Analysis of Titan's neutral upper atmosphere from Cassini Ion Neutral Mass Spectrometer measurements

Cui, Jun; Yelle, R. V.; Vuitton, V.; Waite, J. H.; Kasprzak, W. T.; Gell, D. A.; Niemann, H. B.; Müller‐Wodarg, I. C. F.; Borggren, N.; Fletcher, Greg; Patrick, E. L.; Raaen, E.; Magee, B.

doi:10.1016/j.icarus.2008.12.005

Cited by 296 publications

(425 citation statements)

References 65 publications

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“…Thus, when using the combination of 40 Ar and 14 N/ 15 N to constrain the eddy diffusion coefficient, we find that model A (high-methane homopause simulation) is superior to both models B and model B (HE). Section 4.2 also reproduces and explains the results obtained by Yelle et al [2008], Cui et al [2009], andStrobel [2012]. These earlier studies maintain that the methane homopause is near 880 km, which is obtained by matching the blue data points in Figure 2c.…”

Section: Discussionsupporting

confidence: 80%

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

et al. 2014

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In this study, we develop a best fit description of Titan's upper atmosphere between 500 km and 1500 km, using a one‐dimensional (1‐D) version of the three‐dimensional (3‐D) Titan Global Ionosphere‐Thermosphere Model. For this modeling, we use constraints from several lower atmospheric Cassini‐Huygens investigations and validate our simulation results against in situ Cassini Ion‐Neutral Mass Spectrometer (INMS) measurements of N2, CH4, H2, 40Ar, HCN, and the major stable isotopic ratios of 14N/15N in N2. We focus our investigation on aspects of Titan's upper atmosphere that determine the amount of atmospheric escape required to match the INMS measurements: the amount of turbulence, the inclusion of chemistry, and the effects of including a self‐consistent thermal balance. We systematically examine both hydrodynamic escape scenarios for methane and scenarios with significantly reduced atmospheric escape. Our results show that the optimum configuration of Titan's upper atmosphere is one with a methane homopause near 1000 km and atmospheric escape rates of 1.41–1.47 ×1011 CH4 m−2 s−1 and 1.08 ×1014 H2 m−2 s−1 (scaled relative to the surface). We also demonstrate that simulations consistent with hydrodynamic escape of methane systematically produce inferior fits to the multiple validation points presented here.

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Section: Discussionsupporting

confidence: 80%

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

et al. 2014

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“…All numerical models adapting such HCCN loss chemical schemes predict 10-100 times larger C 4 N 2 abundance than C 2 N 2 around 1,000 km altitudes (13)(14)(15)17). Such preponderance of C 4 N 2 is not observed from the Cassini INMS observations (3,4), implying other chemical pathways for the HCCN radical. One possible channel might be the reactions of HCCN radical with H and CH 3 (29) ( Table 1).…”

Section: Resultsmentioning

confidence: 92%

“…This observation clearly demonstrated the importance of complex organic chemistry in the upper atmosphere induced by extreme ultraviolet (EUV)-vacuum ultraviolet (VUV) photons and Saturn's magnetospheric electrons. The INMS data show the prominent existence of unsaturated hydrocarbons in the gas phase (1,3,4). Although the nitrogenous compounds are definitely suggested as significant components (5), bulk nitrogen fixation in Titan's atmosphere is not well constrained at present (6).…”

mentioning

confidence: 98%

Formation of nitrogenated organic aerosols in the Titan upper atmosphere

Imanaka

Smith

2010

Proc. Natl. Acad. Sci. U.S.A.

105

107

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Many aspects of the nitrogen fixation process by photochemistry in the Titan atmosphere are not fully understood. The recent Cassini mission revealed organic aerosol formation in the upper atmosphere of Titan. It is not clear, however, how much and by what mechanism nitrogen is incorporated in Titan's organic aerosols. Using tunable synchrotron radiation at the Advanced Light Source, we demonstrate the first evidence of nitrogenated organic aerosol production by extreme ultraviolet-vacuum ultraviolet irradiation of a N 2 ∕CH 4 gas mixture. The ultrahigh-mass-resolution study with laser desorption ionization-Fourier transform-ion cyclotron resonance mass spectrometry of N 2 ∕CH 4 photolytic solid products at 60 and 82.5 nm indicates the predominance of highly nitrogenated compounds. The distinct nitrogen incorporations at the elemental abundances of H 2 C 2 N and HCN, respectively, are suggestive of important roles of H 2 C 2 N∕HCCN and HCN∕CN in their formation. The efficient formation of unsaturated hydrocarbons is observed in the gas phase without abundant nitrogenated neutrals at 60 nm, and this is confirmed by separately using 13 C and 15 N isotopically labeled initial gas mixtures. These observations strongly suggest a heterogeneous incorporation mechanism via short lived nitrogenated reactive species, such as HCCN radical, for nitrogenated organic aerosol formation, and imply that substantial amounts of nitrogen is fixed as organic macromolecular aerosols in Titan's atmosphere.

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“…18 This situation renders interpretation of data collected by the Cassini Ion and Neutral Mass Spectrometer (INMS) more difficult for larger masses. 50 In that respect, both kinetic and product detection studies, with isomeric specificity, are central to the identification of chemical pathways and determination of branching fractions in order to assess their relative importance to the formation of higher molecular weight species.…”

Section: Possible Implications For Titan and Combustion Chemistrymentioning

confidence: 99%

Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

Soorkia

Taatjes

Osborn

et al. 2010

Phys. Chem. Chem. Phys.

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Analysis of Titan's neutral upper atmosphere from Cassini Ion Neutral Mass Spectrometer measurements

Cited by 296 publications

References 65 publications

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

Formation of nitrogenated organic aerosols in the Titan upper atmosphere

Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

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