When imagining the long-term future of humanity, many see us leaving Earth. Sometimes this takes the form of an optimistic vision such as the post-scarcity Federation worlds of Star Trek. Less hopeful depictions, like that of The Expanse, emphasize the ways that humanity’s foibles will remain with us even if we venture to other planets. But it is not only in literature and film that humans find themselves looking to the heavens. Some of the world’s wealthiest people—corporate leaders like Jeff Bezos, Elon Musk, and Richard Branson—present space as a source of salvation for humanity, a place to which we may eventually need to flee.

The central question of Daniel Deudney’s recent book, Dark Skies: Space Expansionism, Planetary Geopolitics, and the Ends of Humanity, is whether this goal of becoming a multi-planetary species is actually good for our survival. For Deudney, a professor in the Department of Political Science at Johns Hopkins University, the answer is an emphatic no—humanity would best be served not by establishing colonies on Mars and beyond but by more circumscribed space policies oriented more specifically toward terrestrial problems. It is worth underscoring this point: Deudney is not saying that space exploration lacks any value. Rather, he is arguing that the prospective colonization of space and certain already-existing aspects of the militarization of space are more dangerous to humanity than they are helpful. In the realm of science fiction, Deudney finds his closest match in The Expanse’s Detective Josephus Miller: “Stars are better off without us.”

Avoiding Star Wars

The crux of Deudney’s argument is that humanity’s efforts in space so far have increased the likelihood of global nuclear war. Space colonization, in his view, would so greatly amplify the chances of such a war (or a similarly calamitous event involving some future technology) that he advances a strong claim: “Space colonization is likely to result in human extinction and should be avoided.” While he acknowledges the various benefits that have been derived from some aspects of space exploration—weather satellites and the Global Positioning System, for example—he also notes that space has been dominated by military expenditures to date. Even some of those technologies with benign civilian applications were initiated in whole or in part by state militaries.

For Deudney, however, the most important aspect of the militarization of space is the development of intercontinental ballistic missiles (ICBMs). While not often thought of as a “space” program, ICBMs in fact rely on a trajectory that spends most of its time in space to attain their dramatic speed. On the other side of these weapons, anti-ballistic missile (ABM) technologies are also space programs by Deudney’s definition insofar as they rely on satellites to detect, monitor, and ultimately disrupt the space-bound missiles. The deployment of ABM systems, moreover, Deudney tends to see as destabilizing. (There is a long-running debate on this question that has largely been politicized along the right-left axis in American politics since Ronald Reagan proposed the Strategic Defense Initiative.) For Deudney, to the extent that the United States—or any other state—develops ABM technologies, it just encourages the development of new countermeasures and more advanced potentially (if not conclusively) destabilizing weapons such as hypersonic missiles. As he puts it, “China’s and Russia’s recent moves to expand space counterforce activities, combined with Trump’s recent effort to create a Space Force and expand US military space activities, are likely to further accelerate space weapon deployment.” Between all these weapons and their related command-and-control systems, Deudney presents the continued militarization of space as a grave risk for humanity.

It becomes most clear how all of this combines to make space colonization dangerous in the tenth (and second-to-last) chapter. It is here that Deudney lists six existential threats made significantly more probable by this expansionism: “malefic geopolitics, natural threat amplification, restraint reversal, hierarchy enablement, alien generation, and monster multiplication”. By “malefic geopolitics,” for example, he means the tendency of the different environments in space to create cultural differences among any space-faring colonists that would be a source of division, and the category of “natural threat amplification” includes the increased (even if still slight) possibility of the use of asteroids as “planetoid bombs”. The sixth threat, “monster multiplication,” refers to the proliferation of knowable and unknowable risks inherent in any increasingly complex system. Given these risks that are already rising due to the militarization of space, Deudney warns, “For humanity in space, there is only darkness at the end of the tunnel.”

These threats will sound familiar to scholars of International Relations (IR). He couches his argument about the continuation of geopolitics in space in the realist language of “anarchy,” or the lack of a higher authority that can reliably adjudicate disputes and enforce settlements, and he describes extraterrestrial expansion as likely to create an “extremely offense dominant” system in which it is easier to damage others than it is to defend oneself. In writing about the proliferation of risk, Deudney draws on the cautionary work that Scott Sagan has done with respect to the potential for accidents in nuclear weapons systems. But one need not have taken graduate coursework in IR to recognize some of these threats—this sounds very much like the imagined world of The Expanse, which another IR scholar once dubbed (correctly, in my view), “The best show about international relations on television right now.” Indeed, one of the strengths of Deudney’s book is what makes James S.A. Corey’s series so compelling—it assumes that human beings will be much the same in space as they have been on earth. If colonization on earth has often been bloody and short-sighted, why would that be any less likely in space?

An “Earth-Oriented” Space Program

Deudney’s book arrives at the same time as another, more optimistic book on humanity’s future in space. In seeking to explain what humanity finds so captivating about the heavens, Sarah Stewart Johnson, an Assistant Professor of Planetary Science at Georgetown University, writes in The Sirens of Mars: Searching for Life on Another World, “We are a finite tribe in a temporary world, marching toward our end.” For Johnson, the search for extraterrestrial life is thus “the search for infinity, the search for evidence that our capacious universe might hold life elsewhere, in a different place or at a different time or in a different form. That confirmation . . . would stand in contradistinction to the finite life to which we are confined, to the finite planet we inhabit. Finding life—even if it is the smallest microbe—would, for me, be . . . a shimmering hope that life might not be an ephemeral thing, even if we are.” 

Johnson’s description of humanity’s “search for infinity” echoes Alexis de Tocqueville’s depiction of the human soul. As political theorist Sarah Beth V. Kitch recounts in exploring Tocqueville’s understanding of the role of religion in society, Democracy in America describes humanity as innately interested in transcendent experience: “Man did not give himself the taste for the infinite and the love of what is immortal. These sublime instincts are not born of a caprice of his will: they have their immovable foundation in his nature; they exist despite his efforts. He can hinder and deform them, but not destroy them.”

Deudney acknowledges but is not moved by this sentiment: “Coming of age,” as he writes in the conclusion, “means putting aside the fairy tales of childhood.” Humanity has already found the one celestial body that offers a realistic future, and our task is to ensure that it continues to support human life. As noted above, this does not mean we need to forsake any and all space exploration. But what Deudney proposes is an “Earth-oriented space program,” which he argues ought to focus first on actions that ought not to happen in space—so, for example, states ought to cooperate to relinquish ICBMs and prohibit any colonization of Mars or asteroids. Moreover, there ought to be a prohibition on the development of any state-owned or corporate technology for “asteroidal orbit alteration,” which should instead be crafted as part of an international effort to create a system that could be used for planetary defense but not for a single state’s military purposes. He also suggests strengthening the Outer Space Treaty to prohibit a wider range of potential military activities in space.  

In addition to such precautionary measures, however, Deudney also suggests expanding the study of the earth and the rest of the cosmos—primarily with satellites and robotic probes but also with more collaborative study at the International Space Station. “Only after humanity has figured out how to order its political affairs by effectively regulating nuclear weapons, and not wrecking the planetary life support system,” he concludes, “can space expansion be anything but a potentially dangerous diversion or amplification.”

Ultimately, Deudney’s work is a welcome addition to a debate that has been one-sided so far. The “dark skies” in this rejoinder to the sanguine advocates of rapid extraterrestrial colonization, however, may not be dark enough. The privatization of space, driven by corporations that will not always prioritize long-term global interests over parochial short-term gains, shows no signs of abating, and there is little evidence that the world is moving toward more robust multilateral action on arms control or climate change.

Indeed, even if states were inclined to craft the sort of agreements that Deudney recommends, enforcement could be difficult. While the scale of space-related infrastructure would likely be large enough to make for easy monitoring, any state with the resources necessary for space expansionism might be tempted by the prospect of locking in long-term economic or military advantages or attaining a boost to its status by being the first to colonize Mars or conduct large-scale asteroid mining. Whether the offending state was, say, the United States, China, or another great power, what would other parties to any agreement be willing to do to prevent them from acting on this temptation? As in other areas of international political life, prohibition might not produce optimal results or might simply be unattainable given state interests. If that is likely to be the case, risk mitigation may be the best we can do.

If extraterrestrial sirens beckon, Deudney makes a thought-provoking case—perhaps we ought to tie ourselves to the mast.