Influences of atmospheric variations on Mars's record of small craters

Planetary atmospheres influence cratering rates at small diameters (∼2-250 m) by filtering impactor populations via ablation, aerobraking and breakup of entering objects. The atmosphere of Mars undergoes rapid and drastic obliquity-driven variations in density, corresponding to pressure variations between zero and several tens of millibars. Here a simulation is used to assess the fate of a large population of impactors interacting with the present and predicted past and future martian atmospheres. We find that even Mars's present atmosphere significantly reduces crater production rates at small diameters (<30 m) and past denser atmospheres would have affected cratering even more strongly, and to considerably larger diameters. These effects are increased if the inner Solar System's small impactor population contains significant numbers of icy, cometary bodies. Evidence of recent atmospheric density variations may be detectable in the martian small cratering record with future planned imaging capabilities. Because of martian atmospheric effects and variations, surface ages derived from counts of craters of less than about 250 m on Mars may be underestimated.