Observations of C2H6 and C2H2 in the stratosphere of Saturn

We have performed high-resolution spectral observations at mid-infrared wavelengths of C2H6 (12.16 μm), and C2H2 (13.45 μm) on Saturn. These emission features probe the stratosphere of the planet and provide information on the hydrocarbon photochemical processes taking place in that region of the atmosphere. The observations were performed using our cryogenic echelle spectrometer Celeste, in conjunction with the McMath–Pierce 1.5-m solar telescope in November and December 1994. We used Voyager IRIS CH4 observations (7.67 μm) to derive a temperature profile on the saturnian atmosphere for the P ⩽ ∼ 1.6 mbar region of the stratosphere. This profile was then used in conjunction with height-dependent volume mixing ratios of each hydrocarbon to determine global abundances for ethane and acetylene. Our ground-based measurements indicate abundances of 6.7 −2.3 +3.3 × 10 −6 for C2H6 (1.0 mbar pressure level), and 3.4 −1.1 +1.5 × 10 −7 for C2H2 (1.6 mbar pressure level). We also derived new mixing ratios from the Voyager mid-latitude IRIS observations; 8.6 ± 0.9 × 10 −6 for C2H6 (0.1–3.0 mbar pressure level), and 1.6 ± 0.2 × 10 −7 for C2H2 (2.0 mbar pressure level).