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Re-analysis of the Cassini RPWS/LP data in Titan’s ionosphere. Part II: statistics on 57 flybys.
  • +5
  • Audrey Chatain,
  • Jan-Erik Wahlund,
  • Oleg Shebanits,
  • Lina HADID,
  • Michiko W. Morooka,
  • Niklas J. T. Edberg,
  • Olivier Guaitella,
  • Nathalie Carrasco
Audrey Chatain
Université Paris-Saclay/LATMOS

Corresponding Author:[email protected]

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Jan-Erik Wahlund
Swedish Institute of Space Physics (IRF)
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Oleg Shebanits
Imperial College London
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Lina HADID
Ecole polytechnique/LPP
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Michiko W. Morooka
Swedish Institute of Space Physics
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Niklas J. T. Edberg
Swedish Institute of Space Physics
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Olivier Guaitella
Ecole polytechnique/LPP
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Nathalie Carrasco
Université Paris-Saclay/LATMOS
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Abstract

The ionosphere of Titan hosts a complex ion chemistry leading to the formation of organic dust below 1200 km. Current models cannot explain the observed electron temperature in this dusty environment. To get new clues, we re-analyzed the data taken in the ionosphere of Titan by the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave Science (RPWS) package. A first paper (Chatain et al., n.d.) introduces the new analysis method and discusses the detection of 4 different electron populations. In this second paper, we present a statistical study of the whole LP dataset below 1200 km and gives clues on the origin of the 4 populations. One small population is attributed to photo- or secondary electrons emitted from the surface of the probe boom. A second population is systematically observed, at a globally constant density (~500 cm), and is attributed to background thermalized electrons. The two last populations increase in density with pressure, solar illumination and extreme UV flux. The third population is observed with varying densities at all altitudes (at least up to 1400 km) and solar zenith angles except on the far nightside (SZA > ~140°), with a maximum density of 2700 cm. It is therefore certainly related to photo-ionization and its subsequent active ion chemistry. Finally, a fourth population detected only on the dayside and below 1200 km reaching up to 2000 cm could be photo- or thermo-emitted from dust grains.