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Dec 13, 2004
Io and the “Greatest Surprise”

Pictured above: two views of Jupiter’s closest moon Io, the first a Voyager photograph, the second a higher-resolution image from the more recent Galileo probe, showing the moon's etched surface in sharp relief.

In 1979, the United States’ space probe Voyager I approached Jupiter, passing through its system of moons to take the first close-up pictures of Io, the large moon closest to the gas giant.  A few months later Voyager II followed, adding to the new and spectacular profile of the moon. According to mission scientists with the Jet Propulsion Laboratory (JPL), "probably the greatest surprise" of the Voyager flyby of Jupiter was the discovery of active "volcanoes" on Io, with plumes jetting far into space.  "It appears that activity on Io affects the entire Jovian system", states a JPL fact sheet.

But in many ways the newly discovered "volcanoes" did not behave like volcanoes on earth but showed distinctive features reminiscent of electrical discharge phenomena.  Seeing these patterns, Cornell University astrophysicist Thomas Gold proposed an extraordinary idea in the journal Science (Nov 1979).  He suggested that the plumes were the effect of an electrical exchange between Io and Jupiter.  The suggestion was quickly disputed by a team of five scientists, including Gene Shoemaker (of comet Shoemaker-Levy fame), who argued that an electric discharge would be extremely hot—much hotter than lava—and that sensitive earth-based instruments have not detected such temperatures.  The debate, however, was never completed.  The journal Science decided against publishing Dr. Gold’s rejoinder.

Nevertheless, plasma theorist Anthony Peratt, together with the distinguished Professor A J Dessler, then at Rice University, followed up on Gold’s suggestion.  In the journal Astrophysics and Space Science, No. 144 (1988), the authors related the data on Io’s "volcanoes" to the experimental work of Hannes Alfvén, who had detailed the unique patterns of electrical discharge in laboratory experiments.

Peratt and Dessler recognized that the physics of Io’s plumes answered directly to Alfvén's earlier research on the plasma gun, a device for concentrating electrical energy in an explosive jet.  In fact, the plumes on Io exhibit all of the specific features of the "penumbra" produced by such a discharge, including distinctive filamentation within the plumes and termination in a thin symmetrical ring.  Even the ejection velocity of Io’s "volcano" Prometheus can be predicted by the formula for calculating discharge velocities in a plasma gun.  Describing the electrical phenomena in an article dedicated to Alfvén on his 80th birthday, Peratt and Dessler say, "The apparent filamentary penumbra on Io may be the first direct verification of the plasma gun mechanism at work in the solar system".

Years later, as the Galileo probe began returning data from the Jovian system, NASA scientists were surprised to discover that the plumes on Io were too hot to measure temperatures accurately. For proponents of the electric universe, this was no surprise: the Galileo instruments were designed to measure lava temperatures, not the temperatures of an electric discharge!



David Talbott, Wallace Thornhill
Amy Acheson
  CONTRIBUTING EDITORS: Mel Acheson, Michael Armstrong, Dwardu Cardona,
Ev Cochrane,   Walter Radtke, C.J. Ransom, Don Scott, Rens van der Sluijs, Ian Tresman
  WEBMASTER: Michael Armstrong

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