P/Wirtanen thermal evolution: effects due to the presence of an organic component in the refractory material

In-situ experiments on cometary dust on board GIOTTO and VEGA missions demonstrated that in comet P/Halleyʹs refractory component it is possible to evidentiate a refractory organic phase, the so called CHON, and a Mg-rich silicate phase. The two phases were interspersed in the individual grains. Each of these phases has different average physical properties. Laboratory experiments demonstrated that the characteristics of a crust mainly composed of silicatic particles would be different from that of a crust composed by silicatic and organic particles: thermal conductivities, for example, differ by orders of magnitude. In this paper we want to show how the simulation, in our numerical model of cometary nucleus thermal evolution, of two different dust distributions with different and independent physical properties gives us a much better modeling of the complexity of real phenomena. We attributed to one of these distributions the characteristics, taken mainly from laboratory experiments, of silicatic/organic material, and to the other one the characteristics of purely silicatic material. We applied the model to improve our simulation of comet P/Wirtanen, the target of Rosetta mission. Local temperature and evolution of the crust are different depending on which of the two distribution dominates: the maximum temperature reached by a crust with a strong organic component is lower than that reached by a purely silicatic crust.