LONG TERM EVOLUTION OF THE DART IMPACT EJECTA IN VIEW OF THE HERA MISSION.

The European Space Agency spacecraft Hera is the European contribution to the Asteroid Impact Deflection Assessment (AIDA) international cooperation. Hera is scheduled to launch in October 2024 and to rendezvous with the binary asteroid system Didymos-Dimorphos in 2026. Hera will perform close-up measurements of the effects of the NASA/APL DART probe impact, also releasing two dedicated cubestas. As observed by the Italian Space Agency LICIACube and from space and ground telescopes, the impact generated a massive ejecta cone of particles, with observed sizes ranging from microns to meters. Most of the small particles left the binary system due both to the large ejection velocities and to the push exerted by the solar radiation pressure. Nonetheless, there is the possibility that part of the huge ejecta population, especially in low velocity tail, remains trapped within the binary system due to a number of dynamical interactions [6] (e.g., note that post-impact Hubble Space Telescope images revealed the presence of many m-sized boulders within the system). These trapped particles, if present in the system at the time of Hera arrival, could represent a hazard to the probes, especially if they are below the sensitivity thresholds of the probes instruments. Therefore it is important to understand if and where these particles might be found.