Even in a world of diminished expectations, space scientists continue to dream. Suppose the money spigot was turned back on? Suppose scientific resolve reappeared? How could we return to the moon? Explore the near planets? Reach out to the far planets? In government labs and think tanks, ideas are taking shape for ion-propulsion engines, interplanetary ships with onboard gravity, underground lunar bases, and perhaps most intriguing of all, sprawling, manned bases on Mars--each project a sort of exercise in pure science for engineers freed from the messy considerations of money and politics.
But at least as far as manned exploration of the Red Planet is concerned, it’s probably the longest of long shots. Sure, Mars is near the top of most space planners’ wish lists, but it’s been there for the last 30 years without a jot of progress being made toward an actual mission. Sure, in 1990 the president himself made a rather empty pledge to have human beings on the Red Planet by 2019, but that was before the bean counters announced the cost of the mission at a tidy--and utterly unavailable--$400 billion. And sure, the Soviet Union had been talking for a while about cooperating with the United States on a manned Mars journey, but that was when there still was a Soviet Union; nowadays, the talk is of putting the Russian space station on the block, the Russian shuttle on the shelf, and all plans for more-ambitious missions on indefinite hold. Close to 25 years after the first moon landing, humanity’s exploration envelope has shrunk timidly back to low-Earth orbit. And yet . . .
Recently one of the most ambitious of all space-based what-if plans surfaced. It is a Mars plan, but not just a plan for visiting the planet. Rather it is a plan for colonizing and settling it, and doing so without the need for space suits, rebreathers, or cities under bubbles. It is a plan, in essence, for setting up camp on the fourth planet from the sun and then transforming it into a precise environmental duplicate of the third.
The idea of terraforming Mars is not a completely new one. Space scientists have long believed that our planetary neighbor is rich in many of the elemental components that make life possible on Earth: carbon dioxide in its atmosphere and in the extended ice caps that appear in the winter; water, and thus hydrogen and oxygen, locked in the permafrost, in the smaller ice caps that exist year-round, and even underground; and nitrogen locked in compounds in the soil. Over the past 20 years a wealth of writers, including marquee names like Carl Sagan and James Lovelock, have published papers speculating on what would happen if these life- sustaining ingredients could be freed up and stirred throughout the Martian environment.
Earlier this year planetary scientist Christopher McKay and atmospheric scientist Owen Toon of NASA’s Ames Research Center, along with atmospheric scientist James Kasting of Penn State, added their voices to this Martian chorus. The three researchers published the most comprehensive terraformation paper to date, credibly describing how environmental manipulation could indeed be used to produce a warmer, wetter, gassier Mars, effectively bringing the planet to life.
For years, much of what was written in this area was in obscure literature or even in science fiction, says Toon. We wrote this paper in an attempt to systematize and quantify the field, to make it something you can seriously address.
Scientists contemplating a Martian Pygmalion are starting out with a planet that is inhospitable at best. River channels and other topographical features on Mars suggest that 3.5 billion years ago the planet was a warm place, with water flowing across its surface and with a relatively thick atmosphere. Because of the way Martian soil is structured, however, the atmosphere was probably absorbed into the soil and frittered away by the planet’s low gravity--just .38 that of Earth. Most of the water would have frozen into the soil and contracted into the polar caps; the rest would have escaped with the air in the form of vapor.
The planet today is essentially a bone-dry expanse of frigid, rust-colored desert. The atmosphere is hopelessly tenuous--just .8 percent as thick as Earth’s--and is 95 percent carbon dioxide. Mean Martian temperatures hover at a paralyzing -75 degrees, although they may soar to about 70 degrees at high noon in midsummer at the planet’s equator. Bringing this carcass of a world to life would have to take place in several steps; the first and most vital would involve raising its temperature.
Mars starts off at a disadvantage because it is 1.52 times as far from the sun as Earth is, says Toon. This means it receives only 43 percent as much sunlight as we do. Even on a world with a thick atmosphere this would keep things incredibly cold. On Mars it’s absolutely freezing.
Over the years engineers have come up with all manner of outrageous ways to turn up the Martian heat, including placing giant mirrors in orbit over the planet’s poles and seeding its ice caps with dark, light-absorbing lichens. However, earthbound industries have already perfected a much less exotic yet all-too-effective tool for raising a planet’s temperature: greenhouse gases.
Sunlight streaming to Earth represents an enormous amount of energy, says McKay. Our atmosphere has always been able to capture a lot of that energy; the carbon dioxide and chlorofluorocarbons we’ve been pouring into it make it capture a lot more. On Mars the thin CO2 atmosphere retains a tiny bit of the sun’s output, but not much. The first thing we’d want to do, therefore, is increase the efficiency with which the Martian atmosphere is able to absorb and hold on to heat.
Producing enough greenhouse gases--specifically chlorofluorocarbons (CFCs)--to bring about such a change on Mars would be a theoretical snap. The Martian soil is thought to be rich in chlorine, fluorine, carbon, hydrogen, and other CFC building blocks, and chemists have already shown themselves more than adept at assembling these components into a whole family of different CFC molecules. Assuming the technology existed to transport the chemists and their equipment to Mars (a premise the three researchers grant for the sake of their scientific argument), the gases could be manufactured fairly easily and then discharged into the Martian sky.
Our estimates suggest that it would not take much more than the annual earthly CFC output--several million tons--to begin warming things up on Mars, says Toon. In the first year of production, the gases added to the atmosphere could potentially boost planetary temperature from about -75 degrees to about -22 degrees. This is like going from Antarctica to northern Canada in the winter.
In theory, an almost limitless amount of CFCs could be released into the Martian sky, pushing the temperature above freezing and increasing the atmospheric pressure until it became much more like that of Earth. In practice, however, things would not be so easy. Ultraviolet radiation from the sun has a tendency to break CFC molecules into their constituent atoms and destroy whatever gas is produced.
On Earth this eventual breakdown of CFCs is both good and bad, says McKay. Bad, because when CFCs break down, chlorine is released, which destroys ozone; good, because the breakdown also keeps the greenhouse effect from increasing. So on Mars we’d need to design a CFC that was very absorptive in the heat-producing infrared, which would make it an efficient greenhouse gas, but very resistant to the molecule-destroying ultraviolet light, so we don’t lose the CFCs. But even then we’d constantly have to produce new chlorofluorocarbons to replace what the sun did manage to destroy.
Fortunately, the scientists would not have to rely exclusively on such a designer CFC to shroud the barren planet. When temperatures climbed into the -20s, Mars itself should begin to release that other great greenhouse gas, carbon dioxide. In addition to the CO2 found in Mars’ existing atmosphere and winter polar caps, the gas is thought to be stashed in one other important place: the soil. In Mars’ older, hotter days, the atmosphere was probably dense with carbon dioxide, meaning that the present Martian turf should be fairly saturated with the stuff. In laboratory experiments, a rusty red Martianlike soil called palagonite, found in Hawaiian volcanoes, readily absorbed CO2 molecules and bonded loosely with them.
In the same experiments in which that soil absorbed CO2, says Toon, it was found that when the temperature is gradually raised, the gas boils right back out. The higher the temperature climbs, the more gas escapes.
As CO2 was released into the Martian air, it would work with the CFCs to raise the planet’s temperature even further, triggering the release of still more CO2 and on and on. The warming cycle would continue until planetwide temperatures crested to just above freezing. At this point a third greenhouse ingredient, water vapor, would be added to the atmospheric mix, courtesy of the slowly warming polar caps, permafrost, and subterranean ice sheets.
Just how long it would take for all this outgassing to produce an atmosphere with an earthly pressure and a temperature that stayed at least above freezing is anybody’s guess. If the CO2-saturated soil lay right on the surface of the planet, a century or so of CFC-warming would probably do the trick--practically overnight by planetary standards. If geologic activity has buried the soil deeper, however, warming time could be increased dramatically.
If we have to go down half a kilometer or more to warm the soil, says Toon, it could take 100,000 years to get the CO2 we’d need. The project would still be feasible, but this fact alone could determine whether it could be completed within the lifetime of a human being or the current lifetime of the entire species.
However long this stage of the terraforming took, only when it was completed would Mars be able to support a few hardy plant species. Even then, however, the terraformers would confront serious obstacles. First of all, though Mars would now have more than enough carbon dioxide to sustain plants, the soil might not have enough nitrogen, in the form of nitrites and nitrates, which are also crucial to plant metabolism. Assuming it does, though, scientists would have to release microorganisms into the soil to feast on the salts and free the vital element.
Another problem would concern water. Last spring, reanalysis of temperature data from the Viking Mars probes of the 1970s suggested that buried ice may exist at lower latitudes and shallower depths than planetary scientists thought. Other recent studies of meteors thought to come from Mars (because they contain gases in exactly the same ratios as those measured by the Viking landers) found several milligrams of water trapped in their rocky matrix. Both findings suggest that Mars may be a far wetter place than anyone expected, one that would produce lakes, ponds, and even oceans as soon as the temperature started to rise.
For people interested in spawning life, of course, water is indeed a good thing, in all but one respect: atmospheric CO2 has an affinity for H2O and would slowly begin dissolving into the water, forming deposits of limestone. The longer the water and air were exposed to each other, the more atmospheric carbon dioxide would be lost. On Earth this problem is solved by continental drift, which moves the limestone into the interior of the planet, where it is heated and released back into the atmosphere through volcanoes. On Mars the terraformers would have to handle the job themselves.
We would need some method for recovering the limestone, recycling it, and rereleasing the CO2 back into the sky, says Toon. Otherwise, the newly created atmosphere would slowly be destroyed.
Another type of CO2 destruction, however, would be highly desirable. When earthly plants were introduced into the Martian environment, they would immediately begin drawing some of the carbon dioxide out of the atmosphere and breaking it down into carbon and oxygen. This, of course, would be fine with terraformers, since for humans and animals to survive on Mars, the atmosphere would have to be reformulated to contain about 20 percent O2--roughly the same amount as in earthly air.
Coaxing even a little oxygen out of the Martian flora, however-- let alone a fifth of an atmosphere’s worth--would not be an easy job. Because plants are extraordinarily inefficient oxygen producers, they would need a good 100,000 years to produce enough oxygen to make Mars animal- friendly. To speed things up, the planetary engineers would have to turn the problem over to the genetic engineers.
This part of the project could well be the toughest one of all, says McKay. Plants have been on Earth for billions of years, and producing oxygen is what they do for a living. It’s possible nature has already optimized this process, already gotten as much oxygen out of plants as is possible. If so, it’s unlikely we’d be able to do better. Even if genetic tinkering could yield a population of plants that fairly hyperventilate, however, McKay cautions that it could still take 1,000 years to get the Martian oxygen up to desired levels.
If the O2 levels ever did climb high enough, the Martian atmosphere would eventually become almost eerily Earth-like: the sky would be blue, the clouds would be white and capable of producing rain, nitrogen would serve as a kind of buffer gas to dilute the oxygen (which is toxic in pure form), and there would even be a protective ozone layer. To preserve that new ozone layer and prevent a runaway greenhouse effect, the CFCs manufactured from this point on would have to be ozone-friendly--that is, without chlorine.
The remainder of the atmosphere would be made up principally of CO2, which would be abundant enough to sustain the planet’s plants and could be regularly replenished by soil outgassing and limestone recycling. Once this perfect balance was achieved, the Martian environment would at last be safe for warm-weather oxygen-breathers, and the settlement of the once-red planet by earthly mammals could begin.
The question that remains unanswered by all the scientific theorizing, though, is whether we should even entertain the idea of such a grandiose project. Does a species like ours have any business trying to remake an alien world? Do we have any right? McKay, Toon, and Kasting themselves have doubts.
To me, the single most important reason to go to Mars is to look for present life or to look for fossil evidence of ancient life, says Kasting. Until you do that, you can’t even consider remaking the planet. Suppose you do start terraforming and you cover up a site that once held life-forms. Worse, suppose you cover up microbes that are currently alive. Remember, the Viking landers did not entirely rule out the possibility of life on the planet. They just didn’t find it in the spots where they looked.
McKay’s misgivings are more abstract: The current environmental chic asserts that our planet’s diverse biota is inherently good. But is it? On Earth, the notion of life and the notion of nature are inseparable. But on Mars and in the rest of our solar system, life and nature are two different things. Mars appears to be a dead planet, yet it is undeniably a beautiful, valuable planet. Should we change that natural state? In my own thinking, I think we should, but I concede that it’s a whole new dimension of environmental ethics.
Toon uses similar reasoning to argue against terraforming Mars-- at least for now. We can’t do this just because we’ve made Earth so unpleasant that we don’t want to live here anymore, he says. We have to do this because we’ve managed to solve the problems on Earth--and now we want to live on Mars too.
However the ethical debate shapes up, the scientific allure of Mars is only likely to grow. Whether any of this means that the scientists and policymakers will ever commit the country to so much as a visit to the planet, let alone a wholesale terraformation, is anything but clear. But at least a handful of researchers believe it may indeed be within our powers to work our will on other worlds. All that’s needed is a clarity of vision.
In considering this question, we have to decide first why we want to go to Mars, says historian and policy analyst John Logsdon, head of George Washington University’s Space Policy Institute. If we’re just coming for a visit, we don’t need to terraform. But if we hope to stay for any sustained period, we have to change the planet in some way; otherwise we can’t survive. Even building a small dome, after all, would be a type of terraforming. Of course, we also have to remember that to the degree we modify Mars we may be ruining the very thing we came to study.
