Two more Mariner flybys, both launched in 1969, sent back 57 images that, in the words of the NASA release, "revealed Mars to be heavily cratered, bleak, cold, dry, nearly airless and generally hostile to any Earth-style life-forms." But Mariner 9, an orbiter launched in 1971, dispatched, over 146 days, 7,000 photographs of surprisingly varied and violent topography: volcanoes, of which the greatest, Olympus Mons, is 13 miles high, and a system of canyons, Valles Marineris, that on Earth would stretch from New York City to Los Angeles. Great arroyos and tear-shaped islands testified to massive floods in the Martian past, presumably of water, the sine qua non of life as Earth knows it. In 1976 the two Viking landers safely arrived on the Martian surface; the ingenious chemical experiments aboard yielded, on the question of life on Mars, ambiguous results whose conclusions are still being debated into the 21st century.
In the meantime, our geographical and geological intimacy with Mars grows. The triumphant deployment of the little Sojourner rover in 1997 was followed in 2004 by the even more spectacular success of two more durable rovers, Spirit and Opportunity. In four years of solar-powered travels on the red planet, the twin robots have relayed unprecedentedly detailed images, including many clearly of sedimentary rocks, suggesting the existence of ancient seas. The stark, russet-tinged photographs plant the viewer right on the surface; the ladderlike tracks of Spirit and Opportunity snake and gouge their way across rocks and dust that for eons have rested scarcely disturbed under salmon pink skies and a pearlescent sun. In this tranquil desolation, the irruption of our live curiosity and systematic purpose feels heroic.
Now the Phoenix mission, with its surpassingly intricate arm, scoop, imagers, and analyzers, takes us inches below the surface of dust, sand, and ice in Mars's north polar region. Spoonfuls of another planet's substance, their chemical ingredients volatilized, sorted, and identified, become indexes to cosmic history. Meanwhile, the Mars Reconnaissance Orbiter, the newest of three operational spacecraft circling the planet, feeds computers at the University of Arizona with astoundingly vivid and precise photographs of surface features. Some of these false-color images appear totally abstract, yet they yield to knowledgeable eyes riches of scientific information.
The dead planet is not so dead after all: Avalanches and dust storms are caught on camera, and at the poles a seasonal sublimation of dry ice produces erosion and movement. Dunes shift; dust devils trace dark scribbles on the delicate surface. Whether or not evidence of microbial or lichenous life emerges amid this far-off flux, Mars has become an ever nearer neighbor, a province of human knowledge. Dim and fanciful visions of the twinkling fire planet have led to panoramic close-ups beautiful beyond imagining.