The effect of planetary flybys on singly synchronous binary asteroids

Abstract

The evolution of binary asteroid dynamics are not fully understood. The method of formation is widely accepted as spin-up and fission due to the YORP effect, but it is unclear why systems exist at a variety of energy levels. Binary asteroids are observed in states ranging from relaxed, synchronous equilibriums to chaotic dynamics. Previous planetary encounters may have an effect on the dynamic configuration of binary asteroids. We develop a model for the spherical restricted full three-body problem to simulate a binary asteroid perturbed by a planetary flyby, as well as a method of obtaining initial conditions for a relaxed, singly synchronous binary asteroid system. These are used in a numeric analysis employing a modified version of the General Use Binary Asteroid Simulator, where Monte Carlo simulations are leveraged to investigate how a range of Earth encounters affect the dynamic evolution of a generic binary asteroid system in a singly synchronous equilibrium. The results show that planetary flybys can disrupt the synchronous equilibrium, with the effects dropping off at far encounter distances and fast flyby speeds. After the impulsive perturbation of a planetary flyby, the binary asteroid spin-orbit coupling can prevent the system from settling into a new equilibrium, forcing the system to go through the energy dissipation process to re-equilibrate. It is therefore possible that planetary encounters may have a part in creating chaotic binary asteroid systems from previously relaxed equilibrated systems.