Atmospheric effects on cratering efficiency

The dramatic effects of an atmosphere on impact excavation of particulate targets are investigated, with emphasis on common trends and systematic differences for contrasting target types. The observed differences are reconciled through identification of additional atmospheric effects and consideration of scaling relations. When both static (ambient) and dynamic (drag) atmospheric pressure controls crater growth, the combined factors exhibit a functional dependence consistent with the coupling-parameter exponents suggested by Holsapple and Schmidt (1987). The disturbed air mass accompanying the projectile at laboratory scales is observed to further modify cratering efficiency. The effect of projectile-atmosphere interactions depends on the degree of coupling between the air disturbance and the impactor. At very high velocities (M greater than 10), the air disturbance changes the effective impactor dimension. If the dimensionless scaling parameters can be applied to broader planetary scales, these results have implications for interpreting the size of craters on surfaces with contrasting atmospheric envelopes.