Crater evolutionary tracks

Abstract

A description of crater morphology based on rim height/depth ( h/ d) and depth/diameter ( d/ D) ratios provides a quantitative method for assessing the relative importance of competing crater modification processes. Different classes of processes produce distinctive evolutionary tracks on an h/ d vs d/ D diagram. We have calculated such tracks for three general classes of crater modification: those processes which add material to the crater, those which redistribute material within the crater vicinity, and those which remove material from the crater vicinity. New morphometric data, from Earth-based radar scans and Mariner 9 images of Mars and Apollo metric photography of the Moon, are presented for Martian and lunar craters. We have compared h/ d and d/ D ratios for craters on the Earth, Moon, and Mars with theoretical evolutionary tracks for the general classes of crater modification. Lunar and terrestrial craters occupy similar regions of the h/ d vs d/ D diagram, whereas Martian craters lie distinctly apart. This implies that Martian craters fall on a different evolutionary track from terrestrial or lunar craters. The evolution of the lunar and terrestrial craters can be modeled by a combination of filling and slumping processes. Martian crater evolution, however, cannot be understood on the basis of these two classes of crater modification alone. Instead, a process such as eolian erosion, which removes material from the crater rims, must have been the principal form of modification, and evolutionary tracks based on such a model coupled with weak eolian deposition within the crater can indeed fit the Martian h/ d vs d/ D data.