Abstract

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 (CH ₃C ₂H,C ₄H ₂,CH ₃,C ₂H ₄,C ₆H ₆); (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.