No. 91: Jan-Feb 1994
Atop Hawaii's Mauna Kea, NASA's Infra-red Telescope Facility has detected a pair of infrared-bright spots that race across Jupiter's upper atmosphere in tune with the motion of Io, one of Jupiter's large, Galilean satellites. This synchronism suggests some sort of energy interchange between Io and the top of Jupiter's atmosphere. The theory now in vogue states that Jupiter's rotating magnetic field induces a voltage across 2300-mile-diameter Io, resulting in an electrical current of some 5 million amperes flowing between Io and Jupiter, some 262,000 miles away. In this bizarre electrical circuit, the two moving "terminals" on Jupiter, in the northern and southern hemispheres, are heated by the current flow and show up as fuzzy infrared-bright spots.
(Cowen, R.; "Jupiter and Io: Infrared Spots Mark Link," Science News, 144: 325, 1993.)
Comment. In passing, it should be remarked that Io is mantled by a cloud of electrically conducting sodium vapor. A weird moon in other respects, too, Io occasionally casts double shadows on Jupiter's upper atmosphere during transits. See AJX4 in The Moon and the Planets. In addition, in AJX2, infrared-hot shadows of the satellites Ganymede and Europa are mentioned. Very strange!
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