The sensitivity of Titan's current atmosphere to variations in solar EUV flux and implications for the evolution of the atmosphere

Details The sensitivity of Titan's current atmosphere to variations in solar EUV flux and implications for the evolution of the atmosphere The sensitivity of Titan's current atmosphere to variations in solar EUV flux and implications for the evolution of the atmosphere

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p11a1326m&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #P11A-1326

Mathematics

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[0325] Atmospheric Composition And Structure / Evolution Of The Atmosphere, [6040] Planetary Sciences: Comets And Small Bodies / Origin And Evolution, [6281] Planetary Sciences: Solar System Objects / Titan

Scientific paper

K. E. Mandt, J. Bell, J. H. Waite, Jr. Southwest Research Institute, San Antonio, TX Stable isotope ratios are an important tool for tracing the evolution of an atmosphere. By carefully evaluating processes that fractionate the isotopes (e.g. escape and photochemistry), the inventory of a constituent can be tracked over geological time scales. For Saturn’s largest moon, Titan, the 14N/15N in N2 and the 12C/13C in CH4 can be used to constrain the initial size of the atmosphere and the amount of time that has passed since the current inventory of methane began outgassing into the atmosphere (see Lunine et al. [1999] and Mandt et al. [2009]). Because the processes that fractionate the isotopes are directly tied to the amount of solar EUV/UV energy deposited in the upper atmosphere, it is important to understand the sensitivity of the atmosphere to varying solar EUV flux. On short time scales, the EUV flux can vary by as much as a factor of two during the eleven-year solar cycle. On geologic time scales, the solar EUV flux is believed to have been about 2.5 times greater than the current flux about 2.5 billion years ago, and 6 times the current flux 3.5 billion years ago [Ribas et al. 2005]. Using a 1D version of the 3D Titan Global Ionosphere-Thermosphere Model (T-GITM), we will explore the impact of the eleven-year solar cycle variations on Titan’s upper atmosphere, focusing on the key fractionating processes of photochemistry and escape. We will then discuss the implications of these results for modeling the evolution of the atmosphere over geological time scales. Lunine, J. I., Y. L. Yung and R. D. Lorenz, 1999. On the volatile inventory of Titan from isotopic abundances in nitrogen and methane. Planetary and Space Science, 47, 1291-1303. Mandt, K. E., J. H. Waite, Jr., B. A. Magee, J. Bell, J. Lunine, O. Mousis, D. Cordier, 2009, Isotopic evolution of Titan’s main atmospheric constituents, Planetary and Space Science, 57, 1917-1930. Ribas, I., E. F. Guinan, M. Gudel, and M. Audard, 2005, Evolution of the Solar Activity over Time and Effects on Planetary Atmospheres. I. High-Energy Irradiances (1-1700 A), Astrophysical Journal, 622, 680-694.

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