Mariner 4 made the first successful close flyby of Mars and returned the first close-up images of the planet.
NASA launched Mariner 4 on November 28, 1964. It flew past Mars on July 14–15, 1965, passing within about 9,846 kilometres of the surface. The spacecraft transmitted 22 television images, covering only a small portion of Mars but revealing a cratered, Moon-like landscape.
Those pictures changed scientific expectations. Before Mariner 4, some observers still imagined Mars might have canals, vegetation, or a relatively Earth-like surface. The images instead showed widespread craters and a cold, apparently dry world. The spacecraft also made measurements of Mars’s atmosphere and radiation environment.
Mariner 4 did not enter orbit or land. Mariner 9 became the first spacecraft to orbit Mars in 1971 and later mapped almost the entire planet. Mariner 4’s importance lies in its pioneering flyby and the first successful transmission of close-range Martian photographs to Earth.