One showpiece of the space program has been the explosive growth in the subject of “planetary magnetism” [Russell, 1979, 1980]. Beginning with the December 1962 flyby of Venus by Mariner 2 and continuing through the January 1986 flyby of Uranus by Voyager 2, there have been over 15 spacecraft encounters of Mercury, Venus, the moon, Mars, Jupiter, Saturn, and Uranus, not to mention the planetary satellites. Venus, Mars, and the moon have each been orbited several times. In a sense, and somewhat ironically, the earth has received less magnetic scrutiny than our nearest neighbors in space.