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Mars has long exerted a pull on the human imagination.The erratically moving red star in the sky was seen as sinister or violent by the ancients: The Greeks identified it with Ares, the god of war; the Babylonians named it after Nergal, god of the underworld. To the ancient Chinese, it was Ying-huo, the fire planet. Even after Copernicus proposed, in 1543, that the sun and not the Earth was the center of the local cosmos, the eccentricity of Mars's celestial motions continued as a puzzle until, in 1609, Johannes Kepler analyzed all the planetary orbits as ellipses, with the sun at one focus.
In that same year Galileo first observed Mars through a telescope. By the mid-17th century, telescopes had improved enough to make visible the seasonally growing and shrinking polar ice caps on Mars, and features such as Syrtis Major, a dark patch thought to be a shallow sea. The Italian astronomer Giovanni Cassini was able to observe certain features accurately enough to calculate the planet's rotation. The Martian day, he concluded, was forty minutes longer than our twenty-four hours; he was only three minutes off. While Venus, a closer and larger planetary neighbor, presented an impenetrable cloud cover, Mars showed a surface enough like Earth's to invite speculation about its habitation by life-forms.
Increasingly refined telescopes, challenged by the blurring effect of our own planet's thick and dynamic atmosphere, made possible ever more detailed maps of Mars, specifying seas and even marshes where seasonal variations in presumed vegetation came and went with the fluctuating ice caps. One of the keenest eyed cartographers of the planet was Giovanni Schiaparelli, who employed the Italian word canali for perceived linear connections between presumed bodies of water. The word could have been translated as "channels," but "canals" caught the imagination of the public and in particular that of Percival Lowell, a rich Boston Brahmin who in 1893 took up the cause of the canals as artifacts of a Martian civilization. As an astronomer, Lowell was an amateur and an enthusiast but not a crank. He built his own observatory on a mesa near Flagstaff, Arizona, more than 7,000 feet high and, in his own words, "far from the smoke of men"; his drawings of Mars were regarded as superior to Schiaparelli's even by astronomers hostile to the Bostonian's theories. Lowell proposed that Mars was a dying planet whose highly intelligent inhabitants were combating the increasing desiccation of their globe with a system of irrigation canals that distributed and conserved the dwindling water stored in the polar caps.
This vision, along with Lowell's stern Darwinism, was dramatized by H. G. Wells in one of science fiction's classics, The War of the Worlds (1898). The Earth-invading Martians, though hideous to behold and merciless in action, are allowed a dollop of dispassionate human sympathy. Employing advanced instruments and intelligences honed by "the immediate pressure of necessity," they enviously gaze across space at "our own warmer planet, green with vegetation and grey with water, with a cloudy atmosphere eloquent of fertility, with glimpses through its drifting cloud wisps of broad stretches of populous country and narrow, navy-crowded seas."
In the coming half century of Martian fancy, our neighboring planet served as a shadowy twin onto which earthly concerns, anxieties, and debates were projected. Such burning contemporary issues as colonialism, collectivism, and industrial depletion of natural resources found ample room for exposition in various Martian utopias. A minor vein of science fiction showed Mars as the site, more or less, of a Christian afterlife; C. S. Lewis's Out of the Silent Planet (1938) invented an unfallen world, Malacandra. Edgar Rice Burroughs's wildly popular series of Martian romances presented the dying planet as a rugged, racially diverse frontier where, in the words of its Earthling superhero John Carter, life is "a hard and pitiless struggle for existence." Following Burroughs, pulp science fiction, brushing aside possible anatomical differences, frequently mated Earthlings and Martians, the Martian usually the maiden in the match, and the male a virile Aryan aggressor from our own tough planet. The etiolated, brown-skinned, yellow-eyed Martians of Ray Bradbury's poetic and despairing The Martian Chronicles (1950) vanish under the coarse despoilment that human invasion has brought.
But all the fanciful Martian megafauna—Wells's leathery amalgams of tentacles and hugely evolved heads; American journalist Garrett Serviss's 15-foot-tall quasi red men; Burroughs's 10-foot, 4-armed, olive-skinned Tharks; Lewis's beaver-like hrossa and technically skilled pfifltriggi; and the "polar bear-sized creatures" that Carl Sagan imagined to be possibly roaming the brutally cold Martian surface—were swept into oblivion by the flyby photographs taken by Mariner 4 on July 14, 1965, from 6,000 miles away. The portion of Mars caught on an early digital camera showed no canals, no cities, no water, and no erosion or weathering. Mars more resembled the moon than the Earth. The pristine craters suggested that surface conditions had not changed in more than three billion years. The dying planet had been long dead.
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.