Life is But a Stream: The Distribution of Planetary Systems Along Stellar Streams and their Properties
The majority of discovered exoplanets have been observed orbiting field stars as opposed to within a star cluster. To determine whether the lack of observed exoplanets in star clusters is due to gravitational perturbations or observational limitations, we consider the possibility of studying exoplanets in stellar streams. We present the results of direct $N$-body simulations of planetary systems around stars that orbit within a star cluster. Our simulations demonstrate that stars with early cluster escape times tend to retain all their planets as they spend most of their time orbiting in the cluster's low-density outskirts. Alternatively, stars with later escape times can have a wide range of survival fractions as they are subjected to a range of local densities and encounter types. With respect to the stellar stream that forms as the result of the cluster's dissolution, stars near the edge of the stream are therefore more likely to have unperturbed planetary systems. Conversely, stars near the centre of the stream have a higher chance of having planets pushed to eccentric orbits, inclined orbits, or stripped from the system entirely. From our suite of simulations, we provide an estimate of the probability that a star will host a planet with a given initial semi-major axis $a_0$ based on the star's location along a stellar stream $Δϕ$.