Initial PVO evidence of electron depletion signatures downstream of Venus

Details Initial PVO evidence of electron depletion signatures downstream of Venus Initial PVO evidence of electron depletion signatures downstream of Venus

Dec 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993georl..20.2779i&link_type=abstract

Geophysical Research Letters (ISSN 0094-8276), vol. 20, no. 23, p. 2779-2782

Physics

1

Depletion, Electron Impact, Electrons, Energetic Particles, Planetary Ionospheres, Plasmas (Physics), Signatures, Venus Atmosphere, Atmospheric Entry, Night, Pioneer Venus 1 Spacecraft, Shock Waves

Scientific paper

This 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 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.

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