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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 the 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 provide 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
19990038334
Acquisition Source
Headquarters
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.
(Universidad Nacional Autonoma de Mexico Ensenada, Mexico)
Siscoe, G. L.
(Carmel Research Center Santa Monica, CA United States)
Date Acquired
August 19, 2013
Publication Date
December 14, 1993
Publication Information
Publication: Geophysical Research Letters. Selected Papers on Pioneer Venus Orbiter: Entry Phase
Volume: 20
Issue: 23
Subject Category
Lunar And Planetary Exploration
Report/Patent Number
Paper 93GL02483
Funding Number(s)
CONTRACT_GRANT: NAS2-12912
CONTRACT_GRANT: NASw-4815
Distribution Limits
Public
Copyright
Public Use Permitted.
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