Mariner 4 returned the first close-up photographs of the Martian surface.
NASA launched Mariner 4 on 28 November 1964, and the spacecraft flew past Mars on 14 July 1965. During the encounter it transmitted 22 television images, covering only a small part of the planet but revealing cratered terrain that looked unexpectedly similar to the Moon.
The photographs changed scientific expectations about Mars. Before Mariner 4, some observers still imagined a planet with canals, vegetation, or a relatively Earth-like environment. The images instead showed a cold, dry world with a thin atmosphere, at least in the regions photographed.
Mariner 4 was a flyby spacecraft, not an orbiter or lander. Mariner 9 later became the first spacecraft to orbit Mars and mapped the planet in much greater detail.