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Mars has been the subject of more attempts to explore it, and more failures, than any other planet. Of approximately 37 separate missions to Mars, only 13 have had any success. The planetary scientists of the [[Union of Soviet Socialist Republics]], so successful in exploring [[Venus]], experienced ten mission failures before achieving their first success, seven years after the [[United States]] achieved success with its [[Mariner 4]] mission. That Soviet mission, [[Mars 3]] in 1971, succeeded in placing a lander on Mars, but the lander's system transmitted for only 20 seconds before failing.

Mars has been the subject of more attempts to explore it, and more failures, than any other planet. Of approximately 37 separate missions to Mars, only 13 have had any success. The planetary scientists of the [[Union of Soviet Socialist Republics]], so successful in exploring [[Venus]], experienced ten mission failures before achieving their first success, seven years after the [[United States]] achieved success with its [[Mariner 4]] mission. That Soviet mission, [[Mars 3]] in 1971, succeeded in placing a lander on Mars, but the lander's system transmitted for only 20 seconds before failing.

In 1975, [[Project Viking]] achieved the most notable success by placing two orbiters and two landers on Mars. Neither nation would attempt any further missions to Mars until 1988, when the Soviets lost one craft en route and lost contact with the other ([[Phobos 2]] seconds after its rendezvous with Mars's inner [[moon]] [[Phobos]]. Nor was the United States' program immune to failure; its ''Mars Observer'' vessel was lost prior to arrival after some propulsion systems failed.<ref name=faq/>

In 1975, [[Project Viking]] achieved the most notable success by placing two orbiters and two landers on Mars. Neither nation would attempt any further missions to Mars until 1988, when the Soviets lost one craft en route and lost contact with the other ([[Phobos 2]]) seconds after its rendezvous with Mars's inner [[moon]] [[Phobos]]. Nor was the United States' program immune to failure; its ''Mars Observer'' vessel was lost prior to arrival after some propulsion systems failed.<ref name=faq/>

In 1996 the [[Mars Global Surveyor]] enjoyed the most success to date, returning more images than all previous missions combined. In that same year, the United States landed the first mobile explorer, or "rover," called the [[Mars Pathfinder]].

In 1996 the [[Mars Global Surveyor]] enjoyed the most success to date, returning more images than all previous missions combined. In that same year, the United States landed the first mobile explorer, or "rover," called the [[Mars Pathfinder]].