Images from NASA's Mars Odyssey spacecraft were used to create this mosaic of nighttime infrared images of Gusev Crater, which has been draped over topography data obtained by NASA Mars Global Surveyor. Variations in nighttime temperatures are due to differences in the abundance of rocky materials that retain their heat at night and stay relatively warm (bright). Fine grained dust and sand (dark) cools off more rapidly at night. This image mosaic covers an area approximately 180 kilometers (110 miles) on each side centered near 14 degrees S, 175 degrees E, looking toward the south in this simulated view. http://photojournal.jpl.nasa.gov/catalog/PIA04261