(Image credit Daein Ballard)
It's been said that the significant social challenges that the human race faces today are all a result of overpopulation and our inability to understand the exponential function, and yet there's no end in sight to our species' fruitfulness. We might be forgiven for entertaining wild-eyed escape plans for our descendants - one of which is colonizing Mars.
That Mars has long captivated science fiction (read: fantasy) writers is a cliche, but what is underappreciated is how seriously many very bright people take the prospect, at least in some aspects. There are dedicated advocacy groups like MarsDrive calling for private enterprise to take concrete steps today toward a Mars colony. While I applaud their forward outlook, they have some extraordinary challenges to overcome in building a self-sustaining human presence on Mars. If they have solutions, they aren't discussing them.
There is an important distinction to be drawn between outposts and colonies. Virginia was a colony. Young men left England looking for a fresh start in an untamed land, to start building a permanent, self-sustaining settlement, followed soon after by families. To arrive at a self-sustaining Virginia took five tries: the first colony at Roanoke was founded in 1585 with 76 men, re-stocked later with 117 settlers, and was totally deserted by 1590. Jamestown was founded in 1607 with 105 men and had to be re-stocked twice in 1608, both with supplies and 137 more settlers. In 1610 only 60 colonists still survived when De La Warr arrived with 150 more settlers, and finally the colony grew consistently after that; John Rolfe's successful cultivation of tobacco brought more regular supply (and trade) ships that made the colony economically self-sustaining. It turns out that surviving in a new land with seventeeth century technology isn't easy, even with fresh water, some edible native flora and fauna, a long growing season, and sometimes-friendly locals to trade with. In fact the Virginia colonists planned on surviving solely through trade with the Powhatan Confederacy for the first few years, and had no illusions about becoming self-sufficient immediately.
Ultimately, Virginia was successful, but from our modern perspective, the settlers found a New World that physically wasn't all that different from the Old, some humidity and fevers notwithstanding. There have been previous efforts to compare possible colonization costs of a Mars mission to intra-Earth colonization efforts: for example, Freeman Dyson estimated the per-person costs of both the Mayflower and Mormon colonization endeavors at $144,000 in 2009 inflation-adjusted dollars. In many ways the most impressive colonizations were the ones conducted by Polynesians with no metal or writing, searching for new land. Imagine literally rowing a canoe into the middle of the Pacific, searching for an island that probably isn't there. But Mars isn't Massachusetts, or Utah, or even Rapa Nui. Before we're overtaken by the idea that technology will let us thrive anywhere, or let the romance of a new colonial era on other worlds carry us away, let's step back and realize there's a place right here on Earth that we still haven't been able to successfully colonize, even in the twenty-first century: Antarctica.
In contrast with Virginia, Antarctica has no growing season. It has no locals, it has no flora and very little fauna - and even with twenty-first century technology, Antarctica is not self-sustaining, nor is there any reason to think it will ever become self-sustaining. The oldest continuously occupied base at the South Pole is the South Pole station proper, founded by 18 men with the U.S. Navy in 1956. 52 years later, in 2008, at any one time there are about 1,000 non-permanent staff members in Antarctica, all waiting to go home. A handful of children have been born in Antarctica so far, but none have stayed. Even without counting tourists, there have surely been thousands of people injected into the Antarctic "economy"; none have stayed, and no self-sufficient economy has developed. In comparison, in only 42 years, Virginia had 15,300 permanent residents, and a thriving tobacco economy. It's true that Antarctica staff members do produce some of their own fresh vegetables indoors, and they could hunt seals and penguins if push came to shove, until they ran out of bullets - but if the supply planes stopped coming, it would only be a matter of time before everyone died - two to three years at a guess. Antarctic bases are not a colonies, they're outposts.
Antarctica is often mentioned as a possible proving ground for Martian colonization, mostly because the temperature range in the Antarctic is about the same as the Martian tropics. Unfortunately, in all other respects, Antarctica is an absolute picnic compared to Mars. First, avoiding accusations of physiocratic economic ideas, let's concede that in theory, Antarctica could develop a remote service economy, with programmers trading their services for electronic funds that bring in the food and oil on those flights from Christchurch. This is possible only because Antarctica is much easier to get to than Mars; for that matter, Japan is not nearly self-sufficient in materials either, but it does okay. The point is that Japan is a boat ride away from China, Korea and the U.S., and yes, this makes their (mostly imported) food more expensive. But if you think international postage on a grapefruit is bad, try the interplanetary rates. Also relevant is that Antarctica has air; Mars does not. Antarctica has water; Mars does not, or at least not very much. If we can't build a self-sustaining colony in a closer, friendlier place, it's foolish to assume we can do it in a farther, more hostile place.
It's probably possible, with current or reasonably imaginable technology, to build an outpost on Mars, though caution is warranted here too (remember Biosphere 2?). Outposts have to be regularly re-supplied, and given the difficulty of getting to Mars, this would be a continuously more daunting prospect than in the case of Antarctica. That is to say, maintaining the outpost would be economically draining to the home economy (even if that economy is all of Earth). Mars wouldn't be an escape hatch from an overpopulated Earth, because it would be dependent on Earth.
This is where the discussion of terraforming inevitably begins. A self-sustaining Mars would have to be a habitable Mars - at least, habitable in the sense of a biosphere and native economy dependent on humans and other organisms, as opposed to one based on hand-waving, nanotechnology and unicorns, as it seems to be even in most purportedly serious discussions of the matter. Of course it's anything but clear that we know how to terraform, considering we don't really understand our own climate yet.
the lands around the Aral Sea, haven't worked out so well.
We have trouble fully managing even isolated slivers of our own climate (again our one real example is Biosphere 2). But for the sake of argument, let's assume that we can get people and seeds to Mars without frying them or bankrupting the world's economy. Let's also assume that we somehow figure out how to controllably raise the temperature and oxygen pressure on the surface of Mars to the point where all the ice melts, and vertebrates can respire, and the necessary sequence of terraforming events doesn't present any issues. The problem that remains is water.
For all the romantic fiction around the idea of terraforming Mars and other planets, there has been curiously little somber number-crunching. There have been a few serious facts-and-figures attempts to address the engineering realities of such an enterprise, beginning with a NASA report in 1976 (Averner and MacElroy). Most of the guesses about climactic engineering methods and outcomes are exactly that, but calculating how much water is available for Martian terraforming is simple.
The outstanding novelist Kim Stanley Robinson, pictured with yours truly. KSR's Mars trilogy is the most realistic Martian terraforming series ever written, but still somewhat neglects the inconvenient truths of the Martian environment in favor of the romance of interplanetary colonization.
Let's assume that for effective terraforming we have to cover 50% of the Martian surface with water. 50% is the magic number often given by climatologists for the minimum contiguous water surface area needed for a stable climate; otherwise we have a whole planet suffering from super-continentality, and the nicest vacation spot on the terraformed Mars has the climate of the Tarim Basin.
Start with the Martian polar caps. Together these total about 3.2 million cubic kilometers of ice. A back of the envelope calculation neglecting the increased density of water vs ice and the exact topography of Mars shows that this would cover 50% of the Martian surface with a layer of 44.2 meters of water. Even without modeling in more detail, it's obvious that with seas this shallow, Mars's dramatic relief would likely concentrate the water in less than 50% of the surface. And that's assuming we can melt every drop of the polar caps. Even if tomorrow everybody bought an SUV and all our power plants switched to coal, we couldn't accomplish that right here on Earth, and we're a third closer to the sun.
Now, let's add the just-discovered subterranean glaciers. That raises the depth 30 centimeters to a whopping 44.5 meters. Once again, I'm assuming we can melt every last buried snowflake.
For good measure, let's drop Halley's Comet onto Mars next time it swings by. That raises the depth an astounding 1.2 meters more to 45.7 meters - not to mention introducing lots of ammonia, aromatic hydrocarbons, and other compounds we may not want our already fragile ecosystem to have to deal with. Assuming that Halley's is typical, even if you keep plowing comets into the Red Planet, you only get an extra 1.2 meters of sea level out of each one. At this stage it's worth pointing out that if we weren't already in engineering la-la land, we're getting perilously close now. Assume you're in charge of NASA and you have an unlimited budget. How, operationally, would you drop a comet onto Mars? Bonus if you can do it without kicking up so much dust that there's an ice age which freezes your shallow Martian seas.
While there is more water on Mars than we probably expected to find, there's still not enough to create a truly Earth-like climate - and therefore, not enough to create a stable biosphere and a self-sustaining economy. Science fiction writers are welcome to continue terraforming Mars, but they're writing fantasy, not science.
There are other options mentioned in the pages of science fantasy, like shooting the rings of Saturn cube-by-cube at Mars. They're maybe the volume of Earth's Arctic Ocean. (What's that? I'm being unimaginative? Okay, you're writing the project proposal and you have an unlimited budget. How exactly would you do this?) There's always sucking up water from Earth - amazingly difficult to get it up out of a gravity well, not to mention destructive to the one planet where we live, and which has a climate that works. There's chopping up Europa and using it to water Mars, as in Greg Bear's Forge of God (a feat of made-up aliens who didn't tell the readers how they were doing it). And finally, there's the ever-popular variants on modifying ourselves and other Earth organisms so that our cells no longer rely on aqueous chemistry. What all these alternatives have in common is that the inclusion of unicorns in any of them would make them no more absurd.
In Collapse, Jared Diamond points out that the Inuit went right on surviving in Greenland when the Norse died out. Indeed, the Arctic was the last region of the world to be colonized, only in the last two millennia, by people whose technology had finally become specialized enough to allow an African ape to survive in the tundra. It's tempting to speculate about whether Inuit who emigrated to the Antarctic could become self-sufficient where the twenty-first century military-scientific establishment has not been able to. But even as marginal as it is, Antarctica has air and water. Mars is so alien that nothing less than the full complement of technology produced by the many and specialized members of an industrial society is required for human survival there.
What to Do Then?
Unless we learn to manipulate the periodic table at our whim, or alter our metabolism until we are no longer dependent on aqueous chemistry (both unicorn technologies), there is simply no body in the solar system besides the one you're sitting on where we can ever live sustainably. Period. Everywhere else in the solar system makes Mars look friendly. I strongly agree that it's desirable for humans to expand outward, as insurance for our survival, and as a defense against whatever else we may encounter. But we have to do so by shaping our dreams to the realities of engineering and economics. Seventeenth century Englishmen weren't so naive as to expect smooth sailing and immediate self-sufficiency.
The near-term solution is to continue expanding the international space station. Going forward and thinking economically (which is how we always have to think over the long-term), in zero gravity you can probably manufacture things that are difficult or impossible to manufacture in gravity. Adding a spinning section for simulated gravity and more radiation shielding to allow longer-term occupation is well within our current technology. Even the ever-popular idea to mine an asteroid is not outside our current abilities. Incredibly expensive, yes, but we know how we would do it.
The long-term solution is to look beyond our own solar system and use the space station(s) as the staging area for exploration. If we develop the ability to detect Earth-sized planets around neighboring stars, and if we also can detect oxygen and water vapor, and if there happen to be some of these within the detection range of said instruments (all reasonably imagined technologies), then we can find another possible Earth, with a biosphere that can more reasonably be expected to be self-sustaining. At a guess I expect this to occur in the next century. But I don't expect we can reliably launch vessels with living things over such distances at what amounts to a few pixels in that time period. In fact it may be asking too much to send self-directed vessles capable of maneuvering in a distant system - every interplanetary vessel humans have launched has required gravity assist, a risky technique when aiming at pixels twelve light years away. Maybe eventually we'll have von Neumann probes and ramscoops, and if we do, the next logical step is to send swarms of them out at those pixels. But right now it's all words on paper. A thousand years from now, your descendants - if you have any - will be sitting right here on this same acre of land that all 6.7 billion of us are. So take care of it. No, Virginia, there's no Santa Claus, and there's no Virginia either.
(Added later: an economic policy thinktank paper from 1998 about getting to Mars).