Tidal evolution and spin–orbit dynamics for bodies in the viscous regime.

This study analyzes the secular dynamics of two extended bodies in Keplerian orbits, focusing on tidal effects. It introduces formulas for energy dissipation within each body in a binary system. The bodies can have a finite number of layers with linear viscoelastic rheology. The layers must be sufficiently coupled so that the rotation of each layer remains close to the average rotation of the body. The body is assumed to be in a "viscous regime" (though it may contain purely elastic layers), meaning that the relaxation times of the rheology are much shorter than the typical despinning time and deviations from sphericity are caused only by tidal and centrifugal stresses. The main contribution of this paper is the decomposition of orbital-averaged equations into a fast–slow system. This reduction allows the slow dynamics to be represented as sliding along a torque-free curve with occasional jumps at folding points. This greatly simplifies the analysis of the dynamics as a function of the rheological parameters. [ABSTRACT FROM AUTHOR]