First Results of ISO-SWS Grating Observations of Jupiter

The spectrum of Jupiter has been recorded on April 12, 1996, between 2.75 and 14.5 mu m, with the grating mode of the Short-Wavelength Spectrometer of ISO (Infrared Space Observatory). The resolving power is 1500 and the sensitivity limit is better than 1 Jy. The corresponding S/N ratio is better than 1000 at 2.75 mu m, 4000 at 5 mu m and 20000 at 12 mu m. The main preliminary results of the grating observations are (1) at 3 mu m, the first spectroscopic signature, probably associated with NH_3 ice, of the Jovian cloud at 0.5 bar and (2) the first detection of a thermal emission at the center of the CH_4 nu_3 band at 3.3 mu m, showing evidence for a high temperature in the upper jovian stratosphere (about T=800 K at P=0.16 mu bar). A modelling of the whole spectral range will be presented, with implications on the jovian thermal profile and on the mixing ratios and/or vertical distributions of the atmospheric constituents. A preliminary analysis of these data can be found in Encrenaz et al (submitted to Astron. Astrophys., 1996).