Mars (and Venus) may never support substantial human colonies
The forces of migration suggest our future is on Earth.
With the recent spectacular landing of NASA/JPL’s Mars rover Perseverance, and its incredible 90 seconds of full motion video, the first from the red planet, it seems as if it is only a matter of time before people are living there. But the reality is that Mars is at best suitable for short term habitation by researchers and their robots and at worst a death trap.
It turns out that, despite our imaginings, there is no planet in the solar system that will likely sustain human colonies. And the reason is less technological than it is sociological. As long as human beings remain human, the forces that drive us will likely keep us here on Earth.
Mars
While visions of a terraformed Mars abound in both science fiction and planetary science and proponents of colonization such as Elon Musk have stated that permanent habitation on the planet is not only possible but necessary for humanity’s survival, all things being equal, Mars has very little going for it. It is a small, cold world, with a frozen interior, almost no magnetic field, virtually no atmosphere, and little chance of allowing human beings to dwell on the surface without significant protection from deadly radiation, suffocation, and freezing to death. We might as well open a beach resort in Antarctica as try to live on Mars. We would be stuck living underground or in domed cities.
Indeed, the history of human migration has shown that inhospitable places such as the Arctic tend to develop only small populations. Human beings are naturally drawn to places that have abundant resources. Even the least welcoming climate on Earth is vastly more habitable than those on other planets.
Poor habitability is not the only reason not to want to terraform the planet. The other reason is that Mars is a protected world. It could easily harbor some kind of microbial life and if that life is extraterrestrial, we would be throwing away one of the few opportunities we have to study life that has evolved elsewhere, and for what? A dead frozen world that has little chance of being adequately terraformed thanks to its small size and lack of a magnetic field. These are not things that are easily fixed.
The main reason we have sent so many probes to explore its surface is that, (1) it is relatively close with only a 6 month journey from lift off to touch down, (2) robots can survive there for long periods of time meaning that there is more bang for your research buck to land a rover there rather than some other planet or moon, and (3) as mentioned, it may have life.
Terraforming the world would be extremely difficult because of its inability to hold an atmosphere thanks to the 1/2 Earth gravity, and a thick blanketing atmosphere is the only way to mitigate problems with temperature, pressure, and the lack of a magnetic field. Even then, radiation would be substantial. Unfortunately, Mars does not have enough readily available CO2 to mobilize into the atmosphere to create an effective shield and warming trend. The weak gravity causes most gases to escape the planet where the solar wind carries them away. Even a “Total Recall” style release of gases would be insufficient.
Another world in our solar system seems to have some things Mars lacks. Long before people considered colonizing Mars, Carl Sagan, as early as 1961, was proposing to colonize another world, a world that had come to be associated with the Roman goddess of love but turned out to be more like Hades.
Venus
Venus has received little love from robots compared to the god of war, Mars. While the Soviets sent a handful of landers to Venus, each one lasting only a few hours before succumbing to the intense heat and pressure, America has sent only a few probes and not one lander.
With a pressure of 92 atmospheres, a temperature hot enough to melt lead, no magnetic field, 117 Earth-day solar day, and virtually no water, Venus seems far less hospitable than Mars. Certainly, there is no indication at all that life might have evolved on Venus and if it did it probably isn’t living there now. No human landing crew could possibly survive on Venus without some sort of futuristic protection from the incredible heat and pressure that would make deep sea submarines look like glass diving bells in comparison.
Carl Sagan originally proposed terraforming Venus back in 1961. It involved seeding the Venusian atmosphere with algae to consume the thick carbon dioxide and turn it into oxygen. For a world that is only slightly worse off than Earth, this might have worked, and, with our own carbon dioxide problem, we might find ourselves doing it here one day, but for Venus it is a different story as Sagan related in his book Pale Blue Dot:
Here’s the fatal flaw: In 1961, I thought the atmospheric pressure at the surface of Venus was a few bars … We now know it to be 90 bars, so if the scheme worked, the result would be a surface buried in hundreds of meters of fine graphite, and an atmosphere made of 65 bars of almost pure molecular oxygen. Whether we would first implode under the atmospheric pressure or spontaneously burst into flames in all that oxygen is open to question. However, long before so much oxygen could build up, the graphite would spontaneously burn back into CO2, short-circuiting the process.
Later researchers came up with less naive approaches, but these also failed to deal with the sheer thickness of the atmosphere and the general lack of water of any kind of the planet.
Most proposals involve removing some 99% of the Venusian atmosphere either via chemical sequestering (turning the atmosphere into rock) or physically removing it from the planet. Sequestration turns out to be a monumental planet sized job, which we can assume our descendants can do, perhaps with self-replicating robots.
Any sequestration effort would require pulverizing a large proportion of the surface to create enough raw material to combine the atmosphere with. Creating rocks that contain carbon dioxide such as dolomite is one possibility, although this mineral may not be stable in Venus’s intense heat, so the planet would have to be cooled first, perhaps by orbiting shades. Another is to separate carbon and oxygen as Sagan suggested but somehow sequester the oxygen by oxidizing iron. (This happened on Earth billions of years ago when plants started producing oxygen but on a much smaller scale.)
Another possibility is to remove the atmosphere from the planet entirely. The amount of energy required for this is about 50 Megajoules per kilogram or about a terawatt applied over 850 million years. Blasting the planet with asteroids, effectively sandblasting the atmosphere off, would likely be inefficient and probably a waste of raw material.
Rather than build colonies on the surface, humans could build them so that they float in the Venusian atmosphere at a level with a more Earthlike atmospheric pressure and temperature. If you define “sea level” at the place above the surface where the pressure is one atmosphere, the problem can be defined as the surface of Venus being too far below sea level. The sweet spot above the surface of Venus exists at about 54–56 km above the surface. Here the pressure and temperature are both Earthlike. Although the atmosphere still contains a great deal of sulfuric acid, it is much easier to remove than carbon dioxide.
Still, the above proposal is similar to building Mars colonies underground. It simply emphasizes the lack of habitability of these worlds. Indeed, one could as easily propose having humans live in cities at the bottom of the ocean, and the technological problems with that are far less than building colonies on other worlds.
Misunderstanding Human Migration
Some argue that human beings are on the cusp of a new age of discovery where the difficulties of colonizing new places will be overcome. And surely they can be. But the analogy between colonizing these worlds and the age of discovery is a faulty one. Ultimately, the story of the age of discovery is partly one of government and privately funded expeditions but also about human migration. The forces that drive those two things are very different and even with the former sending us to explore other worlds, the latter is very much lacking.
First of all, the so-called New World was already inhabited when Europeans began to colonize it. It was clearly habitable with minimal requirements for surviving the elements. The original colonists, Ice Age nomadic hunters, were able to move in little by little, adapting as they went, and driven by abundant food sources. European colonists found it attractive partly because of problems in their homelands. Those who sought it out for adventure alone were few.
How bad would it have to get here on Earth to force would-be pioneers to want to live in places that require monumental projects to change them into habitable worlds? One wonders why we would not simply use those technologies to make Earth into a paradise.
Indeed, if the arguments in favor of colonizing Mars or Venus were valid, humans would have already applied them to places on Earth such as Antarctica and the bottom of the ocean. The lack of permanent colonies in those places and the lack of any will to colonize them suggests that the majority of human beings will always be driven more by economic (i.e., resource-based) factors than by some innate drive to live on the frontier. The frontier existed because of the cheap land and resources that could be found there that gave (certain) people autonomy. Those people took huge risks because the reward was equally huge for those who would otherwise just be scraping by. What exists outside of Earth, such as abundant materials in asteroids, is probably most easily harvested by robots not with human habitation.
These days we see human migration driven by much the same forces as centuries ago. Migrants arrive seeking a better life and greater wealth and autonomy. It seems like these are things that Earth provides far better than other worlds.
Life beyond Earth would be anything but autonomous. Societies on other worlds would have to be strictly organized to prevent catastrophic compromise of the technology that sustains the most basic life support systems. Thus, they would have to select their residents carefully, as astronauts are chosen and trained to work together and live as one. It is hard to see it being attractive to the majority of people. The idea of independent homesteaders living on Mars is a fantasy.
The wealth off world is largely in terms of raw materials such as metals. Obviously, there is no fauna or flora to harvest and it is difficult to imagine farming taking off anywhere in the solar system. And, just as mining and farming on Earth have largely been taken over by machines, mining and farming off the Earth will also be machine dominated. After all, providing for the transport, safety, and comfort of human operators would be prohibitively expensive and not make much sense.
Ecopoiesis
Another possibility that has been proposed is that human beings could simply change themselves rather than the worlds they want to live on. This is known as ecopoiesis. If robots can survive there, perhaps humans can simply adopt robot components into their bodies. These robot bodies could even be made, not of crude metallic components, but by nano-technology that grows and adapts, simulating human features. We would be cyborgs, transhumans, capable of tackling hostile environments.
Compared to terraforming, this proposal seems more likely to me as the resources and effort required are vastly smaller and the technological advancements for achieving such a transformation of the human body already well under way and have other uses as treatments for disease.
Nevertheless, it is hard to see forces for human migration appearing even then. Indeed, the kind of society that could transform the human body but still apply the pressure to migrate to other worlds sounds completely dystopian. Imagine a society where your life on Earth is so difficult and/or oppressive that you would submit to having your body altered so completely as to make you able to walk on the surface of Mars without a spacesuit, and then be shipped there because it is better than living here. It is also hard to imagine a society needing human labor so much on other worlds that it would want to force people to migrate (or enslave them) rather than creating robots to do the task.
A Second Home
At present, I don’t see any world in the solar system becoming a second home for humanity. While we will surely have the technology to create such colonies, we are at our core a pragmatic species and living off world simply does not pass a basic cost-benefit analysis. At best, our colonies would be research stations or military outposts. Unless human motivations change substantially in the future, economics will continue to drive migration. And, in my opinion, the best direction for humanity is to remove those pressures so that people can be happy, healthy, and autonomous where they live now. That is not to say that humans will not continue to push out into the solar system and eventually to worlds beyond our star. But those explorers will be funded expeditions, not colonists. One day, humanity may find a second home orbiting another star, an Earth-like planet that we can enjoy, but one would hope that the first colonists will arrive there looking for something better than they can find here on Earth, not simply because the Earth has become inhospitable to them.
Jakosky, Bruce M., and Christopher S. Edwards. “Inventory of CO 2 available for terraforming Mars.” Nature astronomy 2.8 (2018): 634–639.
Landis, Geoffrey. “Terraforming Venus: A Challenging Project for Future Colonization.” AIAA SPACE 2011 Conference & Exposition. 2011.