OBLIQUE IMPACT AND PEAK RING OFFSET: VENUSIAN CRATERS COMPARED TO CHICXULUB

By studying the peak ring offset of Venusian craters from the Magellan data set we seek to determine whether there are systematic variations in the peak ring offset in oblique impacts. We limit our sampling to pristine peak ring craters formed from oblique impacts imaged on the Magellan compressed-once mosaiacked image data record (C-1 MIDR). These peak-ring craters are structurally similar to Chicxulub and the trends in symmetry may help constrain the trajectory path of the bollide that struck Earth 65 ma.

The sampled Venusian craters were chosen for their well-defined uprange forbidden zone or gap in the ejecta blanket, a feature which is characteristic of an oblique impact. The impact direction was manually selected as the azimuthal center of the forbidden zone. All spatial measurements were done using ArcGIS software based on manual picks of the crater structure from the C-1 MIDR radar images. Radar images have inherent complications that inhibit accurate interpretation of topographic features. To avoid these complications we assume that the outer edge of the crater floor mimics the shape of the crater cavity. Under this assumption the offset of the peak ring is proportional to the distance from the outer edge of the crater floor to the outer edge of the peak ring. Assuming a flat crater floor eliminates the need to correct for radar distortions.

The Magellan data set helps our understanding of how surface asymmetries in the peak ring position are affected by oblique impact. This analysis of pristine Venusian craters can be applied to the Chicxulub structure to constrain incident angle and direction. 2005 seismic reflection profiles across Chicxulub show strong subsurface asymmetries suggesting an oblique impact. Comparing Venusian craters with known impact directions to Chicxulub may aid our interpretation of these subsurface asymmetries with potential implications for extinction mechanisms and large impact processes.