Isotopic Ratios in Titan's Atmosphere from Cassini CIRS Limb Sounding: CO 2 at Low and Midlatitudes

Abstract

This Letter reports on a search for infrared emissions of isotopologues of CO 2 in the atmosphere of Titan using spectral data recorded by the Cassini Composite Infrared Spectrometer (CIRS). We have made a successful 6.5 σ detection of 13 CO 2 at a fraction CO 2 / 13 CO 2 = 84 ± 17, consistent with measurements of 12 C/ 13 C in other species, and also the terrestrial value (89). We also And a probable 3.5 σ detection of C 16 O 18 O at a fraction CO 2 / C 16 O 18 O = 173 ± 55, slightly lower than the terrestrial value (253) and consistent with the twofold enhancement in 18 O reported previously in CO, or with an intermediate value as suggested by chemistry. These isotopic ratios provide important constraints on models of the formation, evolution, and current processes in Titan's atmosphere. © 2008, The American Astronomical Society, All rights reserved.