Supercritical carbon dioxide is used as a solvent in supercritical fluid extraction. Supercritical water can be used to decompose biomass via supercritical water gasification of biomass. Another method of extraction is using supercritical and subcritical fluids. Many pressurized gases are actually supercritical fluids. Carbon dioxide is the most common supercritical solvent. The gaseous outer layers of Jupiter and Saturn transition smoothly into oceans of supercritical hydrogen. Aerogels are produced by extracting the liquid component of a gel through supercritical drying. Currently, resinoids are often obtained by extraction with supercritical carbon dioxide. Table 2 shows density, diffusivity and viscosity for typical liquids, gases and supercritical fluids. The liquid is pumped to a heating zone, where it is heated to supercritical conditions. One such design is called the supercritical airfoil. Nuclear fission weapons require a mass of fissile fuel that is prompt supercritical. The supercritical airfoil shape is incorporated into the design of a supercritical wing. CO displaces the rinsing fluid and is heated past the supercritical point. It uses supercritical water as the working fluid.