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

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.