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Initial PVO evidence of electron depletion signatures downstream of VenusThis first analysis of Pioneer Venus Orbiter (PVO) plasma analyzer electron measurements obtained in early 1992 during teh PVO entry phase of the mission indicates the presence downstream from the terminator of a depletion or 'bite out' of energetic ionosheath electrons similar to that observed on Mariner 10. There is more than one possible explanation for this energetic electron depletion. If it is due to atmospheric scattering, the electrons traveling along draped magnetic flux tubes that thread through the Venus neutral atmosphere would lose energy from impact ionization with oxygen. The cross-section for such electron impact ionization of oxygen has a peak near 100 eV, and it remains high above this energy, so atmospheric loss could provde a natural process for electrons at these energies to be selectively removed. In this case, our results are consistent with the Kar et al. (1994) study of PVO atmospheric entry ion mass spectrometer data, which indicates that electron impact plays a significant role in maintaining the nightside ionosphere. Although it is appealing to interpret the energetic electron depletion in terms of direct atmospheric scattering, alternatively it could result from strong draping which connects the depletion region magnetically to the weak downstream bow shock and thereby reduces the electron source strength.
Document ID
19950039571
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Intriligator, D. S.
(Carmel Research Center Santa Monica, CA, United States)
Hartle, R. E.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Perez-De-tejada, H.
(Univ. Nacional Autonoma de Mexico Ensenada, Mexico)
Siscoe, G. L.
(Carmel Research Center Santa Monica, CA, United States)
Date Acquired
August 16, 2013
Publication Date
December 14, 1993
Publication Information
Publication: Geophysical Research Letters
Volume: 20
Issue: 23
ISSN: 0094-8276
Subject Category
Lunar And Planetary Exploration
Accession Number
95A71170
Funding Number(s)
CONTRACT_GRANT: NAS2-12912
CONTRACT_GRANT: NASW-4815
Distribution Limits
Public
Copyright
Other

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