Thermal structure and composition of the atmospheres of Jupiter and Titan from Cassini infrared observations

The Cassini/Huygens spacecraft was launched in October 1997 for a four-year orbital tour of Saturn, its largest moon Titan, and its rings and many icy satellites, with the objective of investigating the origin, formation, and evolution of the solar system. Among the 12 instruments on the spacecraft is the unique Composite Infrared Spectrometer (CIRS), for observations of high-resolution, middle- and far-infrared spectra of planetary atmospheres in both nadir- and limb-viewing modes. A comprehensive analysis of the observed spectra provides a wealth of information about the thermal structure, composition, trace gas distributions, and the physical and dynamical processes in the observed atmospheres.; During the fly-by of Jupiter in December 2000--January 2001, on Cassini's long journey to Saturn, CIRS obtained a large amount of data on the infrared spectra of Jupiter's atmosphere. Since insertion of the spacecraft into Saturn orbit in July 2004, infrared spectra of Titan and Saturn's atmospheres are being obtained during close approaches. These observations constitute a observed dataset of mid- and far-infrared spectra with unprecedented spectral and spatial resolution, including the first limb observations of the atmosphere of Titan.; This dissertation deals with the analytical techniques and numerical modeling programs developed for the retrieval of thermal structure and trace gas distributions from infrared observations of planetary atmospheres. An algorithm for the retrieval of atmospheric properties such as temperature, composition, and aerosol opacity from limb and nadir observations is presented. Results of the analysis of CIRS observations of Jupiter, including global mapping of its thermal structure and trace gas distributions, as well as the astrophysically important nitrogen isotopic ratio 15N/ 14N, are presented.; Retrievals from Titan limb and nadir observations made during July 2004--February 2005 have generated maps of the stratospheric temperature and trace gas abundances. Vertical temperature and mixing ratio profiles of C2H2 and HCN retrieved from uniquely observed infrared spectra of Titan are presented and discussed.