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Search for spatial variation in the jovian N/N ratio from Cassini/CIRS observations |
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| Authors: | Thierry Fouchet Patrick GJ Irwin Simon B Calcutt Conor A Nixon |
| Institution: | a AOPP, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK b LESIA, Observatoire de Paris, 5, place Jules Janssen, 92195 Meudon cedex, France c University of Maryland, College Park, MD 20742, USA d Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, HI 96822, USA |
| Abstract: | We have used the spectra obtained by the Composite Infrared Spectrometer (CIRS) onboard the Cassini spacecraft to search for latitudinal variation in the 15N/14N ratio on Jupiter. We found no variations statistically significant given the observational and model uncertainties. The absence of latitudinal variations demonstrates that 15NH3 is not fractionated in Jupiter's atmosphere, and that the measured 15N/14N represents Jupiter's global value. Our mean value for the global jovian 15N/14N ratio of (2.22±0.52)×10−3 agrees with previous measurements made by Fouchet et al. (2000, Icarus 143, 223-243) and Owen et al. (2001, Astrophys. J. 553, L77-L79). We argue that the jovian isotopic 15N/14N ratio must represent the solar nitrogen isotopic composition. The solar 15N/14N ratio hence significantly differs from the terrestrial value: (15N/14N)⊕=3.68×10−3. This supports the proposition that terrestrial nitrogen originates from a nitrogen reservoir isolated from the main nitrogen reservoir in the proto-solar nebula. The origin and carrier of this isolated reservoir are still unknown. |
| Keywords: | Abundances atmospheres Atmospheres composition Jupiter atmosphere |
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