ISO LWS measurement of the far-infrared spectrum of Saturn
G.R. Davis, M.J. Griffin, D.A. Naylor, P.G. Oldham, B.M. Swinyard, P.A.R. Ade, S.B. Calcutt, Th. Encrenaz, T. De Graauw, D. Gautier, P.G.J. Irwin, E. Lellouch, G.S. Orton, C. Armand, M. Burgdorf, A. Di Giorgio, D. Ewart, C. Gry, K.J. King, T. Lim, S. Molinari, M. Price, S. Sidher, A. Smith, D. Texier, N. Trams and S.J. Unger
Abstract:
The spectrum of Saturn from 43 to 197 
m 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 0.29 m from 43 to 90 m and 0.6 m from
90 to 197 m. 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 
profile in which the tropospheric mixing ratio was increased to 710 
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.
Keywords:
Planets and satellites: Individual: Saturn - Infrared: solar
system