Observational Evidence for Tidal Destruction of Exoplanets

TL;DR

This paper presents observational evidence that tidal forces cause the destruction and inward migration of close-in exoplanets, explaining their orbital distribution and characteristics.

Contribution

It provides observational support for tidal destruction as a common process affecting close-in exoplanets, challenging previous migration stopping mechanisms.

Findings

Good qualitative agreement between observed distributions and tidal theory predictions

Tidal destruction explains the orbital period clustering near three days

Some planets may be on the verge of destruction, with possible stellar signatures

Abstract

The distribution of the orbits of close-in exoplanets shows evidence for on-going removal and destruction by tides. Tides raised on a planet's host star cause the planet's orbit to decay, even after the orbital eccentricity has dropped to zero. Comparison of the observed orbital distribution and predictions of tidal theory show good qualitative agreement, suggesting tidal destruction of close-in exoplanets is common. The process can explain the observed cut-off in small a-values, the clustering of orbital periods near three days, and the relative youth of transiting planets. Contrary to previous considerations, a mechanism to stop the inward migration of close-in planets at their current orbits is not necessarily required. Planets nearing tidal destruction may be found with extremely small a, possibly already stripped of any gaseous envelope. The recently discovered CoRoT-Exo-7 b may be an example of such a planet and will probably be destroyed by tides within the next few Gyrs. Also, where one or more planets have already been accreted, a star may exhibit an unusual composition and/or spin rate.