On the thermal electron balance in Titan's sunlit upper atmosphere

E. Vigren, M. Galand, Roger Yelle, J. Cui, J. E. Wahlund, K. Ågren, P. P. Lavvas, I. C F Mueller-Wodarg, D. F. Strobel, V. Vuitton, A. Bazin

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

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 1200km. In this paper we focus on the T40, T41, T42 and T48 Titan flybys by the Cassini spacecraft and use in situ measurements of N2 and CH4 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 30.38nm). 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 1200km (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.

Original languageEnglish (US)
Pages (from-to)234-251
Number of pages18
JournalIcarus
Volume223
Issue number1
DOIs
StatePublished - Mar 2013

Fingerprint

Titan
upper atmosphere
electron
recombination
electrons
recombination coefficient
electrostatic probes
Cassini mission
ion
ion recombination
probe
solar energy
estimates
in situ measurement
molecular ions
optical thickness
free electrons
mass spectrometers
ionospheres
spacecraft

Keywords

  • Atmospheres, Chemistry
  • Ionospheres
  • Titan

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Vigren, E., Galand, M., Yelle, R., Cui, J., Wahlund, J. E., Ågren, K., ... Bazin, A. (2013). On the thermal electron balance in Titan's sunlit upper atmosphere. Icarus, 223(1), 234-251. https://doi.org/10.1016/j.icarus.2012.12.010

On the thermal electron balance in Titan's sunlit upper atmosphere. / Vigren, E.; Galand, M.; Yelle, Roger; Cui, J.; Wahlund, J. E.; Ågren, K.; Lavvas, P. P.; Mueller-Wodarg, I. C F; Strobel, D. F.; Vuitton, V.; Bazin, A.

In: Icarus, Vol. 223, No. 1, 03.2013, p. 234-251.

Research output: Contribution to journalArticle

Vigren, E, Galand, M, Yelle, R, Cui, J, Wahlund, JE, Ågren, K, Lavvas, PP, Mueller-Wodarg, ICF, Strobel, DF, Vuitton, V & Bazin, A 2013, 'On the thermal electron balance in Titan's sunlit upper atmosphere', Icarus, vol. 223, no. 1, pp. 234-251. https://doi.org/10.1016/j.icarus.2012.12.010
Vigren E, Galand M, Yelle R, Cui J, Wahlund JE, Ågren K et al. On the thermal electron balance in Titan's sunlit upper atmosphere. Icarus. 2013 Mar;223(1):234-251. https://doi.org/10.1016/j.icarus.2012.12.010
Vigren, E. ; Galand, M. ; Yelle, Roger ; Cui, J. ; Wahlund, J. E. ; Ågren, K. ; Lavvas, P. P. ; Mueller-Wodarg, I. C F ; Strobel, D. F. ; Vuitton, V. ; Bazin, A. / On the thermal electron balance in Titan's sunlit upper atmosphere. In: Icarus. 2013 ; Vol. 223, No. 1. pp. 234-251.
@article{5ba36003c13741ddaa9bffd40340d0dc,
title = "On the thermal electron balance in Titan's sunlit upper atmosphere",
abstract = "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 1200km. In this paper we focus on the T40, T41, T42 and T48 Titan flybys by the Cassini spacecraft and use in situ measurements of N2 and CH4 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 30.38nm). 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 1200km (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.",
keywords = "Atmospheres, Chemistry, Ionospheres, Titan",
author = "E. Vigren and M. Galand and Roger Yelle and J. Cui and Wahlund, {J. E.} and K. {\AA}gren and Lavvas, {P. P.} and Mueller-Wodarg, {I. C F} and Strobel, {D. F.} and V. Vuitton and A. Bazin",
year = "2013",
month = "3",
doi = "10.1016/j.icarus.2012.12.010",
language = "English (US)",
volume = "223",
pages = "234--251",
journal = "Icarus",
issn = "0019-1035",
publisher = "Academic Press Inc.",
number = "1",

}

TY - JOUR

T1 - On the thermal electron balance in Titan's sunlit upper atmosphere

AU - Vigren, E.

AU - Galand, M.

AU - Yelle, Roger

AU - Cui, J.

AU - Wahlund, J. E.

AU - Ågren, K.

AU - Lavvas, P. P.

AU - Mueller-Wodarg, I. C F

AU - Strobel, D. F.

AU - Vuitton, V.

AU - Bazin, A.

PY - 2013/3

Y1 - 2013/3

N2 - 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 1200km. In this paper we focus on the T40, T41, T42 and T48 Titan flybys by the Cassini spacecraft and use in situ measurements of N2 and CH4 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 30.38nm). 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 1200km (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.

AB - 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 1200km. In this paper we focus on the T40, T41, T42 and T48 Titan flybys by the Cassini spacecraft and use in situ measurements of N2 and CH4 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 30.38nm). 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 1200km (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.

KW - Atmospheres, Chemistry

KW - Ionospheres

KW - Titan

UR - http://www.scopus.com/inward/record.url?scp=84872254753&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84872254753&partnerID=8YFLogxK

U2 - 10.1016/j.icarus.2012.12.010

DO - 10.1016/j.icarus.2012.12.010

M3 - Article

AN - SCOPUS:84872254753

VL - 223

SP - 234

EP - 251

JO - Icarus

JF - Icarus

SN - 0019-1035

IS - 1

ER -