Chemistry of Titan's atmosphere

doi:10.1017/CBO9780511667398.010

7 - Chemistry of Titan's atmosphere

Published online by Cambridge University Press: 05 January 2014

V. Vuitton ,

O. Dutuit ,

M. A. Smith and

N. Balucani

Edited by

Ingo Müller-Wodarg ,

Caitlin A. Griffith ,

Emmanuel Lellouch and

Thomas E. Cravens

Show author details

V. Vuitton: Affiliation:
CNRS & Université Joseph Fourier
O. Dutuit: Affiliation:
CNRS & Université Joseph Fourier
M. A. Smith: Affiliation:
University of Houston
N. Balucani: Affiliation:
Universitá degli Studi di Perugia
Ingo Müller-Wodarg: Affiliation:
Imperial College London
Caitlin A. Griffith: Affiliation:
University of Arizona
Emmanuel Lellouch: Affiliation:
Observatoire de Paris, Meudon
Thomas E. Cravens: Affiliation:
University of Kansas

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Summary

7.1 Introduction

Understanding Titan's atmospheric chemistry is a daunting task because of the multiplicity of chemical as well as physical processes involved. Chemical processes begin with the dissociation and/or ionization of the most abundant species, N2 and CH4, by a variety of energy sources. The energetic species produced further react to generate a plethora of gaseous molecules that will eventually become heavy enough to become organic aerosols. Thus, molecular growth is driven by gas phase reactions involving radicals and positive and negative ions, all possibly in some excited electronic state, as well as by heterogenous chemistry on the surface of the aerosols. The efficiency and outcome of these reactions depend strongly on the physical characteristics of the atmosphere, namely pressure and temperature. Moreover, the distribution of the species is affected by molecular diffusion and vertical and horizontal winds, as well as escape from the top of the atmosphere and condensation in the lower stratosphere. An illustration of Titan's atmospheric chemistry is presented in Figure 7.1.

Our interest in Titan's chemistry started in the 1970s, when it became apparent that the atmospheric CH4-to-H2 ratio was much larger than that in the atmospheres of the giant planets, rendering Titan's atmosphere better suited for the synthesis of organic compounds. However, ground-based observations indicated that CH4 was the principal atmospheric constituent and, because of this, the photochemical models of Allen et al. (1980) and Strobel (1974) were restricted to hydrocarbon chemistry.

Type: Chapter
Information: Titan
Interior, Surface, Atmosphere, and Space Environment
, pp. 224 - 284

DOI: https://doi.org/10.1017/CBO9780511667398.010 [Opens in a new window]

Publisher: Cambridge University Press

Print publication year: 2014

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