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Title: Increasing positive ion number densities below the peak of ion-electron pair production in Titan's ionosphere

We combine derived ion-electron pair formation rates with Cassini Radio Plasma Wave Science Langmuir Probe measurements of electron and positive ion number densities in Titan's sunlit ionosphere. We show that positive ion number densities in Titan's sunlit ionosphere can increase toward significantly lower altitudes than the peak of ion-electron pair formation despite that the effective ion-electron recombination coefficient increases. This is explained by the increased mixing ratios of negative ions, which are formed by electron attachment to neutrals. While such a process acts as a sink for free electrons, the positive ions become longer-lived as the rate coefficients for ion-anion neutralization reactions are smaller than those for ion-electron dissociative recombination reactions.
Authors:
;  [1] ; ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom)
  2. Swedish Institute of Space Physics, P.O. Box 537, SE-751 21 Uppsala (Sweden)
  3. Department of Physics, Stockholm University, SE-10691 Stockholm (Sweden)
  4. Groupe de Spectrométrie Moléculaire et Atmosphérique, Université Reims Champagne-Ardenne, UMR 7331, F-51687 Reims (France)
  5. Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), UJF-Grenoble/CNRS-INSU, UMR 5274, F-38041 Grenoble (France)
  6. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721-0092 (United States)
Publication Date:
OSTI Identifier:
22357002
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 786; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANIONS; DENSITY; ELECTRON ATTACHMENT; ELECTRON PAIRS; ELECTRONS; IONOSPHERE; LANGMUIR PROBE; MIXING RATIO; PLANETS; PLASMA WAVES; RECOMBINATION; SATELLITES