ISO observations of the giant planets and Titan: what have we learnt?

Infrared spectroscopic observations of the giant planets and Titan with the Infrared Space Observatory (ISO) have brought a significant contribution to our knowledge of these objects. The main discoveries achieved by ISO are: (1) the first detection of an external oxygen source for all giant planets and Titan; (2) the first detection of new stratospheric hydrocarbons (CH3C2H,C4H2,CH3,C2H4,C6H6); (3) a new determination of the D/H ratio on all giant planets and Titan; (4) a measurement of 14N/15N on Jupiter, showing a significant 15N depletion with respect to the terrestrial value. Information has been obtained also on the stratospheric thermal profiles of the giant planets, their eddy diffusion coefficients, and their cloud structures.