The dynamical fate of planetary systems in young star clusters

TL;DR

This study uses N-body simulations to analyze how dynamical interactions in young star clusters influence the survival and evolution of planetary systems, considering various initial cluster conditions and their effects on planetary retention.

Contribution

It introduces a quantitative model for planetary system survival probability based on initial cluster properties and explores how these factors affect planetary retention and free-floating planet populations.

Findings

Survival fraction follows a specific functional form depending on semi-major axis.

Higher initial stellar density increases planetary system survival probability.

Initial substructure impacts the evolution of planetary system retention over time.

Abstract

We carry out N-body simulations to examine the effects of dynamical interactions on planetary systems in young open star clusters. We explore how the planetary populations in these star clusters evolve, and how this evolution depends on the initial amount of substructure, the virial ratio, the cluster mass and density, and the initial semi-major axis of the planetary systems. The fraction of planetary systems that remains intact as a cluster member, fbps, is generally well-described by the functional form fbps=f0(1+[a/a0]^c)^-1, where (1-f0) is the fraction of stars that escapes from the cluster, a0 the critical semi-major axis for survival, and c a measure for the width of the transition region. The effect of the initial amount of substructure over time can be quantified as fbps=A(t)+B(D), where A(t) decreases nearly linearly with time, and B(D) decreases when the clusters are initially more substructured. Provided that the orbital separation of planetary systems is smaller than the critical value a0, those in clusters with a higher initial stellar density (but identical mass) have a larger probability of escaping the cluster intact. These results help us to obtain a better understanding of the difference between the observed fractions of exoplanets-hosting stars in star clusters and in the Galactic field. It also allows us to make predictions about the free-floating planet population over time in different stellar environments.