36th DPS Meeting, 8-12 November 2004
Session 20 Titan
Poster I, Tuesday, November 9, 2004, 4:00-7:00pm, Exhibition Hall 1A

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[20.12] On Titan's Primordial Atmospheric Evolution

E.Y. Adams, S.K. Atreya, W.R. Kuhn (U. Michigan, USA)

Atreya et al. (Science, 201, 611, 1978) demonstrated that photolysis of ammonia on primordial Titan is capable of producing a nitrogen atmosphere substantially thicker than that measured by Voyager. E. Wilson (thesis, U. Michigan, 2002) carried this calculation one step further by including methane and water vapor explicitly in the ammonia photochemistry model, and arrived at a preliminary estimate of time required to accumulate different amounts of nitrogen on Titan. However, neither model considered possible thermal structure of primordial Titan. Since chemistry leading to nitrogen production occurs in the stratosphere, both the thermal structure and saturation effects are important for determining the time constants and amounts of nitrogen production. In this presentation, we discuss preliminary results of a radiative equilibrium model for the primordial middle and lower atmosphere of Titan, which includes H2O, CH4 and NH3 in solar proportion for its initial composition. Furthermore, we explore the effects of enhanced UV solar flux during the solar T- Tauri phase, which would accelerate the conversion of ammonia to nitrogen, but could also speed up the loss of nitrogen. We are in the process of coupling the radiative transfer model to a comprehensive photochemical model (Wilson and Atreya, JGR, 109, E06003, 2004) to assess the role of trace species other than the three starting molecules in the primordial atmosphere.

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