12C/13C ratio in ethane on titan and implications for methane's replenishment.
The (12)C/(13)C abundance ratio in ethane in the atmosphere of Titan has been measured at 822 cm(-1) from high spectral resolution ground-based observations. The value, 89(8), coincides with the telluric standard and also agrees with the ratio seen in the outer planets. It is almost identical to the result for ethane on Titan found by the composite infrared spectrometer (CIRS) on Cassini. The (12)C/(13)C ratio for ethane is higher than the ratio measured in atmospheric methane by Cassini/Huygens GCMS, 82.3(1), representing an enrichment of (12)C in the ethane that might be explained by a kinetic isotope effect of approximately 1.1 in the formation of methyl radicals. If methane is being continuously resupplied to balance photochemical destruction, then we expect the isotopic composition in the ethane product to equilibrate at close to the same (12)C/(13)C ratio as that in the supply. The telluric value of the ratio in ethane then implies that the methane reservoir is primordial.
Jennings
Donald E
DE
NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA. donald.e.jennings@nasa.gov
Romani
Paul N
PN
Bjoraker
Gordon L
GL
Sada
Pedro V
PV
Nixon
Conor A
CA
Lunsford
Allen W
AW
Boyle
Robert J
RJ
Hesman
Brigette E
BE
McCabe
George H
GH