The Jovian spectrum in the 3-μm window

The spectral window of Jupiter at 3 μm is analyzed and compared with previously published spectra. The two components of the spectrum, the thermal and the solar reflected contributions, are calculated at low resolution (30 cm^?1) between 3300 and 3800 cm^?1 for preparing the interpretation of the Galileo Near Infrared Mapping Spectrometer experiment. The calculations yield to the following conclusions: (1) NH₃ is the main absorber between 3300 and 3600 cm^?1 for both the thermal spectrum and the solar reflected spectrum; H₂O appears only in the thermal component above 3600 cm^?1. (2) The thermal component can be seen only on the dark side of Jupiter; the atmosphere is sounded down to temperature levels of about 210°K. (3) The solar reflected component can be modelized by a reflecting layer between 135 and 140°K with an albedo of 0.3; high spatial resolution maps of Jupiter at 3 μm should give access to the NH₃ spatial distribution on Jupiter.