This is a high resolution (12 meters or 39 feet per pixel element) mosaic of images taken by NASA's Galileo spacecraft during a flyby of Io on 22 February 2000. It shows lava flows, bright streaks, and ridged plains at the northern margin of lava flow field at the volcanic center Prometheus. The lava is erupting from a fissure about 40 kilometers (25 miles) east (right) of the edge of this mosaic, and the 100 kilometer (62 mile) tall Prometheus plume is erupting from somewhere near the western end of this mosaic [*** PPJ, please link to other releases]. This mosaic was 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. Instread, we see bright streaks along the margins of the lava.

The darkest areas are warm lava flows. Warm lava is dark because it is either too hot or too recent for significant amounts of sulfur-dioxide frost or snow from the plume to have condensed onto it. The blow-up shows two bright dots where hot lava is breaking out of the edge of one of the dark lava flows. The bright, ridged plains to the north of the lava are probably sulfur-dioxide-rich fields. The formation mechanism for the ridges is unclear. The very bright streaks radiating from where the lava flows overrun the field are where the hot lava recently vaporized the sulfur-dioxide which then coats the lava-facing sides of the ridges.

The Prometheus plume has been seen by both the Voyager and Galileo spacecraft whenever the viewing geometry has been favorable. While the morphology of the plume has been nearly constant, the plume's position jumped about 80 kilometers (50 miles) between the Voyager and Galileo observations. The lava flow field has also migrated a similar distance. Galileo scientists are currently investigating whether fresh lava breakouts overrunning sulfur-dioxide-rich plains can help explain the plume observations.

Image produced by: Moses Milazzo, Planetary Image Research Lab. (PIRL), Lunar and Planetary Lab. (LPL), University of Arizona

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is a division of the California Institute of Technology, Pasadena, CA.

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at http://galileo.jpl.nasa.gov/. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/images/io/ioimages.html.

NASA's Planetary Photojournal PIA-02568

October 26, 2000