EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

On the effective recombination coefficient in Saturn's ionosphere

Joshua Dreyer1,2, Erik Vigren1, Michiko Morooka1, Jan-Erik Wahlund1, Stephan Buchert1, and J. Hunter Waite3
Joshua Dreyer et al.
  • 1Swedish Institute of Space Physics, Space Plasma Physics, Uppsala, Sweden (
  • 2Uppsala University, Department of Physics and Astronomy, Uppsala, Sweden
  • 3Southwest Research Institute, Space Science and Engineering Division, San Antonio, USA

The present study combines RPWS/LP and INMS data from Cassini's orbit 292, which reached an altitude of 1685 km at the lowest point, to constrain the effective recombination coefficient α300 from measured densities and electron temperatures at a reference electron temperature of 300 K. Assuming photochemical equilibrium at these low altitudes and linking established methods to calculate the electron production rate and the dissociative recombination rate results in a formula to calculate an upper limit for α300. This is then compared against rate constants of individual recombination reactions as measured in the laboratory.
We derive upper limits for α300 of ∼ 2.5∗10-7cm3 s-1, which suggest that Saturn's ionospheric positive ions are dominated by species with low recombination rate coefficients. An ionosphere dominated by water group ions or complex hydrocarbons, as previously suggested, is incompatible with this result, as these species have recombination rate constants > 5∗10-7 cm3 s-1 at an electron temperature of 300 K. The results do not give constraints on the nature of the negative ions.

How to cite: Dreyer, J., Vigren, E., Morooka, M., Wahlund, J.-E., Buchert, S., and Waite, J. H.: On the effective recombination coefficient in Saturn's ionosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9813,, 2020

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