The spectrum of Saturn from 43 to 197μm was measured with the ISO Long Wavelength Spectrometer (LWS) during the performance verification phase of the mission. The measurements were made using the LWS in grating mode, with spectral resolutions of 0.29μm from 43 to 90μm and 0.6μm from 90 to 197μm. The spectrum was compared with an atmospheric radiative-transfer model and four results were obtained: first, the slope of the measured continuum within each detector passband is in good agreement with the model; second, absorption features due to ammonia and phosphine were unambiguously detected, and all detected features were attributed to these two molecules; third, the ammonia absorption features agree reasonably well with the nominal model (based on Voyager IRIS measurements); and fourth, the phosphine absorption features disagree with the nominal model. Superior agreement with the measured spectrum was obtained with a modified PH_3_ profile in which the tropospheric mixing ratio was increased to 7x10^-6^ and the cutoff due to photodissociation was lowered to 300mbar. These results are based on trial observations during performance verification of the LWS, and provide an indication of the results we expect to obtain when the spectrum of Saturn is measured comprehensively later in the mission.
Astronomy and Astrophysics
- Pub Date:
- November 1996
- PLANETS AND SATELLITES: INDIVIDUAL: SATURN;
- INFRARED: SOLAR SYSTEM