Too Close for Comfort

The long-term evolution of planetary systems are shaped in part by planet-planet interactions. Studying planetary systems in the context of their stellar environments improves our understanding of system stability. We explore stellar flyby scenarios that are too weak to immediately destabilize the solar system but are nevertheless strong enough to measurably perturb its secular dynamical state. We estimate the strength of such perturbations using a simple analytic model and confirm those estimates with direct n-body simulations. With thousands of long-term solar system integrations, we show that altering the semi-major axis of Neptune by as little as 0.1% can increase the likelihood of instability by ten times.