Surface slope evolution as a function of Dimorphos’s dynamical evolution. (a) Top-down view of the “Didymos-Squannit” system. From this view, the spin and mutual orbit poles are pointing out of the page. (b) Side view. (c) Surface slopes for a Squannit-shaped Dimorphos with a bulk density of ρ_S = 2.2 g cm⁻³ in an idealized, relaxed dynamical state. The black facet corresponds to the sub-Didymos point (at zero libration amplitude) with a longitude and latitude of ϕ ≈ λ ≈ 0°. The white facet has a longitude and latitude of (ϕ, λ)≈(0° ,45° ) and corresponds to the time-series plots in part (e). (d) Spin and orbital evolution for the Squannit-shaped Dimorphos when β = 3 (e = 0.023). The Euler angles are the 1-2-3 Euler angle set (roll-pitch-yaw) expressed in the rotating orbital frame, while the body spin rates are in the secondary’s body-fixed frame. (e) Slope and surface accelerations on the white facet from part (c). The vertical accelerations point along the facet’s surface normal and are generally dominated by self-gravity. The horizontal accelerations are expressed as magnitudes and point parallel to the surface. Initially, the Euler acceleration is relatively small and the tides are the dominant time-varying acceleration. After about 5 days, Dimorphos enters NPA rotation, and the Euler accelerations become comparable to both the tidal and centrifugal accelerations. We refer the reader to Appendix B for an identical plot showing the full 365 d simulation.