This image of Loki Patera on Jupiter's volcanic moon Io shows data taken by the near-infrared mapping spectrometer onboard NASA's Galileo spacecraft during its Io flyby on October 10, 1999, superimposed on a Galileo camera image 162 kilometers (100 miles) across.
The spectrometer observation has been translated into two types of temperature maps. Image A represents brightness temperatures, which are calculated by assuming that each whole pixel is at a uniform temperature. This map shows that the dark caldera floor is warm, while the light-colored island in the middle of the caldera and the terrain outside the caldera are cool. The scale on the side gives the temperatures in degrees Kelvin (280Kelvins = 45 degrees Fahrenheit, warm compared to the temperature of Io's surface, which is about 122 Kelvin, or -240 Fahrenheit). Image B represents color temperatures, which are calculated assuming the areas emitting heat can be smaller than the area of a single pixel. This map shows that the hottest temperatures (up to 460 Kelvin or 370 F) are seen in a crack running through the center of the island. The maps indicate that the floor and crack on the caldera are filled with cooling lava flows, the youngest (and therefore hottest) lavas being those in the crack. These lavas are thought to be a few months old.
The Jet Propulsion Laboratory, Pasadena, CA 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 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.