Are the Kepler Near-Resonance Planet Pairs due to Tidal Dissipation?

TL;DR

This paper investigates whether tidal dissipation can explain the near-resonance configurations of Kepler planet pairs, finding that tides alone are insufficient and other processes may be involved.

Contribution

It provides constraints on planetary properties based on tidal dissipation and highlights the need for additional mechanisms to explain observed orbital configurations.

Findings

Tides alone cannot account for the observed planet pair separations.

Some Kepler planets are likely solid based on tidal dissipation constraints.

Additional dissipative processes are needed to explain the near-resonance distributions.

Abstract

The multiple-planet systems discovered by the Kepler mission show an excess of planet pairs with period ratios just wide of exact commensurability for first-order resonances like 2:1 and 3:2. In principle, these planet pairs could have both resonance angles associated with the resonance librating if the orbital eccentricities are sufficiently small, because the width of first-order resonances diverges in the limit of vanishingly small eccentricity. We consider a widely-held scenario in which pairs of planets were captured into first-order resonances by migration due to planet-disk interactions, and subsequently became detached from the resonances, due to tidal dissipation in the planets. In the context of this scenario, we find a constraint on the ratio of the planet's tidal dissipation function and Love number that implies that some of the Kepler planets are likely solid. However, tides are not strong enough to move many of the planet pairs to the observed separations, suggesting that additional dissipative processes are at play.