The first detection of propane on Saturn
Résumé
We report the first detection of propane, C 3H 8, in Saturn's stratosphere. Observations taken on September 8, 2002 UT at NASA's IRTF using TEXES, show multiple emission lines due to the 748 cm -1nu band of C 3H 8. Using a line-by-line radiative transfer code, we are able to fit the data by scaling the propane vertical mixing ratio profile from the photochemical model of Moses et al. [2000. Icarus 143, 244-298]. Multiplicative factors of 0.7 and 0.65 are required to fit the -20° and -80° planetocentric latitude spectra. The resultant profiles are characterized by a 5 mbar mixing ratio of 2.7±0.8×10 at -20° and 2.5-0.8+1.7×10 at -80° latitude. These results suggest that the time scale for meridional circulation lies between the net photochemical lifetimes of C 2H 2 and C 3H 8, ≈30-600 years.