Tidally driven inertial waves enhance eccentricity damping and spin evolution in planets and stars

Abstract: Tidal interactions influence the orbital motions of binary star systems and extrasolar planets alike. Tides also affect stellar and planetary rotation rates. We demonstrate that in addition to altering spin synchronization and pseudosynchronization, tidally driven inertial waves in the convective envelopes of low-mass stars and gas giant planets can enhance tidal eccentricity damping. Analytically, we find that eccentricity damping by inertial waves can be orders of magnitude faster than equilibrium tides, independent of any eddy viscosity prescription. We use simplified numerical experiments to demonstrate this enhancement, and to explore the effects of different mixing length treatments of convective turbulence, as well as a spin-down torque from magnetic braking. These calculations demonstrate that tidally driven inertial waves can produce an extended cool core of nearly circular binaries, helping to reconcile a longstanding discrepancy between observed and predicted main-sequence binary circularization. Our calculations additionally suggest that tidally driven inertial waves may leave identifiable signatures in the ratios of orbital to rotation periods for stellar binaries, including synchronous and sub-synchronous rotation periods reminiscent of populations identified in Kepler, TESS, and Gaia data.