In the summer of 1965, scientists at the Jet Propulsion Laboratory were so impatient for the first digital image from another planet that they bought pastels and hand-colored the printed numbers on a wall. This episode tells the story of Mariner 4, the 260-kilogram octagonal spacecraft launched on November 28, 1964 that became the first to fly past Mars. We begin with the loss of Mariner 3, whose fiberglass payload shroud delaminated and stayed clamped shut, and the frantic redesign of an all-metal fairing plus Atlas-Agena booster upgrades to make the 26-month launch window.

We explain why deep-space navigation needed the star Canopus, how flecks of dust reflecting sunlight sent the star tracker hopping between Regulus and stray light until engineers removed the brightness limit, and how the July 15, 1965 flyby at 9,846 kilometers returned 21 and a half pictures at 8 and a third bits per second, six hours per frame. The images showed a cratered, moon-like world with atmospheric pressure of 4.1 to 7.0 millibars, daytime temperatures of minus 100 degrees Celsius, and no magnetic field, ending the era of Percival Lowell’s canals. We close with the 1967 comet debris encounter, the exhaustion of nitrogen gas, and the derelict still orbiting the sun.

• Why a pressure differential in the Mariner 3 nose cone trapped a working spacecraft
• How Canopus became the standard navigation reference for decades of deep-space missions
• What it took to transmit a single photograph across millions of miles in 1965
• Why photographing one percent of Mars still overturned centuries of speculation about Martian civilizations
• How the $83.2 million mission laid the groundwork for every later Mars rover and orbiter