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 µm was observed in grating mode, where the SWS provides a spectral resolution of about 1300. For longer waves up to 197 µm 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 the 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 µ mi n both the data and the model. Also PH3 features are present at the expected wavelengths of 113 and 141 µm in both the data and the model. This is the first time that most of these far-infrared features have been detected. The ISOobservations are therefore of interest for the preparation of the planned submillimeter studies of the atmospheres of the Jovian planets with FIRST.