A schematic model of crater modification by gravity

Abstract

Models are proposed to account for the formation of slump terraces, central peaks, peak rings, and concentric rings in large impact structures. Crater slumping and central peak formation is attributed to the process of acoustic fluidization, which endows a volume of the target surrounding the crater with a Bingham plastic rheology for a short time after the impact. The parameters of this Bingham plastic model are remarkably constant throughout the solar system the Bingham yield stress ranges from a maximum of 80 bars on Mercury to a minimum of 7 bars on Callisto. The Bingham viscosity is between 109 and 1010 P at the onset of central peak formation for all bodies studied, although it appears to rise to 1011 P as crater diameter grows to a few hundred kilometers. Asymmetric (or scarp‐bounded) concentric rings are due to a fundamentally different process. They form when the target planet's lithosphere fractures under stresses imposed by the flow of the asthenosphere toward the transient crater cavity. Lithosphere yield strengths of less than a few hundred bars are implied by observed ring development on the moon and Callisto.