Characterization of the DART Ejecta Using Computer Modeling of the Ground-based and HST Photopolarimetric Data

Among the published observations of the DART ejecta, we have identified a set of quasi-simultaneous data acquired on 2022 October 4–5, using different but complementary techniques: polarimetry (FORS2 at the Very Large Telescope (VLT)), spectroscopy (MUSE at the VLT), and imaging (WFC3 at the Hubble Space Telescope (HST)). These data offer a unique opportunity to carry out a novel, detailed analysis of the ejecta particles. At that time, the ejecta exhibited a well-developed tail with the g − r color and B and R polarization remaining unchanged along its length. The observed color and polarization of the ejecta are best explained by a model consisting of agglomerated particles formed from 10 to 20 μm monomers. The model was refined using dynamic modeling, which simulates the motion of ejecta particles from Dimorphos through the observed tail. The best-fit model corresponds to an ensemble of agglomerates with sizes ranging from 10 to 200–5000 μm (depending on the distance from the asteroid), following a power-law size distribution with an index of −3.2. Using the derived particle properties and HST imaging of the tail, we reconstruct the column density and mass distribution of the dust along the tail as well as the total mass of material within the tail as of 2022 October 5.