Comparison of H2O and CO2 ices under hypervelocity impact

We have studied hypervelocity impacts at 5 km s(-1) of 1 mm diameter projectiles on two types of ice: H2O and CO2. We compare crater morphology for the resulting impact craters and find that the craters are smaller in the CO2 ice than in H2O ice. However the crater shape, as expressed by the ratio depth/diameter, is indistinguishable between the two types of ice. Further, we have investigated the dependence of crater size and shape on projectile density. We find that for densities of 2750 to 7850 kg m(-3), the ratio depth/diameter does not have the strong dependence on density suggested elsewhere in the literature. This is true for both types of ice. We thus suggest that whilst the crater size may depend strongly on ice type, the shape does not and is also almost independent of projectile density.