Astronomy Seminar: Flyby encounters between two planetary systems

Stars formed in clustered environment may experience stellar encounters. Here we explore a case where both encountering stars each has its own planetary system of various orbital scales and mass ranges. Besides the immediate effect of the encounter, we have also propagated the systems post-encounter for up to Gyr. So we reveal the effect of a captured planet on a system that survives the encounter itself.

We find that immediately during the encounter, a planet can be ejected from its original host star or captured by the intruding star. Here, the interplanetary interactions are negligible and a planet’s stellar-centric distance is a key factor in constraining its stability.

Then, during the long-term post-encounter evolution, the interplanetary forcing takes control. The larger the perturbation a system acquires immediately during the encounter, the more likely and the earlier it becomes unstable in the later phase. Captured planets intensify the post-encounter instability and they themselves are often lost.