From http://www.jpl.nasa.gov/galileo/

   
                 Color Mosaic and Active Volcanic Plumes on Io
                                       
   
   
   NOTE: This JPEG image is made available in order to share with the
   public the excitement of new discoveries being made via the NASA/JPL
   Galileo spacecraft. Galileo scientists are in the process of
   calibrating and validating this data. The full digital image necessary
   for scientific analysis will be released within one year of receipt of
   this orbit's last data.
   
   This image is available only on the WWW; it is not available in
   hardcopy or other forms.
   
   
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Color Mosaic and Active Volcanic Plumes on Io

   
   
   This color image, acquired during Galileo's ninth orbit (C9) around
   Jupiter, shows two volcanic plumes on Io. One plume was captured on
   the bright limb or edge of the moon, erupting over a caldera (volcanic
   depression) named Pillan Patera. The plume seen by Galileo is 140
   kilometers (86 miles) high, and was also detected by the Hubble Space
   Telescope. The Galileo spacecraft will pass almost directly over
   Pillan Patera in 1999 at a range of only 600 (373 miles). The second
   plume, seen near the terminator, the boundary between day and night,
   is called Prometheus after the Greek fire god). The shadow of the
   airborne plume can be seen extending to the right of the eruption
   vent. (The vent is near the center of the bright and dark rings).
   Plumes on Io have a blue color, so the plume shadow is reddish. The
   Prometheus plume can be seen in every Galileo image with the
   appropriate geometry, as well as every such Voyager image acquired in
   1979. It is possible that this plume has been continuously active for
   more than 18 years. In contrast, a plume has never been seen at Pillan
   Patera prior to the recent Galileo and HST images.
   
   Color images from orbit C9 have been merged with a high resolution
   mosaic of images acquired in various orbits to enhance the surface
   detail.
   
   North is to the top of the picture. The resolution is about 2
   kilometers (1.2 miles) per picture element. This composite uses images
   taken with the green, violet, and near-infrared filters of the Solid
   State Imaging (CCD) system on NASA's Galileo spacecraft. The C9 images
   were obtained on June 28, 1997 at a range of more than 600,000
   kilometers (372,000 miles).
   
   The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo
   mission for NASA's Office of Space Science, Washington, DC. JPL is an
   operating division of California Institute of Technology (Caltech).
   
   This image and other images and data received from Galileo are posted
   on the World Wide Web, on the Galileo mission home page at URL
   http://www.jpl.nasa.gov/galileo. Background information and
   educational context for the images can be found at URL
   http://www.jpl.nasa.gov/galileo/sepo