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Today, newspapers have printed pictures of a barren Martian surface, but the planet still fascinates scientists and science fiction writers. It's the focal point of new disciplines like comparative planetology and terraforming, and a crystal ball for our hopes of civilization and fears of ecological devastation.

Early views

Mars' proximity to Earth and clearly visible surface features once led scientists to conclude that the two planets were nearly identical in climate, geography and life forms.

"[Mars] has a considerable but moderate atmosphere, so that its inhabitants probably enjoy a situation in many respects similar to our own," wrote astronomer William Herschel in 1781.

The supposed similarities were reinforced during the 1777-78 opposition, when Mars comes closest to Earth. Astronomer Giovanni Schiaparelli observed and mapped hundreds of "canali," channels of water that became the famous canals of Mars.

Percival Lowell studied Mars for two decades, and theorized in 1896 that the Martians transported melting water from polar icecaps in the canals to keep the planet from being overrun by deserts.

Lowell imagined Mars as more geographically and culturally evolved than Earth -- a society without political divisions facing a deteriorating planet -- and pointed to Earth's deserts as a sign that our planet faced the same fate.

"Earth, then, is going the way of Mars," Lowell wrote.

Science fiction goes to Mars

Lowell's theories, while hotly debated, sparked the imagination of others.

"Lowell's vision of a dying planet has shaped what writers could imagine and what their readers expect about a fictional Mars," Markley explains. "On the red planet, humans confront the consequences of ecological devastation: sparse resources, vast stretches of desert, and thin or unbreathable air."

H. G. Wells' 1898 novel The War of the Worlds expanded on Lowell's concept of Mars as a reflection of Earth. The story of Martians rampaging through the civilized fields of England became the archetypical alien invasion tale, and Wells intended it to force Westerners to examine their own society.

"Before we judge of them too harshly we must remember what ruthless and utter destruction our own species has wrought, not only upon animals, such as the vanished bison and the dodo, but upon its inferior races," Wells wrote. "Are we such apostles of mercy as to complain if the Martians warred in the same spirit?"

Throughout the 20th century Mars remained a focus for science fiction writers. In the wake of increasing scientific skepticism about advanced life on Mars, novelists began to represent Mars as a barren landscape that supported only primitive life forms.

Even as the evidence that Mars was dead mounted from orbital surveys and probe landings, SF writers continued to find scenarios for life. Explorers found evidence of primitive lichens in Ben Bova's 1992 novel Mars, while Greg Benford found a plausible hiding place for even more complex life in his recent novel The Martian Race.

Mars in Earth's image

Despite the inventiveness of SF writers, the orbital photography of Mariner 4 firmly established Mars as a dead rather than dying planet. When subsequent missions revealed evidence of tectonic activity, volcanic heat and times when water flowed freely on the Martian surface, though, the possibility rose that Mars could be brought back to life.

Carl Sagan and others proposed the "long winter" model of Martian climatology, arguing that Mars had once been a warmer and wetter planet that could have supported life. They also speculated that Mars could be turned into a warm and wet planet once again -- one that might be suitable for human habitation.

The idea of refashioning Mars in Earth's image caught on. Novelists, poets, artists and screenwriters began to explore the possibilities of terraforming and ecopoesis, the engineering of a new Martian ecology.

In the 1990s, Kim Stanley Robinson won critical acclaim and an armful of awards for his "Mars" trilogy, which follows a group of colonists through a century-long quest to transform the planet. He sees the books as reflecting the conditions of our own world.

"The first reason to go learn more about Mars is because that will teach us more about Earth," Robinson says. "And we need to know everything we can possibly know about Earth to get through what I think of as a kind of crisis period, a couple centuries of overcrowded environmental danger."

As they contemplate missions to Mars in the 21st century, however, many scientists see terraforming as the logical extension of humankind's need to exploit the resources of the solar system in order to overcome, or escape, ecological crises on Earth.

Would such action be just another extension of our self-destructive nature, like throwing out an empty pop bottle because we can buy another? Or would the settling of the Martian frontier serve as another example of our boundless reservoir of innovation?

It's too early to say, but the question gives us yet more theories for science and more fodder for fiction. In this light, Mars has never changed.