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1. A series of ill-fated Soviet probes to Mars. Contact was lost with Mars 1, launched in Nov. 1962, after it had traveled 106 million km. Mars 2 and 3 entered orbit around Mars in Nov. and Dec. 1971 after detaching lander capsules: that from Mars 2 crashed and the other stopped transmitting within two minutes of touchdown. The orbiters made surface and atmospheric studies. Mars 4, an intended orbiter, passed the planet in Feb. 1974 after retrorocket failure. Mars 5 entered orbit two days later but ceased functioning after a few days of photographic reconnaissance. Mars 6 flew past Mars in Mar. 1974, ejecting a lander capsule that crashed on the surface. Mars 7 passed Mars three days before Mars 6 but its intended lander missed the planet completely.
2. Space probes to Mars, such as the Mariner, Viking, Mars Global Surveyor, Mars Express, and Mars Odyssey missions.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006