No pseudosynchronous rotation for terrestrial planets and moons

TL;DR

This paper demonstrates that, contrary to previous beliefs based on oversimplified models, terrestrial planets and moons cannot achieve stable pseudosynchronous rotation outside spin-orbit resonances when realistic tidal models are used.

Contribution

The study refutes the existence of stable pseudosynchronous rotation states by applying a detailed tidal model with realistic rheology, improving understanding of planetary spin states.

Findings

No stable pseudosynchronous states exist for solid planets and moons.

Previous models oversimplified tidal torque, leading to incorrect conclusions.

Spin-orbit resonances are the only stable equilibrium states.

Abstract

We reexamine the popular belief that a telluric planet or satellite on an eccentric orbit can, outside a spin-orbit resonance, be captured in a quasi-static tidal equilibrium called pseudosynchronous rotation. The existence of such configurations was deduced from oversimplified tidal models assuming either a constant tidal torque or a torque linear in the tidal frequency. A more accurate treatment requires that the torque be decomposed into the Darwin-Kaula series over the tidal modes, and that this decomposition be combined with a realistic choice of rheological properties of the mantle. This development demonstrates that there exist no stable equilibrium states for solid planets and moons, other than spin-orbit resonances.