insu-03617350
https://insu.hal.science/insu-03617350
doi:10.1016/j.icarus.2012.12.010
[INSU] INSU - Institut National des Sciences de l'Univers
[UNIV-SAVOIE] Université Savoie Mont Blanc
[UGA] HAL Grenoble Alpes
[CNRS] CNRS - Centre national de la recherche scientifique
[UNIV-GRENOBLE1] Université Joseph Fourier - Grenoble I
[URCA] Publications de l'Université de Reims Champagne-Ardenne
[INPG] Institut polytechnique de Grenoble
[IRSTEA] IRSTEA - Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (<b>anciennement Cemagref</b>)
[CNES] CNES - Centre national d'études spatiales
[OSUG] Observatoire des Sciences de la Terre, de l'Univers et de l'Environnement de Grenoble
[IPAG] Institut de Planétologie et d'Astrophysique de Grenoble
[AGREENIUM] Archive ouverte en agrobiosciences
[GSMA] Groupe de spectrométrie moléculaire et atmosphérique - UMR 7331
[INRAE] Institut National de Recherche en Agriculture, Alimentation et Environnement
[USMB-COMUE] Université Savoie Mont Blanc - UGA [* - 2019]
On the thermal electron balance in Titan’s sunlit upper atmosphere
Vigren, E.
Galand, M.
Yelle, R. V.
Cui, J.
Wahlund, J. -E.
Ågren, K.
Lavvas, P. P.
Mueller-Wodarg, I. C. F.
Strobel, D. F.
Vuitton, V.
Bazin, A.
[SDU] Sciences of the Universe [physics]
ART
The Cassini mission has investigated Titan’s upper atmosphere in detail and found that, under solar irradiation, it has a well-developed ionosphere, which peaks between 1000 and 1200 km. In this paper we focus on the T40, T41, T42 and T48 Titan flybys by the Cassini spacecraft and use in situ measurements of N<SUB>2</SUB> and CH<SUB>4</SUB> densities by the Ion Neutral Mass Spectrometer (INMS) as input into a solar energy deposition model to determine electron production rates. We combine these electron production rates with estimates of the effective recombination coefficient based on available laboratory data for Titan ions’ dissociative recombination rates and electron temperatures derived from the Langmuir probe (LP) to predict electron number densities in Titan’s upper atmosphere, assuming photochemical equilibrium and loss of electrons exclusively through dissociative recombination with molecular ions. We then compare these predicted electron number densities with those observed in Titan’s upper atmosphere by the LP. The assumption of photochemical equilibrium is supported by a reasonable agreement between the altitudes where the electron densities are observed to peak and where the electron production rates are calculated to peak (roughly corresponding to the unit optical depth for HeII photons at 30.38 nm). We find, however, that the predicted electron number densities are nearly a factor of two higher than those observed throughout the altitude range between 1050 and 1200 km (where we have made estimates of the effective recombination coefficient). There are different possible reasons for this discrepancy; one possibility is that there may be important loss processes of free electrons other than dissociative recombination in Titan’s upper atmosphere.
2013
en
Icarus
Elsevier