Comet composition: Models and new observations

Summary We discuss structure and composition of comets as they are inferred on the basis of new theoretical models and very recent observations. Many questions are still open, but the efforts performed in coincidence with P/Halley's apparition in 1986 have led to significant improvements. Today we have a better knowledge of the materials which are stored in comet nuclei and new generations of theoretical models are able to give good representations of the surface and inner structure of these bodies. However, much work remains still to be done, also in preparation for ambitious space missions which shall return to Earth actual samples of cometary nuclei. To speed up publication, the proofs were not sent to the authors and were supervised by the Scientific Committee.