Scaling of hypervelocity impact craters in ice with impact angle

Abstract

Hypervelocity oblique impacts using spherical 1 mm diameter aluminum projectiles at velocities of (5.2 ± 0.2) km s-1 were incident at angles ranging from normal (0° to the vertical) to grazing incidence (80°) onto thick polycrystalline H2O ice targets at 253 K. Data were obtained to distinguish changes in crater size and shape. The resultant craters had a deep central pit surrounded by a shallower terrace. Results on crater size showed that volume and crater depth had varying levels of dependence on obliquity for the full angular range, and terrace depth had a dependence only at angles > 45°. Length and width measurements held a strong dependence on obliquity only at angles > 50° from the normal. These results for ice show that it is hard to determine angle of impact from crater morphology. Although crater depth and volume do change with angle, it would be hard to separate this effect from the influence of an impact of a projectile of different speed, density, etc., which might also affect crater depth or crater depth/diameter ratios. Only at extreme angles > 70° do real differences in shape emerge for ice.