The present study of Saturn's atmosphere through thermal infrared imaging has explored two possible ways in interpreting the observed infrared structure of Saturn's atmosphere. The first assumption is the classical one: the tilt of Saturn's spin axis leads to a strong seasonal cycle which produces a thermal asymmetry, the insolated pole being hotter. From a comparison with a radiative transfer code, we showed that, with this hypothesis, the tropospheric temperature is nearly constant with latitude (it decreases by 3K from the equator to 60o N), while the stratospheric temperature is highly variable (the stratospheric temperature at 60o N is about 12K higher than at 40o N).
The second assumption explored the possibility of a variation in ethane and acetylene abundances. From our images, we showed that enhanced ethane and acetylene abundances can explain the features observed with a specific thermal profile. However when we consider previous infared observations in the 20 m window (Tokunaga et al. 1978), it is likely that this hypothesis is not valid. We conclude that Saturn's atmosphere shows a thermal variation constrained by the solar insolation. This variation affects mainly the upper atmosphere above 200-300 mbar. A next step could be to study the influence of such a variation on other atmospheric parameters, such as compound abundances or cloud structure.
© European Southern Observatory (ESO) 2000
Online publication: March 28, 2000