The Production of Organic Molecules in Planetary Atmospheres. (original) (raw)

Abstract

It is now well known that when energy is supplied to a mixture of hydrogen, methane, and ammonia, or of hydrogen, methane, ammonia, and water vapor, organic molecules are produced. Both electric corona discharge and ultraviolet light, which have been successful as laboratory energy sources, are available in planetary atmospheres. Since hydrogen, methane, ammonia, and water vapor are the four most abundant reactive molecules in cold nondiffuse astronomical objects, it is probable that organic molecules are being produced in the solar system today, especially in the Jovian planets. For an organic molecule to be synthesized by solar ultraviolet light in a planetary atmosphere, and to avoid subsequent photolysis, the time for diffusion to depths optically thick in the photodissociating ultraviolet must be exceeded by the time between successive absorptions of photodissociating photons. From this condition, the experimental quantum yields of Groth, and recent theories of solar evolution, rates have been estimated for the net production of organic compounds in the contemporary atmospheres of the Jovian planets, and in the primitive reducing atmospheres of the terrestrial planets. The total surface densities of synthesized molecules during the lifetimes of these atmospheres are of the order of 1000 g cm-2. Applications are made to the origin of life on earth, the reduced carbon fraction of the terrestrial crust, Sinton's identification of hydrocarbons and aldehydes on Mars, the discovery of complex organic matter in carbonaceous chondrites, and the composition of comets. The spectra of some of the more abundant synthesized molecules are described. An infrared spectrophotometric tracing of Jupiter by Kuiper shows a feature near 1 .53~~ which is tentatively attributed to HCN.