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Special type of impact crater

Within the HRSC image frame, mostly flat terrain dominates, with a few dark-layered mesas and an unusual-looking impact crater. The reddish-brown surface gradually darkens from south (left) to north (right), with several brighter patches scattered across the scene (see annotated image). Narrow, linear valleys also appear in places – they belong to a bigger geological structure known as Idaeus Fossae, a system of valleys just a few kilometers west of the image frame (see annotated image).

On the northern (right) side of the image, an elliptical impact crater draws attention, measuring roughly 20 kilometers from east to west and 15 kilometers from north to south (see annotated image). While most impact craters are relatively circular, the elliptical shape of this one suggests an oblique (low-angle) impact. Despite the non-circularity of the crater rim, the asymmetry shape of the ejecta blanket provides evidence of a shallow impact angle. It forms two prominent lobes of material extending north and south of the crater, but is notably absent to the east and west, where ejecta material would typically be expected (see annotated image). Due to their resemblance to the outspread wings of a butterfly, these craters are known as butterfly craters. The ejecta material also shows characteristics of fluidized material, which form when impact debris mixes with water or ice in the subsurface. Such ejecta often displays overlapping lobes and a distinct rounded boundary – a morphology also visible partly in the upper right of the image (see annotated image).