Reinterpretation of the Pioneer 6 bow shock crossing.

This paper re-examines and reinterprets the interesting bow shock crossing of Pioneer 6 on December 16, 1965, by combining the high-resolution data for the magnetic field measurements with all the available plasma data. It is shown that, although a small correction of the magnetic field data improves the validity test of the MHD Rankine-Hugoniot (R-H) conditions, it is the plasma density measurements that are the principal source of the remaining inconsistencies. With the exception of the densities, the best agreement between the measurements and the R-H relations is obtained when the specific heat ratio is slightly less than the classical value of 5/3 expected for a magnetized plasma in the magnetosheath. A more accurate shock normal determination has been made, and it is found that the shock itself is possibly in motion with respect to the earth and that locally it may be approximated as a normal shock.