From interstellar matter to comets: A laboratory view

Comets, formed in the cold outer parts of the solar system, provide a record of pristine material from the parent interstellar cloud. The investigation of outgassing curves from bright comets has provided a relationship to the abundances of interstellar ices and gas phase molecules. However, being porous and stratified in various layers of different densities and temperatures, the outgassing characteristics of comets can not always be directly reconciled with the interstellar composition. This is due to the structure of the nuclear ice component, which contains different coexisting ice phases, clathrates, and trapped gases. Ices, silicates and carbonaceous compounds - studied through astronomical observations and by laboratory simulations - serve as reference material to obtain information on cometary bulk material. A major fraction of cosmic carbon in the interstellar medium, comets and meteorites seems to be incorporated into complex aromatic networks, which are difficult to observe and to identify spectroscopically. However, recent measurements of the macromolecular structure and soluble organic species in carbonaceous meteorites provide a powerful tool to investigate the link of small bodies in the solar system.