Jetting in oblique, asymmetric impacts

Experiments were conducted to determine the composition of jets emitted in asymmetric oblique impacts, The jets were sampled indirectly using witness plates, which were quantitatively analyzed by SEM, The results indicate that decreasing the thickness of the inclined target plate increases the relative abundance of projectile in the jet. Increasing the impact angle has the same effect. No systematic dependence of jet composition on impact velocity was observed, Thin plate theory, variations of which have been applied to several problems in planetary geophysics, gives the jet composition as a function of plate thickness and impact angle, This theory gives compositional dependencies on plate thickness and impact angle that are opposite to the experimentally observed trends and predicts compositional abundances that differ in magnitude from experimental values by over 40 wt% in all cases. A critical review of the theory, which is extended to explicitly include shock entropy production, and a comparison of the theory with hydrocode simulations, reveals several assumptions that are not valid in the present application. The revised thermodynamic model predicts peak jet temperatures that are significantly lower than calculated using earlier models. If the experimentally observed compositional trends apply to the collisions of meteoroids with planets, then the relative abundance of meteoroid in the jet will be greater in oblique impacts than in normal-incidence ones. (C) 1998 Academic Press