This picture of the Martian moon Deimos was taken Oct. 15, 1977, when Viking Orbiter 2 passed only 30 miles (50 kilometers) away. The picture covers 0.74 by 0.93 miles (1.2 by 1.5 kilometers) and shows features as snail as 10 feet (3 meters). Deimos is saturated with craters, but a layer of dust appears to cover craters smaller than 165 feet (50 meters), making Deimos look smoother than the other Martian moon Phobos. Boulders as large as houses -- 33 to 100 feet (10 to 30 meters) across -- are strewn across the face, probably blocks ejected from nearby craters. Viking Orbiter 2 was traveling 3,800 miles an hour (1.7 kilometers per second) relative to the moon when the picture was taken; spacecraft controllers slowed the camera platform one degree per second to reduce image smear. The spacecraft would have been clearly visible to an observer Standing on the surface of Deimos. It would have been easier to target for an impact of Deimos than to fly past at the desired point. Viking guest investigator Thomas Duxbury was in charge of the Deimos flyby. Cal Broom is manager of the Viking Project for the Langley Research Center, Hampton, Va.
