Methane escape from Titan's atmosphere

Measurements of the mole fractions of CH4 and 40Ar by the Ion Neutral Mass Spectrometer on the Cassini orbiter are analyzed to determine the rate of vertical mixing in Titan's atmosphere and the escape flux of CH4. Analysis of the 40Ar data indicates an eddy mixing rate of 2–5 × 107 cm2 s−1, an...

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Bibliographic Details
Published in:Journal of Geophysical Research: Planets 2008-10, Vol.113 (E10), p.n/a
Main Authors: Yelle, R. V., Cui, J., Müller-Wodarg, I. C. F.
Format: Article
Language:English
Subjects:
aeronomy
atmospheres
Earth sciences
Earth, ocean, space
escape
Exact sciences and technology
Titan
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Summary:Measurements of the mole fractions of CH4 and 40Ar by the Ion Neutral Mass Spectrometer on the Cassini orbiter are analyzed to determine the rate of vertical mixing in Titan's atmosphere and the escape flux of CH4. Analysis of the 40Ar data indicates an eddy mixing rate of 2–5 × 107 cm2 s−1, an order of magnitude smaller than previously determined from analysis of the CH4 distribution. The eddy profile determined from the 40Ar data implies that CH4 distribution is best explained by postulating that it is escaping the atmosphere at the diffusion limited rate of 2.5–3.0 × 109 cm−2 s−1, referred to the surface. This represents a significant loss of atmospheric CH4, smaller than but comparable to the photochemical destruction rate. The escape rate is much larger than predicted by the Jeans escape formula and vigorous nonthermal mechanisms are not apparent.
ISSN:0148-0227
2156-2202
DOI:10.1029/2007JE003031