Titan airglow spectra from the Cassini Ultraviolet Imaging Spectrograph: FUV disk analysis

[en] We present a spectral analysis of the far ultraviolet (FUV: 1150–1900 A ° ) disk airglow observations of Titan’s atmosphere by the Cassini Ultraviolet Imaging Spectrograph (UVIS). The FUV spectrum consists of emissions from the Lyman-Birge-Hopfield (LBH) band system of N2 excited by photoelectrons (a 1Pg ! X 1Sg+), N I multiplets from solar photodissociative excitation of N2, resonantly scattered solar H Ly-a and sunlight reflected by N2 in the mesosphere-stratosphere and modified by aerosols (e.g.,tholins) and hydrocarbon absorption. Below 1450 A, the strongest emissions arise from H Ly-a with an intensity of 208 Rayleighs (R), LBH bands with an intensity of 43 R, and the N I multiplets with a combined intensity of 16 R. Above 1450 A , most of the UVIS signal is due to reflected sunlight. Mixing ratios of tholins, C2H2, C2H4 and C4H2 have been derived from the reflected sunlight using a Rayleigh scattering model. The derived mixing ratios are in good agreement with Voyager infrared observations and with FUV photochemical models, assuming solar energy deposition above 1450 A occurs near 250 km (Wilson and Atreya, 2004). We also present the first geometric albedo measurement of Titan from 1500–1900 A

Disciplines :

Space science, astronomy & astrophysics

Author, co-author :

Ajello, Joseph M.

Gustin, Jacques ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Physique des atmosphères et des environnements planétaires

Stewart, Ian

Larsen, Kristopher

Esposito, Larry

Pryor, Wayne

McClintock, William

Stevens, Michael

Malone, Charles

Dziczek, Darius

Language :

English

Title :

Titan airglow spectra from the Cassini Ultraviolet Imaging Spectrograph: FUV disk analysis

Publication date :

2008

Journal title :

Geophysical Research Letters

ISSN :

0094-8276

eISSN :

1944-8007

Publisher :

American Geophysical Union, Washington, United States - District of Columbia

Peer reviewed :

Peer Reviewed verified by ORBi

Available on ORBi :

since 06 August 2012

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Bibliography

Ajello, J. M., and D. E. Shemansky (1985), A re-examination of important N2 cross sections by electron impact with application to the dayglow: The Lyman-Birge Hopfield band system and NI (119.99 nm), J. Geophys. Res., 90, 9845.
Ajello, J. M., G. James, and M. Ciocca (1998), High resolution EUV emission spectroscopy of the N2 c' v' = 3 and 4 levels by electron impact, J. Phys. B At. Mol. Opt. Phys., 31, 2437.
Ajello, J. M., M. H. Stevens, I. Stewart, K. Larsen, L. Esposito, J. Colwell, W. McClintock, G. Holsclaw, J. Gustin, and W. Pryor (2007), Titan airglow spectra from Cassini Ultraviolet Imaging Spectrograph (UVIS): EUV analysis, Geophys. Res. Lett., 34, L24204, doi:10.1029/2007GL031555.
Beegle, L., J. M. Ajello, G. K. James, D. Dziczek, and M. Alvarez (1999), The emission spectrum of the CO (A 1∏ - X 1Σ +) Fourth Positive System by electron impact, Astron. Astrophys., 346, 1.
Bishop, J., and P. Feldman (2003), Analysis of the Astro-1/Hopkins Ultraviolet Telescope EUV-FUV nadir spectral radiance measurements, J. Geophys. Res., 108(A6), 1243, doi:10.1029/2001JA000330.
Broadfoot, A. L., et al. (1981), Extreme UV observations from Voyager 1 encounter of Saturn, Science, 212, 206.
Cohen, L. (1981), An atlas of solar spectra between 1175 and 1950 Å recorded on Skylab with the NRL's Apollo Telescope mount experiment, NASA Ref. Publ., 1069.
Cortin, R., R. Wagener, C. P. McKay, J. Caldwell, K. Fricke, R. Raulin, and P. Bruston (1991), UV spectroscopy of Titan's atmosphere, planetary organic chemistry and prebiological synthesis, Icarus, 90, 43.
Coustenis, A., B. Bezard, D. Gautier, and A. Marten (1991), Titans atmosphere from Voyager 1 observations, III. Vertical distribution of hydrocarbons and nitriles near Titan's north pole, Icarus, 89, 152.
Esposito, L., et al. (2004), The Cassini Ultraviolet Imaging Spectrograph investigation, Space Sci. Rev., 115, 299.
Gladsone, G. R., and Y. L. Yung (1983), An analysis of the reflection spectrum of Jupiter from 1500 to 1740 A, Astrophys. J., 266, 415.
Hanel, R., et al. (1981), Infrared observations of the Saturnian system from Voyager 1, Science, 212, 192.
Khare, B. N., C. Sagan, E. T. Arakawa, F. Suits, T. A. Callicott, and M. W. Williams (1984), Optical constants of organic tholin produced in a simulated Titanian atmosphere: From x-ray to microwave frequencies, Icarus, 60, 127.
Liang, M. A., Y. Yung, and D. E. Shemansky (2007), Photolytically generated aerosols in the mesosphere and thermosphere of Titan, Astrophys. J., 662, L19.
Lilensten, J., O. Witasse, C. Simion, H. Soldi-Lose, O. Dotuit, and R. Thissen (2005), Prediction of a N2++ in the upper atmosphere of Titan, Geophys. Res. Lett., 32, L03203, doi:10.1029/2004GL021432.
McGrath, M., R. Courting, T. E. Smith, P. Feldman, and D. F. Strobel (1998), The ultraviolet albedo of Titan, Icarus, 131, 382.
McKay, C. P., A. Coustenis, R. E. Samuelson, M. T. Lemmon, R. D. Lorenz, M. Cabane, P. Rannou, and P. Rossart (2001), Physical properties of the organic aerosols and clouds on Titan, Planet. Space Sci., 49, 79.
Pang, K. D., J. M. Ajello, B. Franklin, and D. E. Shemansky (1987), Electron impact excitation cross section studies of methane and acetylene, J. Chem. Phys., 86, 2750.
Prekke, P., O. Kjeldseth-Moe, J.-D. F. Bartoe, and G. E. Brueckner (1991), An ultraviolet atlas of a sunspot and an active region 1190-1730 A, Astrophys. J. Suppl. Ser., 75, 1337.
Shemansky, D., I. Stewart, R. West, L. Esposito, J. Hallett, and X. Liu (2005), The Cassini UVIS stellar probe of the Titan atmosphere, Science, 308, 978.
Steffi, A. J., A. I. F. Stewart, and F. Bagenal (2004), Cassini UVIS observations of the Io plasma torus. I. Initial results, Icarus, 172, 78.
Strobel, D. F., and D. E. Shemansky (1982), EUV emission from Titan's upper atmosphere: Voyager 1 encounter, J. Geophys. Res., 87, 1361.
Strobel, D. F., R. R. Meier, M. E. Summers, and D. J. Strickland (1991), Nitrogen airglow sources: Comparison of Triton, Titan and Earth, Geophys. Res. Lett., 18, 689.
Wallach, D., and B. Hapke (1985), Light scattering in a spherical exponential atmosphere, with application to Venus, Icarus, 63, 354.
Wilson, E. H., and S. K. Atreya (2004), Current states of modeling the photochemistry of Titan's mutually dependent atmosphere and ionosphere, J. Geophys. Res., 109, E06002, doi:10.1029/2003JE002181.
Woods, T. N., F. G. Eparvier, S. M. Bailey, P. Chamberlin, J. Lean, G. J. Rottman, S. Solomon, W. K. Tobiska, and D. L. Woodraska (2005), Solar EUV Experiment (SEE): Mission overview and first results, J. Geophys. Res., 110, A01312, doi:10.1029/2004JA010765.