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.

Momentum Transfer from the DART Mission Kinetic Impact on Asteroid Dimorphos

“…Ejecta from the DART impact were observed in situ by the Light Italian Cubesat for Imaging of Asteroids (LICIACube) spacecraft, which performed a flyby of Dimorphos with closest approach about 168 s after the DART impact 3 . The impact ejecta were further observed by Earth-and space-based telescopes, revealing ejecta streams and dust tails similar to those seen in active asteroids thought to be triggered by natural impacts 4 . Ground-based telescopes and radar determined that the DART impact reduced the binary orbit period by 33.0 ± 1.0 (3𝜎) minutes 2 .…”

“…We use observations of the ejecta plume to determine the ejecta momentum direction 𝐸 ̂. The conical ejecta plume was imaged by the LICIACube LUKE camera 3 and the Hubble Space Telescope (HST) 4 . We apply a technique used to derive cometary spin poles 43 to estimate the orientation of the ejecta cone axis.…”

“…However, non-unique combinations of asteroid mechanical properties (e.g., cohesive 5 strength, porosity, and friction angle) can produce similar values of 𝛽 in impact simulations 18 . Future studies that combine estimates of 𝛽 with additional constraints from the DART impact site geology 1 and ejecta observations 3,4 will provide greater insight into Dimorphos's material properties. In addition, ESA's Hera mission 29 is planned to arrive at the Didymos system in late 2026.…”