The impact of internal and external perturbations on exoplanet architectures

Stars do not form in isolation but together with other stars, and often in regions that are initially highly substructured. Using simulations of realistic young star-forming regions, I will show that close encounters are much more numerous than previously assumed in initially smooth, spherically symmetric clusters. These encounters can also affect just forming exoplanetary systems and I will present simulation results of the effect of flybys on a common type of exoplanetary system: close-in Super-Earths often with a distant Giant. Even a single encounter can significantly modify the architecture of exoplanetary systems over their long lifetimes. These flybys can perturb the inner planets, inducing collisions and mutual inclination excitation, as well as placing the outer Giant on eccentric and inclined orbits. They typically induce ~2 collisions per system, reducing an initially 4-planet system to a mutually inclined 2-planet inner system. Previous research has shown that perturbed outer Giants can excite the inner planet system. However, my findings indicate that the presence of the Giant Planet does not change the outcome of collisions or excited mutual inclinations. I will demonstrate how we can use flybys from star cluster formation simulations coupled with planetary N-body simulations to disentangle the impact on the excitation of close-in planetary systems by giant planets and stellar flybys.