Mariner 4

Launched on November 28, 1964, Mariner 4 performed the first successful flyby of Mars on July 15, 1965, passing within 6,118 miles of the surface. Its television camera captured 22 grainy images — the first close-up pictures of another planet ever taken — revealing a cratered, Moon-like landscape that upended popular visions of a living Mars.

Each image took roughly eight hours to transmit back to Earth at 8.33 bits per second, with engineers famously hand-coloring a paint-by-numbers printout of the raw data before the first official image processed. Mariner 4’s success established the template for planetary exploration: solar-powered spacecraft, deep-space navigation, and patient long-distance communication.