Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p33e1807n&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P33E-1807
Mathematics
Logic
[0343] Atmospheric Composition And Structure / Planetary Atmospheres, [5405] Planetary Sciences: Solid Surface Planets / Atmospheres, [5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [6281] Planetary Sciences: Solar System Objects / Titan
Scientific paper
Methane is the second most abundant gas in Titan's chemically reducing atmosphere, with mole fractions of ~1.48% and ~5.65% in the stratosphere and troposphere respectively. Methane loss is continuous, occurring through photolysis, chemical reactions and escape, and models predict that the entire atmospheric inventory will be lost on a timescale of 10-100 Myr: much shorter than the age of the solar system. Therefore, a significant and ongoing controversy concerns the origin and stability of the atmospheric methane, and the nature of any resupply reservoir that may exist. Stable isotopic ratios - those of non-radiogenic isotopes - may provide clues into the origin and evolution of planetary atmospheres. For example, the elevated 15N in Titan's majority gas N2 (~1.5x terrestrial) has been taken as evidence for substantial loss of N2 over geologic time (2-10x present amount), favoring retention of the heavier 15N14N. In methane, two isotopic ratios - D/H and 12C/13C - may be measured in the hope of comparing these to probable formation/reservoir values, and to make subsequent inferences about its history. We present new measurements of these ratios from infrared spectroscopy using the Cassini Composite Infrared Spectrometer (CIRS), yielding: 12C/13C = 86 ± 8, and D/H = (1.59 ± 0.26)x10-4. These values are indistinguishable from terrestrial (89 and 1.56x10-4 respectively), and may indicate a quite different, more recent history for Titan's CH4 compared to N2. Possible scenarios and implications for the atmospheric formation, evolution and fate will be discussed.
Achterberg Richard K.
Bezard Bruno
Coustenis Athena
Flasar Michael F.
Irwin Patrick G.
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