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R. Schulz (ESA/SSD)
Many comets are known to exhibit distinct features (jets, spikes, arcs, shells, etc.) in their comae which are generally believed to result from the ejection of material from discrete active areas on the nucleus. Various conceptual models have been developed in recent years which can explain the formation of such features in principle. However, no unique solution was found so far, that could explain the coma morphology and evolution in gas and dust convincingly for all comets. To better understand the formation of such features and their relevance for the surface of a cometary nucleus, they need to be studied in a large number of comets. Here, the results of the morphological coma analysis of nine comets belonging to different dynamical classes are presented in a comparative overview. The results of the individual studies are put into context to search for communalities and differences and to find clues to possible classification criteria for comets. The comets were searched for distinct features in the gas and dust coma. The structural analysis led to the detection of various types of features in seven of the nine investigated comets. The recorded structures can be divided into stationary and time-variable features in the gas and/or dust coma. None of the investigated comets, for which a detailed coma analysis was feasible, exhibited coinciding gas and dust jets. Hence, gas jets with no observable counterparts in the dust appear to be a rather common phenomenon.