Martian Cratering III: Theory of Crater Obliteration

This paper discusses a theoretical basis for interpretation of Martian crater obliteration. Strong evidence is found that Martian craters are being degraded and obliterated at a rate much faster than on the Moon, but much slower than on Earth. Evidence includes (1) morphology of craters (shallow flat floors, flat rims, lack of "Copernican" ray craters), (2) obliteration theory, which successfully predicts the form of the Martian crater curve and the lifetimes of terrestrial craters against obliteration, and (3) laboratory experiments. The theory obviates the need to interpret the diameter distribution in terms of two classes of impacting bodies, as has been done elsewhere. It is suggested that obliteration is caused by filling of the craters, probably by deposition of dust. Evidence is found in (1) theoretically-demonstrated mobility of Martian dust, (2) shallow depths of craters, (3) observed aerial transport of dust on Mars by dust storms, (4) measurements indicating suspension of micron-sized dust particles in the normal Martian atmosphere, (5) depletion of small craters as predicted by theory, (6) patchy light markings preferentially on the northern half of crater floors in and near Meridiani Sinus, suggesting dust deposits, (7) "resurgence" of dark surfaces suggesting periodic covering and uncovering by aeolian dust, and (8) obliteration of features in the basin Hellas.