Just got a reminder of this:"November 28,1964 Launch Complex 12 at Cape Canaveral came to life with the ignition of an Atlas LV-3 Agena-D rocket leaving the pad carrying the Mariner 4 probe. The NASA and JPL (Jet Propulsion Laboratory) spacecraft conducted scientific tests and observations of Mars during the “flyby” mission. It performed ”field and particle measurements” in the interplanetary space near Mars. Mariner 4 is credited with returning the first close up pictures of Mars to Earth and performing the first Mars flyby. Mariner 4 unexpectedly lasted 3 years after going into a solar orbit. Communication was ended December 21, 1967." (All images courtesy NASA/JPL)Although Voyagers 1 and 2 are by far the most important planetary spacecraft ever built, it strikes me that Mariner 4 probably belongs in the top ten, for changing our understanding of Mars. I think that scientific understanding of the atmosphere was already changing before Mariner 4 reached Mars, but this mission altered not only that, but also our cultural understanding of the Red Planet.