Martian Cratering, 4, Mariner 9 initial analysis of cratering chronology

Abstract

Mars contains a range of crater types similar to the types found on the earth and on the moon and in varying states of preservation. Positive evidence of erosive loss of kilometer scale craters comes from the deficiency of craters on Mars relative to Phobos and Deimos. Although one hemisphere is dominated by large ancient craters, estimated to date back 3–4 aeons, the hemisphere centered on the volcanic region of Tharsis has a much younger surface attributed to volcanic activity about 0.3 aeon ago. The morphology and size distribution of craters in the latter region give very strong evidence that erosion and deposition rates on Mars have been much less in the last 0.6 aeon than in previous time. The major shield volcanoes and the south polar zone (south of −81° latitude) have surface ages of about 0.1 aeon for kilometer scale structures. The relative sequence of events described is more certain than the absolute ages, and the method of estimating absolute ages is reviewed.