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Pioneer 11 vector helium magnetometer observations of Saturn's planetary magnetic field, magnetosphere, magnetopause, and bow shock are presented. Models based on spherical harmonic analyses of measurements inside 8 Rs reveal that the planetary field has a high degree of symmetry about the rotation axis. The vector dipole moment of 0.2 G Rs³ has a tilt angle less than 1° and is offset along the polar axis 0.04±0.02 Rs. Equatorial offsets derived from the models show substantial variability and could be consistent with a very small offset. Beyond 10 Rs, near the noon meridian, the field topology is characteristic of a dipole field being compressed by high‐speed solar wind. There is no evidence of plasma outflow, i.e., a planetary wind. Near the dawn meridian the field lines in the outer magnetosphere are stretched‐out into a nearly equatorial orientation. Crossings of a thin current sheet are observed, apparently caused by motions driven from outside the magnetosphere. The field above and below the current sheet spirals out of the magnetic meridian plane at large distances to point tailward and parallel to the magnetopause. The location of the magnetopause is consistent with a shape that is similar to that of the earth but perhaps more blunt, as suggested by the attitude of the magnetopause near dawn. Near both the noon and dawn magnetopause the field in the magnetosheath equals or exceeds the field in the magnetosphere. The noon observations suggest a piling‐up of magnetosheath field lines adjacent to the magnetopause. Large impulsive field compressions are observed in the magnetosheath near noon. Multiple crossings of the bow shock are observed, and the absence of significant changes in field direction shows that it is quasi‐perpendicular. The speeds of motion of the shock toward and away from Saturn are estimated to be 150 and 50 km/s, respectively. A shock thickness of ∼2000 km is inferred.

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Review of the evidence indicates that a magnetic field of the order of 10~5 gauss probably lies along a spiral arm of the galaxy. If so, any anisotropy observed in high-energy cosmic radiation must be associated with this field. Anisotropy might be due to: (a) acceleration by Fermi's mechanism, either by his longitudinal collisions or by betatron effects; (b) diffusion along field lines toward a region where the cosmic rays escape from the galaxy; (c) inhomogeneities in cosmic-ray density normal to the field lines. From symmetry considerations theoretical expressions are developed for the cosmic-ray flux as a function of direction and for the resulting sidereal time dependence of extensive showers as a function of latitude and the orientation of the detecting apparatus. If atmospheric effects can be corrected for, the main harmonics predicted are the first and second, the second being mainly due to anisotropy produced by acceleration. In the absence of detailed calculations based on a specific theory of the origin of cosmic rays and on the way the extensive showers are detected, the amplitude of the harmonics must be determined from experiment. Preliminary reports of measurements by Cranshaw and Galbraith and by Farley and Storey seem to indicate tentatively that the magnetic field is as described above and that cosmic rays are accelerated by Fermi's mechanism; the measurements of Daudin and Daudin require some other explanation.