FIGURE 3.1 This image shows a portion of the residual southern polar cap. The carbon dioxide has sublimated to expose underlying water ice. Changes from year to year suggest that in the present epoch the amount of carbon dioxide in the residual cap is decreasing. This image from the Mars Orbiter Camera on the Mars Global Surveyor spacecraft is courtesy of NASA/ JPL/Malin Space Science Systems. The image covers an area of 2.9 by 4.8 km.