For Life on Mars, Add Air, Heat--and 100,000 Years : Space: Scientists say it’s a long shot, but man-made greenhouse effect could make the Red Planet habitable.

With a poisonous atmosphere and temperatures so unbearably cold they can plunge to 220 degrees below zero, Mars is an inhospitable place where any unprotected creature from Earth would die instantly.

But a team of NASA scientists, noting that the atmosphere of Earth has changed dramatically throughout history--and apparently is still changing because of human activities--has concluded that it just might be possible to change the atmosphere of Mars so that the Red Planet could support life.

It would all have to be done with resources that are on Mars, and the researchers say it is too early to know if the raw materials are even there. But if they are, it may be that some day, say 100,000 years from now, humans will walk among the trees and flowers they have cultivated on Mars, breathing fresh Martian air that they have altered radically.

That scenario comes from a team of sober-minded experts on the possibility of extraterrestrial life. Two of the researchers work at the National Aeronautics and Space Administration’s Ames Research Center in Mountain View, Calif., and the third is at Pennsylvania State University. The scientists, who are publishing their ideas in today’s issue of the British journal Nature, admit that none of this may come to pass because Mars may not have the materials needed to do the job.

“We’re just trying to encourage some serious thinkers to think about it,” said Brian Toon, one of three authors of the report. The others are Christopher P. McKay of Ames, one of the world’s leading researchers in exobiology--the study of life on other planets--who is in Siberia looking for primitive life forms inside rocks, and James F. Kasting of Pennsylvania State.

The scientists see two scenarios. The more plausible is one in which the planet could be changed enough to support plant life. Once that is accomplished, the plants would produce oxygen, changing the atmosphere of Mars just as plant life transformed the atmosphere of Earth. Eventually, it just may be possible that animals could survive there, perhaps even people, but that goal would be far more difficult to achieve.

One novel approach suggested by the scientists is to establish factories on Mars that would produce gases similar to those on Earth that are believed to be warming the atmosphere through the greenhouse effect. Those gases could also produce a greenhouse effect on Mars, the scientists contend, warming the planet and beginning a series of events that could make it more hospitable.

The scientists published their conclusions partly to rebut science fiction writers, and even some other scientists, who have come up with ideas such as hauling an icy moon from Jupiter to Mars to supply the water that would be essential for life to exist on Mars. That is not possible, the scientists argue, and neither is it conceivable to transport the necessary materials from Earth because the quantities are mind-boggling.

“It would take millions of rockets,” said Toon. “There’s no way you are going to transport the materials to Mars.”

So the only possibility, they conclude, is to use materials that are already there. However, no one knows for sure if Mars has what would be needed, such as water frozen at its polar caps or beneath the soil, and prodigious amounts of carbon dioxide that could be released into the air to make the thin atmosphere denser and the planet warmer.

Atmospheric pressure on the surface of Mars is equivalent to that at 100,000 feet above the Earth, and that is so thin that “if you stepped out your blood would boil,” Toon said.

So three things must be done: The atmospheric pressure must be raised substantially, the planet must be warmed and the chemical composition of its atmosphere must be changed.

“This is not something that is going to happen quickly,” Toon said.

“We suggest that a key goal for future exploration of Mars should be to determine the feasibility of terraforming that planet,” the scientists said in their report, referring to the process by which Mars could be transformed into a more Earth-like planet.

Andrew P. Ingersoll of Caltech, an expert on the atmospheres of other planets, agrees that if Mars is ever to be made habitable, it will have to done with resources that the planet itself can provide.

“The question is whether the materials are there,” he said.

“The only reason for hope is there is evidence that water did flow once on Mars, long ago when the sun was dimmer,” Ingersoll added. “If it happened once, it could happen again.”

The big uncertainty is over what happened to water that once coursed through the ancient riverbeds that can be seen on the surface of Mars today. Did it boil off into space and is thus lost forever? Or is much of it still on Mars, frozen at the poles or in the permafrost that many scientists believe covers much of the planet?

“Biologically, you have to have it,” Toon said. In addition, water vapor in the atmosphere could provide the agent needed to collect solar energy and warm the planet.

The scientists believe it may be possible to start the process in some way, and then let nature take its course and complete the job.

“You would trigger a runaway process,” Toon said.

That might be done through a greenhouse effect. Carbon dioxide, the same gas that is believed to be causing the Earth to grow warmer, might do the job, but it would take a lot of it. About 95% of the current Martian atmosphere is carbon dioxide, but the quantity is not sufficient to make it warm because Mars is so far from the sun. It may be that there is enough carbon dioxide in Mars’ permafrost to satisfy the need, and if the planet could be warmed slightly some of that would probably burst free.

To do that, the scientists suggest that it may be possible to manufacture chlorofluorocarbon gases--the so-called greenhouse gases--on Mars and release them into the atmosphere, beginning the warming process. That slight warming, in turn, could free up carbon dioxide, water and oxygen, thus triggering the “runaway” process.

However, that alone would not solve the problem. If there is too much carbon dioxide in the atmosphere, it would kill any plants. And if there is too much oxygen, it would be toxic and so flammable that it could simply burn up.

Earth’s atmosphere is primarily nitrogen, an inert gas that serves as a buffer so that plants may take up carbon dioxide from the atmosphere and give off oxygen, and the final mix is harmless to humans. The Martian atmosphere would also need a buffer gas, and the scientists conclude nitrogen may be the only answer.

There is very little nitrogen in the Martian atmosphere, but that doesn’t mean it isn’t there.

“Nitrogen may exist in solid reservoirs such as nitrate,” the scientists suggest in their report.

If enough could be produced without mining the whole planet, nitrogen could provide the essential buffer.

All of this, of course, could come to a quick halt if Mars is found to be uncooperative. It could turn out, for example, that most of the carbon dioxide that is needed to warm the atmosphere is not frozen in the soil and ready to burst forth with a slight warming. It may be that it is buried in limestone instead.

“Then you are in trouble,” Toon said.

But if it is in the polar caps, and a nudge can be given in the right direction, perhaps the air will grow warmer, its gases will change, and plants can be grown. They could help the process along, producing oxygen for animal life.

“We know that the climate of Earth has changed,” said Caltech’s Ingersoll. “Living things have transformed the Earth’s atmosphere. We would not have oxygen without it.”

The same process, perhaps, might work on Mars.

Perhaps.

The Unfriendly Planet

Here are a few good reasons to stay away from Mars:

WEATHER: Mars is half again as far from the sun as Earth is, so it gets extremely cold. The maximum temperature is about 70 degrees Fahrenheit, but it can dip as low as 220 degrees below zero.

AIR: The atmosphere is 95% carbon dioxide, which would kill even the hardiest of plants, not to mention animals. The rest is made up of nitrogen (2.7%), argon (1.6%) and only a trace of oxygen, which is essential for humans.

WATER: There is no water, although many scientists believe the planet has ice at its poles. Water may also be trapped in the soil, making it similar to permafrost on Earth.

ATMOSPHERIC PRESSURE: The pressure on the surface of Mars is about the same as it is at 100,000 feet above the Earth--so low that a human’s blood would literally boil.

DUST: Dust storms sometimes blow across the surface so fiercely that much of the planet is hidden beneath a blanket of pinkish-orange haze.