Gravitational Magnetism - the Blackett Effect
When I use the term "gravitational magnetism" I will be referring to the hypothesis that the rotation of an astronomical body, in and of itself, is the cause of the bodies magnetic field.
  When I took geophysics in 1970 I was told that this effect was disproven by Blackett himself. In fact, he only failed to detect the field predicted by one particular interpretation of the hypothesis
   A recent analysis of the magnetic fields of known bodies has shown a good fit with this hypothesis.  I was once told that Mars' very weak magnetism disproved the theory.  Since then Mar's magnetic field has been shown to be much more complicated than that. It is a quadrapole. It has two north poles and two south poles. Their fields partially cancel each other out. The strength of the stonger poles is very much consistent with the Schuester-Blackett hypothesis.
  If this effect is the cause of the Earth's magnetic field, several questions are posed. How is it decided which is the north and which is the south pole; and what happens when the poles flip-flop.
  One clue is given by Richard Stothers. The mean period of magnetic reversals is close to the time that it takes our solar system to circle the galaxy.
  There are also clues from the Sun's sunspot activity. Since the Sun's energy output is inversely proportional to its sunspot activity and since that energy is recorded in tree rings, lake varves, and ice cores; it is possible to correlate the Sun's magnetic activity with its motion.  Jim Shirley has shown that sunspots show a strong correlation with its motion about the center of mass of the solar system. 
Recent  articles on gravitational magnetism:
Saul-Paul Sirag
Enlarged graph
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Martin Kokus/gravitational magnetism