On the amount of heavy molecular ions in Titan's ionosphere

J. E. Wahlund, M. Galand, I. Müller-Wodarg, J. Cui, R. V. Yelle, F. J. Crary, K. Mandt, B. Magee, J. H. Waite, D. T. Young, A. J. Coates, P. Garnier, K. Ågren, M. André, A. I. Eriksson, T. E. Cravens, V. Vuitton, D. A. Gurnett, W. S. Kurth

Research output: Contribution to journalArticlepeer-review

69 Scopus citations


We present observational evidence that the ionosphere of Titan below an altitude of 1150 km is a significant source of heavy (>100 amu) molecular organic species. This study is based on measurements by five instruments (RPWS/LP, RPWS/E, INMS, CAPS/ELS, CAPS/IBS) onboard the Cassini spacecraft during three flybys (T17, T18, T32) of Titan. The ionospheric peaks encountered at altitudes of 950-1300 km had densities in the range 900-3000 cm-3. Below these peaks the number densities of heavy positively charged ions reached 100-2000 cm-3 and approached 50-70% of the total ionospheric density with an increasing trend toward lowest measured altitudes. Simultaneously measured negatively charged ion densities were in the range 50-150 cm-3. These results imply that ~105-106 heavy positively charged ions/m3/s are continuously recombining into heavy neutrals and supply the atmosphere of Titan. The ionosphere may in this way produce 0.1-1 Mt/yr of heavy organic compounds and is therefore a sizable source for aerosol formation. We also predict that Titan's ionosphere is dominated by heavy (>100 amu) molecular ions below 950 km.

Original languageEnglish (US)
Pages (from-to)1857-1865
Number of pages9
JournalPlanetary and Space Science
Issue number14-15
StatePublished - Dec 2009


  • Aerosol formation
  • Cassini
  • Heavy molecular ions
  • Ionospheric physics
  • Titan aeronomy
  • Titan's ionosphere

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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