Tidal Evolution of Close-in Extrasolar Planets: High Stellar Q from New Theoretical Models

TL;DR

This paper presents new theoretical models indicating that the stellar tidal quality factor Q is much higher than previously estimated, implying longer orbital lifetimes for close-in extrasolar planets and affecting their observed orbital evolution.

Contribution

The authors introduce a novel approach to estimate stellar tidal dissipation using numerical simulations, resulting in higher Q values and revised orbital lifetime predictions.

Findings

Stellar Q values range from 10^8 to 3×10^9.

Orbital lifetimes are comparable to or longer than system ages.

Tidal decay signals are below current detection thresholds but may be observable with extended missions.

Abstract

In recent years it has been shown that the tidal coupling between extrasolar planets and their stars could be an important mechanism leading to orbital evolution. Both the tides the planet raises on the star and vice versa are important and dissipation efficiencies ranging over four orders of magnitude are being used. In addition, the discovery of extrasolar planets extremely close to their stars has made it clear that the estimates of the tidal quality factor, Q, of the stars based on Jupiter and its satellite system and on main sequence binary star observations are too low, resulting in lifetimes for the closest planets orders of magnitude smaller than their age. We argue that those estimates of the tidal dissipation efficiency are not applicable for stars with spin periods much longer than the extrasolar planets' orbital period. We address the problem by applying our own values for the dissipation efficiency of tides, based on our numerical simulations of externally perturbed volumes of stellar-like convection. The range of dissipation we find for main-sequence stars corresponds to stellar $Q_*$ of $10^8$ to $3{\times}10^9$. The derived orbit lifetimes are comparable to, or much longer than the ages of the observed extrasolar planetary systems. The predicted orbital decay transit timing variations due to the tidal coupling are below the rate of ms/yr for currently known systems, but within reach of an extended Kepler mission provided such objects are found in its field.