Abstract
The atmosphere of Saturn, like that of the other giant planets, is dominated by hydrogen, helium and minor species in reduced form. Its chemical composition has been studied by remote sensing spectroscopy, especially in the infrared range, from the ground and aboard the Voyager spacecraft. The measurement of abundance ratios in Saturn's troposphere shows an enrichment in C/H and D/H, in agreement with the nucleation formation model of the giant planets. As in the case of the other giant planets, Saturn's stratosphere exhibits an active methane photochemistry and an external oxygen source. The Cassini mission is expected to provide more accurate measurements of some abundance ratios, as well as a spatial and temporal monitoring of the minor atmospheric species. In the future, a space mission including one or more descent probes would be needed, to obtain a complete and precise measurement of the enrichment factor of heavy gases in Saturn, and thus to better understand the planet's formation scenario.
So how do you know the entire planet has this composition?