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[22.05] Cassini-CIRS Observations of Ethylene and Propyne in the Southern Hemisphere of Titan

P. N. Romani, D. E. Jennings, G. L. Bjoraker (NASA - GSFC), C. Nixon (University of Maryland), N. Stone (SP Systems Inc. - Cornell University), CIRS Team

Shortly after Saturn orbit insertion on 1 July 2004 the Cassini spacecraft flew by Titan. The viewing geometry effectively confined observations to that of the southern hemisphere. The Composite Infrared Spectrometer (CIRS) made maps of this hemisphere at 3.0 cm^-1 spectral resolution.

We used these maps to look for latitudinal gradients in ethylene (C₂H₄) and propyne (C₃H₄, a.k.a. methyl acetylene). Both of these species are destroyed by UV sunlight and ethylene is a source for propyne via the CH + C₂H₄ reaction. Observations were binned into 10 degree wide latitude bins, spaced 5 degrees apart, and ranging from 80 S to 5 S. The emission angle ranged from 30 to 60 degrees. Initial analysis based upon line to continuum ratios shows no latitudinal gradient in these species in the range covered. This is in contrast to Roe et al. 2003 (Icarus 169, 440-461) who from Keck images taken in 1999-2002 found a significant accumulation of C₂H₄ confined south of 50 S. Implications for photochemical modeling and lifetimes will be discussed.

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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.