Spectroscopic characterization of hypervelocity jetting: Comparison with a standard theory

Symmetric collision between two identical plates has yielded successful theoretical models for the jetting process. Consequently, assessment of impact jetting at planetary scales has been largely based on the theories developed for such specific types of collisions. Little experimental work has been done, however, to measure both temperature and target-to-projectile mass ratio of jetting created by spherical projectiles impacting planar targets, which typify planetary impacts. The goal of this study is to examine the validity of applying planar-impact theories to jetting due to impacts of spherical projectiles into planar targets. Using a newly developed spectroscopic approach, we observe jetting created by Copper spheres impacting planar dolomite targets at hypervelocities. In contrast with previous experiments using quartz projectiles, the observed mean temperatures of jets due to copper projectiles does not correlate well with the vertical component of impact velocity. Instead, the observed temperatures of jets show much better correlation with impact velocity than the vertical component of impact velocity and impact angle. The experiments also reveal that the target-to-projectile mass ratio within a jet increases with impact angle (measured from the horizontal). In order to understand the significance of these experimental results, they were then compared with a jetting model for asymmetric collisions based on standard theories. Such a comparison indicates qualitative consistencies, uch as complete vaporization of the carbonate target (as opposed to mere degassing of carbon dioxide due to incomplete vaporization of carbonate) and higher target-to-projectile mass ratio in a jet at higher impact angles. Quantitative comparison, however, also reveals significant inconsistencies between theory and experiments, such as an impact-angle effect on jet temperature and a correlation in jet temperatures between projectile and target components. In order to resolve these inconsistencies, new factors such as viscous shear heating and the nonsteady state nature of the jetting processes may need to be considered.