OAKLAND, CALIF. — To the most ancient civilizations, it was simply the "red one" - the only object in the heavens of such distinct color, a badge of terrestrial blood in the ethereal blackness. To the masters of the Enlightenment, it was the world most similar to ours, with an atmosphere, seasons, and caps of polar ice.
And to a generation of dreamers at the birth of the 20th century, it was home to a dying civilization of canal builders and vicious green men, the realm of Queen Azura and the Clay People.
Since humankind first turned its eyes toward the night skies in search of understanding, Mars has been a tableau for the breadth of human imagination - at once familiar and exotic, relatively near and utterly remote. Now, the Spirit rover is adding fresh strokes.
This is not the Mars of antiquity - a harbinger of war and death. Nor is it likely to offer 10-legged lions or superheroes in skintight suits. Instead, it offers a new narrative: The Mars of today's understanding tantalizes - an unsolved mystery for the CSI society. Feathery veins of dust hint at prehistoric torrents of water. Odd rock formations suggest vast ancient lakes.
The clues could lead to the biggest discovery in space science: Life on Mars - now or in the past. At the same time, they bring humans a step closer to the planet that will almost assuredly bear the first footprint.
"There is a scientific question of whether there is life on other worlds, and there is a historical question of whether humanity will be able to become a multiplanet species," says Robert Zubrin, founder of the Mars Society. "Mars is central to both."
Part of the reason for that is purely scientific. Mars is the only planetary candidate for life or human settlement, because all the others are too hot, too cold, or too toxic, or have no solid surface. The other part of the fascination with Mars, though, is pure science fiction.
When an obscure 19th-century Italian astronomer peered through his telescope and penned the word canale to describe deep clefts in the Martian surface, he unwittingly began the invention of the modern Mars myth.
To him, canale simply meant "channel." To astronomer Percival Lowell, though, the word conjured images of canals, and when he studied the Red Planet, he saw an Apocalyptic vision given more to fancy than fact.
Also noting dark patches across Mars's midsection, Lowell came to the only logical conclusion: The dark areas were vegetation, and a dying civilization had constructed an elaborate network of canals to carry water from the frozen poles to the plants at the arid lower latitudes.
The thesis, of course, was preposterous. But Lowell was a respected scientist from a famous family, and his books caused a sensation. Two years after Lowell's first book was published in 1895, H.G. Wells wrote of Martians attacking Earth for its water in "War of the Worlds."
Less than a decade after Lowell's final book was published in 1908, Edgar Rice Burroughs, author of "Tarzan," invented his Martian civilization of Barsoom, where another race was building canals to save the planet, while fighting a race of "green men."
In the astronomical stir at the turn of the century, Mars had become the birthplace of science fiction. And science fiction would return often. Flash Gordon fought Queen Azura and her nitrogen-stealing ray in 1938, while Ray Bradbury, Arthur C. Clarke, and Robert Heinlein have used Mars as a backdrop for stories on human colonization of space.
"Mars is home for science fiction," says Zubrin, who has written his own science-fiction book about the first mission to Mars, called "First Landing."
Recent years, however, have called for a shift in the story line, witnessed in books like Zubrin's, as well as films such as "Red Planet" and "Mission to Mars." Just as clearly as Lowell marked the creation of a Mars myth, the voyage of Mariner 4 in 1965 marked the beginning of a Mars enigma.
Mariner 4 and later missions caught no glimpses of primitive vegetation, much less Barsoomian princesses. But if they ruled out green men and death rays, they made Mars a trove of secrets - about the origins of organic life and about its own past.
Intricate channels and broad swirling patterns in various regions of Mars suggest that, at some time millions - if not billions - of years ago, huge quantities of water coursed over the Martian landscape, perhaps creating conditions for life.
The problem is, satellite analysis of the rocks in those areas seems to show no minerals that would be associated with wet conditions. Elsewhere, those minerals exist, but the landscape shows no signs of water erosion.
Into this confusion come rovers Spirit and Opportunity, which is scheduled to arrive Jan. 24. Perhaps they would have been more aptly named Marple and Poirot, for their primary task is to snoop in the soil and begin to solve this Martian paradox.
Opportunity is targeted to land in an area rich in hematite, a mineral formed with water. Spirit, meanwhile, is preparing for its jaunt around the Gusev Crater, which appears to be in an alluvial basin at the end of a long channel running out of the southern highlands.
"The current Mars is a dry desert," says Michael Carr, an astrogeologist with the United States Geological Survey in Menlo Park, Calif. "In the past, though it was very different, and unraveling that mystery is what is so interesting."