Cassini Ion and Neutral Mass Spectrometer data in Titan's upper atmosphere and exosphere: Observation of a suprathermal corona

V. De La Haye, J. H. Waite, R. E. Johnson, Roger Yelle, T. E. Cravens, J. G. Luhmann, W. T. Kasprzak, D. A. Gell, B. Magee, F. Leblanc, M. Michael, S. Jurac, I. P. Robertson

Research output: Contribution to journalArticle

70 Citations (Scopus)

Abstract

The neutral nitrogen and methane measurements made by Ion and Neutral Mass Spectrometer during Cassini flybys TA, TB, and T 5 in Titan's upper atmosphere and exosphere are presented. Large horizontal variations are observed in the total density, recorded to be twice as large during TA as during T5. Comparison between the atmospheric and exospheric data show evidence for the presence of a significant population of suprathermal molecules. Using a diffusion model to simultaneously fit the N2 and CH4 density profiles below 1500 km, the atmospheric structure parameters are determined, taking into account recent changes in the calibration parameters. The best fits are obtained for isothermal profiles with values 152.8 ± 4.6 K for TA, 149.0 ± 9.2 K for TB, and 157.4 ± 4.9 K for T5, suggesting a temperature ≃5 K warmer at night than at dusk, a trend opposite to that determined by solar-driven models. Using standard exospheric theory and a Maxwellian exobase distribution, a temperature of 20 to 70 K higher would be necessary to fit the TA, TB, and egress-T5 data above 1500 km. The suprathermal component of the corona was fit with various exobase energy distributions, using a method based on the Liouville theorem. This gave a density of suprathermals at the exobase of 4.4 ± 5.1 × 105 cm-3 and 1.1 ± 0.9 × 105 cm-3, and an energy deposition rate at the exobase of 1.1 ± 0.9 × 102 eV cm-3 s_1 and 3.9 ± 3.5 × 101 eV cm-3 s-1 for the hot N 2 and CH4 populations, respectively. The energy deposition rate allowed us to roughly estimate escape rates for nitrogen of ≃7.7 ± 7.1 × 107 N cm-2 s_1 and for methane of ≃ 2.8 ± 2.1 × 107 CH4 cm -2 s-1. Interestingly, no suprathermal component was observed in the ingress-T5 data.

Original languageEnglish (US)
Article numberA07309
JournalJournal of Geophysical Research: Space Physics
Volume112
Issue number7
DOIs
StatePublished - Jul 1 2007

Fingerprint

exosphere
Upper atmosphere
Titan
Methane
upper atmosphere
Mass spectrometers
Deposition rates
coronas
mass spectrometers
corona
Atmospheric structure
spectrometer
Nitrogen
Ions
ion
methane
Liouville theorem
egress
energy
atmospheric structure

ASJC Scopus subject areas

  • Geophysics
  • Space and Planetary Science

Cite this

Cassini Ion and Neutral Mass Spectrometer data in Titan's upper atmosphere and exosphere : Observation of a suprathermal corona. / De La Haye, V.; Waite, J. H.; Johnson, R. E.; Yelle, Roger; Cravens, T. E.; Luhmann, J. G.; Kasprzak, W. T.; Gell, D. A.; Magee, B.; Leblanc, F.; Michael, M.; Jurac, S.; Robertson, I. P.

In: Journal of Geophysical Research: Space Physics, Vol. 112, No. 7, A07309, 01.07.2007.

Research output: Contribution to journalArticle

De La Haye, V, Waite, JH, Johnson, RE, Yelle, R, Cravens, TE, Luhmann, JG, Kasprzak, WT, Gell, DA, Magee, B, Leblanc, F, Michael, M, Jurac, S & Robertson, IP 2007, 'Cassini Ion and Neutral Mass Spectrometer data in Titan's upper atmosphere and exosphere: Observation of a suprathermal corona', Journal of Geophysical Research: Space Physics, vol. 112, no. 7, A07309. https://doi.org/10.1029/2006JA012222
De La Haye, V. ; Waite, J. H. ; Johnson, R. E. ; Yelle, Roger ; Cravens, T. E. ; Luhmann, J. G. ; Kasprzak, W. T. ; Gell, D. A. ; Magee, B. ; Leblanc, F. ; Michael, M. ; Jurac, S. ; Robertson, I. P. / Cassini Ion and Neutral Mass Spectrometer data in Titan's upper atmosphere and exosphere : Observation of a suprathermal corona. In: Journal of Geophysical Research: Space Physics. 2007 ; Vol. 112, No. 7.
@article{21bf059437a048e293df14fc3c324f51,
title = "Cassini Ion and Neutral Mass Spectrometer data in Titan's upper atmosphere and exosphere: Observation of a suprathermal corona",
abstract = "The neutral nitrogen and methane measurements made by Ion and Neutral Mass Spectrometer during Cassini flybys TA, TB, and T 5 in Titan's upper atmosphere and exosphere are presented. Large horizontal variations are observed in the total density, recorded to be twice as large during TA as during T5. Comparison between the atmospheric and exospheric data show evidence for the presence of a significant population of suprathermal molecules. Using a diffusion model to simultaneously fit the N2 and CH4 density profiles below 1500 km, the atmospheric structure parameters are determined, taking into account recent changes in the calibration parameters. The best fits are obtained for isothermal profiles with values 152.8 ± 4.6 K for TA, 149.0 ± 9.2 K for TB, and 157.4 ± 4.9 K for T5, suggesting a temperature ≃5 K warmer at night than at dusk, a trend opposite to that determined by solar-driven models. Using standard exospheric theory and a Maxwellian exobase distribution, a temperature of 20 to 70 K higher would be necessary to fit the TA, TB, and egress-T5 data above 1500 km. The suprathermal component of the corona was fit with various exobase energy distributions, using a method based on the Liouville theorem. This gave a density of suprathermals at the exobase of 4.4 ± 5.1 × 105 cm-3 and 1.1 ± 0.9 × 105 cm-3, and an energy deposition rate at the exobase of 1.1 ± 0.9 × 102 eV cm-3 s_1 and 3.9 ± 3.5 × 101 eV cm-3 s-1 for the hot N 2 and CH4 populations, respectively. The energy deposition rate allowed us to roughly estimate escape rates for nitrogen of ≃7.7 ± 7.1 × 107 N cm-2 s_1 and for methane of ≃ 2.8 ± 2.1 × 107 CH4 cm -2 s-1. Interestingly, no suprathermal component was observed in the ingress-T5 data.",
author = "{De La Haye}, V. and Waite, {J. H.} and Johnson, {R. E.} and Roger Yelle and Cravens, {T. E.} and Luhmann, {J. G.} and Kasprzak, {W. T.} and Gell, {D. A.} and B. Magee and F. Leblanc and M. Michael and S. Jurac and Robertson, {I. P.}",
year = "2007",
month = "7",
day = "1",
doi = "10.1029/2006JA012222",
language = "English (US)",
volume = "112",
journal = "Journal of Geophysical Research: Space Physics",
issn = "2169-9380",
publisher = "Wiley-Blackwell",
number = "7",

}

TY - JOUR

T1 - Cassini Ion and Neutral Mass Spectrometer data in Titan's upper atmosphere and exosphere

T2 - Observation of a suprathermal corona

AU - De La Haye, V.

AU - Waite, J. H.

AU - Johnson, R. E.

AU - Yelle, Roger

AU - Cravens, T. E.

AU - Luhmann, J. G.

AU - Kasprzak, W. T.

AU - Gell, D. A.

AU - Magee, B.

AU - Leblanc, F.

AU - Michael, M.

AU - Jurac, S.

AU - Robertson, I. P.

PY - 2007/7/1

Y1 - 2007/7/1

N2 - The neutral nitrogen and methane measurements made by Ion and Neutral Mass Spectrometer during Cassini flybys TA, TB, and T 5 in Titan's upper atmosphere and exosphere are presented. Large horizontal variations are observed in the total density, recorded to be twice as large during TA as during T5. Comparison between the atmospheric and exospheric data show evidence for the presence of a significant population of suprathermal molecules. Using a diffusion model to simultaneously fit the N2 and CH4 density profiles below 1500 km, the atmospheric structure parameters are determined, taking into account recent changes in the calibration parameters. The best fits are obtained for isothermal profiles with values 152.8 ± 4.6 K for TA, 149.0 ± 9.2 K for TB, and 157.4 ± 4.9 K for T5, suggesting a temperature ≃5 K warmer at night than at dusk, a trend opposite to that determined by solar-driven models. Using standard exospheric theory and a Maxwellian exobase distribution, a temperature of 20 to 70 K higher would be necessary to fit the TA, TB, and egress-T5 data above 1500 km. The suprathermal component of the corona was fit with various exobase energy distributions, using a method based on the Liouville theorem. This gave a density of suprathermals at the exobase of 4.4 ± 5.1 × 105 cm-3 and 1.1 ± 0.9 × 105 cm-3, and an energy deposition rate at the exobase of 1.1 ± 0.9 × 102 eV cm-3 s_1 and 3.9 ± 3.5 × 101 eV cm-3 s-1 for the hot N 2 and CH4 populations, respectively. The energy deposition rate allowed us to roughly estimate escape rates for nitrogen of ≃7.7 ± 7.1 × 107 N cm-2 s_1 and for methane of ≃ 2.8 ± 2.1 × 107 CH4 cm -2 s-1. Interestingly, no suprathermal component was observed in the ingress-T5 data.

AB - The neutral nitrogen and methane measurements made by Ion and Neutral Mass Spectrometer during Cassini flybys TA, TB, and T 5 in Titan's upper atmosphere and exosphere are presented. Large horizontal variations are observed in the total density, recorded to be twice as large during TA as during T5. Comparison between the atmospheric and exospheric data show evidence for the presence of a significant population of suprathermal molecules. Using a diffusion model to simultaneously fit the N2 and CH4 density profiles below 1500 km, the atmospheric structure parameters are determined, taking into account recent changes in the calibration parameters. The best fits are obtained for isothermal profiles with values 152.8 ± 4.6 K for TA, 149.0 ± 9.2 K for TB, and 157.4 ± 4.9 K for T5, suggesting a temperature ≃5 K warmer at night than at dusk, a trend opposite to that determined by solar-driven models. Using standard exospheric theory and a Maxwellian exobase distribution, a temperature of 20 to 70 K higher would be necessary to fit the TA, TB, and egress-T5 data above 1500 km. The suprathermal component of the corona was fit with various exobase energy distributions, using a method based on the Liouville theorem. This gave a density of suprathermals at the exobase of 4.4 ± 5.1 × 105 cm-3 and 1.1 ± 0.9 × 105 cm-3, and an energy deposition rate at the exobase of 1.1 ± 0.9 × 102 eV cm-3 s_1 and 3.9 ± 3.5 × 101 eV cm-3 s-1 for the hot N 2 and CH4 populations, respectively. The energy deposition rate allowed us to roughly estimate escape rates for nitrogen of ≃7.7 ± 7.1 × 107 N cm-2 s_1 and for methane of ≃ 2.8 ± 2.1 × 107 CH4 cm -2 s-1. Interestingly, no suprathermal component was observed in the ingress-T5 data.

UR - http://www.scopus.com/inward/record.url?scp=34548595645&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=34548595645&partnerID=8YFLogxK

U2 - 10.1029/2006JA012222

DO - 10.1029/2006JA012222

M3 - Article

AN - SCOPUS:34548595645

VL - 112

JO - Journal of Geophysical Research: Space Physics

JF - Journal of Geophysical Research: Space Physics

SN - 2169-9380

IS - 7

M1 - A07309

ER -