Icy grains as a source of CO in comet 29P/Schwassmann-Wachmann 1

Reaction rates included in photochemical models of planetary atmospheres carry with them a level of imprecision. This imprecision leads to an uncertainty in computed mole fractions of chemical species. We present estimations of the uncertainties on mole fraction profiles, obtained using a 1-D photochemical model applied to the study of hydrocarbon compounds in Saturnʹs atmosphere. We calculate the uncertainties as a function of altitude for each compound and derive the mean value and the standard deviation of the mole fraction. We show that the uncertainties on the mole fraction of hydrocarbons determined from a photochemical model are very significant. Ethane and acetylene, the most abundant hydrocarbons in Saturnʹs atmosphere after methane, are affected by an uncertainty factor of about 1.5, and the mole fraction of complex hydrocarbons, which are the products of a more complex chemistry, are affected by a large uncertainty factor which can reach 24. We discuss the implications for the determination of the eddy diffusion coefficient. In particular, we show that uncertainties on the calculated mole fractions produce a large uncertainty on the eddy diffusion coefficient profile in the lower atmosphere.