Ionization processes in the atmosphere of Titan

Abstract

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.

CRITICAL REVIEW OF N, N + , N + 2 , N ++ , And N ++ 2 MAIN PRODUCTION PROCESSES AND REACTIONS OF RELEVANCE TO TITAN'S ATMOSPHERE

“…However at low altitudes, termolecular chemistry can occur with ions formed by galactic cosmic rays (Gronoff et al 2009a(Gronoff et al , 2009b(Gronoff et al , 2011Molina-Cuberos et al 1999). Anicich & McEwan (Anicich & McEwan 2001;Anicich et al 2000;Milligan et al 2001) studied experimentally termolecular ion-molecule reactions of the main ions of Titan's atmosphere.…”

Solar energetic particle interactions with the Venusian atmosphere

“…The Geant4-based ATMOCOSMICS code , usually combined with MAGNE-TOCOSMICS, simulates the interaction of cosmic rays with the Earth's atmosphere, allowing the computation of the flux of secondaries at different atmospheric depths and/or altitudes. PLANETOCOSMICS is a more evolved code with respect to MAGNETOCOSMICS and ATMOCOSMICS, extensively applied in the field of planetary cosmic ray studies, including Mars (Gronoff et al, 2015;Ehresmann et al, 2011;Gurtner et al, 2005), Mercury (Gurtner et al, 2006), Venus Dartnell et al, 2015) and Titan (Gronoff et al (2009a(Gronoff et al ( , b, 2011. The recently developed DYASTIMA code includes many of the same features considered in PLANETOCOSMICS (e.g input of a custom atmospheric description, detection of primary and secondary fluxes and directions at given altitudes, user-defined primary cosmic ray spectra).…”

Ionization processes in the atmosphere of Titan

“…In our previous paper (Gronoff et al 2009a, Paper I), we computed the ionization due to pure proton cosmic rays with the Planetocosmic model. The computed peak, at 65 km altitude, was consistent with the observations.…”