Finite element method approach for quantifying the conditions for shape deformation of the primary of binary asteroid Didymos after the DART impact

NASA's DART mission will send a spacecraft to impact the smaller component (the secondary) of binary asteroid Didymos. During this impact process, impact ejecta will be generated, and some may reach the larger component (the primary). Because of collisions of such impact ejecta, the primary will subsequently receive kinetic energy that may cause seismic shaking. As the primary is rotating at a spin period of 2.26 hr, for which the structure may be close to its critical condition (depending on its cohesive strength and bulk density), such seismic shaking may induce resurfacing processes and change the shape if the input energy is high enough. If this process happens, it will have an additional effect on the orbital perturbation of the Didymos system. Here, we introduce a dynamic Finite Element Method simulation package, aiming to quantify this resurfacing mechanism by using predicted physical and dynamical properties (the DART impact process and the ejecta dynamics). While some are high-speed ejecta, the majority may have low kinetic energy, implying that the majority of energy input may result from low-speed impacts. In this case, impact processes may mainly produce elastic waves, which consist of shear and compressive waves, rather than plastic waves. However, given a series of such wave generations, some regions of the surface may reach their structural limits, triggering resurfacing processes due to the current spin condition of the primary. If there is shape deformation of the Didymos primary due to the DART impact, Earth-based telescopic observations will detect and quantify a change in the spin period of the primary. Using this observed quantity, the developed FEM package may provide constraints on the shape deformation process, which may in turn help determine the momentum transfer coefficient for the DART impact (e.g., Hirabayashi et al., 2017, 2018).