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The Z 3 model of Saturn's magnetic field and the Pioneer 11 vector helium magnetometer observations

1984; American Geophysical Union; Volume: 89; Issue: A9 Linguagem: Inglês

10.1029/ja089ia09p07541

2156-2202

J. E. P. Connerney, M. H. Acuña, N. F. Ness,

Ionosphere and magnetosphere dynamics

Magnetic field observations obtained by the Pioneer 11 vector helium magnetometer are compared with the Z 3 model magnetic field. These Pioneer 11 observations, obtained at close‐in radial distances, constitute an important and independent test of the Z 3 zonal harmonic model, which was derived from Voyager 1 and Voyager 2 flux gate magnetometer observations. Differences between the Pioneer 11 magnetometer and the Z 3 model field are found to be small (∼1%) and quantitatively consistent with the expected instrumental accuracy. A detailed examination of these differences in spacecraft payload coordinates shows that they are uniquely associated with the instrument frame of reference and operation. A much improved fit to the Pioneer 11 observations is obtained by rotation of the instrument coordinate system about the spacecraft spin axis by 1.4°. With this adjustment, possibly associated with an instrumental phase lag or roll attitude error, the Pioneer 11 vector helium magnetometer observations are fully consistent with the Voyager Z 3 model. No evidence is found for any significant departure from axisymmetry of Saturn's internal magnetic field.