Atmospheric composition and structure of HD209458b
  Transiting planets like HD209458b offer a unique opportunity to scrutinize their atmospheric composition and structure. Transit spectroscopy probes the transition region between the day and night sides, called limb. We present a re-analysis of existing archived HST/STIS transmission spectra of HD209458b's atmosphere. From these observations we: Identify H2 Rayleigh scattering, derive the absolute Sodium abundance and quantify its depletion in the upper atmosphere, extract a stratospheric T-P profile with a temperature inversion and explain broad band absorptions with the presence of TiO and VO molecules in the atmosphere of this planet. 
J.-M. D\'esert, A. Vidal-Madjar, A. Lecavelier des Etangs, D. Sing, D.   Ehrenreich, G. H\'ebrard and R. Ferlet