to sustain human life. Consider the Ganymede greenhouses in The Expanse, the ever‐necessary photosynthetic plants to produce oxygen in the Belt colonies, or even the ferns that humans end up carrying with them to another solar system.14 In fact, self‐sustainable ecosystems that would allow long‐term human survival probably require a high degree of biodiversity, upwards of 4,000 different species.15 The expansion of humans beyond Earth would also be the expansion of Earth life beyond its native planet. And that would certainly be a good thing.
It matters that those planets are lifeless, however.
If we found life on Mars, for example, we would face a moral dilemma. We might decide that we would still have overwhelming reasons to colonize Mars, but we would at the very least also have a strong reason to preserve any native Martian life. The alien protomolecule makers seem to have had no such qualms. They produced a technology capable of destroying all life on a planet, just to build a galaxy wormhole super‐highway for themselves. We don’t know their motivations, but it’s possible that the alien civilization that created the protomolecule just didn’t care about any species other than themselves. Or they might have been under the impression that most life in the universe is simple and unicellular. Yet, this should not be a reason to disregard it or consider it without value. Imagine if the protomolecule had arrived on Earth instead of getting stuck in the outer planets. Complex life on Earth might never have evolved.
The difference between the careless destruction of other life forms by the protomolecule makers and the prospect of humans (along with other Earth life) expanding to lifeless planets is the difference between morally objectionable colonization, where a particular people (or, in this case, alien species) takes some territory or resources for themselves, without regard for its original inhabitants, and the positively desirable biological colonization of new habitats, which arguably increases the amount of value in the universe.16
Unfortunately, in Cibola Burn, the first planet outside the solar system that humans colonize is already teeming with native life. The colonization is morally objectionable, not only from the point of view of the preservation of biodiversity, but also because it is dangerous for the colonists themselves.
Hedging Our Bets Against Extinction Risk
While we might not be facing interplanetary war or the unpredictable consequences of ancient alien technology, many serious dangers face the human species today. We are quite resilient and have survived numerous disasters in the past, including floods, earthquakes, famine, pandemics, and wars.17 However, we have never faced a real threat to our existence as a species. Most disasters are localized and kill many people, but within a geographically restricted area. Even highly contagious diseases with high mortality rates never kill the entire population; some individuals tend to be immune. However, some disasters might affect the entire human population or even all complex life on Earth.
Although it seems to have somewhat faded from public consciousness, the possibility of nuclear war remains a major danger. Some authors argue that, even though the probability of deliberate use of nuclear weapons might have declined (and that itself is arguable), the probability of accidentally triggered nuclear war has actually increased over time, due to obsolete automated systems and a faulty logic of “preventive” and retaliatory strikes.18 A scenario of runaway climate change is even more likely, in which a moderate increase in greenhouse gases generated by human activity raises temperature sufficiently to initiate permafrost thaw, releasing large amounts of methane and carbon dioxide. This in turn increases the greenhouse effect, leading to more thaw, triggering an unstoppable feedback loop. Other possible threats to human existence include uncontrollable biological weapons or nano‐machines (think of a human‐made protomolecule), a large meteor strike, artificial intelligence gone wrong, or even unforeseen effects of high‐energy physics experiments in future supercolliders.19
Small population size and restricted distribution range are factors that increase a species’ extinction risk. For instance, animals or plants that occur only in one small oceanic island are at high risk of extinction. Humans might seem to be relatively protected from that risk, although our enormous population size is in itself cause for concern, due to the depletion of resources. However, any terrestrial species is powerless against threats to all life on Earth. A planet is much like an island. As astrobiologist and philosopher Milan M. Ćirković puts it, “the terrestrial biosphere is (…) a single system—and uniqueness is always more fragile than multiplicity.”20 In this context, human expansion beyond Earth seems like a prudent move, which would certainly increase our chances of survival in the long run. That is, if we don’t end up killing each other, because, as amply demonstrated throughout The Expanse, warfare is one extinction risk that might follow us into space.
Colonizing other planets will not be easy. The most obvious candidate is Mars, due to its proximity, the existence of an atmosphere, water ice, relatively similar day/night cycles, and other features.21 Making it habitable, however, will be arduous. In The Expanse, the terraforming of Mars is an ongoing process, one which, incidentally, brings the Martian people together under a common cause. The truth is that no other planet in the solar system is as hospitable as Earth. Even in The Expanse, when humanity is already spread out across the entire solar system (but before interstellar expansion), Mars and the Belt are still dependent on Earth. When Holden is contemplating the possibility that Eros might crash into the Earth, causing the protomolecule to terraform the entire planet, he muses that “Mars would survive, for a while. Pockets of the Belt would hold out even longer, probably. They had a culture of making do, surviving on scraps, living on the bleeding edge of their resources. But in the end, without Earth, everything would eventually die.”22
Dependence on Earth might seem to contradict the idea that human expansion would function as a “backup” in case of disaster on Earth. We must bear in mind, though, that expansion to other planets is a long‐term plan. Colonization does not avoid our having to take measures to prevent runaway climate change, unfettered population growth, and resource depletion. You can’t build a self‐sustaining ecosystem on a desert planet overnight. Terraforming a planet can take between 1,000 and 100,000 years. Still, that is a lot quicker than the 1.5 billion years evolution took to get from the beginning of life on Earth to an oxygen‐rich atmosphere.
Pessimists will say it can’t be done; that it’s a waste of resources. The obstacles are indeed tremendous, but we should not give up before we start. Air travel and landing on the moon were once thought to be impossible. Furthermore, space exploration promises us a better understanding of our own planet in the context of other planets. This advance in knowledge deflates the argument about the waste of resources. Some people will argue that we should invest more in the protection of our own planet instead—in the prevention of climate change, biodiversity loss, and so on.23 But we must do both, if we are to hedge our bets against extinction. Interplanetary expansion is a very long‐term prospect; it is not a replacement for having to solve the problems we have here now.
Astrobiologist Charles S. Cockell argues that, in fact, the goals of environmental conservation on Earth and space exploration, far from being incompatible, are actually beneficial to one another.24 As an example, he asks us to
