Energy deposition and primary chemical products in Titan's upper atmosphere

P. Lavvas, M. Galand, R. V. Yelle, A. N. Heays, B. R. Lewis, G. R. Lewis, A. J. Coates

Research output: Contribution to journalArticle

89 Scopus citations

Abstract

Cassini results indicate that solar photons dominate energy deposition in Titan's upper atmosphere. These dissociate and ionize nitrogen and methane and drive the subsequent complex organic chemistry. The improved constraints on the atmospheric composition from Cassini measurements demand greater precision in the photochemical modeling. Therefore, in order to quantify the role of solar radiation in the primary chemical production, we have performed detailed calculations for the energy deposition of photons and photoelectrons in the atmosphere of Titan and we validate our results with the Cassini measurements for the electron fluxes and the EUV/FUV emissions. We use high-resolution cross sections for the neutral photodissociation of N2, which we present here, and show that they provide a different picture of energy deposition compared to results based on low-resolution cross sections. Furthermore, we introduce a simple model for the energy degradation of photoelectrons based on the local deposition approximation and show that our results are in agreement with detailed calculations including transport, in the altitude region below 1200km, where the effects of transport are negligible. Our calculated, daytime, electron fluxes are in good agreement with the measured fluxes by the Cassini Plasma Spectrometer (CAPS), and the same holds for the measured FUV emissions by the Ultraviolet Imaging Spectrometer (UVIS). Finally, we present the vertical production profiles of radicals and ions originating from the interaction of photons and electrons with the main components of Titan's atmosphere, along with the column integrated production rates at different solar zenith angles. These can be used as basis for any further photochemical calculations.

Original languageEnglish (US)
Pages (from-to)233-251
Number of pages19
JournalIcarus
Volume213
Issue number1
DOIs
StatePublished - May 1 2011

Keywords

  • Photochemistry
  • Titan

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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    Lavvas, P., Galand, M., Yelle, R. V., Heays, A. N., Lewis, B. R., Lewis, G. R., & Coates, A. J. (2011). Energy deposition and primary chemical products in Titan's upper atmosphere. Icarus, 213(1), 233-251. https://doi.org/10.1016/j.icarus.2011.03.001