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5 - The composition of Titan's atmosphere

Published online by Cambridge University Press:  05 January 2014

By
B. Bézard ,
R. V. Yelle  and
C. A. Nixon
Edited by
Ingo Müller-Wodarg ,
Caitlin A. Griffith ,
Emmanuel Lellouch  and
Thomas E. Cravens
B. Bézard
Affiliation:
LESIA, Observatoire de Paris, Section de Meudon
R. V. Yelle
Affiliation:
University of Arizona
C. A. Nixon
Affiliation:
University of Martland
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

5.1 Introduction

Titan's atmosphere harbors a suite of hydrocarbons and nitrogen-bearing compounds formed from the dissociation of the two main species, nitrogen (N2)and methane (CH4). It also contains oxygen compounds, likely produced from an influx of water and/or oxygen. The mixing ratios of these photochemical species vary with altitude, latitude, and time as a consequence of various chemical sources and sinks and of the atmospheric transport that redistributes them both vertically and horizontally. It is important to characterize and monitor the distribution of these chemical species because they play an important role in the radiative budget and provide insight into the seasonally varying atmospheric circulation. They can also help us understand the complex chemistry at work in Titan's atmosphere, leading to the formation of thick haze layers, which in turn affect the heat balance and general circulation. This chapter reviews the neutral composition of Titan's atmosphere, from the troposphere up to the thermosphere (~ 1400 km), and its vertical, horizontal, and temporal variations. These topics are interwoven with the origin and evolution, the general circulation, the clouds and weather, and the atmospheric chemistry of Titan that are the subjects of Chapters 1, 4, 6, and 7.

5.1.1 Historical perspective

The first unquestionable evidence for an atmosphere on Titan was the discovery of several absorption bands of methane in near-infrared spectra of the satellite (Kuiper, 1944). But it was not until the 1970s that Titan became an object of intense study.

Type
Chapter
Information
Titan
Interior, Surface, Atmosphere, and Space Environment
 , pp. 158 - 189
Publisher: Cambridge University Press
Print publication year: 2014

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