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Let's go to Mars

Mariner 9 arrives into a planet-wide dust storm

The first spacecraft ever to orbit another planet reached Mars to find the surface hidden by dust. It waited, then mapped volcanoes, a 4,000 km canyon and dry riverbeds.

A black and white photograph of Mars against black space. The disc is lit from the right and about half in shadow, its surface a smooth, almost featureless pale grey, with one small dark smudge near the top of the lit side and a few tiny black specks elsewhere on it.
Mariner 9's approach view of Mars, taken on 11 November 1971 from about 660,000 kilometres out, three days before the spacecraft entered orbit. Dust from the global storm covered the planet; the dark patch near the top was tentatively identified as Nix Olympica, the albedo feature Mariner 9 showed to be the volcano now named Olympus Mons. · Image: NASA/JPL

Mariner 8 was to map most of the surface while Mariner 9 watched the planet change beneath it. Instead Mariner 8 went into the Atlantic on 9 May 1971, when a failed integrated circuit in the Centaur's pitch guidance module cost the upper stage its control 4.7 minutes after launch, and both jobs were rewritten onto the one survivor. Mariner 9 launched on 30 May, flew 167 days and on 14 November 1971 fired its engine for 15 minutes 23 seconds to enter orbit, the first spacecraft from Earth to orbit another planet.

A dust storm that began on 22 September in the Noachis region had grown into one of the largest global storms ever recorded, and the surface lay under opaque haze. The first images were a featureless orange blank, four dark spots showing through near Tharsis and the south polar cap faintly visible. The team stopped the pre-loaded imaging sequence, held it and waited.

The storm cleared through December and January, and the four dark spots resolved into the summits of the largest volcanoes in the solar system. The biggest, then Nix Olympica and now Olympus Mons, stands about 22 kilometres above the surrounding plains. East of Tharsis the cameras found a canyon system more than 4,000 kilometres long and over 7 kilometres deep in places, later named Valles Marineris after the spacecraft. Branching, sinuous channels with tributaries, islands and scour marks threaded across the older terrain, features that on Earth are cut by running water.

When the attitude-control gas ran out on 27 October 1972, Mariner 9 had returned 7,329 images covering 85 percent of the planet, plus the first close looks at Phobos and Deimos. Mariners 4, 6 and 7 had photographed the ancient southern highlands and concluded the planet was geologically dead. One orbiter with global coverage showed active volcanism, tectonics, wind-driven dust on a planetary scale, and the tracks of water that no longer flows.