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Cometary surfaces can change significantly and rapidly due to the sublimationof their volatile material. Many authors have investigated this evolution;Vincent et al. (2017) have used topographic data from all comets visited byspacecrafts to derive a quantitative model which relates large scale roughness(i.e. topography) with the evolution state of the nucleus for Jupiter FamilyComets (JFCs). Meanwhile, ground based observers have published measurements ofthe phase functions of many JFCs and reported a trend in the phase darkening,with primitive objects showing a stronger darkening than evolved ones).  In this paper, we use a numerical implementation of the topographicdescription by Vincent et al. (2017) to build virtual comets and measure thephase darkening induced by the different levels of macro-roughness. We thencompare our model with the values published by Kokotanekova et al. (2018)  We find that pure geometric effects like self-shadowing can represent up to22% of the darkening observed for more primitive objects, and 15% for evolvedsurfaces. This shows that although physical and chemical properties remain themajor contributor to the phase darkening, the additional effect of thetopography cannot be neglected.

Cometary topography and phase darkening