Nitrogen Chemistry in Titan’s Upper Atmosphere
J. A. Kammer1, D. E. Shemansky2, X. Zhang1, Y. L. Yung1
1Division
of Geological and Planetary Sciences, California Institute of Technology,
Pasadena, CA
2Planetary and Space Science Division, Space Environment Technologies, Pasadena,
CA
jak@gps.caltech.edu
Titan’s atmosphere has evolved over time into its current state through
complex photochemical processes (Yung et al. 1984), involving nitrogen (N 2),
the dominant molecular species in the atmosphere, as well as methane (CH4).
It has been proposed that this composition may be analogous to the early
Earth’s, as it certainly provides an abundance of hydrocarbons the like from
which early life may have arisen (Coustenis & Taylor 1999; Lunine 2005).
Recent results from the Cassini spacecraft have greatly improved our
knowledge of the current state of Titan’s atmosphere, and measurements
made by the Ultraviolet Imaging Spectrograph (UVIS) in particular are able
to probe the region of interest from 400 km to 1500 km in altitude where
much of the photochemistry on Titan occurs (Shemansky et al. 2005,
Koskinen et al. 2011). This photochemistry in part converts nitrogen from
stable N2 molecules and incorporates it into detectable hydrocarbon products
such as HCN, HC3N, and other heavier compounds. Therefore the nitrogen
story is of particular interest, and we examine UVIS occultation observations
in both the EUV and FUV regions of the spectrum in order to directly
retrieve the vertical profiles of N2 in addition to its related hydrocarbon
derivatives. Constraints from UVIS on temperature profiles of the upper
atmosphere are also examined and compared to current results from the Ion
and Neutral Mass Spectrometer (INMS), which probes a region above 1000
km altitude in Titan’s atmosphere (Westlake et al. 2011).
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Shemansky, D. E., et al.: “The Cassini UVIS stellar probe of the Titan
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