Empirical evidence for tidal evolution in transiting planetary systems

TL;DR

This paper reviews empirical evidence for tidal interactions in transiting planetary systems, highlighting how tidal forces influence stellar rotation and planetary orbital evolution, and discusses implications for planetary system development.

Contribution

It provides new empirical evidence for tidal spin-up of stars and suggests tidal evolution significantly impacts the observed properties of close-in gas giants.

Findings

Empirical evidence for stellar spin-up due to tidal forces.

Tidal interactions may explain the mass-period relation of close-in gas giants.

Some planets may have spiraled inward significantly since formation.

Abstract

Most transiting planets orbit very close to their parent star, causing strong tidal forces between the two bodies. Tidal interaction can modify the dynamics of the system through orbital alignment, circularisation, synchronisation, and orbital decay by exchange of angular moment. Evidence for tidal circularisation in close-in giant planet is well-known. Here we review the evidence for excess rotation of the parent stars due to the pull of tidal forces towards spin-orbit synchronisation. We find suggestive empirical evidence for such a process in the present sample of transiting planetary systems. The corresponding angular momentum exchange would imply that some planets have spiralled towards their star by substantial amounts since the dissipation of the protoplanetary disc. We suggest that this could quantitatively account for the observed mass-period relation of close-in gas giants. We discuss how this scenario can be further tested and point out some consequences for theoretical studies of tidal interactions and for the detection and confirmation of transiting planets from radial-velocity and photometric surveys.