homeaboutessential guidepicture of the daythunderblogsnewsmultimediapredictionsproductsget involvedcontact

Credit: NASA/JPL


pic of the day
  subject index
  abstract archive



Electric Cosmos

The Universe

Plasma Cosmology

Society for



Dec 17, 2004
Io's "Volcanoes" Blur Scientific Vision

Don’t be misled by the sheets of “flame” depicted in the above images of the Tvashtar region of Io, Jupiter’s closest moon. Planetary scientists have colored in bleached-out areas on the photographs taken by the Galileo probe, converting the images into what they had expected to find—lava fountains.

The Galileo spacecraft caught the “volcanic eruption” of the top photograph on November 25, 1999, and the NASA release explains: “The molten lava was hot enough, and therefore bright enough, to saturate, or overexpose, Galileo’s camera.” The original image is inset in the lower right corner of the photograph. According to the release, “surface flows shown in the color image were assembled as an interpretive drawing by Galileo scientists”.

Yet no lava flow ever witnessed has exhibited temperatures so high as to produce the effect seen in the original Galileo image.

The lower photograph, taken on February 22, 2000, shows a super-heated region that is more than 60 kilometers (37 miles) long. NASA released the picture in false color, leaving the unfounded impression that the picture is showing a conventional lava fountain. “The lava appears to be producing fountains to heights of up to 1.5 kilometers (5,000 feet) above the surface”.

This image is actually a processed mosaic combining images taken in the near-infrared, clear, and violet filters. All that later analysis could determine is that temperatures exceeded 1200 K. To place the matter in perspective, with attention to the alternative electrical explanation: a lightning discharge "pinches" down to a few centimeters diameter (or possibly meters in the case of the diffuse discharge on Io) where it meets a conducting electrode. So if the instruments were detecting an electric discharge any temperature reading, averaged over a much larger region than the actual heat source, would have greatly understated the real temperature.

Nevertheless, the radiation was so intense that it overloaded the Galileo camera, as if it were looking at a line of arc lights, producing "whiteouts" on the electronic images.

The electric interpretation suggests that continuous electrical arcing has etched the surface of Io, creating flat plains and bluffs with scalloped edges. In much the same way, electric arcs are used in industry to machine metallic surfaces to a high level of precision. The most recent etching in this region has exposed the dark surface below the falling sulfur dioxide snow, and in the lower picture we see two bright spots where it appears that arcs are continuing to extend the excavated area in two directions.



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

Copyright 2004: