A curious and unexpected result of the impact of P/Shoemaker Levy 9 with Jupiter was the production of enormous amounts of molecular sulfur (S2). Here we show that S2 is the natural product of disequilibrium chemistry at low pressures in shocked jovian air, its formation a byproduct of hydrogen recombination. The species observed by the HST-S2, CS2, and H2S-imply that the G fragment penetrated the NH4SH cloud but did not reach the water table. A typical impact within or below the NH4SH clouds produces about 0.03--0.1 impactor masses of S2. Because comets are relatively hydrogen-poor. SO2, not S2, is the major product of shocking a water-rich comet, while S2, CS2, and OCS are major products of a dessicated comet. In all cases we find that as the gas cools S2 converts to the stable low temperature allotrope S8, although other chemical fates not modeled here might intervene first. ¿ American Geophysical Union 1995