Leverett Davis

Saturn's magnetic field and magnetosphere

The Pioneer Saturn vector helium magnetometer has detected a bow shock and magnetopause at Saturn and has provided an accurate characterization of the planetary field. The equatorial surface field is 0.20 gauss, a factor of 3 to 5 times smaller than anticipated on the basis of attempted scalings from Earth and Jupiter. The tilt angle between the magnetic dipole axis and Saturns rotation axis is < 1�, a surprisingly small value. Spherical harmonic analysis of the measurements shows that the ratio of quadrupole to dipole moments is < 10 percent, indicating that the field is more uniform than those of the Earth or Jupiter and consistent with Saturn having a relatively small core. The field in the outer magnetosphere shows systematic departures from the dipole field, principally a compression of the field near noon and an equatorial orientation associated with a current sheet near dawn. A hydromagnetic wake resulting from the interaction of Titan with the rotating magnetosphere appears to have been observed.

Mariner V: Plasma and Magnetic Fields Observed near Venus.

Abrupt changes in the amplitude of the magnetic fluctuations, in the field strength, and in the plasma properties, were observed with Mariner V near Venus. They provide clear evidence for the presence of a bow shock around the planet, similar to, but much smaller than, that observed at Earth. The observations appear consistent with an interaction of the solar wind with the ionosphere of Venus. No planetary field could be detected, but a steady radial field and very low plasma density were found 10,000 to 20,000 kilometers behind Venus and 8,000 to 12,000 kilometers from the Sun-Venus line. These observations may be interpreted as relating to an expansion wave tending to fill the cavity produced by Venus in the solar wind. The upper limit to the magnetic dipole moment of Venus is estimated to be within a factor of 2 of 10-3 items that of Earth.

Jupiter's Magnetic Field. Magnetosphere, and Interaction with the Solar Wind: Pioneer 11

The Pioneer 11 vector helium magnetometer provided precise, contititious measurements of the magnetic fields in interplanetary space, inside Jupiters magnetosphere, and in the near vicinity of Jupiter. As with the Pioneer 10 data, evidence was seen of the dynanmic interaction of Jupiter with the solar wind which leads to a variety of phenomena (bow shock, upstream waves, nonlinear magnetosheath impulses) and to changes in the dimension of the dayside magnetosphere by as much as a factor of 2. The magnetosphere clearly appears to be blunt, not disk-shaped, with a well-defined outer boundary. In the outer magnetosphere, the magnetic field is irregular but exhibits a persistent southward component indicative of a closed magnetosphere. The data contain the first clear evidence in the dayside magnetosphere of the current sheet, apparently associated with centrifugal forces, that was a donminatnt feature of the outbound Pionieer 10 data. A modest westward spiraling of the field was again evident inbound but not outbound at higher latitudes and nearer the Sun-Jupiter direction. Measurements near periapsis, which were nearer the planet and provide better latitude and longitude coverage than Pioneer 10, have revealed a 5 percent discrepancy with the Pioneer 10 offset dipole mnodel (D2). A revised offset dipole (6-parameter fit) is presented as well as the results of a spherical harmonic analysis (23 parameters) consisting of an interior dipole, quadrupole, and octopole and an external dipole and quadrupole. The dipole moment and the composite field appear moderately larger than inferred from Pioneer 10. Maximum surface fields of 14 and 11 gauss in the northern and southern hemispheres are inferred. Jupiters planetary field is found to be slightly more irregular than that of 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.

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.

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 7R J and is dominated by the basically dipolar field. The outer magnetosphere, on the sunward side, occupies a layer roughly 15R 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 2R J) warped current sheet in which the magnetic field appears to be very weak and mainly southward.

Theories of interstellar polarization

Abstract The experimental data to be explained by any theory of interstellar polarization are summarized. The expression for the ratio of polarization to absorption produced by a cloud of partially aligned small dust grains is put in a form applicable to all current theories of alignment. A semi-quantitative treatment is given of Golds proposal that alignment is due to relative motion of dust through gas and this mechanism is shown to be inadequate to produce the observed polarization. Magnetic alignment theories are preferred. Equations are given for use when starlight passes through several clouds with various orientations. Any orienting mechanism can be tested by a statistical study of the observed distribution of polarization over neighbouring stars. Thus it appears tentatively that it is more plausible to assume that a galactic magnetic field lies along a spiral arm than that the field is randomly directed in the plane of the galaxy.

Scientific Results of the Mariner II Voyage to Venus

Mariner II was launched on August 27, 1962, passed at a distance of only 41000 km from the center of Venus on December 14, and transmitted its last scientific and engineering data to earth on January 2, 1963. It was remarkably successful for the first vehicle of its type whose launching was satisfactory. A large part of the emphasis on this first flight was engineering and a great amount of important technological information was obtained from it. The history of this voyage, including a discussion of the engineering and scientific problems and results, is surveyed by James (1963). My discussion this morning will be restricted to the scientific results obtained to date by the seven groups of experimenters. The emphasis given each experiment will be governed by my own interests and what I happen to know.

AN ORBIT-BENDER TO ASSIST INJECTION INTO BETATRONS

It is suggested that the fraction of the beam in a betatron or synchrotron that is lost by striking the injector might be decreased by a suitable transient bending of the steady‐state orbit during injection.