If humans are going to inhabit Mars, it will have to be warmer and wetter. One way to accomplish that is to use the gases environmentalists say threaten life on Earth, PAUL TAYLOR reports in the last instalment of a special two-part series.

By PAUL TAYLOR

Saturday, June 11, 2005 Page F9

Mars is an inhospitable place. Its barren rock-strewn surface resembles a polar desert, with a bone-chilling average temperature of minus 53 Celsius. And the atmosphere is so tenuous it barely provides any protection against comic rays from deep space.

In short, the Red Planet is cold, dry and frequently bombarded by hazardous radiation. But some scientists are convinced that it can be transformed by using greenhouse gases to thicken the atmosphere and melt the planet's polar ice caps. Indeed, the gases environmentalists say threaten life on Earth could be used to make Mars a warmer, wetter and more welcoming place.

These scientists believe that "terraforming" Mars -- making it more like Earth -- is necessary if humans are going to colonize the fourth rock from the sun.

Since the 1960s, serious scientists, including the late Carl Sagan, have been writing academic papers about altering the planets to suit human needs. But their musings now have greater relevance after U.S. President George W. Bush set a goal of sending American astronauts back to the moon and eventually to Mars.

"This would be a great benefit to Mars colonists," said Robert Zubrin, president of the Mars Society, a non-governmental group of space enthusiasts dedicated to putting Mars on the public agenda.

It is conceivable, he adds, that the rust-coloured surface of Mars could be covered in vegetation some day.

However, not everyone is a fan of turning the Red Planet into a green one. As a matter of principle, some are opposed to tampering with a pristine world. And some just fear that the massive and complex undertaking is bound to fail.

"It would be very easy to mess it up," said Terrence Dickinson, editor of SkyNews, a Canadian magazine of astronomy and stargazing. "That to me is the biggest danger . . . and you could end up with a man-made junk Mars."

Terraforming is not a job for the shortsighted. It could take hundreds of years to get the ball rolling and possibly thousands of years to complete.

Warming Mars and increasing its atmospheric pressure are the key requirements for making the planet suitable for human life.

The average atmospheric pressure on the planet's surface is currently less than 1 per cent of Earth's. In fact, the Martian surface pressure is roughly equivalent to the atmosphere 40 kilometres above Earth.

At that extremely low pressure, water cannot exist as a liquid. If a block of ice melted on Mars, it would be immediately converted into a gas.

That low pressure also does nasty things to living organisms. For example, if astronauts ventured outside without wearing protective spacesuits, the liquids in their bodies would vaporize. In other words, their blood would boil.

"It would not be a pretty picture," says Margarita Marinova, a Mars researcher at the California Institute of Technology in Pasadena, Calif.

Despite these extreme conditions, it might not take much to get the terraforming process started, says Chris McKay, a planetary scientist at the U.S. National Aeronautics and Space Administration's Ames Research Center in Moffett Field, Calif.

Dr. McKay believes that the Martian atmosphere could be beefed up to the desired level by releasing the large amounts of carbon dioxide frozen in the polar ice gaps.

It is also believed that the planet's soil holds huge stores of carbon dioxide, which could be liberated if there was a big thaw.

And this is where so-called greenhouse gases could play a critical role in the initial stages of the terraforming process. Right now, the sun's rays strike the surface of the planet, which then radiates most of this heat back into space as infrared energy. If man-made greenhouse gases were pumped into the upper atmosphere of Mars, they could act as an insulating blanket to hold in the sun's precious heat.

Once the temperature begins to rise, frozen carbon dioxide will be released from the poles and underground. As more carbon dioxide enters the atmosphere, Mars should get warmer and warmer -- because carbon dioxide is itself a greenhouse gas. At that stage, a self-sustaining runaway greenhouse effect should kick in, Dr. McKay says.

But what if there are already living organisms on Mars? Although the odds are against it, researchers think it's possible that primitive forms of life might have evolved on Mars in the distant past, when the planet was a warmer, wetter world. Some scientists have speculated that micro-organisms might still exist underground.

Dr. McKay believes that Mars should be left alone if it is home to a truly distinct branch of evolution.

"If we go there and find a common type of life -- bacteria that is the same as our bacteria -- we might as well move in because they are our cousins anyways," he says. "But if it's a very different type of life, . . . I would advocate letting the life grow separately."

However, the discovery of life would not stand in the way of some other terraforming advocates.

"We are talking about . . . the value of an entire world for new branches of the human civilization to grow and flourish," says Dr. Zubrin, who is the author of the best-selling book The Case For Mars, which lays out a detailed plan for inhabiting the Red Planet.

He sees the successful colonization of Mars as a monumental milestone in the history of human evolution and a jumping-off point to other parts of the universe. And he compares the current space age to that pivotal time when ancestral humans left their birthplace in Africa and began spreading across the globe.

Still, critics are not swayed by Dr. Zubrin's grand vision. Before mucking about with Mars, Mr. Dickinson says, it makes more sense to send probes to nearby stars to search for suitable planets for settlement.

Either way -- terraforming Mars or launching interstellar probes -- the task will take centuries, if not millennia.

But no matter how much people debate the issue today, the final decision will ultimately rest with the future colonists of Mars, Dr. Zubrin says. And he believes they will be drawn to terraforming for purely practical reasons. After all, it would make life a lot easier if you didn't have to put on a spacesuit just to go for a walk.

Paul Taylor is a Globe and Mail assistant national editor, responsible for health and science coverage.