Microimpact phenomena on Australasian microtektites: Implications for ejecta plume characteristics and lunar surface processes

Detailed investigations of the microimpact phenomena on Australasian microt ektites from four samples from the Central Indian Basin reveal an array of features, such as very low-velocity captured droplets, welded projectiles, angular fragments and dust, craters generated by projectiles defining an ob lique trajectory, high-velocity "pitless" craters, and the conventional hyp ervelocity craters with well-defined central pits and radial and concentric cracks-found commonly on lunar surface materials. The microimpacts are a c onsequence of interparticle collisions within the ejecta plume (as suggeste d by their chemistry) subsequent to a major impact and, therefore, reveal p rocesses inherent in an impact-generated plume. All the impact phenomena ob served here have taken place while the targets and projectiles were in flig ht and are therefore secondary impacts in lunar terms. However, some of the resultant features are analogous to lunar microcraters attributed to prima ry impacts by cosmic dust. Therefore, ballistic sedimentation on the Moon i s likely to contain plume collisional debris as well.