Vigren, E;
Galand, M;
Wellbrock, A;
Coates, AJ;
Cui, J;
Edberg, NJT;
Lavvas, P;
... Wahlund, JE; + view all
(2016)
Suprathermal electrons in Titan's sunlit ionosphere: Model-observation comparisons.
The Astrophysical Journal
, 826
(2)
, Article 131. 10.3847/0004-637X/826/2/131.
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Abstract
The dayside ionosphere of the Saturnian satellite Titan is generated mainly from photoionization of N2 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 N2 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 ∼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.
| Type: | Article |
|---|---|
| Title: | Suprathermal electrons in Titan's sunlit ionosphere: Model-observation comparisons |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.3847/0004-637X/826/2/131 |
| Publisher version: | http://doi.org/10.3847/0004-637X/826/2/131 |
| Language: | English |
| Additional information: | © 2016. The American Astronomical Society. All rights reserved. |
| Keywords: | Science & Technology, Physical Sciences, Astronomy & Astrophysics, molecular processes, planets and satellites: individual (Titan), PHOTOIONIZATION CROSS-SECTIONS, UPPER-ATMOSPHERE, SPECTROMETER, IONIZATION, DENSITIES, MOLECULES, BALANCE |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery.ucl.ac.uk/id/eprint/1513956 |
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