So. Space settlements. Have we really thought this through?

If humanity survives the next few centuries, it’s probable we’ll expand into space. People, nations, and the international community have options about how to proceed. The choices we make now—about the pace of expansion and the rules underpinning it—will shape that future in ways we can’t yet imagine. The wrong choices wouldn’t merely slow us down, they might create existential risk for humanity.

We can’t make these choices properly unless people actually know what the truth is about space settlement. All of it. Not just the size of the rocket or the power needs of a settlement or the available minerals in asteroids, but the big, open questions about things like medicine, reproduction, law, ecology, economics, sociology, and warfare. Detailed treatments that are honest about the severe difficulty of these things are almost invariably left out of books and documentaries about space settlement.

Why is this discourse so often bad? We believe there are two major reasons. First, the general public knows very little about space. Most people can name exactly one astronaut, and with an appropriate mnemonic can say the planets in order. Outside of a few weirdos, most of us don’t know things like what lunar soil is made of, or what the Outer Space Treaty says, or the history of nuclear weapon detonation in space.

Given the limited public knowledge of space science in general, knowledge of its weird little cousin—space-settlement science—is almost nonexistent. And that’s where we arrive at the second problem. If you are ignorant about space settlement and want to become educated, many of the articles you’ll read, many of the documentaries you’ll watch, and pretty much every single book on the topic have been created by an advocate for space settlement.

Now look, there’s nothing wrong with advocacy. The space-settlement geeks we’ve met are smart, thoughtful people. Most of them, anyway. But reading about space settlement today is kind of like reading about what quantity of beer is safe to drink in a world where all the relevant books are written by breweries. Even when they’re trying to be evenhanded, they leave things out. One of the most prominent books on space settlement, The Case for Mars, is over 400 pages long, including obscure historical information on Mars conferences of the 1980s as well as detailed chemical equations for plastic production at the Martian surface, but never once mentions the existence of international space law. Of the five decades of legal precedent that will dictate the political nature and geopolitical consequences of any Martian future, not a word.

The little book you’re reading right now, which admittedly begins with a Uranus joke and contains an explainer on space cannibalism (stay tuned), is nevertheless the only popular science book we’re aware of that offers the whole picture without trying to sell you on the idea of near-term space expansion.[*] Rather, we’ll try to clear up a lot of misconceptions and then replace them with a much more realistic view of how feasible space settlements are and what they might mean for humanity.

But first, we should introduce ourselves. Hi. We’re Kelly and Zach Weinersmith. Kelly is a biologist and Zach is a cartoonist. We’re also a wife-and-husband research team who’ve spent the last four years trying to understand how humans will become space settlers. We’ve gone to conferences, conducted endless interviews, and collected, at last count, twenty-seven shelves of books and papers on space settlement and related subjects. We are space geeks. We love rocket launches and zero gravity antics. We love space history’s strange corners like red cubes and tampon bandoliers. We love visionary plans for a glorious future. We are also very skeptical people. If you want to visualize us, imagine John F. Kennedy giving a beautiful, uplifting speech on sailing “this new ocean,” and then notice in the background two people squinting at the middle distance, thinking “but is it really like an ocean?”

After a few years of researching space settlements, we began in secret to refer to ourselves as the “space bastards” because we found we were more pessimistic than almost everyone in the space-settlement field, and especially skeptical about the most grand plans of space geeks. We weren’t always this way. The data made us do it. Frankly, we are cowards and would very much like to agree with the consensus. We didn’t like being this pessimistic, especially about an endeavor that so many people think embodies the best of human nature. It makes one feel like, well, a bastard.

We think space settlement is possible, but the discourse needs more realism—not in order to ruin everyone’s fun, but to provide guardrails against genuinely dangerous directions for planet Earth.