Ejecta Evolution Following a Planned Impact into an Asteroid: the First Five Weeks

The impact of the Double Asteroid Redirection Test spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos's orbit substantially, largely from the ejection of material. We present results from 12 Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of similar to 1.4 mag, we find consistent dimming rates of 0.11-0.12 mag day-1 in the first week, and 0.08-0.09 mag day-1 over the entire study period. The system returned to its pre-impact brightness 24.3-25.3 days after impact though the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, though movement of the primary ejecta through the aperture likely played a role.