Methane and its isotopologues on Saturn from Cassini/CIRS observations
High spectral resolution observations from the Cassini Composite Infrared Spectrometer [Flasar, F.M., and 44 colleagues, 2004. Space Sci. Rev. 115, 169-297] are analysed to derive new estimates for the mole fractions of CH4, CH3D and 13CH4 of (4.7 ± 0.2) × 10-3, (3.0 ± 0.2) × 10-7 and (5.1 ± 0.2) ×...
| Main Authors: | , , , , |
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| Format: | Journal article |
| Language: | English |
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2009
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| _version_ | 1797099699685031936 |
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| author | Fletcher, L Orton, G Teanby, N Irwin, P Bjoraker, G |
| author_facet | Fletcher, L Orton, G Teanby, N Irwin, P Bjoraker, G |
| author_sort | Fletcher, L |
| collection | OXFORD |
| description | High spectral resolution observations from the Cassini Composite Infrared Spectrometer [Flasar, F.M., and 44 colleagues, 2004. Space Sci. Rev. 115, 169-297] are analysed to derive new estimates for the mole fractions of CH4, CH3D and 13CH4 of (4.7 ± 0.2) × 10-3, (3.0 ± 0.2) × 10-7 and (5.1 ± 0.2) × 10-5 respectively. The mole fractions show no hemispherical asymmetries or latitudinal variability. The analysis combines data from the far-IR methane rotational lines and the mid-IR features of methane and its isotopologues, using both the correlated-k retrieval algorithm of Irwin et al. [Irwin, P., and 9 colleagues, 2008. J. Quant. Spectrosc. Radiat. Trans. 109, 1136-1150] and a line-by-line approach to evaluate the reliability of the retrieved quantities. C/H was found to be enhanced by 10.9 ± 0.5 times the solar composition of Grevesse et al. [Grevesse, N., Asplund, M., Sauval, A., 2007. Space Sci. Rev. 130 (1), 105-114], 2.25 ± 0.55 times larger than the enrichment on Jupiter, and supporting the increasing fractional core mass with distance from the Sun predicted by the core accretion model of planetary formation. A comparison of the jovian and saturnian C/N, C/S and C/P ratios suggests different reservoirs of the trapped volatiles in a primordial solar nebula whose composition varies with distance from the Sun. This is supported by our derived D/H ratio in methane of (1.6 ± 0.2) × 10-5, which appears to be smaller than the jovian value of Lellouch et al. [Lellouch, E., Bézard, B., Fouchet, T., Feuchtgruber, H., Encrenaz, T., de Graauw, T., 2001. Astron. Astrophys. 370, 610-622]. Mid-IR emission features provided an estimate of 12C / 13C = 91.8-7.8+8.4, which is consistent with both the terrestrial ratio and jovian ratio, suggesting that carbon was accreted from a shared reservoir for all of the planets. © 2008 Elsevier Inc. |
| first_indexed | 2024-03-07T05:27:19Z |
| format | Journal article |
| id | oxford-uuid:e1019bf7-47a3-4aba-bf2f-c43250c7317e |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T05:27:19Z |
| publishDate | 2009 |
| record_format | dspace |
| spelling | oxford-uuid:e1019bf7-47a3-4aba-bf2f-c43250c7317e2022-03-27T09:51:19ZMethane and its isotopologues on Saturn from Cassini/CIRS observationsJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:e1019bf7-47a3-4aba-bf2f-c43250c7317eEnglishSymplectic Elements at Oxford2009Fletcher, LOrton, GTeanby, NIrwin, PBjoraker, GHigh spectral resolution observations from the Cassini Composite Infrared Spectrometer [Flasar, F.M., and 44 colleagues, 2004. Space Sci. Rev. 115, 169-297] are analysed to derive new estimates for the mole fractions of CH4, CH3D and 13CH4 of (4.7 ± 0.2) × 10-3, (3.0 ± 0.2) × 10-7 and (5.1 ± 0.2) × 10-5 respectively. The mole fractions show no hemispherical asymmetries or latitudinal variability. The analysis combines data from the far-IR methane rotational lines and the mid-IR features of methane and its isotopologues, using both the correlated-k retrieval algorithm of Irwin et al. [Irwin, P., and 9 colleagues, 2008. J. Quant. Spectrosc. Radiat. Trans. 109, 1136-1150] and a line-by-line approach to evaluate the reliability of the retrieved quantities. C/H was found to be enhanced by 10.9 ± 0.5 times the solar composition of Grevesse et al. [Grevesse, N., Asplund, M., Sauval, A., 2007. Space Sci. Rev. 130 (1), 105-114], 2.25 ± 0.55 times larger than the enrichment on Jupiter, and supporting the increasing fractional core mass with distance from the Sun predicted by the core accretion model of planetary formation. A comparison of the jovian and saturnian C/N, C/S and C/P ratios suggests different reservoirs of the trapped volatiles in a primordial solar nebula whose composition varies with distance from the Sun. This is supported by our derived D/H ratio in methane of (1.6 ± 0.2) × 10-5, which appears to be smaller than the jovian value of Lellouch et al. [Lellouch, E., Bézard, B., Fouchet, T., Feuchtgruber, H., Encrenaz, T., de Graauw, T., 2001. Astron. Astrophys. 370, 610-622]. Mid-IR emission features provided an estimate of 12C / 13C = 91.8-7.8+8.4, which is consistent with both the terrestrial ratio and jovian ratio, suggesting that carbon was accreted from a shared reservoir for all of the planets. © 2008 Elsevier Inc. |
| spellingShingle | Fletcher, L Orton, G Teanby, N Irwin, P Bjoraker, G Methane and its isotopologues on Saturn from Cassini/CIRS observations |
| title | Methane and its isotopologues on Saturn from Cassini/CIRS observations |
| title_full | Methane and its isotopologues on Saturn from Cassini/CIRS observations |
| title_fullStr | Methane and its isotopologues on Saturn from Cassini/CIRS observations |
| title_full_unstemmed | Methane and its isotopologues on Saturn from Cassini/CIRS observations |
| title_short | Methane and its isotopologues on Saturn from Cassini/CIRS observations |
| title_sort | methane and its isotopologues on saturn from cassini cirs observations |
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