The Dynamical Evolution of Dimorphos’s Ejecta from the DART Impact Revealed by the Hubble Space Telescope

NASA’s Double Asteroid Redirection Test (DART) spacecraft successfully impacted the asteroid Dimorphos on September 26, 2022. The DART experiment provided a unique opportunity for understanding the ejecta evolution from asteroidal impacts, where for the first time clear information on several aspects of the system were known, allowing the dynamical evolution to be placed in a clearer context. This presentation will summarize the observations of the DART-driven ejecta with the Hubble Space Telescope from impact time T+15 min and provide a discussion on the dynamical evolution that was seen. The images revealed distinct features and complex patterns in the ejecta formed by the gravity of Didymos and solar radiation pressure (SRP). The particle size, ejection speed, and direction significantly influenced the evolution of the ejecta. Ejecta with speeds ≳2 m/s escaped the binary system directly, forming a cone-shaped morphology viewed from the side within T+8 hours. Slower ejecta with speeds a few times the escape speed were appreciably influenced by the gravity of Didymos, which slowly distorted the base of the ejecta cone to form curved and rotating features within a few days after the impact. About a week after the impact a transient double tail was also seen, possibly related to internal effects or the complex evolution of the tail. Our interpretation of these phenomenon indicate that some of them may be unique for ejecta in a binary system. In the meantime, SRP pushed the ejecta toward the antisolar direction, continuously modifying the cone morphology and leading to a pattern with overlapping streaks. The slowest dust formed a long, narrow tail starting from ~T+3 hours and lasting for months after the impact. Modeling suggested μm- to cm-sized particles in the tail with broken power law slopes of -2.6 and -3.7 for dust ≲3 mm and larger, respectively. The similar morphology of Dimorphos’s tail to those of some active asteroids thought to be due to impulsive dust emission caused by impact or rotational instability unambiguously demonstrates that impact is one key driver to generating active asteroids.