Photochemistry of Hydrocarbons in the Jovian Upper Atmosphere

Abstract

The recent remarkable success of Pioneer 10 has greatly expanded the arena of planetary aeronomy. New and invigorating incentives and justifications now exist for more thorough studies in Jovian upper atmospheric physics and chemistry. One important problem in this area is the problem of the photochemistry of the hydrocarbons. Apart from being interesting in its own right, knowledge of the distributions of the various hydrocarbons is needed in many other studies, too (e.g., the thermal structure). The recent occultation of the multiple star system β-Scorpii by Jupiter, which occurred on March 13, 1971, provided another opportunity to probe the Jovian atmospheric conditions. Utilizing this event and the advancements in technology that have taken place since the time of the last occurrence of a similar occultation studied by Baum and Code (1953), Hubbard et al. (1972) and Veverka et al. (1974) have reported the existence of several smaller scale stratified thermal structures. In analogy with the heating produced by methane absorption in the 3.3, µ band (Gillet et al., 1969), it has been suggested by Hubbard (1969) that these smaller scale layers may be the result of a similar absorption process in hydrocarbon or other trace constituents. Some hydrocarbons are good infrared radiators also, and could influence the thermal structure on the manner discussed by McGovern and Burk (1972), and Strobel and Smith (1973). Another important area of study where a knowledge of the height profile of the hydrocarbons could be extremely useful, relates to Jovian ionospheric structure and conductivities. It may be noted that CH₃ has the lowest ionization potential compared to all the other major constituents in the Jovian atmosphere.