Which mission achieved the first fully successful Mars landing that operated for an extended period?

Fact

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The Soviet Mars 3 probe made the first soft landing on Mars in December 1971, but stopped transmitting about twenty seconds after its arrival. Viking 1, an American mission, landed in Chryse Planitia on July 20, 1976 and sent lasting images and scientific data. Its lander operated for more than six years and notably carried out experiments on the Martian soil and atmosphere. Viking 1 was therefore the first fully successful and long-lasting Martian landing, but not the first soft contact. This precision reconciles the chronology of Mars 3 with the scientific importance of Viking.