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D. Shemansky, P. Gangopadhyay, X. Liu, J. Tew (USC), Cassini UVIS Team
Cassini EUV observations of the Jupiter dayglow reported by Shemansky et al.(2001) show strong atomic hydrogen higher Rydberg series emission lines, that by comparison are not measurable in auroral spectra obtained at the same time. The observations have important implications for the interpretation of the source process and altitude in the atmosphere. The H Ly\beta line in these observations is about 120 R. The only other measurement of this transition was obtained from the Voyager UVS ( 65 R - 80 R, Shemansky(1985)). The presence of the H Ly\gamma and H Ly\delta lines is also indicated in the Cassini spectra. The H Ly\beta feature is an order of magnitude brighter than can be accounted for by solar resonance scattering. Monte Carlo multiple scattering calculations in spherical geometry require electron excitation an altitude of 2000 km above 1 bar, at 9. X 1015 cm-2 foreground abundance (exobase: 2. X 1014 cm-2) to scale the brightness to the observation. The required electron energy input rate is sufficient to explain the upper atmospheric temperature thru dissociative excitation of H2 and related processes. Issues of physical chemistry in the containment of the H population will be discussed.
Funding for this work is supported by Cassini Program support of the UVIS experiment, and NASA Grant NAG5-8939 to the University of Southern California.
The author(s) of this abstract have provided an email address for comments about the abstract: http://lasp.colorado.edu/cassini/