The physics and chemistry of cometary water ice and gas-laden ice can be studied with thin, 0.1-100 microns, ice samples which were deposited on a cold plate. The structural changes in the ice and the evolution of water vapor and gases from it are studied by a variety of methods.It was found that the changes in the ice structure,between 20K and its complete sublimation at ~200K, follow a very complex pattern. The release of trapped gas from the ice follows these changes. The amount of trapped gas in the ice depends exponentially on the ice formation temperature. Thus, from the CO/H₂O ratio, it was found that comets Halley, Hyakutake and Hale-Bopp were formed between 54 and 66K. A comparison between the Ar/Kr/Xe ratios when trapped in the ice and the ratios in Earth's atmosphere, suggest that comets delivered a considerable amount of these gases to Earth. Isotopic enrichments within each noble gas, as found experimentally, support this idea. The lack of isotopic enrichment in HDO/H₂O, when water vapor freezes to ice, suggests that the HDO/H₂O enrichment in all the three comets, above the D/H ratio in the solar nebula, point to an interstellar origin, in a 50-60K warm clump of a giant molecular cloud. A further step in comet simulation is the KOSI experiment and the new machine at Tel-Aviv University, which produces a 20 cm diameter and a few cm thick sample of gas-laden amorphous ice. Experimental results from both experiments will be described.