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Dec 15, 2004
Predicting the Electrical Etching of Io

The most compelling advances in scientific theory come from successful prediction, and over the past 25 years the Jovian system has provided a laboratory in space for testing the predictive ability of the “electric universe”.

After the Voyager probes revealed surprising “volcanic” activity on Jupiter’s moon Io, plasma researchers had an opportunity to anticipate what a closer look might reveal. That closer look came with the sophisticated Galileo probe, launched in 1989 and reaching the Jovian system in 1996.  In anticipation of new and higher-resolution photographs and measurements, Wallace Thornhill, following the lead of Cornell astrophysicist Thomas Gold, and plasma scientists Anthony Peratt and A J Dessler, registered these claims in advance of Galileo’s arrival:

• the vents of the "volcanic" plumes will be much hotter than lava;
• the plumes are the jets of cathode arcs, and they do not explode from a volcanic vent but move around and erode the periphery of dark areas (called "lava lakes" by planetary geologists);
• the "lava lakes" themselves are merely the solid surface of Io etched electrically by cathode arcs and exposed from beneath the sulfur dioxide "snow" deposited by continuous discharge activity.  Therefore, they will not reveal the expected heat of a recent lava flow.

Each of these predictions received stunning confirmation by the Galileo probe. The spacecraft measured the temperatures of Io’s "volcanic" hot spots and gave readings, averaged over a pixel, that were hotter than any lava on Earth—in fact, too hot to be measured by Galileo’s instruments.

As predicted by Thornhill, the discharging was discovered to be focused on the edges of the so-called "lava lakes”, though the rest of these dark fields are comparatively cold.  None of the expected volcanic vents could be found.  Rather, the plumes of the "volcanoes" are actually moving across the surface of Io, an exclamation point being provided by the plume of Prometheus which, in the years since Voyager, has moved more than 80 kilometers. (See tomorrow’s Picture of the Day.)

Much to the astonishment of mission scientists, it was discovered that the "volcanic" plumes emit ultraviolet light, something inconceivable under normal conditions of volcanic venting. Ultraviolet light is, of course, characteristic of an electric arc.  It is why arc welders wear darkened welding masks!

  EXECUTIVE EDITORS: David Talbott, Wallace Thornhill
MANAGING EDITOR: 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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