The architectures of planetary systems discovered by Kepler are poorly understood. There

are far more single-transiting planets than expected from the analysis of the number of

multi-transiting systems, assuming that all planetary systems are co-planar. However, stars

are not born in isolation, and interactions between stars can perturb their planetary


This project uses N-body simulations to investigate the dynamical evolution of

different young planetary systems containing close-in Super-Earths that are subjected to

stellar fly-bys at different distances. The fly-bys are set up to mirror those occurring in young

star-forming regions. We have run a large set of long-term planetary integrations to show

that planetary architectures can be significantly modified after only a single fly-by

event. The example in the plot shows the evolution of the mutual inclination between two

Super-Earths in two different simulations, each covering a period of 100 Myr. These

simulations differ in the initial separation between the planets. The same close fly-by

(occurring at 10 kyr) can either result in a considerable difference in the mutual inclination

of up to ~6 degrees (for an initial separation of 10 mutual Hill radii) or when initially placed

further apart (14 mutual Hill radii) of less than 0.1 degrees.

Categories: 2022 Highlights