Coupled orbital and spin evolution of the CoRoT-7 two-planet system using a Maxwell viscoelastic rheology

TL;DR

This study models the coupled orbital and spin evolution of the CoRoT-7 two-planet system using a Maxwell viscoelastic approach, revealing how planetary relaxation times influence eccentricity evolution and potentially explain observed high eccentricities.

Contribution

It introduces a Maxwell rheology-based model for planetary deformation, showing how relaxation times affect orbital eccentricity evolution in close-in planetary systems.

Findings

Short relaxation times damp eccentricity as in classic tidal theories.

Long relaxation times can secularly excite eccentricity to high values.

The model explains the high eccentricity of CoRoT-7 b and similar exoplanets.

Abstract

We investigate the orbital and rotational evolution of the CoRoT-7 two-planet system, assuming that the innermost planet behaves like a Maxwell body. We numerically resolve the coupled differential equations governing the instantaneous deformation of the inner planet together with the orbital motion of the system. We show that, depending on the relaxation time for the deformation of the planet, the orbital evolution has two distinct behaviours: for relaxation times shorter than the orbital period, we reproduce the results from classic tidal theories, for which the eccentricity is always damped. However, for longer relaxation times, the eccentricity of the inner orbit is secularly excited and can grow to high values. This mechanism provides an explanation for the present high eccentricity observed for CoRoT-7 b, as well as for other close-in super-Earths in multiple planetary systems.