Models of the ISO 3-µm Reflection Spectrum of Jupiter

Abstract

A spectrum of Jupiter in the 3-μm region obtained with the Infrared Space Observatory (ISO) shows evidence for the long-sought spectral signature of NH₃ice particles in the jovian atmosphere. We calculated Jupiter 3-μm reflection spectrum, including multiple scattering by spherical cloud particles. Models containing reflection from two cloud decks along with NH₃gas absorption reproduce the sharp drop in Jupiter's reflectance longward of 2.7 μm. Inclusion of cloud particles composed of NH₃ice in the upper cloud near 0.55 bar improves the fit to the spectrum near 3.0 μm, due to the N-H stretch absorption of solid NH₃. For models with a single size for the NH₃ice, particles with radiusa≈ 10 μm give the best fit. For a model with a bimodal distribution ofa= 1 μm anda= 10 μm NH₃ice particles, the large particles need to dominate the 3-μm NH₃ice particle opacity to provide absorption that is sufficiently broad.