Report of the Working Group on Ice and Related Topics

Abstract

Ice mantles are accreted on refractory cores (mainly silicates) in interstellar grains (ISG). Their identification has been possible by comparison of astronomical infrared absorption spectra with those known from laboratory spectra (e.g. the 3.1 µm feature of water). Grains are believed to be the sites where molecules (e.g. H2) can be formed and under certain circumstances returned to the gas phase. Again, ice mantles are subjected to erosion processes as sublimation (in regions where the temperature is high enough), photo (?) and ion sputtering, grain-grain collisions. Erosion processes are of fundamental importance in many contexts as e.g. in explaining why some material is left over in dense clouds in the gas phase instead to completely condense on cold grains. The ultimate fate of ice mantles (together with their cores) is to partecipate to the collapse of the cloud to which they belong to form, at least in the case of the Sun, a planetary system. Here different scenarios are possible: at one extreme there are researchers who believe that ISG are completely destroyed before planetary objects are formed, on the other extreme it is belived that grains, included ice mantles, have never experienced high (> 150 K) temperatures and that they preserve their status e.g. in comets where now we can go to search for them. During all their life ice grains suffer a continuum irradiation by external agents, as photons and ions, inducing not only erosion phenomena but also chemical alteration. These include formation of new organic materials due to the formation of radicals and their reactions. The presence of all the above sketched phenomena had, have and will have to be supported by laboratory work. This working group discussed, in some cases with great technical detail, some of those laboratory works. We report here some of these items.