A model of the macro-features of the surface layer of a cometary nucleus

The macro-features of the surface layer of a 'fresh' cometary nucleus are m odelled by assuming that the dust and the snow particles of which it consis ts both have a mass distribution index of 1.65, and that the dust/gas mass ratio is 0.45. Conclusions are drawn as to how this model helps us to under stand the cometary sublimation process and the cometary surface layer. The latter most probably consists of weak, low-density, friable, slightly dusty snow. Its ability effectively to support even the small weight of, say, th e Rosetta landing probe is in considerable doubt.