On the Dynamical Erasure of Initial Conditions in Multi-Planetary Systems

TL;DR

This paper investigates how dynamical processes in multi-planet systems erase initial migration signatures, leading to a flat period distribution observed in mature systems, supported by N-body simulations and observational data.

Contribution

It demonstrates that post-disk dynamical instabilities and mergers can erase initial migration imprints in planetary period distributions, aligning with observed data.

Findings

Dynamical instabilities erase initial period distribution signatures.

Younger systems show more resonant pairs than older systems.

N-body simulations support the erasure of initial conditions over 10-100 Myr.

Abstract

Do sub-Neptunes assemble close to where we see them or do they form full-fledged farther away from their host star then migrate inwards? We explore this question using the distribution of measured orbital periods, one of the most fundamental observable parameters. Under disk-induced migration, planet occurrence rate is expected to decrease towards shorter orbital periods. Presently, the observed sub-Neptune period distribution is flat in log period, between 10 and 300 days. We show, using N-body integration, how post-disk dynamical instabilities and mergers in multi-planetary systems erase the initial conditions of migration emplaced in period distributions over 10s to 100 Myr timescale, in rough agreement with an observational hint of the abundance of resonant pairs for systems younger than 100 Myr which drops dramatically for more evolved systems. We comment on caveats and future work.