An analysis of the structure of Saturn's magnetic field using charged particle absorption signatures

A new technique is derived for determining the structure of Saturn's magnetic field. This technique uses the observed positions of charged particle absorption signatures due to the satellites and rings of Saturn to determine the parameters of an axially symmetric, spherical harmonic model of the magnetic field using the method of least squares. Absorption signatures observed along the Pioneer 11, Voyager 1, and Voyager 2 spacecraft trajectories are used to derive values for the orientation of the magnetic symmetry axis relative to Saturn's axis of rotation, the axial displacement of the center of the magnetic dipole from the center of Saturn, and the magnitude of the external field component. Comparing these results with the magnetic field model parameters deduced from analyses of magnetometer data leads us to prefer models that incorporate a northward offset of the dipole center by about 0.05 R_s

August 1972 solar-terrestrial events: Observations of interplanetary shocks at 2.2 AU

Pioneer 10 magnetic field measurements, supplemented by previously published plasma data, have been used to identify shocks at 2.2 AU associated with the large solar flares of early August 1972. The first three flares, which gave rise to three forward shocks at Pioneer 9 and at earth, led to only a single forward shock at Pioneer 10. The plasma driver accompanying the shock has been tentatively identified. A local shock velocity at Pioneer 10 of 717 km/s has been estimated by assuming that the shock was propagating radially across the interplanetary magnetic field. This velocity and the rise time of ≃2 s imply a shock thickness of ∼1400 km, which appears to be large in comparison with the characteristic plasma lengths customarily used to account for the thickness of the earth's bow shock. This Pioneer 10 shock is identified with the second forward shock observed at Pioneer 9, which was then at 0.8 AU and radially aligned with Pioneer 10, since it was apparently the only Pioneer 9 shock that was also driven. The local velocity of the Pioneer 9 shock of 670 km/s, previously inferred by other authors, compares reasonably well with the local velocity at Pioneer 10, but both values are significantly smaller than the average value computed from the time interval required for the shock to propagate from the sun to Pioneer 9 (2220 km/s). The velocity implied by the time required to propagate from Pioneer 9 to Pioneer 10 (770 km/s) is in reasonable agreement with the local velocities. The fourth solar flare also gave rise to a forward shock at Pioneer 10 as well as at Pioneer 9. The local velocity at Pioneer 10, estimated on the basis of quasi-perpendicularity, is 660 km/s, a value which again agrees well with previously derived velocities for the Pioneer 9 shock of 670 km/s. The local velocities for this shock and the velocity between Pioneer 9 and Pioneer 10 (635 km/s) are also significantly less than the average velocity of propagation from the sun to Pioneer 9 (830 km/s). The general finding that the local velocities of both shocks are approximately equal at 0.8 and 2.2 AU but significantly slower than the average speeds nearer the sun is interpreted as evidence of a major deceleration of the shocks as they propagate outward from the sun that is essentially completed when the shocks reach 0.8 AU, there being little, if any, subsequent deceleration. This conclusion is qualitatively inconsistent with previous inferences of a deceleration of the shocks as they propagate from 0.8 to 2.2 AU. A third, reverse shock is also identified in the Pioneer 10 data which was not seen either at Pioneer 9 or at earth. The estimated speed of this shock is 530 km/s, and its estimated thickness is ≲500 km, which compares well with an anticipated proton inertial length of 500 km

The Jovian Magnetosphere And Magnetopause

It is convenient to divide the magnetosphere into three regions. The inner magnetosphere extends from the surface to about 25 R_J and is dominated by the basically dipolar field. The outer magnetosphere, on the sunward side, occupies a layer roughly 15 R_J thick just inside the magnetopause. Here the field direction was found by Pioneers 10 and 11 to have a strong southward component, 5 to 10 times as strong as expected if one scales the observations in the Earth’s magnetosphere. The middle magnetosphere is the remaining region. Its thickness, again on the sunward side, varies greatly as the magnetopause moves in and out. In this region the field direction turns as one goes outward from nearly dipolar to nearly radial but with a persistent southward component. The field is outward in the northern hemisphere, inward in the southern, separated by a thin (~1 or 2 R_J) warped current sheet in which the magnetic field appears to be very weak and mainly southward

Interplanetary Magnetic Fields

Preliminary analysis of Mariner II magnetometer data indicates a persistent interplanetary field varying between a least 2 and 10 gamma (1γ = 10^(-5) gauss). The interplanetary field appears to lie mainly in the ecliptic plane, although there is a substantial, fluctuating, transverse component. The Mariner II data agree reasonably well with the prior Pioneer V observations. Typically, variations as large as 5 to 10 gamma in the field component radial from the sun are measured. Correlations with the Mariner II plasma measurements have been observed

Magnetic Field

Mariner II magnetometer data gave no indication of a Venusian magnetic field. This implies, by comparison with spacecraft measurements near Earth and with theoretical models, that the magnetic dipole moment of Venus is at most 1/10 to 1/20 that of the earth

Magnetic Field Measurements near Mars

During the encounter between Mariner IV and Mars on 14-15 July, no magnetic effect that could be definitely associated with the planet was evident in the magnetometer data. This observation implies that the Martian magnetic dipole moment is, at most, 3 x 10^(-4) times that of the earth