DART Determination of Momentum Transfer from Kinetic Impact: Ejecta Plume observations and Modeling

Abstract:

The Double Asteroid Redirection Test (DART) mission will impact Dimorphos, the secondary member of the [65803] Didymos binary asteroid in September – October, 2022 in order to perform the first test of asteroid deflection by kinetic impact, that is, modification of the orbit of the moon through momentum transfer. The DART kinetic impact on the 160-m secondary will be the first hypervelocity impact experiment on an asteroid at a realistic scale relevant to planetary defense. Determination of the momentum transfer to the target body from the kinetic impact is a primary planetary defense objective, using ground-based telescopic observations of the orbital period change of Didymos and imaging of the DART impact ejecta plume by the LICIACube cubesat, along with modeling and simulation of the DART impact. LICIACube, contributed by the Italian Space Agency, will perform a flyby of Didymos a few minutes after the DART impact, to resolve the ejecta plume spatial structure and to study the temporal evolution. LICIACube ejecta plume images will help determine the vector momentum transfer from the DART impact, by determining or constraining the direction and the magnitude of the momentum carried by ejecta. A model is developed for the impact ejecta plume optical depth, using a point source scaling model of the DART impact. The model shows how the plume images enable characterization of the ejecta mass versus velocity distribution, because the ejecta plume structure, as it evolves over time, is determined by the amount of ejecta that has reached a given altitude at a given time. The evolution of the plume optical depth profiles determined from LICIACube images can distinguish between strength-controlled and gravity-controlled impacts, by distinguishing the respective mass versus velocity distributions. LICIACube plume images discriminate the differences in plume structure and evolution that result from different target physical properties, mainly strength and porosity, thereby allowing inference of these properties to improve the determination of momentum transfer.