Observation of Vertically Ejected Plumes Generated by the Impact of Hollow Projectiles at Various Velocities

Recently, impact experiments in space have been conducted in planetary exploration using hollow or internally structured projectiles. In laboratory experiments using hollow projectiles to investigate the differences in crater and ejecta from the case of solid projectiles, a plume perpendicular to the target surface has been observed, which has not been seen in conventional cratering experiments using solid projectiles. In this study, we conducted crater-formation experiments using hollow resin projectiles to understand the mechanism through which vertical plumes form in the case of hollow projectiles. We examined the generation of a vertical plume as a function of the impact velocity, v (imp). We found that (i) no vertical plume occurs at v (imp) < 200 m s(-1), (ii) the cases with or without a vertical plume are mixed at 200 < v (imp) < 350 m s(-1), (iii) no vertical plume occurs at 350 < v (imp) < 800 m s(-1), and (iv) a vertical plume occurs at 2 < v (imp) < 3 km s(-1). We qualitatively discussed the generation mechanism of the vertical plume using the results of recovered projectiles. Depending on v (imp), an empty hole in which there is no projectile materials can be opened along the central axis, resulting in the generation of a vertical plume.