Regolith evolution in the laboratory: Scaling dissimilar comminution experiments

Abstract— Repeated impacts into fragmental targets simulating unconsolidated debris on planetary surfaces have provided empirical insight into the evolution of planetary regoliths. Quantitative understanding and interpretation of these results, however, are often made difficult by the complex, multivariate nature of the impact process, even under controlled laboratory conditions. The techniques of dimensional analysis have been employed to quantify and examine the relationships between the more important variables in the evolution of these experimental regoliths. Application of this method to the results of ten experimental series shows that the quantity of comminuted target mass is directly proportional to (a) the number of impacts sustained by the target, (b) the diameter of the projectile, (c) the mean size of the crystals composing the target rock, (d) the mean grain-size of the evolving “regolith,” (e) the total target mass, (f) the impactor density, and (g) the ratio of the impact velocity to the velocity of sound in the target rock. The comminuted mass is inversely proportional to the density of the target rock and the sorting of the “regolith.” Similar results hold for the creation of new surfaces by fracturing, except that the initial surface area possessed by the target takes the place of the total target mass. In addition, the ease with which new surfaces are created is independent of the mean crystal-size. Although it appears that the ratio between impactor and target densities is an important parameter in both cases, more experiments will be necessary to establish the quantitative contribution of that parameter, as well as those of the total target mass and the effective strengths of the individual minerals composing the target rock.