Abstract
Data obtained by the Pioneer 10 vector helium magnetometer are presented along with models of the intrinsic magnetic field of Jupiter and its magnetosphere. Data acquired between 2.84 and 6.0 RJ, where the intensity of the planetary field ranged between 1900 and 18,400γ, were used to develop a six-parameter eccentric dipole model of the field. The dipole so derived has a moment of 4.0 G RJ³ and a tilt angle with respect to Jupiter's rotation axis of 11°. The system III (epoch 1957) longitude of the magnetic pole in the northern hemisphere, which is a north-seeking pole, is 222°. The dipole is displaced from the center of Jupiter by 0.11 RJ in the direction of latitude 16° and system III longitude 176°. The dipole tilt and the longitude of the pole are in good agreement with values inferred from radio astronomy measurements. The magnetic moment and the offset derived from the Pioneer measurements represent a significant improvement in our knowledge of the planetary field. A model of the Jovian magnetosphere is presented in which the essential feature is an eastward current sheet that forms an annulus with Jupiter at the center. At large distances from the planet the current sheet is nearly parallel to Jupiter's equator but, in general, does not lie in it. The current sheet is warped, so that it is above the equator on one side and below it on the other. The current sheet rotates with the planet, more or less like a rigid body; this behavior causes an apparent up and down motion and periodic crossings of the current sheet by Pioneer. The origin of the current sheet appears to be the very large centrifugal force, associated with Jupiter's great size and rapid rotation, acting on trapped low-energy magnetospheric plasma. The density of this plasma is estimated to be approximately 1 particle cm−3. A retrograde spiraling of field lines out of meridian planes is also observed, presumably as a result of azimuthal drag forces exerted on the outer magnetosphere.
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