Orbit-Attitude Coupled Tidal-BYORP Evolution of Didymos After DART

One of the most influential phenomena on the long-term evolution of binary asteroid systems is the binary Yarkovsky–O’Keefe–Radzievskii–Paddack (BYORP) effect. This effect occurs when solar radiation pressure (SRP) acts on the smaller, secondary body of a binary asteroid system when in synchronous rotation. Due to asymmetry of the secondary’s shape, the net SRP force imparted on the body is not constant over one orbit period, leading to secular changes in the binary orbit on timescales of tens to hundreds of thousands of years. Depending on the exact conditions of the system, the BYORP effect can lead to expansion or contraction of the mutual orbit. When paired with tidal effects, which work to expand orbits for binary NEAs, this drives the overall lifecycle and possible end states of rubble pile asteroids.

In this work, we numerically simulate the evolution of the Didymos binary system. While prior studies (Quillen et al., 2022; Ćuk et al., 2021) have simulated non-planar evolution of binary systems for short timescales, this work produces high-fidelity simulations of long-term tidal-BYORP evolution. Non-planar librations about the secondary’s synchronous state are included in the coupled orbital dynamics and secondary attitude propagation, allowing non-planar mutual orbit evolution to be possible. We generate BYORP coefficients based on the shape of the secondary and use them to simulate the effect of SRP on the system as a function of orbit/attitude state. The classical tidal model from Murray and Dermott (1999) is employed, in which the tidal torque on the system is driven by the tidal dissipation function, Q, and Love number, k₂. We simulate a BYORP-tide equilibrium, which is believed to have been the state of the Didymos system prior to DART impact, to constrain estimates on tidal parameters for Dimorphos. Various other attitude cases are also investigated to evaluate the stability of the Didymos system post-impact, including conditions for barrel instability of Dimorphos.

Lastly, we look at BYORP coefficient sets corresponding to different post-DART Dimorphos shape models, including various crater morphologies and widescale reshaping of the body (such as sub-catastrophic collapse along its principal axes).