The KOSI experiments

Whipple's icy conglomerate model of the comet nucleus has enjoyed progressively increasing acceptance and success in explaining Earth‐based observations of comets since its very inception (Whipple, 1950, 1951). According to this model, the nucleus is a solid body composed of frozen gases and dust. The missions to Comet Halley in 1986, in particular the Vega and the Giotto missions, have confirmed that there is a single solid nucleus that is the root of all the observed phenomena that can be associated with an active comet. Two new comet missions (CRAF and Rosetta) are planned by NASA and ESA to extract further details about the structure and composition of the nucleus. Laboratory experiments play an important role in defining and identifying the objectives of these missions: Why are there small areas of activity on the surface while the largest parts of the nucleus appear to be dormant? What are the details of the development of the dusty gas atmosphere (coma)? What is the average tensile strength of the nucleus material? What is its detailed composition and how heterogeneous is it? What is the temperature profile below tie surface? Credible limits on the ranges of these physical and chemical properties and processes can be obtained from laboratory experiments. Although such experiments have been carried out in many laboratories in Europe, the Soviet Union, the USA, Israel, and Japan, the KOSI experiments are the first large‐scale investigations (in spatial dimensions and duration). (KOSI is an acronym for Kometensimulation, German for comet simulation.)