On July 14, 1965, Mariner 4 swooped over Mars. It was a moment of high drama. Six other probes had already tried to reach the red planet and failed. Since the days of H.G. Wells (War of the Worlds, 1898), people had been hearing about life on Mars, and they were ready to see the canals and cities. The wait was becoming excruciating.
Finally, all was revealed. With flawless precision, Mariner 4 dipped less than 10,000 km above the planet’s surface and took 22 pictures. Mars was covered with desert sand and ancient craters. No cities. No canals. No Martians. No one would ever look at the red planet the same way again.
Most histories of the mission end right there, with Mariner 4 buzzing Mars—”the first spacecraft to visit the red planet”– and throwing cold water on a lot of good science fiction. But there’s more to the story. After the flyby, something strange happened to Mariner 4, setting the stage for a 40-year mystery…