Modeling the Chaotic Dynamics of Binary Asteroid 1991 VH

Binary asteroid 1991 VH is a target of the upcoming Janus mission, launching later this year. This system is unique in that it exists in a chaotic state and not in a synchronous spin-orbit resonance, unlike most similar near-Earth binary asteroids. Unfortunately, the shape of the secondary in this system is unconstrained. We simulate the dynamics of 1991 VH using the General Use Binary Asteroid Simulator (GUBAS) testing a variety of secondary shapes and spin states. GUBAS allows for the use of a polyhedron shape model for the primary, calculating the fourth degree and order gravity field. Given the uncertainty on the secondary’s shape, we approximate it as an ellipsoid. We find that the system dynamics are strongly dependent on the shape, spin, and orientation of the secondary.

Beyond the secondary geometry and spin, we also find that out-of-plane excitation can have a significant impact on the system’s dynamics. Systems that are stable in planar orbits can become chaotic when inclination or out-of-plane rotation is added to the system. This is important to consider, as chaotic systems may be less efficient at dissipating energy through tidal forces.

In preparation of the Janus flyby of 1991 VH in 2026, we simulate a variety of different systems fitting within the current system uncertainty. These simulations demonstrate the wide variety of dynamics possible in this system and shed light on the cause of its chaotic state. By comparing our results to observations of the system’s mutual orbit period, we attempt to constrain the possible combinations of system geometry and dynamics and build expectations to be tested by the flyby data.