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English: Galileo color image of anti-Jupiter hemisphere of Io from August 2001. The new dark/light concentric feature in the center of the northern hemisphere of this image - the location of a new eruption site - was named Thor by the International Astronomical Union in 2006, after the publication of the original NASA caption, copied below. This image data is discussed, along with the Thor eruption site in this image, in Turtle, E. P.; et al. (2004). "The final Galileo SSI observations of Io: orbits G28-I33". Icarus 169: 3–28. doi:10.1016/j.icarus.2003.10.014.

One of the more fully illuminated color images of Io (second image from right) reveals a bull's-eye ring of new dark and light materials marking the eruption site. No obvious volcanic center had previously been seen at this location, 41 degrees north latitude and 133 degrees west longitude. The bright material of the new plume deposit overlies the red-ring plume deposit encircling the Tvashtar volcano at 63 degrees north, 123 degrees west. Tvashtar's ring deposit was first seen in Galileo images taken in late December 2000.

Another new full-disc color image of Io (far right) reveals yet another new plume deposit near Io's north pole, encircling the Dazhbog Patera volcanic site. This red ring has a diameter of about 1,000 kilometers (620 miles), suggesting a plume height of about 300 kilometers (190 miles). This plume deposit was not present in January 2001, so it is evidence of a new eruption.

Io is about the same size as Earth's Moon. All four images have resolutions of 18 to 20 kilometers (11 to 12 miles) per picture element. Unlabeled versions are also available. Click on the thumbnail versions below.

Infrared imagery from Galileo or Earth-based telescopes has detected intense hot spots at the sites of all three of these giant plumes. Giant polar plumes represent a class of eruption seen by the Voyager spacecraft in 1979, but not during Galileo's first five years of orbiting Jupiter. Voyager was unable to measure temperatures or other properties of these eruptions, so scientists are pleased Galileo has survived long enough to do so. Galileo reached Jupiter in late 1995. Its original two-year orbital mission has been extended three times to take advantage of the spacecraft's continuing capability to return valuable scientific information about the Jupiter system.

The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. Additional information about Galileo and its discoveries is available on the Galileo mission home page at http://galileo.jpl.nasa.gov.