Properties of mantles on cometary nuclei

The formation, structure, and properties of dusty mantles on cometary nuclei are investigated using various theoretical arguments and experimental data. It is shown how the growth of the mantle is affected by the varying thermal conductivity and how an initial chemically undifferentiated surface layer changes into a mechanically rather weak, less than 10 to the 7th dyn /sq cm, mantle which then strengthens to reach values of the order of 10 to the 8th dyn/sq cm. Organic CHON decomposition products may lower the porosity below the expected value of about 0.5 and lead to an increase of the surface temperature. They may also further strengthen the overall bonding of the mantle.