Heavily Cratered Terrain and Smooth Plain

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This photograph of Mercury was taken by the Mariner 10 spacecraft froma range of 34,860 miles (55,340 kilometers) during the first Mercury encounteron March 29, 1974. It shows an area in the northern hemisphere in the general area of photography to be obtained during the thrid encounter, Sunday, March 16, 1975. Seen in the photograph is a transition from heavily cratered terrain to a smooth plain. These smooth plains areas on Mercury are thought to be volcanic in origin with lava flows filling in heavily cratered areas. The photograph area is about 308 miles (490 kilometers) wide. Posted on: 17 Mar, 2003