This image is the highest-resolution thermal, or heat image, ever made of Amirani, a large volcano on Jupiter's moon Io. It was taken on October 10, 1999, by the near-infrared mapping spectrometer onboard NASA's Galileo spacecraft. Amirani is on the side of Io that permanently faces away from Jupiter.

This image of Amirani was taken at a distance of less than 25,000 kilometers (16,000 miles). The picture scale is approximately 6.5 kilometers (4 miles) per spectrometer pixel. The center and right images show views of Amirani as seen by the spectrometer at two wavelengths, 1.0 and 4.6 microns. These images can be compared with a visible wavelength image (on the left) of the same area obtained by Galileo's camera during a previous orbit. The visible light image shows extensive lava flows and a dark-floored caldera with associated bright red deposits of material fed from the volcano. The spectrometer observation was made in daylight. The center image, taken at a wavelength of 1 micron, shows light and dark areas on the surface that can be used to line up the spectrometer data with the camera image. The image on the right shows the same area at a wavelength of 4.6 microns, which reveals the thermal emission from three separate volcanic areas. The locations of these three "hot spots" correspond to the darkest features in the camera image, reinforcing a previously held belief by Galileo scientists that there is a correlation between the dark areas and the hot spots.

The three spectrometer hot spots are located at the eastern edge of the caldera at the bottom of the camera image, and two locations along the massive Amirani flows. These are most likely active lava flows on the surface.

Launched in October 1989, Galileo entered orbit around Jupiter on December 7, 1995 on a mission to study the giant planet, its largest moons and its magnetic environment. JPL manages the 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://solarsystem.nasa.gov/galileo/. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/gallery/io.cfm.