Effects of surface topography on the crater formation process of rubble-pile asteroids

Abstract

High velocity impact experiments were conducted on a conical shaped sand target, simulating a large-scale cratering formed in gravity-dominated regime, which could be affected by a surface topography such as curvature of bodies. The target material consists of dry quartz sand, prepared in conical shape with its vertex angle 120° A spherical Al projectile with its diameter of 2 mm was impacted vertically on the top part of a cone at the velocity from 1 to 4 km/s. After the impact, a top part of the conical target was excavated to form a shallow bowl-shaped crater on the top. The target resembled a trapezoid when observed from the side. The crater rim radius was able to be scaled by a conventional π-scaling relationship although it's radius was about 10 % smaller than that of the crater formed on semi-infinite flat surface. This might be caused by the geometrical effect of the target. The ejecta opening angle was measured at the time of crater formation and it was about 130°, where this is larger than that of the ejecta curtain, <90°, formed over the target of semi-infinite flat surface. This wider ejecta opening angle on conical target was able to be well reproduced by utilizing the Maxwell Z-model to a conical target.