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Viking

Either of two unmanned U.S. spacecraft launched by NASA in 1975. After nearly yearlong journeys, Vikings 1 and 2 entered orbits around Mars and released landers that touched down on the planet and relayed measurements of properties of its atmosphere and soil, as well as colour photographs of its surface. Experiments designed to detect evidence of living organisms provided no convincing evidence of life on the surface. The orbiters transmitted photographs of large expanses of the Martian surface.

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