Ever since people began to think seriously about the prospects for space travel, visionaries have looked beyond the near-term prospects — flights into Earth orbit, space stations, and even journeys to the Moon — and toward the red planet: Mars. Unlike Venus, eternally shrouded by clouds, or the other planets which were too hot or cold to sustain life as we know it, Mars, about half the size of the Earth, had an atmosphere, a day just a little longer than the Earth’s, seasons, and polar caps which grew and shrank with the seasons. There were no oceans, but water from the polar caps might sustain life on the surface, and there are dark markings that appeared to change during the martian year. Some people interpreted this as plant life that flourished as polar caps melted in the spring and receded as they grew in the fall.

In an age where we have high-resolution imagery of the entire martian globe — obtained from orbiting spacecraft, telescopes orbiting Earth, and ground-based telescopes with advanced electronic instrumentation — it is often difficult to remember just how little was known about Mars in the 1950s, when people first started to think about how we might go there. Mars is the next planet outward from the Sun, so its distance and apparent size vary substantially depending upon its relative position to Earth in their respective orbits. About every two years, Earth “laps” Mars and it is closest (“at opposition”) and most easily observed. But because the orbit of Mars is elliptic, its distance varies from one opposition to the next, and it is only every 15 to 17 years that a near-simultaneous opposition and perihelion render Mars most accessible to Earth-based observation.