Review of Ames Research Center Plasma-Probe Results from Pioneers 6 and 7

  • J. H. Wolfe
  • D. D. McKibbin
Conference paper
Part of the Astrophysics and Space Science Library book series (ASSL, volume 10)


Pertinent to the subject of this summer institute, the Pioneer 6 and 7 results presented here entail only those important aspects associated with the magnetosphere. In this regard two unique results obtained from the Pioneer missions are discussed. The first concerns the observation made by Pioneer 6 during the unusually quiet transit of the magnetosheath near the evening meridian. Pioneer 6, launched on December 16, 1965, traversed the magnetosheath near local sunset a few degrees below the ecliptic plane. At this time, interplanetary conditions, as determined by subsequent flight data, were extremely quiet with Ap ≈ 0. The data revealed a density spike associated with the shock front and a density increase of approximately a factor of 3 as the flow crosses the shock. The density increases in the spike itself by over an order of magnitude above the free-stream value. The solar wind electrons appear to increase in temperature by approximately a factor of 4 at the shock front and subsequently cool by about a factor of 2 as the flow proceeds downstream. The solar wind ions, on the other hand, although also heated to approximately the same extent as the electrons in the vicinity of the shock front, do not appear to cool downstream and, in addition, reveal non-thermal characteristics. The data also indicate that 100 eV electrons may be injected into the magnetosphere at the Earth’s magnetic field boundary and undergo further heating in the outer part of the magnetosphere.

The second result discussed involves a preliminary account of what is presumed to be geomagnetic tail associated phenomena observed by Pioneer 7 at a distance of approximately 1000 earth radii downstream from the earth. The interplanetary spacecraft, Pioneer 7, launched August 17, 1966, had an outward trajectory that passed through the sun-earth line 36 days after launch at a distance of approximately 820 earth radii downstream from the earth. Three days subsequent to this time the plasma probe revealed anomalous plasma characteristics which continued intermittently for about 6 days and which have been tentatively identified with the effects of an extended magnetospheric tail. Preliminary data are presented which verify the non-radial flow of the solar wind and reveal a high degree of gross motion of the magnetospheric tail at these large distances. Comparison of plasma energy and angular distributions indicate the presence of plasma fluctuations within the frequency range 0.1–10 Hz. Although the data presented do not warrant the explicit application of any known theoretical tail structure at this distance, the results are discussed with regard to those phenomena which shed light on several possible models.


Solar Wind Shock Front Interplanetary Medium Earth Radius Shock Transition 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© D. Reidel Publishing Company, Dordrecht, Holland 1968

Authors and Affiliations

  • J. H. Wolfe
    • 1
  • D. D. McKibbin
    • 1
  1. 1.Space Sciences Division, Ames Research CenterNASAMoffett FieldUSA

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