INITIAL OBSERVATIONS OF THE PIONEER VENUS ORBITER SOLAR-WIND PLASMA EXPERIMENT

Initial results of observations of the solar wind interaction with Venus indicate that Venus has a well-defined, strong, standing bow shock wave. Downstream from the shock, an ionosheath is observed in which the compressed and heated postshock plasma evidently interacts directly with the Venus ionosphere. Plasma ion velocity deflections observed within the ionosheath are consistent with flow around the blunt shape of the ionopause. The ionopause boundary is observed and defined by this experiment as the location where the ionosheath ion flow is first excluded. The positions of the bow shock and ionopause are variable and appear to respond to changes in the external solar wind pressure. Near the terminator the bow shock was observed at altitudes of ∼ 4600 to ∼ 12,000 kilometers. The ionopause altitude ranged from as low as ∼450 to ∼ 1950 kilometers. Within the Venus ionosphere low-energy ions (energy per unit charge < 30 volts) were detected and have been tentatively identified as nonflowing ionospheric ions incident from a direction along the spacecraft velocity vector. Copyright © 1979 AAAS.