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Suprathermal Electrons In Titan's Sunlit Ionosphere: Model-Observation Comparisons
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
Imperial Coll London, Dept Phys, London SW7 2AZ, England..
Univ Coll London, Mullard Space Sci Lab, Dorking RH5 6NT, Surrey, England..
Univ Coll London, Mullard Space Sci Lab, Dorking RH5 6NT, Surrey, England..
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2016 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 826, no 2, 131Article in journal (Refereed) Published
Abstract [en]

The dayside ionosphere of the Saturnian satellite Titan is generated mainly from photoionization of N-2 and CH4. We compare model-derived suprathermal electron intensities with spectra measured by the Cassini Plasma Spectrometer/Electron Spectrometer (CAPS/ELS) in Titan's sunlit ionosphere (altitudes of 970-1250 km) focusing on the T40, T41, T42, and T48 Titan flybys by the Cassini spacecraft. The model accounts only for photoelectrons and associated secondary electrons, with a main input being the impinging solar EUV spectra as measured by the Thermosphere Ionosphere Mesosphere Energy and Dynamics/Solar EUV Experiment and extrapolated to Saturn. Associated electron-impact electron production rates have been derived from ambient number densities of N-2 and CH4 (measured by the Ion Neutral Mass Spectrometer/Closed Source Neutral mode) and related energy-dependent electron-impact ionization cross sections. When integrating up to electron energies of 60 eV, covering the bulk of the photoelectrons, the model-based values exceed the observationally based values typically by factors of similar to 3 +/- 1. This finding is possibly related to current difficulties in accurately reproducing the observed electron number densities in Titan's dayside ionosphere. We compare the utilized dayside CAPS/ELS spectra with ones measured in Titan's nightside ionosphere during the T55-T59 flybys. The investigated nightside locations were associated with higher fluxes of high-energy (>100 eV) electrons than the dayside locations. As expected, for similar neutral number densities, electrons with energies <60 eV give a higher relative contribution to the total electron-impact ionization rates on the dayside (due to the contribution from photoelectrons) than on the nightside.

Place, publisher, year, edition, pages
2016. Vol. 826, no 2, 131
Keyword [en]
molecular processes, planets and satellites: individual (Titan)
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-304230DOI: 10.3847/0004-637X/826/2/131ISI: 000381977900031OAI: oai:DiVA.org:uu-304230DiVA: diva2:1039466
Funder
Swedish National Space Board, DNR 14/166Swedish Research Council
Available from: 2016-10-24 Created: 2016-10-03 Last updated: 2016-10-24Bibliographically approved

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Vigren, ErikEdberg, Niklas J. T.Wahlund, Jan-Erik
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