Two-stage disruption of resonant chains

TL;DR

This paper proposes a two-stage disruption model for resonant chains of super-Earths, involving eccentricity excitation and subsequent dynamical instability, explaining observed resonance breakage and period ratio features.

Contribution

It introduces a novel disruption scenario triggered by impactor-induced eccentricities, aligning with TESS observations of resonance decline over 100 Myr.

Findings

Impacts from Mercury-sized bodies can excite eccentricities and cause resonance disruption.

The model explains the decline in system multiplicity and resonance occupation over time.

Impacts may originate from debris leftover from earlier planet formation stages.

Abstract

TESS has made clear that most close-in planets were born in chains of mean-motion resonances that break on a characteristic timescale of 100 Myr. This observation is surprising because the same dissipative forces that capture planets into resonance render their orbits long-term stable. We explore a two-stage disruption scenario for resonant chains of super-Earths. First, the chains have their (free) eccentricities excited by some mechanism. We show that any such mechanism that seeds eccentricities of a few percent sets in motion a second stage of dynamical instability on a ~100 Myr timescale. A possible stage-one mechanism is the accretion of a handful of Mercury-sized bodies totaling a few percent of the planetary system mass, which excites the requisite eccentricities and triggers a stage two that reproduces the observed decline in the incidence of resonance. Impacts from such bodies can also explain why some young systems have period ratios narrow of commensurability. We sketch how these impactors may have grown out of debris left over from an earlier epoch of planet formation. We also identify two new trends in the observational data: a decline in multiplicity on the same timescale as the decline in the incidence of resonance, and an increase in the occupation of resonances with multiplicity.