Three Pathways for Observed Resonant Chains

TL;DR

This study examines whether observed planetary resonant chains can form through long-scale migration, short-scale migration, or eccentricity damping, finding all three mechanisms can reproduce the observed configurations.

Contribution

The paper compares three different formation mechanisms for resonant chains using N-body simulations, showing all are plausible explanations for observed systems.

Findings

All three mechanisms can reproduce observed resonant chains.

Long-scale migration is not the sole explanation for resonant chains.

Resonant chains may be compatible with in situ formation.

Abstract

A question driving many studies is whether the thousands of exoplanets known today typically formed where we observe them or formed further out in the disk and migrated in. Early discoveries of giant exoplanets orbiting near their host stars and exoplanets in or near mean motion resonances were interpreted as evidence for migration and its crucial role in the beginnings of planetary systems. long-scale migration has been invoked to explain systems of planets in mean motion resonant chains consisting of three or more planets linked by integer period ratios. However, recent studies have reproduced specific resonant chains in systems via short-scale migration, and eccentricity damping has been shown to capture planets into resonant chains. We investigate whether the observed resonant chains in Kepler-80, Kepler-223, Kepler-60, and TRAPPIST-1 can be established through long-scale migration, short-scale migration, and/or only eccentricity damping by running suites of N-body simulations. We find that, for each system, all three mechanisms are able to reproduce the observed resonant chains. long-scale migration is not the only plausible explanation for resonant chains in these systems, and resonant chains are potentially compatible with in situ formation.