Architectures of Compact Super-Earth Systems Shaped by Instabilities

Abstract

Compact non-resonant super-Earth systems are a common outcome of planet formation and display dramatic signatures of intra-system uniformity, but the details of their formation and early evolution are poorly-known. During the protoplanetary disk phase, planets are expected to form outside of their current positions and migrate inwards, capturing into mean motion resonances. Dynamical instabilities can later destabilize these resonances. Here, we 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 observed sample. Furthermore, we demonstrate that primordial mass uniformity, motivated by the sample of resonant chains coupled with dynamical sculpting, naturally produces uniformity in period spacing similar to what is observed. Finally, we find that almost all collisions lead to perfect mergers, but some sort of post-instability damping and accretion are likely needed to completely reproduce the present-day dynamically cold architectures of sub-Jovian exoplanets.