AS15-2510(M)

Figure 180

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The crater Humboldt, on the east limb of the Moon, as seen from Earth, is 200 km across, a little larger than Tsiolkovsky. This view by the Apollo 15 mapping camera looks southward across Humboldt's ejecta blanket and into the crater. Irregular secondary craters partly covered by the ejecta are in the foreground, and a long chain of secondaries extends from Humboldt's rim to the foreground. Humboldt is one of the largest craters known to have a prominent central peak. If the crater is like terrestrial impact structures, the peak may expose rock uplifted about 10 percent of the crater's width, on the order of 20 km from beneath the crater floor. This would be an exciting find for future astronauts. A spider web of cracks on the crater floor suggested to R. B. Baldwin (1968) that the floor was bowed up in the middle. Later, dark mare lavas flooded low areas in the outer part of the floor and covered the cracks. A peculiar "bull's eye" double crater on the crater floor has several counterparts elsewhere on the Moon. The origin of these double craters is a continuing puzzle.  -K.A.H.