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First results of ISO-SWS observations of Saturn: detection of CO_2_, CH_3_C_2_H, C_4_H_2_ and tropospheric H_2_O.
Th. de Graauw, H. Feuchtgruber, Bruno Bézard, P. Drossart, Th. Encrenaz, D. A. Beintema, Michael Griffin, A. M. Heras, Martin Kessler, K. Leech, E. Lellouch, P. A. Morris, Pieter R. Roelfsema, Maarten Roos‐Serote, A. Salama, Bart K. Vandenbussche, Edwin A. Valentijn, G. R. Davis, D. A. Naylor
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Abstract
The spectrum of Saturn has been recorded between 4.5 and 16.0 mu m with the grating mode of the Short-Wavelength Spectrometer (SWS) of ISO. The resolving power is 1500. The main results of this observation are (1) the detection of CO2 CH3C2H and C4H2 in the stratosphere and (2) the detection of H2O in the troposphere. In the 4.5-5.5 mu m range, information is retrieved on the tropospheric composition (NH3, PH3, AsH3, GeH4, CH3D and H2O) down to pressure levels of several bars. Above 7 mu m, the Saturn spectrum probes the upper troposphere and the lower stratosphere, at pressure levels ranging from 0.5 bar to 0.4 mbar. The CH4 emission band at 7.7 mu m and the H-2-He continuum longward of 11 mu m are used to retrieve the thermal profile, which is then used to derive the vertical distributions of minor species: NH3, PH3, CH3D in the troposphere, and C2H2 and C2H6 in the stratosphere. Estimates of the CO2, CH3C2H and C4H2 mean mixing ratios (above the 10-mbar level) are 3 10(-10), 6 10(-10) and 9 10(-11) respectively. The retrieved disk-averaged thermal profile is found to be colder in the stratosphere than the Voyager 1 ingress radio-occultation profile by about 7 K at P = 0.5 mbar, and slightly warmer in the troposphere (about 5 K at 400 mbar and 3 K at 150 mb).