The Role of Nitrogen in Titan’s Upper Atmospheric Hydrocarbon Chemistry Over the Solar Cycle

Luspay‐Kuti, A.; Mandt, K.; Westlake, J. H.; Plessis, S.; Greathouse, Thomas

doi:10.3847/0004-637x/823/2/163

Cited by 6 publications

(2 citation statements)

References 36 publications

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“…This general trend is the same as observed by Luspay-Kuti et al (2016), although their very small CH 3 abundance ratio above 1000 km in their Figure 1 does not seem realistic to us, especially looking at their C 2 H 6 profile. CH 3 plays a lead role in the photochemistry of Titan's upper atmosphere, and is especially important for the production of C 2 H 6 and HCN (R n 90, R n 290b).…”

Section: Lifetimessupporting

confidence: 69%

Simulating the density of organic species in the atmosphere of Titan with a coupled ion-neutral photochemical model

Vuitton

Yelle

Klippenstein

et al. 2019

Icarus

172

362

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We present a one-dimensional coupled ion-neutral photochemical kinetics and diffusion model to study the atmospheric composition of Titan in light of new theoretical kinetics calculations and scientific findings from the Cassini-Huygens mission. The model extends from the surface to the exobase. The atmospheric background, boundary conditions, vertical transport and aerosol opacity are all constrained by the Cassini-Huygens observations. The chemical network includes reactions between hydrocarbons, nitrogen and oxygen bearing species. It takes into account neutrals and both positive and negative ions with masses extending up to about 100 u. We incorporate high-resolution isotopic photoabsorption and photodissociation cross sections for N 2 as well as new photodissociation branching ratios for CH 4 and C 2 H 2 . Ab initio transition state theory calculations are performed in order to estimate the rate coefficients and products for critical reactions.Main reactions of production and loss for neutrals and ions are quantitatively assessed and thoroughly discussed. The vertical distributions of neutrals and ions predicted by the model generally reproduce observational data, suggesting that for the small species most chemical processes in Titan's atmosphere and ionosphere are adequately described and understood; some differences are highlighted. Notable remaining issues include (i) the total positive ion density (essentially HCNH + ) in the upper ionosphere, (ii) the low mass negative ion densities (CN -, C 3 N -/C 4 H -) in the upper atmosphere, and (iii) the minor oxygen-bearing species (CO 2 , H 2 O) density in the stratosphere. Pathways towards complex molecules and the impact of aerosols (UV shielding, atomic and molecular hydrogen budget, nitriles heterogeneous chemistry and condensation) are evaluated in the model, along with lifetimes and solar cycle variations.

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Section: Lifetimessupporting

confidence: 69%

Simulating the density of organic species in the atmosphere of Titan with a coupled ion-neutral photochemical model

Vuitton

Yelle

Klippenstein

et al. 2019

Icarus

172

362

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“…The solar minimum simulation is constrained by Cassini observations made during solar minimum conditions. For solar moderate and maximum conditions the only parameter that was changed was the solar flux to isolate the influence of a changing photon flux on the chemistry(Luspay-Kuti et al 2016).…”

mentioning

confidence: 99%

Photochemistry on Pluto: part II HCN and nitrogen isotope fractionation

Mandt

Luspay‐Kuti

Hamel

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We have converted our Titan one-dimensional photochemical model to simulate the photochemistry of Pluto's atmosphere and include condensation and aerosol trapping in the model. We find that condensation and aerosol trapping are important processes in producing the HCN altitude profile observed by the Atacama Large Millimeter Array (ALMA). The nitrogen iso-tope chemistry in Pluto's atmosphere does not appear to significantly fractionate the isotope ratio between N 2 and HCN as occurs at Titan. However, our simulations only cover a brief period of time in a Pluto year, and thus only a brief portion of the solar forcing conditions that Pluto's atmosphere experiences. More work is needed to evaluate photochemical fractionation over a Pluto year. Condensation and aerosol trapping appear to have a major impact on the altitude profile of the isotope ratio in HCN. Since ALMA did not detect HC 15 N in Pluto's atmosphere, we conclude that condensation and aerosol trapping must be much more efficient for HC 15 N compared to HC 14 N. The large uncertainty in photochemical fractionation makes it difficult to use any potential current measurement of 14 N/ 15 N in N 2 to determine the origin of Pluto's nitrogen. More work is needed to understand photochemical fractionation and to evaluate how condensation, sublimation and aerosol trapping will fractionate N 2 and HCN.

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Methyl Radical (CH3)

Irvine¹

2019

Encyclopedia of Astrobiology

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The Role of Nitrogen in Titan’s Upper Atmospheric Hydrocarbon Chemistry Over the Solar Cycle

Cited by 6 publications

References 36 publications

Simulating the density of organic species in the atmosphere of Titan with a coupled ion-neutral photochemical model

Simulating the density of organic species in the atmosphere of Titan with a coupled ion-neutral photochemical model

Photochemistry on Pluto: part II HCN and nitrogen isotope fractionation

Methyl Radical (CH3)

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