Mariner 4 Launches: First Glimpse of Mars from Space

NASA launched the Mariner 4 probe toward Mars on November 28, 1964, from Cape Canaveral, Florida. Eight months later, on July 14-15, 1965, it became the first spacecraft to successfully fly by Mars and return close-up images of the planet's surface. What it revealed shattered a century of hopeful speculation. Before Mariner 4, Mars was imagined as a world that might support life. Percival Lowell had mapped what he believed were canals built by an intelligent civilization. Science fiction writers had populated the planet with everything from Wells's tentacled invaders to Bradbury's poetic ancient Martians. Even scientists expected to see evidence of vegetation, possibly water features, and a thin but present atmosphere. Mariner 4 returned 22 photographs. They showed a cratered, barren, moon-like surface with no canals, no water, no vegetation, and no sign of any geological activity that might support life. The images covered about one percent of the Martian surface, concentrated in the southern hemisphere, and every frame showed the same desolation: impact craters, dust, and rock. The atmospheric measurements were equally discouraging: the surface pressure was only about 1 percent of Earth's, far too low for liquid water to exist. The psychological impact was significant. A generation of scientists and the general public had to abandon their romantic image of Mars in a single week. The search for Martian life, which had been a driving motivation for planetary exploration, had to be reframed. Future missions would look for microbial life, past water, or chemical signatures rather than civilizations or forests. Mariner 4 was a technical triumph. The spacecraft used a television camera, a tape recorder, and a transmitter with only 10 watts of power, equivalent to a dim light bulb, to send its data across 134 million miles. The first image took over eight hours to transmit. Engineers at JPL were so impatient that they colored the first image by hand with pastels as the data came in, number by number, before the computer processing was complete.