Hydrogen cyanide polymers from the impact of comet P/Shoemaker-Levy 9 on Jupiter.

Hydrogen cyanide polymers--heterogeneous solids ranging in color from yellow to orange to brown to black--may be among the organic macromolecules most readily formed within the Solar System. The non-volatile black crust of comet Halley, for example, as well as the extensive orange-brown streaks in the atmosphere of Jupiter, might consist largely of such polymers synthesized from HCN formed by photolysis of methane and ammonia. Laboratory studies of these ubiquitous compounds point to the presence of polyamidine structures synthesized directly from hydrogen cyanide. These would be converted by water to polypeptides which can be further hydrolyzed to alpha-amino acids. Other polymers and multimers with ladder structures derived from HCN would also be present and might well be the source of the many nitrogen heterocycles, adenine included, detected by thermochemolytic analysis. The dark brown color arising from the impacts of comet P/Shoemaker-Levy 9 on Jupiter could therefore be mainly caused by the presence of HCN polymers, whether originally present, deposited by the impactor or synthesized from freshly formed HCN. Spectroscopic detection of these predicted macromolecules and their hydrolytic and pyrolytic by-products would strengthen significantly the hypothesis that cyanide polymerization is a preferred pathway for prebiotic and extraterrestrial chemistry.