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Accueil > Séminaires > Archive des séminaires d’Utinam > 2013

Kathleen E. Mandt

Understanding the Evolution of Titan’s Atmosphere through Isotope Ratio Measurements : Potential Applications to Earth

lundi 2 septembre 2013, 10h30

salle de conférences de l’observatoire

Kathleen E. Mandt, Ph.D., Research Scientist
Southwest Research Institute, San Antonio, Texas, Etats-Unis

Résumé :

We investigate the evolution of Titan’s atmosphere utilizing measurements of the stable isotope ratios in molecular nitrogen and methane and photochemical and dynamical models of the upper atmosphere. The Cassini Ion Neutral Mass Spectrometer (INMS) and Huygens Gas Chromatograph Mass Spectrometer (GCMS) measurements of the 14N/15N in N2 and 12C/13C in CH4, along with Cassini Infrared Spectrometer (CIRS) measurements of 12C/13C in CH4 are used to constrain processes involved in the evolution of the nitrogen and methane in Titan’s atmosphere.
By modeling the evolution of the nitrogen isotopes over geological times scales based on chemistry and escape, we find that the initial 14N/15N is limited to a heavier value than the 14N/15N observed in the Earth’s atmosphere ; even allowing for extensive hydrodynamic escape of the atmosphere in the distant past. We also find that because the 12C/13C at Titan is close to the primordial value, fractionation of the isotope ratio over time due to escape and photochemistry suggests that methane has been present in Titan’s atmosphere for no more than one billion years.
The methodologies developed for studying evolution of Titan’s atmosphere are relevant not only to Titan, but also to Earth. We will discuss applications of these methodologies to current Earth science issues with a particular focus on the impact of climate change on the upper atmosphere.