ASYMMETRIC EJECTA IN OBLIQUE IMPACTS

Most impact craters on the Earth and other planets (even those resulting from oblique impacts) are near circular, however, the impact angle can strongly influence ejecta deposition (see e.g. Pierazzo and Melosh, 2000). This influence was first demonstrated in experiments by Gault and Wedekind (1978). Since their paper a shape of the ejecta deposits is considered as the most prominent indicator of oblique impacts.

However, simple estimates show that the asymmetry of ejecta blanket resulting from oblique type of impact could strongly depend on impact scale. Numerical simulations of oblique impacts produced by asteroids with the sizes from 100 m to 10 km were performed to study this influence. The results show that the asymmetry of ejecta deposits increases as the impact scale increases (at the same impact angle). In particular, this means, that the results of laboratory low scale experiments can not be used for any quantitative estimates of impact angles in real planetary impacts.

References:

Gault D. E. and Wedekind J. A. (1978) Experimental studies of oblique impact. Proc. Lunar Planet. Sci. Conf. 9th, 3843-3875.

Pierazzo E. and Melosh H. J. (2000) Understanding Oblique impacts from Experiments, Observations, and Modeling. Annu. Rev. Earth Plannet Sci. 28, 141-167.