Caption: "Close up of the Martian Moon Phobos taken by Viking Orbiter 1 on February 20, 1977. Viking Orbiter 1 took this close-up photo of the Martian satellite phobos from a range of 120 kilometers at 5:15 p.m. (PST) February 20, 1977. That is the closest range at which any spacecraft has photographed the tiny satellite. At that range, Phobos is too large to be captured in a single frame. This picture covers an area 3 by 3.5 kilometers across. However, the high relative speed of Orbiter 1 and Phobos caused some image smear so that the smallest surface feature identifiable is between 10 and 15 meters (32 and 49 feet) across. Special processing in JPL's Image Processing Lab should improve resolution. The picture shows a region in the northern hemisphere of Phobos that has striations and is heavily cratered. The striations, which appear to be grooves rather than crater chains, are about 100 to 200 meters wide and tens of kilometers long. Craters range in size from 10 meters to 1.2 kilometers in diameter. The surface of Phobos appears similar to the highland regions of the Moon which also was heavily cratered and ancient terrain. The dark region above the limb of Phobos is an artifact of processing and does not indicate an atmosphere.
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