1971

First Mars Orbiters

Robotic planetary exploration for the past 50 years has followed a progression of ever more daring and technologically challenging space missions. Initially the goals were simply to learn how to navigate remote probes in space and make them fly by (or fly into) the Moon and other planets, sending back data in the form of pictures and other measurements. The next logical step is to try to establish orbiting satellites around other worlds—not only so that we can spend time learning about an alien environment but also so that we can map an extraterrestrial surface or atmosphere.

The first satellite to take this leap to the next level of planetary exploration and orbit another planet was NASA’s Mariner 9 space probe. Mariner 9 arrived at Mars in November 1971, during the throes of what astronomers had noticed was a planetwide dust storm. While the spacecraft’s spectrometers were taking data on dust properties and atmospheric temperatures, the probe’s television cameras were seeing primarily a bland, dusty cue ball of a world, with a few dark spots poking out of the dust.

After almost an Earth year in orbit, however, the dust had cleared enough for the mission to begin to map the planet’s surface in unprecedented detail. The Mars that was revealed in the Mariner 9 images was a geologic wonderland of giant towering volcanoes (the dark spots seen during the dust storm), enormous tectonically formed canyon systems, ancient river channels, and countless impact craters. It was a far cry from the impact-crater-dominated glimpse of Mars that had come from the previous Mariner flyby missions in 1965 and 1969.

The Soviet Union also took advantage of the opportunity to launch two Mars orbiters of their own in 1971, called Mars 2 and Mars 3. Both went into orbit a few weeks after Mariner 9, and both returned useful scientific information about the atmosphere and surface (once the dust had cleared). Both also deployed small landers and mini rovers to explore the surface. Though neither lander was successful, they became the first human artifacts to impact the surface of Mars.

Part of a Mariner 9 photograph of a maze of ridges, troughs, mesas, and impact craters called Noctis Labyrinthus. This region is about 190 miles (300 kilometers) across and is near the largest canyon system on Mars, Valles Marineris (Mariner Valleys), named after the Mariner 9 probe (left).