Tidal decay of circumbinary planetary systems

TL;DR

This paper demonstrates that tidal decay in circumbinary planetary systems causes orbital shrinkage, potentially explaining the scarcity of close-in planets around binary stars and contributing to the population of rogue planets.

Contribution

It introduces the concept of universal tidal decay in circumbinary systems and explores its implications for planetary system evolution and observed planet distributions.

Findings

Tidal decay causes orbit shrinkage in circumbinary planets.

It may explain the lack of close-in planets around binary stars.

The mechanism could contribute to the population of rogue planets.

Abstract

It is shown that circumbinary planetary systems are subject to universal tidal decay (shrinkage of orbits), caused by the forced orbital eccentricity inherent to them. Circumbinary planets (CBP) are liberated from parent systems, when, owing to the shrinkage, they enter the circumbinary chaotic zone. On shorter timescales (less than the current age of the Universe), the effect may explain, at least partially, the observed lack of CBP of close-enough (with periods < 5 days) stellar binaries; on longer timescales (greater than the age of the Universe but well within stellar lifetimes), it may provide massive liberation of chemically evolved CBP. Observational signatures of the effect may comprise (1) a prevalence of large rocky planets (super-Earths) in the whole population of rogue planets (if this mechanism were the only source of rogue planets); (2) a mass-dependent paucity of CBP in systems of low-mass binaries: the lower the stellar mass, the greater the paucity.