Intruder Alert: Breaking Resonant Chains with Planetesimal Flybys

TL;DR

This paper explores how intermittent flybys of planetesimals can break mean-motion resonance chains in compact exoplanet systems, potentially explaining observed dynamical architectures.

Contribution

It introduces a new mechanism involving planetesimal flybys to disrupt resonance chains, supported by simulations and analytical calculations.

Findings

A planetesimal reservoir of >0.04 Earth masses can disrupt MMR chains.

Disrupted systems often become unstable within ~100 Myr.

The mechanism predicts an anti-correlation between resonant and active outer systems.

Abstract

The orbital architectures of compact exoplanet systems record their complicated dynamical histories. Recent research supports the ``breaking-the-chains'' hypothesis, which proposes that compact systems typically form in chains of mean-motion resonances (MMRs) but subsequently break out on a $\sim 100$Myr timescale. We investigate a scenario for breaking the chains through intermittent flybys of planetesimals originating from a distant reservoir. Using $N$-body simulations and semi-analytical calculations, we characterize the disruption of MMRs through these flybys. We find a planetesimal reservoir of total mass $\gtrsim 0.04 M_{\oplus}$ is required to disrupt MMR chains, depending on the mass distribution and the typical number of flybys executed by each planetesimal. We verify that systems disrupted in this way are frequently unstable to close encounters within $\sim 100$Myr of the final flyby. This mechanism operates in systems with both a sufficiently massive reservoir and an efficient mechanism for planetesimal injection. Consequently, we predict an anti-correlation between resonant inner systems and dynamically active outer configurations.