Estimating crater size for hypervelocity impacts on small icy bodies (e.g. comet nucleus)

The morphology and size expected for impact craters on small icy bodies are presented. Such bodies are for example minor satellites of the outer planets (some of which are ice covered) or comet nuclei. The differences between the impact craters that result on such bodies, compared to those on more traditional ice targets (effectively large, well consolidated, semi-infinite ice surfaces) is discussed with particular reference to the impact on a comet nucleus expected in the Deep Impact space mission. Finally extrapolation of laboratory scale experiments is carried out to try and quantify crater size and shape for impacts on small, porous bodies. It is found that given our present knowledge, simple scaling with impact energy produces a result compatible to scaling via more sophisticated methods. The handling of the influence of the detailed composition of the ice target (porosity, volatile content, silicate content etc.) is less certain.