Ejecta Formation, Early Collisional Processes, and Dynamical Evolution after the DART Impact on Dimorphos

NASA’s DART spacecraft is planned to reach and impact asteroid Dimorphos, the small moon of binary asteroid (65803) Didymos, at a velocity of 6 km s−1 in late 2022 September. DART will be the first mission to test the “kinetic impactor” technique, aimed at deflecting the orbital path of a potentially hazardous asteroid. The success and effectiveness of this technique resides in the efficiency of momentum exchange between the spacecraft and the impacted target. This depends on many factors, including the cratering process, the formation of ejecta, and their fate, as they remain in the system or escape from it, carrying momentum away. Here we provide an overview of the cratering process, including ejecta formation and their subsequent dynamical evolution. We use different methodologies to model the physics of the problem, including smoothed particle hydrodynamics to model the cratering and ejecta formation process after the hypervelocity impact, N-body granular simulations to model early collisional processes between ejecta fragments right after cratering, and high-fidelity planetary propagation to model the dynamical evolution of ejecta during their purely ballistic phase. We highlight the key features of each phase and their role in defining the dynamical fate of ejecta. We investigate the effect of surface cohesion in the impacted target and identify the qualitative behavior of ejecta particles as a function of the key parameters of the problem. We provide quantitative estimates for the specific case study related to the DART–Dimorphos scenario and a selected range of target properties.