The Photochemistry of Methane in the Jovian Atmosphere

Abstract

The photochemistry of methane in the Jovian atmosphere is reviewed and the photolysis of acetylene, ethylene and ethane is discussed. Approximate photochemical calculations are made for a mixed atmosphere of CH₄ and H₂ with a CH₄ mixing ratio of 10⁻³. In regions where diffusion effects axe important, the solutions are modified to include these effects. Ethane is found to he the most abundant hydrocarbon produced in the photolysis of methane and has a mixing ratio on the order of 10⁻⁸ to 10⁻⁷. The densities of CH₃, C₂H₂ and C₂H₂ are also given as a function of the H₂ density. In the model CH₄ is irreversibly converted into more complex hydrocarbons. It is suggested that the CH₄ abundance is maintained on Jupiter by the downward transport of the more complex hydrocarbons into the hotter regions of the atmosphere where they undergo thermal decomposition to produce methane, which in turn is transported upward to replenish the methane lost in phoatolysis.