Any of a series of unmanned U.S. space probes sent near Venus, Mars, and Mercury. Mariners 2 (1962) and 5 (1967) passed Venus within 22,000 mi (35,000 km) and 2,500 mi (4,000 km), respectively, and made measurements of temperature and atmospheric density. Mariners 4 (1965), 6 and 7 (1969), and 9 (1971–72) obtained striking photographs of the surface of Mars and analyzed its atmosphere and magnetic field. Mariner 10 is the only spacecraft ever to have visited Mercury (1974–75).

This entry comes from Encyclopædia Britannica Concise.
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