Grain size evolution and fractionation trends in an experimental regolith

The communication of blocky planetary surfaces into fine-grained regoliths was simulated by impacting a fragmental gabbro target 200 times with stainless steel projectiles. It is found that the comminution efficiency of the surfaces changes with time, being highest in the early stages of regolith formation and decreasing gradually. The relationship between mean grain size and cumulative energy is not linear. Individual, fine-grained regolith components can be generated very early from relatively large progenitor fragments without going through intermediate-size fractions. Impact comminution is capable of producing fractionated fines as postulated by Papike et al. (1982). The role of grain-size selective, lateral transport to explain the fractionated nature of lunar regolith fines may have been overestimated in the past.