Dec 13, 2004
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 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,
filamentary penumbra on Io may be the first
direct verification of the plasma gun mechanism at work in the
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!