Spectroscopic characterization of hypervelocity jetting: Comparison with astandard theory

Symmetric collision between two identical plates has yielded successful the oretical models for the jetting process. Consequently, assessment of impact jetting at planetary scales has been largely based on the theories develop ed for such specific types of collisions. Little experimental work has been done, however, to measure both temperature and target-to-projectile mass r atio of jetting created by spherical projectiles impacting planar targets, which typify planetary impacts. The goal of this study is to examine the va lidity of applying planar-impact theories to jetting due to impacts of sphe rical projectiles into planar targets, Using a newly developed spectroscopi c approach, we observe jetting created by copper spheres impacting planar d olomite targets at hypervelocities. In contrast with previous experiments u sing quartz projectiles, the observed mean temperatures of jets due to copp er projectiles does not correlate well with the vertical component of impac t velocity. Instead, the observed temperatures of jets show much better cor relation with impact velocity than the vertical component of impact velocit y and impact angle, The experiments also reveal that the target-to-projecti le mass ratio within a jet increases with impact angle (measured from the h orizontal). In order to understand the significance of these experimental r esults, they were then compared with a jetting model for asymmetric collisi ons based on standard theories. Such a comparison indicates qualitative con sistencies, such as complete vaporization of the carbonate target (as oppos ed to mere degassing of carbon dioxide due to incomplete vaporization of ca rbonate) and higher target-to-projectile mass ratio in a jet at higher impa ct angles. Quantitative comparison, however, also reveals significant incon sistencies between theory and experiments, such as an impact-angle effect o n jet temperature and a correlation in jet temperatures between projectile and target components. In order to resolve these inconsistencies, new facto rs such as viscous shear heating and the nonsteady state nature of the jett ing processes may need to be considered.