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Numlock Sunday: Zach Weinersmith talks A City on Mars
Numlock Sunday: Zach Weinersmith talks A City on Mars

By Walt Hickey

Welcome to the Numlock Sunday edition.

This week, I spoke to Zach Weinersmith, who with his wife Kelly Weinersmith wrote the brand new book A City On Mars: Can we settle space, should we settle space, and have we really thought this through?, which is out this week.

I loved this book. I’ve been looking forward to it for years since they announced it, and I loved their previous book, Soonish. It’s an in-depth look at what exactly it’s going to take to get a permanent human settlement on another world. Zach and Kelly investigate not just the physics problem of getting people and material there, but also the long-term social, legal and biological issues inherent in this kind of venture. It’s an amazing read, and it’s available wherever books are sold.

Beyond A City on Mars, Zach can be found at his iconic webcomic, Saturday Morning Breakfast Cereal, and you should check out his other books, which include Soonish and Bea Wolf, his children’s book adaptation of Beowulf.

Remember, you can subscribe to the Numlock Podcast on Apple Podcasts and Spotify. This interview has been condensed and edited.

Zach, thank you so much for coming on.

I'm excited to talk about space nerd stuff.

Boy, are you. You have written a book called A City on Mars. You ask all sorts of really exciting questions throughout the book. It is not just a book about the physics of getting to Mars, which I think a lot of people fixate on. It is a book about sociology. It is a book about how communities work. It is a book about all sorts of different exciting things. Your research process was incredibly thorough. I guess just before we dive in, what was it like to write this thing? What was it like to report it out and dive into the science?

Oh man, it was kind of awful. And you know what it was? I think when you do pop science, there's this fantasy you have of, "What if I got a topic and I was out ahead of other people and it was really controversial and awesome." And you'd think that would be romantic and be like a montage. But we were so anxious, because we felt like we were really going against a lot of strongly held views by smart people. And when you do that, you feel like you really have to know what you're talking about so that you can stand your own when they are going to come at you.

And so the result of that, and our just general dorkwad-ery, was that there was just a ton of primary and technical source reading, which is awesome. Actually, it's like what I do in my free time, as a boring person. But when at some point I was reading a hundred-something pages a day of hard stuff and like you roll out of bed and you're like, "What? I have to read 50 pages of seabed international law to understand that!" It was brutal. I mean absolutely wonderful kitchen table conversations during this time, but it was tough.

Yeah, a lot of it is very compelling because again, you've had some of the finest minds that our society's produced consider what it would take to get us into space and stay there. And that I imagine has got to be a lot of fun. But then you also, you really consider all sides of this, man. You’ve got sociology, but you just mentioned you have the law.

There's a lot of legal precedent when it comes to these interesting spaces that are not owned land but nevertheless are important. Do you want to walk people through the structure of the book and what angles you take and how you dive in?

So we ended up artificially separating it into six sections, which hopefully I can actually remember, because we fussed a lot with the structure; this is a book that, as you say, goes from lots of angles. There were lots of options for how to structure it and we actually originally had it as we'll go through orders of magnitude from one person to 10 people, then 100 people. And it just turns out, I learned that sociologists don't believe there are actual meaningful, emergent obvious things different between a hundred and a thousand people where you can be like, "Okay, here's what happens now."

We ended up instead saying, "We're going to start off with what it does to your body." So that's like sex and reproduction, that's physiology, what space does to your body, and then also psychiatry stuff which was nontrivial. Then we move on to the place you might actually put that body. Ideal spaces are probably the moon or Mars, and especially Mars is probably best, which we could get into.

Then we move to how you might keep that body in that place from dying. That is to say, habitat construction. How do you build a facility in one of these places? Where might you go and what are the future goals there and the problems you need to solve. But mostly having to do with energy and shielding and also making food and oxygen and consumables.

And then at that point, we dive into the law and sociology. So then we go to a brief rundown on the "cynical history," we call it, of outer space. And the basic point of that is to position you to understand that human spacefaring is almost always purely political. It's about making declarations as a superpower and showing up other countries.

That prepares you to think about how the space law as we have it is. So we go into how the law actually works, which a lot of geeks think doesn't matter, they don't think international law exists, but it does. We know it constrains the behavior of countries and people. From there we get into some sociological questions. We'll talk about this a little more later; the sociology was at one point quite extensive, and the editor was like, "You just can't do this to readers. This is just too much," so we cut it down to looking at company towns as a potential model, and a couple other things.

Then we close out with some questions having to do with the future, in the sense of what numbers are we talking about to avoid too much inbreeding, to have economic autarchy — that is to say, being able to survive the death of Earth.

Then finally what would happen in the case of space war and how to think about the idea of space war. Yeah, so we're really trying for every angle. I could tell you, we did still leave out stuff. There was stuff we had to cut, but we tried to be as thorough as possible.

I'm so glad that you brought up the "cynical history of space," because I thought that that was just such a very thorough look. Space is one of the most romanticized things. I think that's one reason that again, this topic is so compelling, is that we just have so many stories that we tell each other about space and its role and there's a fundamental yearning to it. There's a fundamental ambition to it. You could tell a lot of stories set in space, and we have.

Whereas the cynical history of space was really just bringing things down to as brass tacks as possible. It was turning this romance into the physics and politics that it truly is, and I really appreciated it. Do you want to dive in a little bit on that, a brief cynical history of space?

Yeah, I'd love to. So it's funny. There's a power law, I can say this for your audience. There's a power law for what space stuff is about. So it's like 90 percent of all space books are about Apollo 11, in particular, where we landed on the moon. And then 90 percent of what's left is either Apollo 8, where we first went around the moon, or Apollo 13, where everything went wrong and there was a movie about it. And then down from that, it's everything else.

There's a subgenre in all this that is the political history. There are only a couple books about this, and they're mostly more scholarly because I guess regular people just don't want to read about the sort of geopolitical theory about why countries do this sort of thing. What's funny is that in those fields, and people who study the law and history, if you said, "Hey, Kennedy went to space as a purely political act," it would be like saying, "I know how to tie my shoes." It's just the most obvious thing in the world.


But if you say that to a space geek, it's like you're poking something beautiful. But we have the evidence! I mean you never know what's in a person's heart, but we know, there's evidence that after Sputnik Kennedy thought space was stupid. We really only did that big speech to Congress, which sometimes gets conflated with the one at Rice. He only did his big speech to Congress basically saying, "Give me a huge pile of money," after Bay of Pigs.

And then very shortly after, Yuri Gagarin became the first person in space and he was of course, a Soviet. So Kennedy looked like garbage and he knew it, and he was a smart PR operator. So we have private transcripts of stuff he said basically saying, "There's no reason to do this." He uses the phrase, "I'm not that into space." He just says it very explicitly, "We need to show them that we won." And that's it.

And his own science advisor, I don't think we put this in the book, but my recollection is, Jerome Wiesner, his science advisor, refused to go along with the idea that this was about science. He was not cool with it. So there's just very robust evidence that this was politics all the way down on both the American and the Soviet side. That unfortunately the great mass of the public around the world overestimates the importance of rocketry to the dominance of nations and their technological capacity. Whereas, I think you could easily argue that the U.S. was ahead the whole time in everything that mattered, but people are just beguiled by rocket technology.

Again, part of this is some stuff that I've read, but it seems like a lot of people's mentality about space is derived from Disneyland and a lot of sci-fi aesthetic stuff.

Yeah, it's that. I have an older brother as a poli-sci professor and he said when he gets students and he says, "Who's the best president ever?" They still to this day often say, "Kennedy." And when you ask them why, they cite a speech or something, which is not afforded to any other president! Any other president, it's like, what did they do? But with Kennedy for some reason — probably because he was assassinated while young and handsome, and there's this sort of legend about it — people are like, "Well..." Here's the history of space: Kennedy said, "We go to space because we're amazing and we need new frontiers." And so we went and that's it. And you want to come in and say it was about politics, how dare you.

Readers might recognize you from your book Soonish. A City on Mars you wrote with your wife, Kelly, as you did with Soonish. One carryover from Soonish that I really dig in this book is that you kept the Nota Benes, which are chances to dive in on perhaps things that are a little offbeat, but fun elements. I really love all of them.

The one that I really enjoyed the most that felt very relevant to the next step of this conversation is Antarctica and violence around it. We have a place that is very inhospitable to human life that we send people to occasionally, where sometimes people do crimes, and it is called Antarctica. And that is the best indication of what might be the situation in space.

So there's a little bit of a nuance to this. Sometimes when people work in space psychiatry, space psychology, they'll say one of the things that's important is, "Did you know one time a guy got stabbed in Antarctica for spoiling novels?" And then there's another famous story where, as the story goes, there were two Russians at Vostok station having a chess match and one killed the other or attacked him with an axe or something. So they banned chess.

And so both of those stories, actually, they're not really true. They got passed around the internet all day and all night. I think the one about the chess thing is just not true. Or at least, we couldn't find evidence. We talked to a guy who had been at Vostok station for a long time, he's a Russian guy. And he was like, "I'd never heard of this or about the chess ban." And it also just utterly smacks of Russian stereotyping.

A hundred percent, yeah.

Right. There's no dancing bear or whatever, but it's pretty close. The story about the spoiling novels, the novel thing was just a weird detail it was fixated on. It was more like the guy was just hazing him and bullying him for a long time and finally went too far and the other guy stabbed him. And it's sort of a bit more of a conventional stabbing story.

Our perspective, and there's reasonably robust data on this, is actually that in Antarctica where it is dark and cramped and awful and somewhat space-like, you actually don't get a higher rate of psychiatric problems. Maybe even there's some evidence it's lower. That's probably to do with the fact that people are screened before they come and they're probably somewhat self-selected.

But that doesn't mean you get to just be like, "Don't worry about it." Right? Because it has been the case in Antarctica that we've had to handle murders. There have actually been murders. There's one that’s well-documented where a guy accidentally shot another guy during an altercation having to do with raisin wine. Which, I hadn't by the way heard about raisin wine, but it's I guess a sort of low-quality homemade wine.

It'll bring a new meaning to the phrase “moonshine” if we pull that off in space.

This is a whole funny thing that we would joke about, and we talk about making food in space. We found a quote by Andy Weir of The Martian who wrote the foreword to a book called Alcohol in Space, which is actually a quite wonderful book, what you would think. And he says, "Mark Watney, the star of The Martian, would not have made vodka because why would you waste all those potatoes?"

But we actually, if you look into the history of biosphere, the place where people stayed for two years in confinement to see if you could do this? They were starving, and they still made alcohol. I love that story. It's like they're literally losing 10 percent body mass, but they still made the worst quality wine out of bananas or raisins. Humans are a problem.

Is that the case for a lot of this? Humans are the problem with space travel?

I think the way I would say it is, humans are the problem, but in that they're humans. Because people tend to think like, "Oh, you'll go mad in space." Or whatever. And there's just no evidence of that extreme thing. It is just that they're going to be humans. So on Earth, when you're a human, you expect all sorts of basic services. Some humans, from time to time, have acute psychiatric problems or whatever, and they need to be taken care of. And this is just usually not imagined when people talk about sending a thousand people to Mars.

Let's talk about where to, right? You have an entire chapter where you talk about Mars, you talk about the moon, you talk about a rotating space station, which is not the worst option. Then you talk about some other options, too. Why don't you walk us through, give us a little tour of the buffet here and where you come down as the angle?

The deal is, the solar system is really, really big. Space is really, really big. But the places you might maybe sort of survive on are eeny, weeny weeny.

Mercury is basically a nonstarter. It's way too hot and it's actually fairly hard to get to because you have to drop toward the sun and then carefully get into orbit.

Then you've got Venus, which is incredibly hot, high pressure, and has sulfuric acid clouds. There are weirdly a couple people who still think it would be good. Their argument is, and this is true, it's a very thick atmosphere, so you should almost think of it as something like a fluid. There's a place in the atmosphere that does have Earth-like temperature and pressure and carbon dioxide. When you're in this mode of like, "Well, does it literally have the elements of existence and maybe sounds compelling?" I think it's crazy, but it does have its people.

Then you have Mars, which is the place. Basically, it has Earth-like elemental composition. It has an atmosphere, although it's quite thin. But it's an atmosphere with carbon dioxide, and carbon and oxygen are both nice things to have.

Then beyond that, of course, there's Earth and there's Earth's moon. The moon is great, but it's very low in water, it's carbon-poor, and humans are made of carbon as there are things we like to eat. So the moon is good as a place to launch from, but not for building a permanent settlement unless you're really going to ameliorate it.

Then beyond that, you've got the asteroid belt. A lot of people think it'd be great to live in asteroids, but actually asteroids are typically rubble piles. They're dusty rocks that are kind of drawn together. They're actually quite distant from each other. It's not like in Star Wars where you're dodging big potatoes, and you actually usually can't see one from another. They're quite sparse and beyond that—


It's extremely sparse. Then going further out, you just have the gas giants where there's not even a surface to land on, and the icy planets. And then there are a couple moons, there have been here and there proposals for landing on Titan, but you're talking about extraordinary distance and all sorts of other problems.

So really, it's the moon or Mars, which have a combined surface area smaller than Earth, and they're both just awful. The reason we say the moon is cool is because it's always the same distance, and the distance is not too far. It's about two days by rocket, but there's almost no water on it, contrary to what you might've heard in articles in Bloomberg about this trans-lunar economy we're supposedly going to build. The surface is made of this really nasty stuff called regolith that probably damages equipment, and may cause health problems.

The main appeal of Mars is basically that it has Earth-like days, it has access to water, and it has some atmosphere. So all the stuff is there to not die, which is really not true anywhere else.

Best I got.

So it's the best option that we’ve got. But it doesn't sound like it's necessarily a great option.

No, and it's also, unless some exotic technology comes along, it's six months in, about a year stay, six months back. There's a long period where you're there and you cannot go home because Earth has raced ahead of you around the sun.

Oh wow. There are a lot of fascinating problems that present themselves. And again, one thing that I love about your and Kelly's work is that you really just talk to a lot of really smart people. You do a lot of the in-depth research.

One thing I have to ask you about is that you actually published an article in space policy: To Each According to Their Space-Need: Communes in Outer Space. I just love that this is the depth to which you did it, where you did get a scientific paper out of this one, too.

We did! Yeah. And I should say that that scientific paper had many more jokes and illustrations in it when it was in the book. It was originally a chapter.

We worked with two other guys. One was Ran Abramitzky, who's a big deal sociologist, who is the kibbutz and commune studies guy, and then John Lehr, who's the absolute expert on how to write communes. We did this paper together. The reason it got cut from an earlier version of this book is, we were like, "Let's look at tons of sociological models." All that's left from that is company towns. The basic feeling from our editor, which I think was correct, was, "Each one of these models is starting your audience over in a completely new topic. It's just too much to ask for a pop science audience."

But communes are really interesting. People often want to talk about stuff in space society, but usually you can't do science on it. So you can't be like, how should we form society? That's hard. But if you start with, well, what if it is a company town, then you can say stuff, because we know stuff about that structure.

One structure — and a lot of this is due to Ran Abramitzky — we know a lot about is communes. He did this book called The Mystery of the Kibbutz, and the mystery is how did you actually get humans to behave communally for about a hundred years? He actually does a standard, delightful neoclassical economic analysis of how they manage human incentive structures to get people to behave in a basically communal way.

What's absolutely fascinating is when you look throughout history going back hundreds of years throughout communes, they converge on the exact same sets of problems and the exact same sets of solutions. Hutterites, who are this very— certainly by my standards — very sort of patriarchal, old world Anabaptist religion, they will shun you and shame you if you fail to do certain communal things.

But if you go to the surviving hippie communes? Amazingly, they do the exact same stuff. They do it in a hippie way, but they still do it. And so it's just astonishing. So if you say, "Oh, space is going to be like a commune," you can really do some cool stuff. I mean, I don't know if it will be, but you can at least say we can do some deep analysis and we can read primary literature. It's just really cool.

It is cool because again, finding experiments is hard because everything that would involve an experiment here is either drastically immoral or extremely expensive. It is cool that for company towns, there's a huge economic record of that. You have an amazing chapter in the book about that. And I dig this article because it's just cool how much terrestrially really we do have to work with here.

It's amazing. One of my absolute favorite things. For a numbers audience like yours, this is really cool. A lot of people are into space stuff. Would it be better to have a religious community, because they're going to need to be sort of cohesive? It's set in a hand-wavy way, but you can actually compare secular versus religious kibbutzim. You actually find that the religious ones have a measurable – like quantifiable with shekels, like with money – difference in retention ability.

You can actually kind put a number on religion as a retention, at least in this context. I don't know, maybe Anabaptists are better than Jews at retaining people, or maybe worse. But it's amazing and it's not trivial, but it's also not huge. It's not like an order of magnitude, but it is a real difference. People are more willing to stay. This is less true for Jews, but in Anabaptism, like if you leave the commune, you go to hell in Hutterite Anabaptism. So that's probably quite motivating. But yeah, just amazing that you can put a number on something like that.

I mean that's the thing, man; if you leave the commune on Mars, you do go to Mars.

That's right. You die. You do die very quickly. Yeah, but that's interesting because that adds to the analysis, because a classic commune problem is when people can get opportunity elsewhere, they do. But if you die, if you go outside, that's probably different.

I would be in total violation of all journalistic principles if I did not ask you about the possibility of space war. What did you find on this matter?

We try really hard not to be too speculative. The way we did it is, we talked about short-term, medium, long-term, right? Short-term, people talk about space war. It probably won't happen, basically because there's no reason to do it. Without getting too in-depth, there is some cool analysis about space weapons you can look up. Space weapons sound awesome and they are awesome. I will say, guiltily, there are some zany designs from the Reagan era for these pumped X-ray lasers that were going to blast the Soviets. Crazy shit.

I'm a simple guy. If you call it a "Rod from God," you have my attention.

Totally. But the basic problem: All of us already have nuclear weapons. Insanely, if Russia decided they wanted to nuke Washington, I don't know, we do have defenses and stuff. But do they get the advantage from setting the nuke in the space before firing it? I think the answer is probably no. It does get there faster, but it's also totally exposed while it's up there. It's probably in low Earth orbit. It's constantly pissing off everyone on Earth while it's up there. And at the end of the day it saves you some number of minutes. It might be as much as 20 or 30 minutes. I'd have to look at it. But we're talking about just a slightly accelerated doomsday situation. There's only a really narrow set of circumstances for you to actually want this stuff, and it's really expensive and hard to maintain.

So short-term, probably not going to happen.

For space settlements, a space settlement would probably never want to make war on another space settlement or on Earth because it would be so easy to destroy. I mean, you're talking about survival bubbles in the doom void. One EMP and it's toast; one big hole and you all die. It's just, you're so vulnerable and also so dependent on Earth, it's unlikely. So in a Heinlein scenario where the moon is like, "We're going to mess you up,” it's like, "No." All Earth would have to do is hover some nukes over your base and blast the electric system and you're gone.

So the more interesting question we got into, I thought, was we talk about this as a long-term issue.

On Earth, there are different theories on this, but there's this question of, why don't we use gas weapons typically? Why don't we use bio weapons typically? And there are sort of cultural theories, but maybe we just decided not to. It depends on how cynical you want to be about humans, whether you believe that or not.

But part of why we don't use these weapons is that they're unpredictable. So there are like these horrific cases from World War I where people try gas weapons, and the wind blows, then it just goes right back at them. Of course, with bio stuff, it's even more obvious how that could go wrong. It’s also true, by the way, that part of why we don't test nukes anymore is because we started finding radioactive byproducts in babies’ teeth, which is pretty motivating for most humans.

But if you're down two separate gravity wells? If it's Mars versus Earth? You can drop this stuff and there is no risk of blowback.

So the only reason we bring that up is basically because a lot of space geeks say, "We need to colonize Mars to reduce existential risk." But we don't know that the equation adds up to a reduced risk! There are many ways it could add up to increased risk.

When we're not sharing the same atmosphere all of a sudden things go back on the table.

Right. Yeah, exactly.

The book is called A City on Mars: Can we settle space, should we settle space, and have we really thought this through? It is great. I really loved your book Soonish and when you announced it, I was really, really intrigued that this was your follow-up to Soonish. Because Soonish is all about technologies that are just on the horizon. And when you announced this, I was like, "Well, clearly there was something left over in the reporter's notebook going into that."


And so I guess I'll just ask, what was it like moving on to this next topic and how soon-ish would you say this stuff is?

Oh, man. Well, I would say I have set back my timeline a little, having researched it.

I mean, part of why we got into this in the first place is we did think it was coming relatively soon, and was awesome. And it was surprising the extent to which advocates were not dealing with the details. So the project ended up becoming like, we're going to actually get into the primary literature about all these questions.

My view is, I doubt we have a settlement, meaning people are having children and families on Mars; certainly not in my lifetime. What I would add is that it's almost certainly undesirable for it to happen that quickly because not enough of the science is in. It would be morally quite dubious to try to have children in these places with the lack of science we have.

But to be slightly uplifting, I have two directions on it. One uplifting direction would be, well, you never know. Maybe AI's going to take all our jobs in two weeks and we'll just tell it to take us to Mars and we'll be fine. I don't know. I mean there's some world in which 30 years from now there are fusion drives and advanced robotics and everything I'm saying sounds quaint. And then maybe it does happen.

The other thing to say, though, is a lot of the stuff we need to do to make this possible and safe is stuff that would be nice to do anyway. So without getting into it, it would be nice to have a legal framework on Earth where war wasn't a serious possibility, or a thing that's currently happening in many places at once. Because in space, there's lots of stuff going fast. And if you get a world where there are millions and millions of tons of spacecraft going at high speeds, that's a dangerous world with our current geopolitics. So we need to solve that if it can be solved.

Yeah. I loved how much of the book wasn't just the physics. It was really exciting to see that it's not just can we or how would we, it's should we and what will happen?

Yeah, the law to me, I mean we really tried to add some sugar to it because everybody does not want to read international law. We have all these great stories. There's this story about the times like Nazis showed up in Antarctica to heil a penguin. They actually heiled a penguin. I love this story.

Oh no.

Yeah, yeah, yeah. The penguin apparently was not impressed, but—

Rock on, penguin.

It's a funny story, but it matters so much. I think a lot of people are reluctant to get into it. But for me, gosh, it's amazing. Most of the planet Earth is regulated under commons established in the middle of the 20th century. The whole world changed in a 30-year period under these new international law frameworks. And it's like nobody cares or knows. I want a T-shirt that says, "THE RULES-BASED INTERNATIONAL ORDER IS NOT PERFECT BUT IT'S PRETTY GOOD." And you really come to appreciate it. I hope people get that reading our book.

Amazing. Zach, you write Saturday Morning Breakfast Cereal, one of my favorite things. You've been at it for so long, and it's such an admirable project. You've written the book Soonish, which if people have not already gotten, they should get. The new book is A City on Mars by Kelly and Zach Weinersmith. I could not love it any more. Where can folks find the book?

They can find it at fine bookstores everywhere. Or if you go to, there are a bunch of purchasing options listed.

All right, thanks for coming on.

Yeah, thanks for having me. It was fun.

If you have anything you’d like to see in this Sunday special, shoot me an email. Comment below! Thanks for reading, and thanks so much for supporting Numlock.

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Send links to me on Twitter at @WaltHickey or email me with numbers, tips or feedback at

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Numlock News is a daily morning newsletter that pops out fascinating numbers buried in the news, highlighting awesome stories you're missing out on. Every Sunday, Walt Hickey interviews someone cool. Sometimes he records it in quality befitting a podcast.