title: Titan's atmosphere composition:  certainties and speculations.
abstract: Firm results concerning the thermal structure, the composition, the seasonal effects of the atmosphere of Titan, as well as the superotation of its stratosphere are reviewed.  The nature of the surface of the satellite, the possible presence of argon in the atmosphere and the structure and composition of clouds and aerosols are, among other topics, still speculative.  The implications of the observed deuterium enrichment on the origin of ices in the outer part of the nebula are controversial.
authors.affiliation: Dèpartement de Recherches Spatiales, Observatoire de Paris-Meudon, France.
authors.forename: D
authors.initials: D
authors.lastname: Gautier
mesh_terms: D001128:Argon / Q000032:analysis; D001272:Atmosphere / Q000032:analysis*; D003903:Deuterium / Q000032:analysis; D005118:Extraterrestrial Environment; D005740:Gases / Q000032:analysis; D006859:Hydrogen / Q000032:analysis; D008697:Methane / Q000032:analysis; D009584:Nitrogen / Q000032:analysis; D018539:Saturn; D013026:Space Flight; D013696:Temperature
chemical_list: D005740:Gases; D001128:Argon; D006859:Hydrogen; D003903:Deuterium; D009584:Nitrogen; D008697:Methane