Figure 6-2 RIVUXG Impact Craters These images, all taken from spacecraft, show impact craters on three different worlds. (a) The Moon’s surface has craters of all sizes. The large crater near the middle of this image is about 50 mi (80 km) in diameter, equal to the length of San Francisco Bay. (b) Manicouagan Reservoir in Quebec is the relic of a crater formed by an impact more than 200 million years ago. The crater was eroded over the ages by the advance and retreat of glaciers, leaving a ring lake 60 mi (100 km) across. (c) Lowell Crater in the southern highlands of Mars is 125 mi (200 km) across. Like the image of the Moon in (a), there are craters on top of craters. Note the light-colored frost formed by condensation of carbon dioxide from the Martian atmosphere.