Hydrocarbon photochemistry and Lyman alpha albedo of Jupiter

Abstract

A combined study of hydrocarbon and atomic hydrogen photochemistry is made to calculate self-consistently the Lɑ albedo of Jupiter. It is shown that the Lɑ emissions observed by Voyagers I and II can be explained by resonance scattering of sunlight. Precipitation-of energetic particles from the magnetosphere can provide the large required source of atomic hydrogen, although the contribution of direct particle excitation to the disk-averaged brightness is insignificant. The variability of the Lɑ brightness inferred from many observations in recent years is examined. The large difference in the brightness of the He 584 Å resonance line observed by Pioneer and Voyager is briefly discussed. Driving the photochemistry by solar ultraviolet radiation alone yields a maximum mixing ratio of C_2H_6 + C_2H_2 at 10^(-2) atm of about 4 x 10^(-6). The possibility of additional CH_4 dissociation from precipitation of magnetospheric particles is discussed. The photochemistry of C_2H_2 and C_2H_3 is sufficiently uncertain not to permit accurate calculations of their densities and the ratio C_2H_6/C_2H_2.

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