Influence of Planetary Flyby Events on Binary Asteroid’s Impact Risk

Abstract Binary asteroids (BAs) may collide, stay in orbit, or dissociate after a close planetary flyby. The outcome is uncertain due to uncertainties in both the BA’s heliocentric orbit and mutual orbit. In the case of dissociation, the two asteroids enter distinct heliocentric orbits. For a slow flyby with a well-determined preflyby heliocentric orbit, the separation between the two asteroids’ new heliocentric orbits is found to be comparable to or exceed the uncertainty of the original heliocentric orbit. Consequently, postflyby impact risk assessment based on the original heliocentric orbit is invalid. Furthermore, during a slow flyby, the two asteroids’ shapes and rotations, when coupled with the Earth’s strong external torque at the perigee, are found to be able to influence the flyby outcome. A critical flyby distance, which varies with the BA’s orbit size, is introduced. BAs entering within this critical flyby distance have a high probability to dissociate, necessitating the determination of new heliocentric orbits for the components. For currently known near-Earth BAs, we compute this critical flyby distance and the probability for them to enter within this distance using the well-established line of variation method. Ours analysis indicates that all these BAs are currently moving on safe orbits that do not cross the critical flyby distance in the next 100 yr.