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| Titel |
The stronly bifurcated H2 electronic emission system in the Saturn atmosphere |
| VerfasserIn |
Donald Shemansky, Xianming Liu, Henrik Melin |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250034871
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| Zusammenfassung |
| Image cubes of the Saturn atmosphere and magnetosphere in EUV/FUV spectra obtained
using the Cassini Ultraviolet Imaging Spectrograph (UVIS) show the presence of strongly
bifurcated H2 atmospheric electronic band emission features that are both spatially and
spectrally separated. The forks are spectrally distinguished as readily isolated non-resonant
and multiple strong resonant feature components. The resonant components are
inferred to be directly responsible for upper thermosphere mid latitude heating and the
observed escape of atomic hydrogen from the top of the thermosphere. The resonance
features apparently require solar photon flux catalysis, but the spatial structure of the
emission does not correspond to the uniformity of solar input. Spatially non-uniform
electro-dynamic processes are evidently necessary to explain the magnitude of the
inferred energy deposition. The resonance features do not appear in the aurora. The
non-resonant component shows relatively uniform emission at sunlit mid latitudes
and strong polar auroral features, resulting in starkly different surface-brightness
images. The Cassini UVIS observations show, for the first time, emission from
an activated hydrogenic planetary atmosphere displaying apparently independent
properties within the same electronic band system. This behavior internal to a single
species is made possible in this case because the emission system is homonuclear,
allowing exceedingly long lived states to act as independent systems. The fact that this
has occurred at Saturn is remarkable, but what is more important is the physical
mechanics of the forcing process that appears to be responsible for explaining the long
standing problem of high temperatures in giant outer planet upper thermospheres.
The energy deposition rate in the upper thermosphere dayglow is 10 to 50 times
the auroral rate. The explanation for the forcing of the inferred electrodynamics
system will not be simple given the observed structure and temporal variability of the
ionosphere. The next step forward is to identify, through the modeling process,
the specific states in the H2 system that are responsible for the observed spectra. |
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