Simulation of the cometary 10μm band by means of laboratory results on silicatic grains.

The observations of comet P/Halley have shown, for the first time, that the emission band at 10 μm, typical of silicatic materials, is characterized by different spectral components. Namely, peaks falling around 9.8 and 11.3 μm have been isolated. This property is not a peculiarity of P/Halley as also other comets such as Bradfield and Levy present similar features. There is a wide debate on the identification of the specific silicate components able to simulate the observations. In the present work we report the results of laboratory experiments performed on various kinds of submicron grains which can be considered as representative of different classes of silicates. Infrared spectra have been obtained which are free from effects possibly produced by matrices, commonly used to embed dust to perform spectroscopic measurements. These data have been used as input in a computational code to fit quantitatively emission spectra from comets P/Halley and P/Levy in the 10 μm band region. Our results confirm previous findings that mixtures of olivine-type and pyroxene-type grains are able to provide satisfactory fits of observations. Moreover, from the simulation it appears that the relative amounts of the various silicate species are different in the two comets considered. In the future, the extension of the simulation to other comets could provide useful information so that the variations in the spectral profile of the 10 μm band could be correlated with different intrinsic and/or evolutionary properties of the comets.