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Credit: Planetary Image Research Lab. (PIRL), Lunar and Planetary Lab. (LPL), University of Arizona


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Dec 16, 2004
Io's "Volcano" Prometheus

The photograph above was taken by the Galileo probe from a position over the plume of the “volcano” Prometheus on Jupiter’s moon Io, as it spewed material 100 kilometers (62 miles) into space. The NASA release in October, 2000 reported that the insets for this photograph “were acquired to search for and image the plume vent or vents. We expected to see a small crater surrounded by radial streaks, but no such central vent can be seen in these or other images.  Instead, we see bright streaks along the margins of the lava”. 

In the electrical interpretation, the two bright spots in the highest resolution inset are cathode arcs seen diffusely through their jets, as they continue to encircle the darker area exposed by prior etching of the surface. The hot spots are exactly where the electric model, as proposed by Wallace Thornhill, had predicted. Finding no volcano, NASA scientists were left to speculate on how a “lava lake” could generate the observed plumes and jets many miles above the surface.

Over time, the fall of sulfur dioxide snow, resulting from the etching process, will cover the darker areas in the photograph. Electric theorists identify these regions as the burnt surface of the moon exposed beneath the “snow”, noting that these dark areas continually move with the movement of the Prometheus plume.  Since the Voyager observations in the late 1970s, Prometheus and the exposed regions have traveled more than 80 kilometers (50 miles)! 

No doubt it was this discovery that inspired one plasma scientist to find humor in the standard theory of Io’s “volcanic” activity. “On Io, volcanoes go south for the winter”.



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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