Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010apj...708..342a&link_type=abstract
The Astrophysical Journal, Volume 708, Issue 1, pp. 342-353 (2010).
Astronomy and Astrophysics
Astronomy
4
Molecular Data, Planetary Nebulae: Individual: Saturn, Planets And Satellites: Individual: Saturn Titan
Scientific paper
The Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft, launched in 1997 October and inserted into Saturn's orbit in 2004 July for exploration of the Saturnian system, has been making observations of Titan during its close flybys. The infrared spectra of Titan observed over a wide range of latitudes cover the 10-1400 cm-1 spectral region with variable apodized resolutions from 0.53 to 15 cm-1. The spectra exhibit features of the ν4 band of methane (CH4) in the 1300 cm-1 region, and the deuterated isotope of methane (CH3D) centered around 1156 cm-1, along with features of many trace constituents in other spectral regions, comprising hydrocarbons and nitriles in Titan's atmosphere. An analysis of the observed infrared spectra in the 1300 cm-1 and 1156 cm-1 regions, respectively, permits retrieval of the thermal structure and the CH3D distributions of Titan's atmosphere. In this paper, we present a comprehensive analysis of the CIRS infrared spectra for retrieval of the CH3D abundance and the corresponding D/H ratio in Titan's atmosphere. The analysis is based on the 0.53 cm-1 resolution infrared spectra obtained during the Titan flybys from 2004 July 3 to 2008 May 28 over a range of latitudes extending from 74fdg4 N to 84fdg9 S. Using the CH4 mixing ratio of 1.4 × 10-2 as measured by the Gas Chromatograph and Mass Spectrometer on the Huygens probe on the Cassini mission, we determine the D/H ratio of Titan as (1.58 ± 0.16) × 10-4, where the 1σ uncertainty includes the standard deviation due to spectral noise and the estimated errors arising from uncertainties in the temperature retrieval, the mixing ratio of CH4, and the spectral line parameters. Comparison of this value with the previously measured values for Titan as well as in other astrophysical sources, and its possible implications are discussed.
Abbas Merza
Achterberg Richard K.
Bjoraker Gordon
Brasunas J.
Carlson Robert
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