balance true (TPW) order analyze existing approximations. For fast rotating bodies such as Earth, show that rotation axis is always aligned with maximum principal inertia (w||MMOI) once free oscillations are damped. w||MMOI assumption re-derived theoretically. Contrary previous beliefs, demonstrate it necessarily linked quasi-fluid simplification body's viscoelastic response loading rotation, but an expression Coriolis Euler forces motion. slowly Venus, full together analysis indicate estimates TPW direction need be revisited. numerical code LIOUSHELL made freely available.