Atmospheric Composition and Structure: Airglow and aurora; Ionosphere: Ionosphere/magnetosphere interactions (2736); Ionosphere: Particle precipitation; Planetary Sciences: Solar System Objects: Titan; Solar Physics; Astrophysics; and Astronomy: Ultraviolet emissions
Abstract :
[en] In this paper we present the first nightside EUV and FUV airglow limb spectra of Titan showing molecular emissions. The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed photon emissions of Titan's day and night limb-airglow and disk-airglow on multiple occasions, including during an eclipse observation. The 71 airglow observations analyzed in this paper show EUV (600-1150 Å) and FUV (1150-1900 Å) atomic multiplet lines and band emissions arising from either photoelectron induced fluorescence and solar photo-fragmentation of molecular nitrogen (N[SUB]2[/SUB]) or excitation by magnetosphere plasma. The altitude of the peak UV emissions on the limb during daylight occurred inside the thermosphere at the altitude of the topside ionosphere (near 1000 km altitude). However, at night on the limb, a subset of emission features, much weaker in intensity, arise in the atmosphere with two different geometries. First, there is a twilight photoelectron-excited glow that persists with solar depression angle up to 25-30 degrees past the terminator, until the solar XUV shadow height passes the altitude of the topside ionosphere (1000-1200 km). The UV twilight glow spectrum is similar to the dayglow but weaker in intensity. Second, beyond 120° solar zenith angle, when the upper atmosphere of Titan is in total XUV darkness, there is indication of weak and sporadic nightside UV airglow emissions excited by magnetosphere plasma collisions with ambient thermosphere gas, with similar N[SUB]2[/SUB] excited features as above in the daylight or twilight glow over an extended altitude range.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Ajello, Joseph M.; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
West, Robert A.; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
Gustin, Jacques ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Physique des atmosphères et des environnements planétaires
Larsen, Kristopher; Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA
Stewart, A. Ian F.; Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA
Esposito, Larry W.; Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA
McClintock, William E.; Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA
Holsclaw, Gregory M.; Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, Boulder, Colorado, USA
Bradley, E. Todd; Department of Physics, University of Central Florida, Orlando, Florida, USA)
Language :
English
Title :
Cassini UVIS observations of Titan nightglow spectra
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