Hypervelocity Impact in NASA’s DART mission

Planetary defense test mission by NASA have used the philosophy of Kinetic impactor in its DART (Double Asteroid Redirection Test) mission. The primary concept in these hypervelocity impact events lies in impacting an asteroid (target) with a spacecraft (projectile) such that ejecta produced from it results in mass loss (ejecta particles exceeds the escape velocity). The change in mass of the target is anticipated to change the orbital motion of the asteroid. This hypothesis was successfully tested by NASA on Sept 26, 2022 as the DART spacecraft (579 kg impacting at 6.14 km/s) impacted the moonlet Dimorphos in the binary asteroid system of Didymos. Large amount of ejecta was produced leading to significant changes in the binary orbital period (33.0 +/-1 (3σ) minutes measured via ground based telescope and radars). The entire event of impact was recorded by DART’s DRACO (Didymos Reconnaissance and Asteroid Camera for OpNav) camera as well as LICIACube’s color LUKE imager prior to and after the event respectively. The amount and morphology of the ejecta is typically dependent upon the target site of the impact. DRACO images show significant distribution of large boulders on the surface of Dimorphos. For this study the entire surface of the Dimorphos has been modelled and kinetic impact study has been carried out to probe the crater and ejecta morphology.
The model of the asteroid consisting of 50% boulder and the rest as rubble-pile (granular material) is developed and subjected to a hypervelcoity impact (simulating the DART impact). The ejecta cloud formed in addition to that of crater morphology is determined. The role played by gravity in these ejecta and crater morphology is also determined. The models used for this study is based upon previously developed models for brittle ceramic materials by Ramesh and group.