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Neutral Composition Measurements by the Pioneer Venus Neutral Mass Spectrometer During Orbiter Re-EntryMeasurements by the Pioneer Venus Orbiter Neutral Mass Spectrometer (ONMS) instrument during Orbiter re-entry have been made from 18-24 hours local solar time, above 170 km, of He, and from midnight to 4.5 hours below 200 km of He, N, O, CO, N2, and CO2. Preliminary results indicate that in the post-midnight sector He is the dominant species above 170 km, O the dominant species from 140-170 km and CO2 the dominant species below 140 km. Estimated scale height temperatures for He, O and CO2 of about 105-120 K are similar to those observed in 1978-80 at higher solar activity. The densities at 1 am local solar time and at 150 km are within 35% of those measured earlier. The He bulge is also similar to that observed in 1978-80 confirming that thermosphere superrotation is still present. Comparison with the results of a Venus Thermosphere General Circulation Model suggests the nightside is not sensitive to changes in solar activity due to the isolation of the day and night thermospheres. Apparently, the relatively small changes in the dayside thermosphere with solar activity have little impact on the nightside thermosphere.
Document ID
19990038326
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Kasprzak, W. T.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Niemann, H. B.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Hedin, A. E.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Bougher, S. W.
(Arizona Univ. Tucson, AZ United States)
Hunten, D. M.
(Arizona Univ. Tucson, AZ 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 93GL02241
Distribution Limits
Public
Copyright
Public Use Permitted.
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