Figure 7-11 RIVUXG Neptune from Voyager 2 When this picture of Neptune’s southern hemisphere was taken in 1989, the Great Dark Spot measured about 7500 mi by 5000 mi (12,000 km by 8000 km) comparable in size to Earth. (A smaller storm appears at the lower left.) The white clouds are thought to be composed of crystals of methane ice. The color contrast in this image has been exaggerated to emphasize the differences between dark and light areas.