A very active volcano on Jupiter's moon Io, probably composed of erupting lava fountains, was seen by the Near-Infrared Mapping Spectrometer onboard NASA's Galileo spacecraft. The volcano is shown here (in color) superimposed on the camera image that was taken almost simultaneously. The spectrometer observation covers the eastern part of the active caldera and shows a hot, active region (in red). The blue color represents cool terrain surrounding the caldera. The spectrometer instrument can detect heat from active volcanic regions by imaging them in near-infrared light (0.7 to 5.2 micron wavelengths). Determining temperatures of the hot region has been difficult because the lava is so hot that it exceeded the upper limit that the instrument could measure. The lava is at least 700 degrees Celsius 1,292 degrees F), but the hotter regions within the caldera probably exceed 1,200 Celsius (2,192 degrees F)

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 Galileo mission home page at http://solarsystem.nasa.gov/galileo/. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/gallery/io.cfm.