Exoplanets, -moons, -comets

Formation And Disruption Of Resonant Chains Of Super-Earths: Secular Perturbations From Outer Eccentric Embryos

By Keith Cowing

Status Report

astro-ph.EP

November 21, 2025

Filed under astro-ph.EP, astrogeology, exoplanet, planetary embryos, Protoplanetary Disk, super Earth

Formation And Disruption Of Resonant Chains Of Super-Earths: Secular Perturbations From Outer Eccentric Embryos — (a)–(c) Time evolution of the eccentricity of an inner super-Earth with a1 = 0.3 au and M1 = 3 M_⊕, perturbed by an outer planet with different values of a₂, M₂, and e₂₀. Solid lines show the simulated eccentricity of the inner super-Earth, dashed lines show the evolution predicted by the analytic expression, and dotted lines show the eccentricity of the outer perturber. The analytic solutions are shown only for the first few oscillation cycles in each case. (d)–(f) Results of N-body simulations with multiple outer perturbers. Solid lines indicate the eccentricity evolution of the inner super-Earth, while dotted lines indicate the maximum eccentricity of the outer perturbers. All panels are plotted with a logarithmic spacing of 0.05 dex intervals. — astro-ph.EP

Recent observations have revealed the distribution of orbital period ratios of adjacent planets in multiple super-Earth systems and how these distributions change with time.

The aim of this study is to clarify under what conditions the observed features of orbital period ratios of super-Earths can be explained, and to identify what causes the dynamical instability of super-Earths captured into resonant chains.

We perform N-body simulations for 100 Myr that follow the formation and orbital evolution of super-Earths originating from a ring of planetary embryos at 1 au from the star. The simulations show that super-Earths undergo inward migration in the disk and are captured into mean-motion resonances with their neighbors. As a result, several resonant pairs form a resonant chain.

After disk dispersal, some of these chains become dynamically unstable. In such cases, the final distribution of orbital period ratios and their time evolution can be consistent with recent observations. The instabilities of resonant chains are likely triggered by secular perturbations from embryos that remain on outer orbits beyond 1 au, indicating that not only giant planets but also small embryos can disrupt the resonances among inner super-Earths.

We therefore further investigate the secular perturbations from outer embryos using analytic formulas and additional orbital calculations. We discuss the conditions required to excite the eccentricities of inner super-Earths on a timescale of about 100 Myr. These conditions include the need for large eccentricities of the outer embryos, as well as constraints on their masses and semimajor axes.

Masahiro Ogihara, Masanobu Kunitomo

Comments: 15 pages, 8 figures, accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2511.11328 [astro-ph.EP] (or arXiv:2511.11328v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2511.11328
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Submission history
From: Masahiro Ogihara
[v1] Fri, 14 Nov 2025 14:02:02 UTC (1,364 KB)
https://arxiv.org/abs/2511.11328

Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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