Architectures of Compact Super-Earth Systems Shaped by Instabilities

TL;DR

This paper uses N-body simulations to show that dynamical instabilities in resonant chains of sub-Jovian planets can explain the observed uniformity in their masses, radii, and orbital spacings, highlighting the role of collisions and post-instability damping.

Contribution

It demonstrates that post-nebular dynamical instabilities can reproduce observed exoplanet system architectures and mass uniformity, providing insights into their formation and evolution.

Findings

Instabilities reproduce observed period ratio distribution.

Collisions modify mass uniformity consistent with data.

Primordial mass uniformity leads to orbital spacing uniformity.

Abstract

Compact non-resonant systems of sub-Jovian planets are the most common outcome of the planet formation process. Despite exhibiting broad overall diversity, these planets also display dramatic signatures of intra-system uniformity in their masses, radii, and orbital spacings. Although the details of their formation and early evolution are poorly known, sub-Jovian planets are expected to emerge from their natal nebulae as multi-resonant chains, owing to planet-disk interactions. Within the context of this scenario, the architectures of observed exoplanet systems can be broadly replicated if resonances are disrupted through post-nebular dynamical instabilities. Here, we generate an ad-hoc sample of resonant chains and use a suite of N-body simulations to show that instabilities can not only reproduce the observed period ratio distribution, but that the resulting collisions also modify the mass uniformity in a way that is consistent with the data. Furthermore, we demonstrate that primordial mass uniformity, motivated by the sample of resonant chains coupled with dynamical sculpting, naturally generates uniformity in orbital period spacing similar to what is observed. Finally, we find that almost all collisions lead to perfect mergers, but some form of post-instability damping is likely needed to fully account for the present-day dynamically cold architectures of sub-Jovian exoplanets.