Are HCN polymers responsible for the CN extended source in comets? Results from experimentation and modeling.

Some molecules or radicals observed in cometary atmospheres present so-called "extended sources". It means that their distribution in comae cannot be explained by a direct sublimation from the nucleus or by the photolysis of gaseous parent molecules. The origin of those extended sources is still an unsolved question. In order to explain the distribution of CN radical in comets, a new process in addition of HCN photolysis might be required. This second process of CN production could be the degradation of solid HCN polymers present on cometary grains. Indeed solid polymers on grains could release gaseous products when heated and/or UV irradiated. Therefore we have experimentally studied the degradation of HCN polymers. The resulting gaseous products have been identified; the production kinetics by heating and the quantum yields by irradiation of each product have been measured. Those new quantitative data allow us to fit the CN column density observed in comets and then determine whether or not a fraction of CN is produced by the degradation of solid polymers. We will present the results of this new model.