Complex crater on Mars. Computer artwork showing a large complex impact crater (left) on the surface on Mars. The crater has a central peak, and concentric rings of hills (a multi-ring basin). Material thrown out from the crater during the impact, known as the ejecta blanket, can be seen as lobes spreading outside the crater. This morphology is thought to be caused by the impacting object melting subsurface ice, and forming muddy slurry that flows along the surface.