Magnetic fields affect the plasma of electrically charged particles in interplanetary space and control the flow of this plasma as it spreads out from the Sun across the orbits of the planets. Before the mission of Pioneer 10 these effects had been only observed and measured out to the orbit of Mars. Scientists were still uncertain about many specific details about the interplanetary medium and particularly the extent to which the Sun's magnetic field controlled the flow of plasma beyond Mars to the outer regions of the Solar System. The outer boundaries of this influence were vague, and interactions between the plasma and fields of the Solar System and those of the Galactic System puzzled scientists. Pioneer 10 and Pioneer 11 explored the regions beyond the orbit of Jupiter and made measurements that helped to define the transition region of solar influence (heliosphere).
This experiment used a sensitive magnetometer at the tip of a lightweight boom, which extended 6.6 meters from the center of the spacecraft to reduce the effects of the residual spacecraft magnetic field, and to assist the balance of this spin stabilized spacecraft.
The helium vector magnetometer measured the fine structure of the interplanetary field, maped the Jovian field, and provided field measurements to evaluate solar wind interaction with Jupiter. The magnetometer operated in one of eight different ranges, the lowest of which covered magnetic fields from +/-0.01 to +/-4.0 gamma; the highest, fields up to +/-140,000 gamma (i.e. +/-l.4 Gauss). The ranges were selected by ground command or automatically by the instrument itself as it reached the limits of a given range.