Planetary Astronomy; an Appraisal of Ground-Based Opportunities (1968) / Chapter Skim
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Interiors and Magnetic Fields
Interiors and Magnetic Fields
Pages 39-45
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From page 39... ...
A knowledge of the structure and composition of planetary interiors is essential to a better understanding of the present state of the planetary system, how it was formed, and the manner in which it evolved. The only method that has so far been applied to observe planetary magnetic fields from the Earth's surface is to detect radiation from charged particles trapped in the field.
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From page 40... ...
In the case of the Earth, some boundaries can be predicted when experimental data on chemically similar isomorphic structures are available, but, for other planetary interiors, the questions of phase boundaries are likely to remain enigmatic for a long period. A second area of difficulty involves thermal transport.
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From page 41... ...
Convection is well understood in gases and certain liquids when nonturbulent; but even here any slight complexity in geometry raises severe mathematical difficulties. Convection of very imperfect gases, or convection in condensed systems exhibiting phase changes coupled with the presence of gyroscopic forces (magnetic or Coriolis)
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From page 42... ...
PLANETARY MAGNETIC FIELDS AND MAGNETOSPHERES Planetary magnetic fields are of interest because of the plasma phenomena produced by the interaction of the fields with the solar wind, and because, being produced by processes occurring deep within the planet, they provide a clue to the nature and extent of those processes. In principle there are four kinds of observational evidence from which the existence of a planetary magnetic field may be inferred: space-probe magnetometer measurements; nonthermal electromagnetic radiation from the planet of appropriate frequency, polarization, and intensity; evidence that in modulating the solar wind the effective planetary cross section greatly exceeds the cross section of the visible planet; and Faraday rotation of the plane of linear polarization either of
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From page 43... ...
Magnetometer data obtained as Mariner IV flew past Mars at a distance of about two planetary radii from its center gave no evidence at any point on the trajectory of a Martian magnetic field. If a fluctuation in field strength observed by Mariner IV was a shock front associated with the Martian magnetosphere, the ratio of the magnetic moment of Mars to that of the Earth is <2xlO~*
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From page 44... ...
A gradual change in the rotation period of the radio source was first suspected, but the observed apparent period may be influenced by changes with time in the source-observer geometry or in the radio-noise storm duration. The polarization of the radiation, except at the longer wavelengths, is measured as predominantly righthand elliptical or partially right-hand circular, implying a magnetic field of at least several gauss.
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From page 45... ...
If this is indeed the case, variations in the motions of the Red Spot and of the radio sources could be manifestations of hydromagnetic torsional oscillations of the planet. Moreover, the "topographical feature" with which the Red Spot may be associated might be magnetic in nature.
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