The role of impactor shape and obliquity on crater evolution in celestial impacts

The effect of impactor obliquity and shape on crater evolution for a typical celestial impact event is examined in this numerical study. An important overall finding is that for a given obliquity angle, crater volume is not independent of impactor shape. The most varied behavior occurs at large obliquity angles, where the crater crest becomes highly elliptical and the ejecta pattern exhibits characteristic butterfly wings. Impacts at large obliquity angles can also produce craters with roughly equivalent dimensions from a wide range of impactor shapes and volumes. Conventional energy scaling can be applied to these results at moderate obliquities if the energy based on the vertical component of the velocity is used. For example, for a given impactor shape the crater volume scales with this energy and the depth with the cube root of this energy. However, at large obliquities, these relationships are invalid. Applying these results to the meteor crater at Odessa [Littlefield DL, Bauman PT, Molineux A. Analysis of formation of the Odessa Crater. Int J Impact Eng, accepted for publication.], some interesting conjectures can be made. First, the small depth-to-diameter ratio of that particular crater suggests that the impact occurred at a large obliquity angle, with a trajectory extending from the southwest to the northeast. Second, the circular entrance hole and the absence of additional impact craters along this trajectory suggest that the meteor may have been either disk-like or highly elliptical in shape.