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Ionospheric dynamo theory for production of far ultraviolet emissions on UranusA model is presented to explain diffuse FUV emissions from the outer planets, specifically Uranus, in excess of those diffuse emissions that are currently explainable by scattering of sunlight and/or excitation by photoelectrons. These electroglow emissions in H Ly-alpha and H2 bands, which occur in the sunlit hemisphere slightly above the homopause, appear to require particle excitation in the 10- to 50-eV range. An in situ mechanism for accelerating photoelectrons (and ions is proposed, involving neutral wind dynamo generation of field-aligned currents analogous to what occurs in the earth's equatorial E and F regions. Sufficiently strong field-aligned currents are found in the model calculation for Uranus to produce a potential drop of about 100 eV or greater between the F peak and homopause, concentrated at lower altitudes, and capable in principle of accelerating photoelectrons (and ions) to the 10- to 50-eV energies required to explain the observed emissions. The fact that the excitation and ionization cross sections are larger than elastic scattering cross sections in an H2 atmosphere at these energies makes in situ acceleration feasible for the production of UV on the outer planets.
Document ID
19890056282
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Hudson, M. K.
(Dartmouth Coll. Hanover, NH, United States)
Warren, J. A.
(Dartmouth College Hanover, NH, United States)
Clarke, J. T.
(Michigan, University Ann Arbor, United States)
Date Acquired
August 14, 2013
Publication Date
June 1, 1989
Publication Information
Publication: Journal of Geophysical Research
Volume: 94
ISSN: 0148-0227
Subject Category
Lunar And Planetary Exploration
Accession Number
89A43653
Funding Number(s)
CONTRACT_GRANT: NAG5-1077
CONTRACT_GRANT: NAGW-809
Distribution Limits
Public
Copyright
Other

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