Man is one world, and hath
Another to attend him.
—George Herbert, “Man”
In the 1960s Jim Lovelock, an English scientist, found himself spending quite a lot of time in Pasadena. Lovelock’s claim to fame was an ability to invent chemical detectors of immense sensitivity; indeed, his detectors’ unprecedented sensitivity was changing the world. It was Lovelock’s electron-capture detector that picked up traces of organic pesticides throughout the food chain, thus providing much of the spur for Rachel Carson’s Silent Spring. In the 1970s his technology would reveal how widespread the chlorofluorocarbons (CFCs) used in aerosols and refrigerators had become in the environment at large and thus trigger the global debate on the ozone layer. JPL wanted to use similar instruments to study the environments of other planets, and Lovelock, who had taken the bold and unusual step of leaving an enviable position at a world-class laboratory to become a freelance researcher, was happy to be a consultant to them.
In 1964, Lovelock went to a meeting about instruments that might look for life on Mars. Vance Oyama described ways of looking for chemicals typically produced by living organisms; Wolf Vishniac discussed ways to try to encourage measurable growth in microorganisms by feeding them certain nutrients. (On Earth this method—called the “Wolf trap”—proved highly sensitive; on the Antarctic trip that would end in his death, Vishniac proved the existence of life in places previous studies had proclaimed sterile.) Love-lock was not impressed. These approaches would detect Martian life only if the lander chanced upon soil that contained living creatures and if those living creatures had metabolisms like those of earthly microorganisms. A true test for life on another planet, Lovelock thought, should be one that looked at the planet as a whole, rather than a particular place, and one that looked for some sort of marker that would necessarily be common to all conceivable forms of life.
Guided by these ideas, Lovelock came up with a different approach to the search for life. Schrodinger had suggested that the fundamental property of life was to reverse entropy—to impose local order on a universe that was, in general, running down into chaos. The particular type of order that Lovelock decided to look at was chemical (he was trained as a chemist) and planetary: the makeup of the atmosphere. On the Earth, he argued, life’s presence is clearly seen in the atmosphere, which life uses as both a source of raw materials and as a place to dump its waste. The fact that life keeps using the atmosphere in both these ways means that it is out of balance, containing a mixture of chemicals that can react with each other. Methane and oxygen, for example, react together quite vigorously (which is why Zubrin’s rockets use them as propellants), and yet both are present in the Earth’s atmosphere. This is only possible because life is endlessly replenishing the atmosphere’s reactive gases; without life the atmosphere would quickly reach chemical equilibrium, the state in which every chemical reaction that could make a difference has already done so. Chemical equilibrium means maximal entropy; to maintain a state far from equilibrium means entropy must be actively reduced.
Lovelock decided that a sufficiently off-balance atmosphere would constitute clear evidence for an entropy reduction caused by life. It didn’t have to be off balance in the same way that the Earth’s atmosphere was; it just had to contain chemicals that, left to themselves, would react together. Soon after, earth-based spectroscopy confirmed that the Martian atmosphere was as close to chemical equilibrium as makes no matter. To Lovelock the case was more or less proven: Mars was dead and the biology experiments being discussed at JPL—the experiments that would end up on the Viking landers—were more or less pointless. This was not what JPL wanted to hear. But though the experimental results were not absolutely clear-cut, the post-Viking consensus ended up exactly as Lovelock had predicted: There was no life on Mars.*
If Jim Lovelock’s insights did little to change the way JPL approached Mars, they did a lot to change the way he himself looked at the Earth. The Earth’s atmosphere is not just far from chemical equilibrium; it is also, bizarrely, pretty stable. Oxygen levels, for example, have changed only a little over the past 250 million years. Lovelock came to the conclusion that this, too, was evidence of life—that living things somehow acted to regulate the instabilities they caused in their environment. Life and its physical environment, he came to believe, were not separate entities to be dealt with by biology or geology, as the case might be; they were part of a single self-regulating system. Following the advice of his neighbor, the novelist William Golding, Lovelock took to calling that self-regulating system Gaia, after the ancient Greek goddess of the earth.
In the 1970s, Lovelock’s ideas were by and large rejected by the scientific establishment while eagerly received by the green New Age fringe; neither group really understood what he was saying. But Boulder’s original Mars Underground, somewhere between the two, grokked him in fullness.† Gaia was not just a theory about the Earth; it was a theory about life as a planetary phenomenon. And as such it could be applied to Mars.
The question of life on Mars raises problems on at least two counts. The first is that a longing to answer it in the positive encourages people to mislead themselves on the subject. The second is that, if you see the search for life as a search for individual living organisms, it is almost impossible to answer in the negative; to say categorically that there is no living thing on Mars would require knowing the planet with an intimacy that is hard to imagine, especially now that the deep subsurface has been brought into play. How long do you have to look for fossils before you decide there can’t be any? If you do find fossils, how long must you scour the ice to be sure that not a single viable bacterial spore survives?
An alternative, in many ways more illuminating, approach is to look for possibilities rather than facts. Instead of asking whether there is life on Mars, ask whether there could be. This opens up new routes of inquiry. It focuses the mind on the many complex links between life and its environment. And it is not limited to the past and present. It is a question that applies to the future.
By 1976, this mostly idle notion had a name—terraforming—and a history, most of it in science fiction, but some of it in articles in reputable journals. There had even been a small workshop on the subject at NASA Ames. In Boulder, the Underground seized on the idea. Faced with a huge amount of information about a seemingly lifeless planet, it was a topic that appealed to their scientific romanticism more than any other (except for the dream of actually going there). Terraforming was the scientific story of the planet’s decline translated into technology and told in reverse. It was not all that they were interested in—far from it—but it helped to give structure to everything else. And much of that structure came from Love-lock’s ideas, which by the late 1970s had been synthesized in his book Gaia: A New Look at Life on Earth. Traditional terraforming, if we can speak of such a thing, was largely about physical alterations of the environment that would make life possible: The first novel to deal with terraforming Mars, Arthur C. Clarke’s The Sands of Mars, imagined using nuclear power to turn Phobos into a second sun. Lovelock’s vision led Chris McKay, Penny Boston, and the rest of the Boulder gang to distrust such pure engineering ideas as too simplistic. Terraforming should not just be about creating a new environment for life through force majeure, but about finding ways to allow life to create a new environment for itself.
These ideas were helped along by the belief that in some respects terraforming Mars might be quite easy. Carl Sagan’s idea that Mars’s orbital cycles might create “long winters” suggested that the climate had two distinct states: The one we see in which much of the atmosphere is frozen into the ice caps and the soil; and one in which the atmosphere was freed to warm the surface through the greenhouse effect. If the terraformers could switch the climate from one natural state to the other, then they’d be well on their way. To make things easier, the switch was weighted in the terraformers’ favor; given a gentle nudge, it would snap itself all the way on. If you could just get a little extra carbon dioxide into the air, you’d warm up the planet enough to get a bit more; that would warm the planet yet further and get you a bit more; and so on. The greenhouse effect would amplify itself by coaxing more and more carbon dioxide from the caps and the frozen soil. For evidence that such a thing was possible its proponents could point to Venus, which owes its intolerably hot surface to just such a runaway greenhouse effect. On Mars, where solar radiation is only a quarter what it is on Venus, intolerable heat was not going to be a problem, but less bitter cold was a definite possibility.
Warming the planet’s carbon dioxide reservoirs a little might thus trigger a process that warmed the whole thing a lot. The most obvious way to do this was to add some soot or dust to the polar caps, making them less reflective. Or you could put mirrors into orbit to focus extra sunlight on them. Or, taking a more Gaian approach, you might be able to design a dark algal crust that would spread over them. By the time of the first public colloquium on terraforming, organized by James Oberg* and held as an evening satellite meeting at the 1979 Lunar and Planetary Science meeting in Houston, some form of polar melting was seen as the established first step in terraforming Mars, despite the fact that Sagan’s ideas about natural “long winters” were by that time out of favor, having been largely replaced by the far slower, noncyclic climate change championed by Jim Pollack. At the most recent major discussion of terraforming, held at NASA Ames in late 2000—a meeting attended by a surprising number of the people who had met in Houston more than twenty years before—getting carbon dioxide out of the caps and soil and into the atmosphere was still seen as the obvious first step.
The positive feedback in such an approach—the fact that enough energy to heat up the planet by 1°F can, thanks to the greenhouse effect, actually produce 12°F of warming—definitely makes it powerful. But changing a planet’s climate still takes quite a lot of effort. Sagan calculated that you might be able to release enough carbon dioxide to kick the process off by covering just 6 percent of the caps with just a twenty-fifth of an inch of soot. This may not sound like much, but it still means moving a hundred million tons of material. And since you wouldn’t have soot available, you’d need to use powdered basalt, a less efficient heat absorber, and cover more of the cap. And a layer a twenty-fifth of an inch thick would blow away in the wind; you might want ten or a hundred times more of the stuff. Even this simple modification requires pulverizing and redistributing billions of tons of rock.
Mirrors might be simpler. Instead of increasing the efficiency with which the cap absorbs sunlight, mirrors poised in orbit above it could simply increase the amount of sunlight it receives. According to calculations made by Robert Zubrin and Chris McKay in the early 1990s, a space-based mirror 150 miles or so across would do the job nicely. Made from very thin foil, such a mirror might have a mass of two hundred thousand tons, which compares well with the billions of tons of crap needed to darken the cap. At two hundred thousand tons, such a mirror would be only half the mass of the largest oil tankers. What’s more, it could be delivered in self-propelling installments. Light bouncing off a mirror exerts a small pressure as it does so; a very thin foil mirror could literally sail on sunlight, navigating the solar system without using any fuel at all. One can imagine sail after sail being produced at a smelter on an aluminum-rich asteroid and tacking through the sunshine to Mars, where they could use the pressure of the sun to balance the force of gravity and hover steadily a half a million or so miles away from the planet, reflecting sunlight to the polar cap. It’s not necessarily the case that such industrial capabilities will ever be developed in space, but it’s not impossible. And flying in two hundred thousand tons of foil from the asteroid belt compares pretty well with moving billions of tons of dirt over the surface of the planet.*
A further possibility was raised in the 1980s by Jim Lovelock himself, drawing on his own experience. On the Earth, CFCs have come to be seen as a problem both because they deplete the stratospheric ozone layer and because they trap infrared radiation that is leaving the Earth far more effectively than more prevalent green-house gases like carbon dioxide do. On Mars, Lovelock realized, these greenhousing powers might be just what are needed. Concentrations of CFCs as low as a few parts per billion might warm the planet enough to kick off the desired runaway greenhouse effect. His tongue in his cheek, Lovelock suggested shipping the CFCs not wanted on the Earth over to Mars as soon as possible.
When Chris McKay started to analyze this idea, it did not look promising. For a start, even a gas present in the atmosphere at levels of only a few parts per billion is still there in large quantities, since an atmosphere, even a thin one, is a very big thing. Shipping from the Earth would be impossible. What’s worse, the CFCs would be broken down by ultraviolet light; the only reason they last long enough on the Earth to percolate up to the stratosphere is that the ozone layer they attack when they get there protects them on the way up. On Mars, hard ultraviolet rays would start destroying the CFCs as soon as they left the factory chimneys, which would mean the factories had to labor even harder in order to keep a satisfactory CFC greenhouse in place. According to calculations McKay and his colleagues made for a terraforming article that the prestigious journal Nature published in 1991, a CFC greenhouse would require an industrial base capable of producing a trillion tons of gas a year. That’s something like a million times the amount that was produced on the Earth when the use of CFCs was at its peak.
When McKay did the calculations in the early 1990s, this vast level of production made the supergreenhouse effect look unattractive even by the exuberant standards of techno-maximalist terraformers. By the time of the 2000 meeting at Ames, though, things were looking up. Gases that were far better infrared absorbers than everyday CFCs had been discovered, and theory suggested that even better supergreenhouse gases might be possible. (Unsurprisingly, not much research goes into making better greenhouse gases. But a handful of theorists find such ideas interesting.) Better still, these new gases were much less susceptible to UV, and might last in the Martian atmosphere for thousands of years. It was possible that a remarkably effective supergreenhouse could be maintained through the production of just a few hundred thousand tons of supergreenhouse gas every year. There would be no need for the mass production of solar sails at asteroid factories; a dozen chemical plants and a few large mines would do fine. (A facility on the scale of South Africa’s Vergenoeg mine, a large fluorspar extraction operation, could produce the raw material for about fifty thousand tons of gas a year.) If Mars has fluorine resources comparable to the Earth’s, it would be possible to keep this up for thousands of years; geochemists suspect Mars may in fact be significantly richer in fluorine than the Earth is.
In the long run, such factories and mines might not be necessary. It is conceivable that such gases might eventually be synthesized by plants and bacteria. The genetic engineering involved would be heroic, as it would involve the design of entirely new metabolic pathways, but it is not unimaginable. So it might be possible to create a fluorine-bearing-gas cycle on Mars that would naturally maintain the greenhouse: When the gases were broken down in the atmosphere, living creatures would metabolize their remains and create fresh supplies of the stuff. A few hundred thousand tons a year, while still quite a lot by industrial standards, is relatively small change by the standards of a living planet. One of Lovelock’s early Gaian insights was that oceanic plankton pump sulfur out of the water and into the atmosphere, thus making the stuff available for creatures on the land; they do this by releasing about seventy million tons of dimethyl sulfide every year. Martian plankton would have to produce less than a tenth that much supergreenhouse gas to keep their planet warm.
One way or another, triggering a runaway carbon-dioxide green-house on Mars, and thus providing enough warmth and air pressure to allow liquid water on the surface for a significant part of the year, seems to be technically feasible. It’s not possible today, nor will it necessarily be possible this century, but if humanity’s technological prowess continues to grow, and if the technologies of spaceflight are part of that growth, at some point this first stage of warming will become a practical proposition. The question then will be whether to make it happen—and what to do next.
This is one of the central questions of Kim Stanley Robinson’s epic Mars books. Some of his settlers want to terraform their planet as quickly as possible; others want to leave it as it is. In a nice play on earthly politics, the groups become known as Greens and Reds respectively. The logic of the novels requires the Greens to triumph, but the Red case is taken seriously and portrayed with sympathy. Robinson is a man who prefers bare granite to soft limestone. He knows that the surface of Mars is a vast natural sculpture, a billion-year symphony of slow stone. Barren, yes—and beautiful not so much despite that as because of it. Warm it and you deface it. Melting permafrost causes crater rims and ridges in the high latitudes to slump undefined to the even plains; opened aquifers undermine the ground itself, causing its chaotic collapse. Once moisture gets into the air the dust turns into mud all over the planet. The mud slides. Clear skies turn to cloud; wind-carved rocks are eaten up by acid rain (with that much carbon dioxide in the atmosphere, all rain will be acidic). Newly thickened storms blow away the delicate strata of the terraced terrains; dirty fizzy waters lap up over the sand dunes of the northern erg. What was once simple and grand becomes messy and muddy.
While Robinson faces up to much of this, he avoids a couple of key issues. He makes the terraforming far faster than is conceivable given current knowledge, producing an atmosphere that humans can breathe within a century or two. And he ignores the question of native life. His books, conceived in the 1980s, make the reasonable simplifying assumption that there is no native life on Mars and never has been. In reality, though, that case is not proven.
To some it doesn’t matter. When he first started talking about terraforming in the early 1990s, Zubrin seemed to take some delight in not caring about what effect, if any, the process might have on indigenous life. After all, indigenous Martians, if there are any, would almost certainly just be bacteria—and anaerobic bacteria to boot, creatures humans associate only with decay, at home only in the cesspit and the gangrenous wound. As Zubrin pointed out, we kill such creatures in their millions with bleach and antibiotics whenever they discommode us. If similar creatures are to be found on Mars, then study them by all means—but don’t let their existence alter your plans to change the planet.
When Zubrin was a brilliant loudmouth speaking only for himself, this contentious view was not much of a problem. Once he was founding president of the Mars Society, though, it became an issue. The Mars Society is an undeniably utopian and escapist organization, and there is nothing wrong with that. As J. R. R. Tolkien once remarked, to be opposed to escape is to put oneself on the side of the jailers. What the society’s members think they are escaping, though, is a matter on which opinions differ. Zubrin wants to escape the stifled world that lacks a frontier for a utopia of human victory over natural obstacles. But many of those who came to the founding convention of the Mars Society wanted to cherish the environment, not overcome it. Where Zubrin wanted to restart the history of the frontier, they wanted to rewrite it—and to do it better this time. They looked back at frontier America with mixed feelings, delighting in the land that was revealed and passed on to them but dismayed at the human and environmental costs of the expansion. Zubrin’s damn-the-torpedoes disregard for Martian life was exactly the sort of attitude they wanted to escape; to the extent they wanted to terraform at all, they saw the act as a restitution, even an atonement. They didn’t want a new America; they wanted a dream of America done differently. They wanted a Martian wilderness wherein might lie the preservation of the human world.
The war of these world-views was played out on the evening of the second day of the Mars Society’s first convention. The terraforming panel was dominated by people with views as robust as Zubrin’s or even more so: The general tone was that Mars was there to be taken and terraforming was the way to take it. The voices from the floor were angry. Mars was something wonderful, something worthy of respect, not just a means to an end—and if it had life-forms, even lowly ones, they were worthy of respect and wonder, too. When the panel talked of manifest destiny, or indeed genetic destiny, the discontents in the audience talked of the slaughter of the native Americans. Such talk got under Zubrin’s skin: To equate humans with Martian bacteria was madness. It was offensive and, almost as bad if not worse, it missed the point. Going to Mars, to Zubrin, is not really about Mars. It’s about the human race doing what it does best.
His antagonists, though, are as interested in the environment as in the people, or at least try to be. Look at a painting of the Americas as wilderness by Cole or Church and you see the sort of thing they yearn for: unspoiled land from which to take solace. They see such wilderness not as a resource, but as a source—the source of the life that they themselves share. They want a life at one with nature, and they ignore—possibly perversely, and possibly with a great, unacknowledged insight into the nature of creation—a basic truth about Mars: that it looks like a place where nature and life are separated. Life may simply not be in the nature of Mars; the nature of Mars may be to be barren.
This is why the Martian environment and its possible protection make such a fascinating topic for discussion. In offering nature without life, Mars reveals itself as a precise complement to what may be the major cultural shift of the twenty-first century: The realization that the living and the natural are not necessarily the same. Biotechnology throws the relationship between life and nature into question. As biotechnological abilities progress, we will be forced to recognize that living things are not necessarily natural, and to disentangle the respect we feel for nature and the respect we feel for life. Thinking about terraforming brings the distinction into a peculiarly clear focus. To honor and value life on Mars is not to value nature, at least not if Martian nature is lifeless. To spread life on Mars would be an act of destruction as well as of creation. This insight will not lay the issue to rest; but it may help us think about it better. And for all the appeal of the great empty desert in the sky, it may help us to see that, in the end, it is life that we value most highly.
Though such ideas may come to have a growing cultural resonance, in the Mars Society at least they are no longer proving divisive. The rhetoric has been toned down: The term “Lebensraum” was only ever used on the fringe (and then much to Zubrin’s distaste) and is not heard today; Stan Robinson, speaking at the Society’s second convention, argued persuasively that “Manifest Destiny,” too, should be dropped from the lexicon on the simple fourword basis that “it reeks of murder.” The differences of opinion remain—how could they not, in an organization with such different dreams that Robinson can write novels about a Mars with little or no private property while Zubrin wonders how to get legal authority to sell off land rights—but have been used to define a latitudinarianism in the Society, a quality a collection of highly focused engineering types sorely needs. The members have found ways respectfully to disagree on the issue. At that first convention, though, the debate was not just rowdy; it was rancorous, and it lasted long into the night.
Chris McKay, who had the unhappy task of trying to moderate that debate, had undoubtedly thought longer and harder about the issues than anyone on the panel. In the late 1980s he’d started writing papers that looked at the ethics of terraforming, as well as the technologies. He’d asked himself what rights an ecosystem had: What were the rights of life, and what were the rights of rocks that had no life? And he’d wondered what difference the provenance of the life on Mars might make. If there are Martian microbes still alive in the depths—which, despite having been one of the authors of the first paper to discuss the subject, McKay doubts—where did they come from?
The problem with life on Earth is that for all its bewildering variety it is in some respects all the same. Every living thing on Earth shares a common ancestor; every living thing uses the same basic biochemistry of nucleic and amino acids. It is thus very difficult to distinguish between those attributes of life that must be common to all living things everywhere and those attributes that are simply aspects of the way that life has evolved on Earth. This is one of the reasons why the idea of finding life beyond the Earth is scientifically fascinating; until you have two different examples of what life can be like, you’re very limited in your understanding of what exactly it is and of how it can get started in the first place.
Discovering life on Mars might provide a way to answer those questions. But it might not. One thing that ALH 84001 and the rest of the Martian meteorites prove beyond doubt is that rocks can travel between the surfaces of planets; the theory is that the shock wave from a large asteroid impact sweeps them up and shoots them off like a primitive and rather rougher version of a launching catapult. There is no reason to believe that this process would sterilize the rocks launched into space. Space itself will not necessarily sterilize them, either. Apollo 12 landed near an earlier automated moon probe, Surveyor 3, and took samples from it back to Earth. Some of these samples proved to have viable bacteria on them, hitchhikers not notably incommoded by their trip to the moon and back. The Long Duration Exposure Facility, a NASA satellite that was put into orbit by the shuttle Challenger in 1984 and recovered by the Columbia in 1990 (a rather longer duration of exposure than intended, due to the Challenger’s subsequent accident), also returned to Earth with its bacterial entourage intact. And bacteria do not need an Apollo mission or a space shuttle to bring them down to Earth safely; careful analysis of ALH 84001 by Joe Kirschvink shows that most of the meteorite came through the process of entry into the Earth’s atmosphere without being heated up to anything like the temperature needed to pasteurize the passengers. (Meteorites heat the atmosphere as they slough their surface layers off in it, which is why we see them as shooting stars, but what remains when they hit the ground is not necessarily warmed up in the process.)
Martian meteorites are not common, but nor are they extraordinarily rare. Estimates suggest that there are a million or so orbiting the sun at the moment, and over time many of them will hit the Earth. In the early solar system, when there were many more asteroid and comet impacts to launch the things, Mars rocks would have been far more numerous. And although it is harder to launch rocks from the Earth than it is from Mars, there would have been a steady stream of meteorites headed in the opposite direction, too. Mars and the Earth, as McKay likes to put it, have been swapping spit for billions of years.
There has been life on Earth for at least 3.8 billion years. It is inconceivable that in that time no rocks carrying earthly bacteria have made the journey to Mars. While it may be that most of those that made the journey were sterilized by vacuum and radiation—the fact that bacteria can survive a few years in space does not guarantee that they will survive a few million years—some will have reached Mars relatively quickly, with the bacteria on board still viable. And it is quite plausible that, if they found conditions on Mars to their liking, those bacteria made themselves at home. If living creatures or fossils are ever found on Mars, the possibility that they are related to life on Earth will have to be investigated. If all there is to work with is a bunch of fossils, the question may never be answered. But if there are living samples—or dead samples that have been preserved in deep ice for billions of years, rather than turned to rock—molecular biology will come to our aid. If the “Martians” use the same genetic code that earthlife does, then it will be a racing certainty that they are our cousins most removed.
Indeed, it would be quite possible that they, not we, represent the ancestral branch of the family tree. The basalt in ALH 84001 predates the great collision that threw the makings of the moon into orbit round the Earth. Regardless of whether ALH 84001 carries signs of life, it shows that Mars has had a solid surface for longer than the Earth has. And if Mars has relatively little water—enough for a small northern ocean but not much more—that may have helped keep it habitable throughout the solar system’s boisterous youth. Really big impacts on a water-rich early Earth would have boiled the oceans and produced a temporary atmosphere of pure steam. Since steam is opaque, it takes a long time to cool down, because the heat within it can’t be radiated away. The steam-bath atmosphere would thus persist for a couple of thousand years and the planet’s surface would be thoroughly sterilized down to a considerable depth. If Mars were less well endowed with water its surface would never be steamed in quite the same way. So to some Mars looks like a more likely site for the origin of life than the Earth. The ever-inventive Norm Sleep, of Stanford, has suggested that a Martian origin might explain why life on Earth is separated into three distinct lineages, the prokarya and archaea (all single-celled) and the eukarya (animals, plants, fungi, and all sorts of other good stuff). The three great families might represent three distinct sowings of Martian seed across the interplanetary void.
For Chris McKay these events in the past have a crucial impact on the morality of the future. If there are no Martians, planetary engineering raises few problems; a world with life represents an unconditional improvement on one without. If the Martians are our longest-lost cousins the situation is similar; we share the Earth with all sorts of strange distant relatives and we can do the same on Mars. But if the Martians are not related to us, things are different. We would not be justified, he thinks, in exterminating the only truly alien life we know, nor in appropriating its environment to our own ends. But that does not mean we should do nothing. After all, any Martians around today are hardly pulling their weight as good Gaians: They show no evidence of keeping an intrinsically unstable environment stable, of being part of a self-regulating system. Perhaps they need a helping hand. Providing them with a warm, wet surface might be just the new opportunity that they needed—as long as we leave them alone to make of it what they will.
At this point we are talking about something other than terraforming as the term is usually understood. The idea is no longer to make something like the Earth; it is to make something new, or re-create something old, with only passing reference to the Earth. The late Canadian biologist Robert Haynes—whose name was given to Haynes Ridge at Haughton Crater, the site of the Mars Society’s Flashline hab—coined a more general word for such an undertaking: ecopoiesis, from the Greek roots meaning abode (eco, as in economics or ecology) and fabrication (poiesis, as in poetry). It is quite possible that, if there is life on Mars, a limited ecopoiesis aimed at allowing that life to spread back to the surface would be more acceptable to public opinion than true terraforming aimed at making that surface habitable to humans. It is certain that the ecopoiesis would be much easier. For such an ecopoiesis the relatively quick and gentle warming and dampening of the planet that might be brought about by triggering a runaway carbon-dioxide greenhouse would probably be enough, and might be achieved in a couple of centuries. Terraforming proper—making Mars an environment where earthlife can prosper—is a much harder proposition. Ideally it requires an annual average temperature above 32°F, a relatively copious supply of water at the surface, and an atmosphere of oxygen and nitrogen.
The temperature might be the simplest thing: After initial warming with a runaway greenhouse, the temperature could probably be regulated reasonably well using supergreenhouse gases. If there were enough carbon dioxide released by the original warming, the oxygen could be produced through photosynthesis, if you had hardy enough plants and were willing to wait for a few thousand years. But there’s a drawback to photosynthesis: It creates organic carbon compounds—leaves, wood, and the like—as well as oxygen, and those would have to be disposed of. Otherwise bacteria would just use up the oxygen while eating dead plants, reproducing the carbon dioxide you’d started with as they did so.
Releasing an ocean frozen into the megaregolith would be a help here, because oceans are great places for burying organic carbon. The problem is that releasing such an ocean would be a titanic undertaking; melting ice caps is child’s play by comparison. Simply heating the surface and waiting is not an option: Because the rocks are cold and heat takes a long time to diffuse, it would take more than a million years for the top two miles of the planet to thaw out, and a large part of the water is probably a fair bit deeper than that. The only way of melting that water that we can easily imagine is through the use of nuclear explosives in numbers that would make Dr. Strangelove quail—vast fallout-free hydrogen bombs made from Mars’s reasonably copious supplies of deuterium. According to Martyn Fogg’s authoritative book Terraforming: Engineering Planetary Environments, something between a hundred million megatons and ten billion megatons of nuclear explosives would be required to release a serious ocean if it were frozen solid (if it were liquid under a cap of ice, things get much easier).*
While we’re on the subject, nuclear explosives might also help with the nitrogen. The Martian atmosphere has very low levels of nitrogen, but it is conceivable, even likely, that there is a good bit more stowed away as solid nitrates in the crust. There are bacteria that turn nitrates into pure nitrogen; they do it constantly on the Earth, producing three hundred million tons a year of it, mostly from decaying organic matter. Unfortunately, at that rate it would take over half a million years to produce enough nitrogen for a vaguely earthlike atmosphere on Mars. If there are concentrated beds of nitrate, nuking them might get the stuff out quicker and release some helpful oxygen, too. But if the nitrates are spread all over the planet this becomes difficult. It would probably be simpler to ship in the nitrogen from somewhere where it’s plentiful, such as Saturn’s moon Titan, which has an atmosphere full of it. If, that is, you can find a way to move trillions of tons of gas billions of miles across the solar system. Another possibility is hitting the planet with large comets rich in nitrogen-bearing ammonia: Position the impacts over ice deposits and you might reduce the need for underground nukes considerably. One should be careful, though, not to spray too much of the water released by the impacts straight back into space. That would be wasteful. Mike Carr’s ghost would object.
It is clear that true terraforming requires technologies that are almost inconceivable. The almost, though, is important. As McKay’s papers, Fogg’s textbook, and the Ames workshops show, the almost inconceivable is, in fact, conceivable; we can imagine the terraforming of Mars much more realistically than Julius Caesar could have imagined a jumbo jet, or Socrates a Saturn V. That something is conceivable does not, in itself, prove anything. It may simply be that ours is a time in which the technological imagination is far less tightly bound to the state of the technological art than used to be the case. But at the same time, our technology has become capable of operating at planetary scales.
Humankind had never really seen a planet-wide weather phenomenon before Mariner 9 sent back images of the great dust storm of 1971; within a decade or so, spurred on in part by those observations of Mars, researchers at Ames and elsewhere had shown that a similar atmospheric shroud might be brought about in days by means of a nuclear winter. Though we don’t have tools designed for terraforming, we do have many tools of the same general kind, even if they are abacuses to computers. We don’t know how to design complex ecosystems, or long-term life-support systems; but we know how to build spacecraft and hydrogen bombs and genetically engineered organisms and greenhouse gas factories. And we know that we can change a planet’s atmosphere and climate. No one seriously denies that CFCs have eaten away at the Earth’s ozone layer. Though there are, as of this writing, some people who think that anthropogenic increases in carbon dioxide, methane, and CFC levels are not responsible for the global warming seen over the past century, no one thinks that, if we were deliberately to try to warm the Earth with supergreenhouse gases, we wouldn’t succeed.
For thousands of years, humanity has increased its power to reshape the Earth. The pharaohs built pyramids; the Dutch built half a country. China and Europe lost their forests; large parts of the American West were irrigated. Today humanity moves more soil around the world than all the rains and rivers combined. At the moment, we are wisely trying to minimize our impact on the Earth; helping the ozone layer to replenish itself, limiting the amount of global warming we are responsible for, attempting to curb our tendency to drive our fellow creatures extinct. In time, though, we may see reasons to take a more active role in things. Sometime in the next few centuries, we can expect to have occasion to move aside an asteroid or comet and save some region of the earth—even, possibly, the Earth as a whole—from a ghastly devastation. Sometime in the next few millennia we will in all likelihood have to choose between adapting to an ice age and averting one.
Civilization—the art of living in environments designed by humans rather than those found in nature—is only about ten thousand years old. Though it is still a fragile thing, and not to be taken for granted, there is no reason to suppose it is near its end. And if it persists to twice its present age, it will be through designing those environments on a planetary scale with both greater care and greater ambition, protecting them from bolts from the blue and changes in the climate and other calamities that would once have been acts of God. If this civilization spreads to Mars, might it not reshape the planet to suit its purposes? And even if Mars is not settled, might it not, in this long run, be reshaped anyway? Robert Zubrin speaks of terraforming Mars as a natural consequence of settlement—making worlds, he argues, is what people do. This is not quite the nineteenth-century assertion that “rain follows the plow”—an assertion that proved horribly untrue in the dust-bowl years—but it’s not terribly far off. Others suggest planetary engineering might be undertaken as a grand ecological experiment; Martyn Fogg’s book opens with a striking quotation from the physicist Richard Feynman, “What I cannot create, I do not understand.” Reengineering might be a moral act, an observant restitution on behalf of the hidden Martian biota, an ecopoiesis for bacteria and plants, rather than a terraforming for humans. It might be a spiritual act, the creation of a new wilderness as solace or penance. Or it might be a work of art: a landscape recrafted the better to be itself and fit the cosmos, a vast Roden Crater.
Terraforming might be economic, scientific, religious, or aesthetic; it might be a mixture of some or all of them; it might be none. The fact that we can imagine the tools that would be necessary does not mean we can know the motivations for using them. The future, like the past, is a foreign country, a place where the connections between people and their values are all too often opaque to us. The various threads that I see tying our world together when I look down the Thames from Greenwich Park were already being woven when Queen Elizabeth I looked out from the same heights: Ships sailed down the Thames and around the world (just), trade prospered across oceans, manufacturing was becoming newly dependent on capital, information was beginning to flow more freely thanks to the printing press. But no one then could have seen where those potentialities would lead: the squat bulk of Reuters, the towers of the banks, the trade routes revealed by the landing lights on aircraft.
Though it flows from the present, the distant future is another world. We cannot know the future for what it is, because as yet it isn’t; we cannot know it for what it will be, because by the time it is, we won’t be. It is connected to us—its seeds are in us—but we are not connected to it. Though it is human, it is in some ways more alien than a distant but knowable planet can ever be. Mars is tied to us only loosely—you could ignore it for a lifetime and not be thought strange—but it is part of our world, tied to us by Airy and observation, by science and escapism, by novels that use it to articulate today’s concerns and paintings that try to inspire our tomorrows. In its small, distant manner it is more a part of our shared world than the undiscovered future downstream can ever be.
*The hypothesis of life deep below the surface does not necessarily contradict Love-lock’s ideas, inasmuch as he explicitly assumed that life would be in a position to make continuous use of the atmosphere, which would not be the case for a deep biosphere.
†In the Martian religion central to Robert Hemlein’s Stranger in a Strange Land to grok, literally to drink, is a signifier of understanding and oneness.
*Who also wrote the first book on the topic, New Earths.
*However, there is another, nontechnical issue here that might throw Zubrin’s ideas off track. If asteroid mining is advanced enough to produce fleets of orbiting mirrors for a terraforming project, it might be a serious competitor to any mining on Mars and thus reduce the need for a Martian frontier. Zubrin’s answer—he always has one—is that if miners go to the asteroids, Mars can get rich by supplying them with food and other replenishables much more cheaply than the Earth could.
*Ralph Lorenz, a planetary scientist who works with Peter Smith at the University of Arizona, has pointed out that the tides raised in such an ocean would significantly speed up the decay of Phobos’s orbit, hastening the moon’s destruction by many millions of years. Long-term planners, take note.