Model-data comparisons for Titan's nightside ionosphere

Cravens, T. E.; Robertson, I. P.; Waite, J. H.; Yelle, R. V.; Vuitton, V.; Coates, A. J.; Wahlund, J. E.; Ågren, Karin; Richard, M. S.; Haye, V. de La; Wellbrock, A.; Neubauer, F. M.

doi:10.1016/j.icarus.2008.09.005

Cited by 112 publications

(152 citation statements)

References 63 publications

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Section: The Electron Precipitation Sourcementioning

confidence: 99%

“…1 was taken from the measurements of the T5 fly-by (Cravens et al 2009). It was measured by the Cassini electron spectrometer (CAPS ELS) (Coates et al 2007;Cravens et al 2009) from 0.6 eV to 28.250 keV (Young et al 2004). These electrons come from the magnetosphere of Saturn and are embedded in the magnetic field draped around Titan (Modolo & Chanteur 2008;Cravens et al 2009).…”

Section: The Electron Precipitation Sourcementioning

confidence: 99%

“…It was measured by the Cassini electron spectrometer (CAPS ELS) (Coates et al 2007;Cravens et al 2009) from 0.6 eV to 28.250 keV (Young et al 2004). These electrons come from the magnetosphere of Saturn and are embedded in the magnetic field draped around Titan (Modolo & Chanteur 2008;Cravens et al 2009). In Cravens et al (2009), the electron spectrum measured at 2700 km had to be divided by a factor of 10 to have the model fit the measurement correctly at an altitude of 1200 km.…”

Section: The Electron Precipitation Sourcementioning

confidence: 99%

“…The electron impact has been studied in Agren et al (2007), and re-analyzed in Cravens et al (2008Cravens et al ( , 2009, with an updated precipitation flux (used in this work). In order to fit the flux measurements at 1200 km with the model using a precipitation flux measured at 2730 km, the authors had to divide by 10 the input flux.…”

Section: Comparison With Other Modelsmentioning

confidence: 99%

“…Each source has a main ionization altitude that creates several ionosphere layers above 50 km (Cravens et al 2008(Cravens et al , 2009Hamelin et al 2007;López-Moreno et al 2008, and references therein). While Titan can be inside or outside of the Saturn's magnetosphere, particle precipitation, hence ionization can be very variable depending on the position of the satellite and local plasma conditions.…”

Section: Introductionmentioning

confidence: 99%

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Ionization processes in the atmosphere of Titan

Gronoff¹,

Lilensten²,

Desorgher

et al. 2009

A&A

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Context. The Cassini probe regularly passes in the vicinity of Titan, revealing new insights into particle precipitation thanks to the electron and proton spectrometer. Moreover, the Huygens probe has revealed an ionized layer at 65 km induced by cosmic rays. The impact of these different particles on the chemistry of Titan is probably very strong. Aims. In this article, we compute the whole ionization in the atmosphere of Titan: from the cosmic rays near the ground to the EUV in the upper atmosphere. The meteoritic layer is not taken into account. Methods. We used the transTitan model to compute the electron and EUV impact, and the planetocosmics code to compute the influence of protons and oxygen ions. We coupled the two models to study the influence of the secondary electrons obtained by planetocosmics through the transTitan code. The resulting model improves the accuracy of the calculation through the transport of electrons in the atmosphere. Results. The whole ionization is computed and studied in details. During the day, the cosmic ray ionization peak is as strong as the UV-EUV one. Electrons and protons are very important depending the precipitation conditions. Protons can create a layer at 500 km, while electrons tend to ionize near 800 km. The oxygen ion impact is near 900 km. The results shows few differences to precedent models for the nightside T5 fly-by of Cassini, and can highlight the sources of the different ion layers detected by radio measurements. Conclusions. The new model successfully computes the ion production in the atmosphere of Titan. For the first time, a full electron and ion profile has been computed from 0 to 1600 km, which compares qualitatively with measurements. This result can be used by chemical models.

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Section: The Electron Precipitation Sourcementioning

confidence: 99%

Section: The Electron Precipitation Sourcementioning

confidence: 99%

Section: The Electron Precipitation Sourcementioning

confidence: 99%

Section: Comparison With Other Modelsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ionization processes in the atmosphere of Titan

Gronoff¹,

Lilensten²,

Desorgher

et al. 2009

A&A

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An empirical approach to modeling ion production rates in Titan's ionosphere I: Ion production rates on the dayside and globally

et al. 2015

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Titan's ionosphere is created when solar photons, energetic magnetospheric electrons or ions, and cosmic rays ionize the neutral atmosphere. Electron densities generated by current theoretical models are much larger than densities measured by instruments on board the Cassini orbiter. This model density overabundance must result either from overproduction or from insufficient loss of ions. This is the first of two papers that examines ion production rates in Titan's ionosphere, for the dayside and nightside ionosphere, respectively. The first (current) paper focuses on dayside ion production rates which are computed using solar ionization sources (photoionization and electron impact ionization by photoelectrons) between 1000 and 1400 km. In addition to theoretical ion production rates, empirical ion production rates are derived from CH 4 , CH 3 + , and CH 4 + densities measured by the INMS (Ion Neutral Mass Spectrometer) for many Titan passes.The modeled and empirical production rate profiles from measured densities of N 2 + and CH 4 + are found to be in good agreement (to within 20%) for solar zenith angles between 15 and 90°. This suggests that the overabundance of electrons in theoretical models of Titan's dayside ionosphere is not due to overproduction but to insufficient ion losses.

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The role of ion‐molecule reactions in the growth of heavy ions in Titan's ionosphere

et al. 2014

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The Ion and Neutral Mass Spectrometer (INMS) and Cassini Plasma Spectrometer (CAPS) have observed Titan's ionospheric composition and structure over several targeted flybys. In this work we study the altitude profiles of the heavy ion population observed by the Cassini Plasma Spectrometer-Ion Beam Spectrometer (CAPS-IBS) during the nightside T57 flyby. We produce altitude profiles of heavy ions from the C6-C13 group (C i indicates the number, i, of heavy atoms in the molecule) using a CAPS-IBS/INMS cross calibration. These altitude profiles reveal structure that indicates a region of initial formation and growth at altitudes below 1200 km followed by a stagnation and dropoff at the lowest altitudes (1050 km). We suggest that an ion-molecule reaction pathway could be responsible for the production of the heavy ions, namely reactions that utilize abundant building blocks such as C 2 H 2 and C 2 H 4 , which have been shown to be energetically favorable and that have already been identified as ion growth patterns for the lighter ions detected by the INMS. We contrast this growth scenario with alternative growth scenarios determining the implications for the densities of the source heavy neutrals in each scenario. We show that the high-mass ion density profiles are consistent with ion-molecule reactions as the primary mechanism for large ion growth. We derive a production rate for benzene from electron recombination of C 6 H 7 + of 2.4 × 10 À16 g cm À2 s À1and a total production rate for large molecules of 7.1 × 10 À16 g cm À2 s À1 .

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Model-data comparisons for Titan's nightside ionosphere

Cited by 112 publications

References 63 publications

Ionization processes in the atmosphere of Titan

Ionization processes in the atmosphere of Titan

An empirical approach to modeling ion production rates in Titan's ionosphere I: Ion production rates on the dayside and globally

The role of ion‐molecule reactions in the growth of heavy ions in Titan's ionosphere

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