Modelling of cometary nuclei: Planetary missions preparation

The planning of planetary missions requires the knowledge as much as possible accurate of the target. This knowledge, which cannot be obtained only by ground based observations, can be supported by theoretical modeling. This is particularly true in the case of Rosetta, a cornerstone ESA mission that will be launched in January 2003, and of its target, the comet 46P/Wirtanen. In this paper we show how, using a nucleus thermal evolution model, it is possible to foresee the temperature of the nucleus surface and the activity level along the orbit and define the range of possible values for these properties. Activity level close to the aphelion depends on the presence of CO. Surface temperatures depend on the physical properties attributed to the dust: temperatures reached by a crust mainly composed by silicatic grains differ from the temperatures reached by a crust mainly composed by organic grains.