Atmospheric effects on Martian ejecta emplacement.

The paper presents analytical descriptions of crater growth and numerical calculations of aerodynamic drag to evaluate the possible effects of drag on impact crater ejecta emplacement on Mars. The critical particle size below which ejecta deposition is restricted in range increases with crater size; models of ejecta trajectories in the current Martian atmosphere under hydrostatic equilibrium reveal critical particle diameters ranging from 0.4 to 20 cm, noting that ejecta approaching the critical particle size may impact with crater radius of the excavation crater rim. Ejecta larger than the critical particle size are undecelerated and form secondary impact craters modified by the later arriving decelerated ejecta cloud; thus, ejecta emplacement will be multiphased, but the process depends on the ejecta size distribution.