been difficult to confirm observationally. For solar elemental abundances, NH 3 is predicted to condense out at T Ȃ A spectrum of Jupiter in the 3-m region obtained with the Infrared Space Observatory (ISO) shows evidence for the long-150 K near p Ȃ 0.7 bars, and solid NH 4 SH should form at sought spectral signature of NH 3 ice particles in the jovian T Ȃ 200 K near p Ȃ 2.0 bars (West et al. 1986). The Galileo atmosphere. We calculated Jupiter 3-m reflection spectrum, probe recently detected evidence for clouds near roughly including multiple scattering by spherical cloud particles. Mod-0.6 and 1.4 bar (Sromovsky et al. 1996, Ragent et al. 1996), els containing reflection from two cloud decks along with NH 3 which may be due to these species. But spectral signatures gas absorption reproduce the sharp drop in Jupiter's reflectance of the cloud components have not been clearly detected.
longward of 2.7 m. Inclusion of cloud particles composed of
The N-H stretch absorptions of both of these suspected NH 3 ice in the upper cloud near 0.55 bar improves the fit to cloud constituents occur in the 3-Ȑm region, where Jupithe spectrum near 3.0 m, due to the N-H stretch absorption ter's flux as seen from the Earth is due to sunlight reflected of solid NH 3 . For models with a single size for the NH 3 ice, off of clouds. Thus, this is a logical wavelength region to particles with radius a Ȃ 10 m give the best fit. For a model with a bimodal distribution of a ؍ 1 m and a ؍ 10 m NH 3 search for cloud spectral signatures.
ice particles, the large particles need to dominate the 3-m
Jupiter exhibits a reflectance peak near 2.7 Ȑm (Larson NH 3 ice particle opacity to provide absorption that is sufficiently et al. 1984). The short wavelength side of this window is broad.