A quantitative model for comet nucleus topography

Topography of the surface of a comet nucleus is likely rough at all scales smaller than the mean effective radius. We present a flexible and easily scalable model for quantitative calculations simulating the effects of comet nucleus topography on gas release and dust mantle evolution. The topographic features we describe must be large enough (typically> 10 m) so that they will not erode in one orbit of the nucleus around the Sun. The maximum effective size of a hill is about 1/√2 times the effective radius of the nucleus. If it is larger, then an ellipsoidal shape of the nucleus is more appropriate. The procedure described here also permits for inhomogeneous composition of the topographic features, leading to locally different rates of gas production (e.g., jet-like features and filaments) or different thicknesses of the dust mantle. It also can give rise to different temperature patches, locally varying albedos and emissivities, and may explain the formation of permanent dust mantles.