ISO far-infrared spectroscopic observations of Jupiter

We present the far-infrared spectrum of Jupiter that was measured with the Short and Long Wavelength Spectrometers (SWS and LWS) aboard the Infrared Space Observatory (ISO). The region between 38 and 44 mum was observed in grating mode, where the SWS provides a spectral resolution of about 1300. For longer waves up to 197 mum the LWS-FP (Fabry-Perot) was used to achieve a resolution. of several thousand. The observations were made between 23 and 26 May 1997 during ISO's revolutions 554, 556 and 557. The Jovian spectrum in the far-infrared is compared to an atmospheric radiative transfer model using expected values for the vertical profiles of die atmospheric constituents. Rotational transitions of ammonia and phosphine are responsible for the absorption features observed: Strong ammonia absorption manifolds are obvious against the background continuum slope, appearing at 39, 42, 46, 51, 56, 63, 72, 84, 100 and 125 mum in both the data and the model. Also PH3 features are present at the expected wavelengths of 113 and 141 mum in both the data and the model. This is the first time that most of these far-infrared features have been detected. The ISO observations axe therefore of interest for the preparation of the planned submillimeter studios of the atmospheres of the Jovian planets with FIRST.