A Bayesian Monte Carlo assessment of orbital stability in the late stages of planetary system formation

Abstract

ABSTRACT The final orbital configuration of a planetary system is shaped by both its early star–disc environment and late-stage gravitational interactions. Assessing the relative importance of each of these factors is not straightforward due to the observed diversity of planetary systems compounded by observational biases. Our goal is to understand how a planetary system may change when planetesimal accretion and planet migrations stop and secular gravitational effects take over. Our approach starts with a novel classification of planetary systems based on their orbital architecture, validated using Approximate Bayesian Computation methods. We apply this scheme to observed planetary systems and also to ∼400 synthetic systems hosting ∼5000 planets, synthesized from a Monte Carlo planet population model. Our classification scheme robustly yields four system classes according to their planet masses and semimajor axes, for both observed and synthetic systems. We then estimate the orbital distribution density of each of the synthetic systems before and after dynamically evolving for 0.1–1 Myr using a gravitational + collisional N-body code. Using the Kullback–Leibler divergence to statistically measure orbital configuration changes, we find that ≲10 per cent of synthetic planetary systems experience such changes. We also find that this fraction belongs to a class of systems for which their centre of mass is very close to their host star. Although changes in the orbital configuration of planetary systems may not be very common, they are more likely to happen in systems with close-in, massive planets, with F- and G-type host-stars and stellar metallicities [Fe/H] >0.2.