Ejecta from the DART-produced active asteroid Dimorphos

Abstract NASA’s Double Asteroid Redirection Test (DART) mission performed the first ever kinetic impact to deflect an asteroid1. The DART kinetic impact test artificially activated an asteroid with a hypervelocity impact, providing a unique opportunity for an extensive observing campaign to monitor the evolutionary process from the formation of the ejecta to its dispersion via a sustained tail. Here we report observations of the impact ejecta with the Hubble Space Telescope (HST) from impact time (T)+15 minutes to T+18.5 days at a resolution of 2.1 km per pixel. Our observations showed that the gravitational interaction between the binary system and dust under the influence of solar radiation pressure produced a complex morphology during the evolution of the ejecta. The dust ejected at speeds much higher than the escape speed of the binary system (0.25 m/s) is directly ejected out of the system. The dust moving at speeds just above the escape speed displayed signatures of gravitational interaction with the binary asteroid system, forming spirals and extended features. Slow ejecta is ultimately pushed in the antisolar direction (nearly opposite the impact direction) by solar radiation pressure to form a tail. These dynamical processes are highly dependent on particle size and ejection direction. The ejecta evolution following DART’s kinetic impact offers a framework for understanding the fundamental mechanisms acting on asteroids disrupted by natural impact2,3 for the first time.