Atmospheric effects on ejecta emplacement

The effects of impactor, target, and atmospheric environment on ejecta facies morphology in laboratory conditions are reviewed. The effect of these variables on ejecta curtain evolution allows correlation with the dynamics of ejecta-atmosphere interactions. Ejecta dynamics and ejecta morphology are considered in terms of processes of ejecta emplacement, thereby forming a basis for physical models. It is concluded that ejecta flows around Martian craters may reflect entrainment of ejecta in winds and turbulence generated in response to the outward moving ejecta curtain. Different emplacement styles may reflect the degree of ejecta entrainment in the dynamics of atmospheric response which in turn depends on crater and ejecta size. Onset diameter for nonballistic ejecta emplacement styles may indicate critical conditions required for drag deceleration and entrainment of ejecta rather than the presence of volatiles. Variations in atmospheric pressure exceeding a factor of 5 could change the style of emplacement from rampart to runout flow for a given lithology at a given crater diameter over the last 3 billion yr.