Planetary systems in a star cluster I: the Solar system scenario

Francesco Flammini Dotti,M B N Kouwenhoven,Rainer Spurzem,Maxwell Xu Cai

doi:10.1093/mnras/stz2346

Abstract

ABSTRACTYoung stars are mostly found in dense stellar environments, and even our own Solar system may have formed in a star cluster. Here, we numerically explore the evolution of planetary systems similar to our own Solar system in star clusters. We investigate the evolution of planetary systems in star clusters. Most stellar encounters are tidal, hyperbolic, and adiabatic. A small fraction of the planetary systems escape from the star cluster within 50 Myr; those with low escape speeds often remain intact during and after the escape process. While most planetary systems inside the star cluster remain intact, a subset is strongly perturbed during the first 50 Myr. Over the course of time, $0.3\!-\!5.3{{\ \rm per\ cent}}$ of the planets escape, sometimes up to tens of millions of years after a stellar encounter occurred. Survival rates are highest for Jupiter, while Uranus and Neptune have the highest escape rates. Unless directly affected by a stellar encounter itself, Jupiter frequently serves as a barrier that protects the terrestrial planets from perturbations in the outer planetary system. In low-density environments, Jupiter provides protection from perturbations in the outer planetary system, while in high-density environments, direct perturbations of Jupiter by neighbouring stars is disruptive to habitable-zone planets. The diversity amongst planetary systems that is present in the star clusters at 50 Myr, and amongst the escaping planetary systems, is high, which contributes to explaining the high diversity of observed exoplanet systems in star clusters and in the Galactic field.

Highlights

It is commonly accepted that a large fraction of stars in the Galaxy hosts one or more planetary companions (e.g., Mayo et al 2018; Thompson et al 2018); and even binary star systems are known to host exoplanets (Gould et al 2014)
Young stars are mostly found in dense stellar environments, and even our own Solar system may have formed in a star cluster
We have carried out a set of comprehensive N -body simulations in order to characterise the dynamical evolution of planetary systems similar to our own Solar system in different star cluster environments

Summary

Introduction

It is commonly accepted that a large fraction of stars in the Galaxy hosts one or more planetary companions (e.g., Mayo et al 2018; Thompson et al 2018); and even binary star systems are known to host exoplanets (Gould et al 2014). The current paradigm for the formation of stars suggests that stars are formed in groups in gaseous environments, which are similar to, but slightly less massive and concentrated, than the progenitors of the longer-lived open clusters Most of these young groups of stars disperse within 10 − 50 Myr, after which their member stars become part of the field star population, while others remain bound for hundreds of millions to billions of years (e.g., de Grijs et al 2008; de Grijs 2009). Isotope analysis in meteorites has shown that the proto-planetary disk of our Sun was polluted by a nearby supernova (e.g., Hester et al 2004; Looney 2006) This suggests that even our own Solar System may have formed in a clustered stellar environment, in a star cluster of size rvir = 0.75 ± 0.25 pc, together with 2500 ± 300 other stars (Adams 2010; Portegies Zwart et al 2018)

Methods

Results

Conclusion