Pioneer 6 plasma measurements in the magnetosheath

Measurements of the magnetosheath plasma made by the MIT plasma experiment during the outbound passage of Pioneer 6 in the dusk meridian (December 16, 1965) are presented and compared with theoretical predictions and other simultaneous experimental measurements for the same region. Though comparison with theory indicates that the plasma flow around the earth agrees in many ways with a gasdynamic model, observed discrepancies in the density ratio across the bow shock and the non‐Maxwellian velocity distribution in the magnetosheath warrant further explanation. Proton observations in the magnetosheath next to the bow shock indicate that the non‐Maxwellian high‐energy tail of the proton velocity distribution may be due in part to an effect that is independent of the main flow. Magnetosphere and magnetosheath low‐energy electron measurements indicate a region of anisotropic flux in the magnetosphere near the magnetopause.