Local activity of comets: an indicator of non-uniform composition

In this paper, we investigate the conditions for the local ejection of a metamorphosed surface layer of material from a comet. We have calculated the strengthening of the material of the nucleus of comet 67P/Churyumov–Gerasimenko and the increase of gas pressure in pores. We are interested in the boundary between the regions Anhur and Bes, where an active pit has been identified. We show that material rich in ice can be exposed as a result of the local ejection of the strengthened layer of material several metres thick. This process does not require locally increased concentrations of very volatile components, such as carbon monoxide. A sufficient condition is the heterogeneity of material granulation.