Saturn's magnetosphere and its interaction with the solar wind

Authors:
  • ESEdward J. Smith
    Edward J. Smith
  • LDLeverett Davis
    Leverett Davis
  • DJDouglas E. Jones
    Douglas E. Jones
  • PCPaul J. Coleman
    Paul J. Coleman
  • DCDavid S. Colburn
    David S. Colburn
  • PDPalmer Dyal
    Palmer Dyal
  • CSCharles P. Sonett
    Charles P. Sonett
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Abstract
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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