19.13-P

Models of the ISO 3- Reflection Spectrum of Jupiter

R.F. Knacke (Penn State Erie), T.Y. Brooke (Penn State Erie and JPL), D. Crisp (JPL), Th. Encrenaz, P. Drossart (Obs. Paris, Meudon), H. H. Feuchtengruber (ISO Center, Villafranca), Th. de Graauw (SRON, Gronigen)

Spectra of Jupiter obtained recently with the Infrared Space Observatory show evidence for the signature of NH ice particles in the jovian atmosphere. Thermochemical theory predicts that Jupiter's upper atmosphere should contain NH ice, but until now it has been difficult to find spectroscopic evidence of solid NH . To interpret the new spectra, we constructed models of Jupiter's 2.7-3.2 reflection spectrum, including multiple scattering by spherical cloud particles. Model atmospheres containing two cloud decks and NH gas absorption best reproduce a sharp drop in Jupiter's reflectance longward of 2.7 . The model upper cloud deck is located near the NH condensation level at 0.6 bar. The lower cloud, which must be optically thick, is at 1.4 bar, the altitude of a cloud detected by the Galileo nephelometer. Inclusion of NH ice particles in the upper cloud gives much improved agreement with the jovian ISO spectrum near 3 , primarily because of absorption by the broad 2.95 N-H stretch vibration band of solid NH . NH ice particles with radius 10 and cloud visible optical depths of 1 give the best fit. This is strong evidence for the long-sought spectral signature of NH ice particles in Jupiter's atmosphere, although the uniqueness of the fit has not yet been conclusively demonstrated. This research was supported by NASA grants NAGW-3415 and NAG 5-3368 to Penn State Erie.