February 24, 1969 (Mariner 6); March 27, 1969 (Mariner 7)
Mariner 6 and 7 were the second pair of Mars missions in NASA's Mariner series of solar system exploration in the 1960s and early 1970s. As with the other Mariners, each launched on an Atlas rocket with either an Agena or Centaur upper-stage booster, and weighed less than half a ton (without onboard rocket propellant).
In 1969, Mariner 6 and Mariner 7 completed the first dual mission to Mars, flying by over the equator and south polar regions and analyzing the Martian atmosphere and surface with remote sensors, as well as recording and relaying hundreds of pictures. By chance, both flew over cratered regions and missed both the giant northern volcanoes and the equatorial grand canyon that was discovered later. Their approach pictures did, however, show that the dark features on the surface long seen from Earth were not canals, as once interpreted in the 1800s.