How planetary systems are shaped by their birthplace

We want to find out whether and how the currently observed diverse planetary systems still contain some key information about the conditions at the time they were formed in a stellar association or open cluster. Due to the complexity of evolutionary processes in star clusters and multi-planetary systems this will be anything but a linear logical process. We use realistic N-body star cluster modelling rather than statistical ensembles of few body scatterings. Our results can be compared with observational data in this SPP and elsewhere on populations of extrasolar planets. At first the model would use very simple classes of initial configurations of multi-planetary systems, such as “standard”, “compact”, “resonant”, “eccentric”, or “massive”.

In a next step we aim to provide a comprehensive picture of the contribution of star cluster environments to the diversity of extrasolar planetary systems. Delayed triggered instabilities of planetary systems from stellar encounters in star clusters have been shown to play an important role; for these reasons the dynamical study of star clusters with embedded planetary systems is of great importance to understand the origin of diversity of extrasolar planets. We will explore the interesting processes with improved numerical methods, and a wider range of star cluster and planetary system parameters. Two new processes will be taken nto account soon: one is the role of free-floating planets and re-capture, both for lensing studies and for obtaining information about how re-captured objects can account for highly eccentric planets and other low-mass objects (planetesimals, comets, like ‘Oumuamua) in the outermost regions of planetary systems and to what extent gravitational lensing studies would be able to provide observational limits on free floating planets in star clusters; the second is the inclusion of stellar binaries, both as partners for gravitational encounters (so far only done in approximate Monte Carlo scattering models) and as host objects of planetary systems – S-type (circumstellar) or P-type (circumbinary).

Katja Stock

Delayed triggered instabilities of planetary systems from stellar encounters in star clusters have been shown to play an important role; for these reasons the dynamical study of star clusters with embedded planetary systems is of great importance to understand the origin of diversity of extrasolar planets.

We use data of our star cluster simulations with planetary systems obtained in the study by Katja Reichert to follow the paths of liberated planets in the star cluster, and estimate possible microlensing events caused by them.

Stefan Blenkle

This work studies the dynamics of massless particles (MLPs) in star clusters. MLPs, such as comets, asteroids, planetesimals, and free-floating planets, are continuously injected into the intra-cluster environment by their host stars. We carry out numerical simulations to investigate the dynamical evolution of MLP populations in star clusters, including their ejection rates and capture rates, using NBODY6++GPU-MASSLESS, a modified version of the N-body simulation code NBODY6++GPU.

Unlike stars, MLPs do not participate in the mass segregation process. Instead, MLPs primarily follow the gravitational potential of the star cluster, which gradually decreases due to stellar ejections and stellar evolution. The decrease in the number of MLPs is stronger for clusters with a stronger external tidal field, and for clusters with a smaller initial stellar mass range. MLPs are regularly captured into wide, highly-eccentric star-MLP binaries, most of which are disrupted within 10 Myr. These systems occasionally have periastron distances small enough to allow dynamical interaction between the MLP and an existing planetary system, if present.

As a star cluster evolves, the population of (initially) free-floating MLPs evolves to a dynamical equilibrium in which a fraction 10⁻⁴ of the MLPs is part of a star-MLP binary. Under the assumption that other stars have similar formation histories and cometary ejection rates as our Solar system, we estimate that young star clusters contain large numbers of ≈10¹⁷ free-floating comets, and that each star typically hosts ≈10⁵ captured comets at a given time. We speculate that our own Solar system, which may have formed in a star cluster of similar size, hosts a comparable number of captured exocomets in the Oort cloud, and that the famous object Oumuamua belongs to this class of objects.

Shu Qi

We speculate that our own Solar system, which may have formed in a star cluster of similar size, hosts a comparable number of captured exocomets in the Oort cloud, and that the famous object Oumuamua belongs to this class of objects.