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On the Discovery of CO Nighttime Emissions on Titan by Cassini/VIMS: Derived Stratospheric Abundances and Geological ImplicationsWe present a quantitative analysis of CO thermal emissions discovered on the nightside of Titan by Baines et al. [2005. The atmospheres of Saturn and Titan in the near-infrared: First results of Cassini/VIMS. Earth, Moon, and Planets, 96, 119-147] in Cassini/VIMS spectral imagery. We identify these emission features as the P and R branches of the 1-0 vibrational band of carbon monoxide (CO) near 4.65 microns. For CH3D, the prominent Q branch of the nu(2) fundamental band of CH3D near 4.55 microns is apparent. CO2 emissions from the strong nu(3) vibrational band are virtually absent, indicating a CO2 abundance several orders of magnitude less than CO, in agreement with previous investigations. Analysis of CO emission spectra obtained over a variety of altitudes on Titan's nightside limb indicates that the stratospheric abundance of CO is 32 +/- 15 ppm, and together with other recent determinations, suggests a vertical distribution of CO nearly constant at this value from the surface throughout the troposphere to at least the stratopause near 300 km altitude. The corresponding total atmospheric content of CO in Titan is similar to 2.9 +/- 1.5 x 10(exp 14) kg. Given the long lifetime of CO in the oxygen-poor Titan atmosphere (similar to 0.5-1.0 Gyr), we find a mean CO atmospheric production rate of 6 +/- 3 x 10(exp 5) kg yr(exp -1). Given the lack of primordial heavy noble gases observed by Huygens [Niemann et al., 2005. The abundances of constituents of Titan's atmosphere from the GCMS on the Huygens probe. Nature, 438, 779-784], the primary source of atmospheric CO is likely surface emissions. The implied CO/CH4 mixing ratio of near-surface material is 1.8 +/- 0.9 x 10(exp -4), based on an average methane surface emission rate over the past 0.5 Gyr of 1.3 x 10(exp -13) gm cm(exp -2) s(exp -1) as required to balance hydrocarbon haze production via methane photolysis [Wilson and Atreya, 2004. Current state of modeling the photochemistry of Titan's mutually dependent atmosphere and ionosphere. J. Geophys. Res. 109, E06002 Doi: 10.1029/2003JE002181]. This low CO/CH4 ratio is much lower than expected for the sub-nebular formation region of Titan and supports the hypothesis [e.g., Atreya et al., 2005. Methane on Titan: photochemical-meteorological-hydrogeochemical cycle. Bull. Am. Astron. Soc. 37, 735] that the conversion of primordial CO and other carbon-bearing materials into CH4-enriched clathrate-hydrates occurs within the deep interior of Titan via the release of hydrogen through the serpentinization process followed by Fischer-Tropsch catalysis. The time-averaged predicted emission rate of methane-rich surface materials is approximately 0.02 km(exp 3) yr (exp -1), a value significantly lower than the rate of silicate lava production for the Earth and Venus, but nonetheless indicative of significant geological processes reshaping the surface of Titan.
Document ID
Document Type
Reprint (Version printed in journal)
Bainesa, Kevin H. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Drossart, Pierre (Centre National de la Recherche Scientifique Meudon, France)
Lopez-Valverde, Miguel A. (Instituto de Astrofisica de Andalucia Granada, Spain)
Atreya, Sushil K. (Michigan Univ. Ann Arbor, MI, United States)
Sotin, Christophe (Nantes Univ. France)
Momary, Thomas W. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Brown, Robert H. (Arizona Univ. Tucson, AZ, United States)
Buratti, Bonnie J. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Clark, Roger N. (Geological Survey Denver, CO, United States)
Nicholson, Philip D. (Cornell Univ. Ithaca, NY, United States)
Date Acquired
August 24, 2013
Publication Date
December 1, 2006
Publication Information
Publication: Planetary and Space Science
Volume: Vo 54
Issue: 15
Subject Category
Lunar and Planetary Science and Exploration
Distribution Limits
carbon compounds
planetary atmospheres
astronomical spectra
organic compounds
planetary satellites