Bringing Life to Mars; The Future of Space Exploration; Scientific American Presents; by McKay; 6 Page(s)

Four billion years ago Mars was a warm and wet planet, possibly teeming with life. Spacecraft orbiting Mars have returned images of canyons and flood valleys-features that suggest that liquid water once flowed on the planet's surface. Today, however, Mars is a cold, dry, desertlike world with a thin atmosphere. In the absence of liquid water-the quintessential ingredient for life-no known organism could survive on the Red Planet.

More than 20 years ago the Mariner and Viking missions failed to find evidence that life exists on Mars's surface, although all the chemical elements needed for life were present. That result inspired biologists Maurice Averner and Robert D. MacElroy of the National Aeronautics and Space Administration Ames Research Center to consider seriously whether Mars's environment could be made hospitable to colonization by Earthbased life-forms. Since then, several scientists, using climate models and ecological theory, have concluded that the answer is probably yes: With today's technology, we could transform the climate on the planet Mars, making it suitable once more for life. Such an experiment would allow us to examine, on a grand scale, how biospheres grow and evolve. And it would give us the opportunity to spread and study life beyond Earth.