Empirical Constraints on Tidal Dissipation in Exoplanet Host Stars

The orbits of short-period exoplanets are sculpted by tidal dissipation. However, the mechanism and efficiency of these tidal interactions are poorly constrained. We present robust constraints on the tidal quality factors of the host stars of short-period exoplanets through the usage of a novel empirical technique. The method is based on analyzing structures in the population-level distribution of decay times, defined as the time remaining before a planet spirals into its host star due to stellar tides. Using simple synthetic planet population simulations and analytic theory, we show that there exists a steady-state portion of the decay time distribution with an approximately power-law form. This steady-state feature is clearly evident in the decay time distribution of the observed short-period planet population. We use this to constrain both the magnitude and frequency dependence of the stellar quality factor and show that the stellar Q’ must decrease sharply with planetary orbital period. This disagrees with the predictions of internal gravity wave dissipation and suggests that another tidal mechanism is dominant. Our results offer the first strong constraints on stellar tidal properties from planetary demographics. They are also highly informative for the interpretation of the observable effects of tides, including planetary orbital decay and engulfment.