Two hundred years ago, nobody had access to electric power. To stay warm or read at night you burned wood.  Trains had not yet been invented so nobody traveled faster than a horse could run (40 miles an hour) - unless they were falling to their death.

I remind you of this because a very open mind is required to think about what humans will be doing in the next two or three hundred years.  In particular, many of those future humans may not even be living on Earth.  The question I want to explore briefly today is what kind of life might they live? To be specific: where might they live?

If humanity overcomes the (considerable) challenges it faces over the next decades, the prize waiting for us at the end of all that work will be the solar system. We’re probably not going to the stars anytime soon.  They’re just too far away (a topic for another post).  But with technologies that we can imagine today, like fusion rockets, we could reach every object in the solar system in just months. That’s why it’s not hard to imagine that 250 years from now, millions or even billions of human beings might live elsewhere in interplanetary space.

When most people think of settling the solar system, they think of Mars. It’s a staple of science fiction stories.  But the problem with building settlements on planets (like Mars or even the big Moons of Jupiter and Saturn) is their surfaces lie at the bottom of deep gravity wells.  Powerful rockets are needed to get down those wells safely without crashing. Powerful rockets are also needed to blast off and climb back out into space again. Combating gravity makes settlements on a planet extra difficult.  There is, however, another target for a human civilization in space that’s been getting more attention recently: Asteroids.

Asteroids are construction debris left over from the assembly of the solar system. They’re space rocks ranging in size from a football field to a small moon.  While most of them orbit in the aptly-named Asteroid Belt (lying between Mars and Jupiter), there are many others scattered about the solar system.  This includes some that come pretty close to Earth.   Altogether, there are millions of asteroids out there. They add up to alot of easily accessible real estate compared to the Martian surface.

One option is to take the big asteroids, hollow them out and then use rockets to start them spinning.  The spin is important because human bodies need gravity to thrive (one reason planets like Mars are attractive).  With a fast enough rotation comes the centrifugal force that seems to push things outward, away from the spin axis.  You’ve felt this if you’ve ever been on that spinning amusement park ride where the floor drops away and you get pinned to the wall (as much as I love the physics of that ride, it always makes me want to puke afterwards).  On a hollowed-out asteroid, this kind of “spin gravity” would let people use the inner walls as a floor. “Down” would be away from the spin axis and the centrifugal “spin gravity” would let people walk around as they go about their space-city business.

During COVID I convinced some of my colleagues to help me look into this idea.  We did a bunch of calculations and found that the big asteroids were not the best way to go. Their rock was just too brittle to handle the spin gravity. It would just break apart as you tried to spin them up.  But we did find that smaller asteroids could work if you did the right kind of space-engineering.  I leave out the details for now (you can read more in this Atlantic article I wrote on our research). The good news is there are way more small asteroids than big ones.  

So instead of cities on Mars, imagine a future with hundreds of thousands of vast rotating cylindrical space cities built from asteroids.  Each one could have the same habitable inner surface as New York City.  Scattered across the solar system each one would be an experiment in human society and, hopefully, human flourishing.  People could create the societies they want. Some might be Morman city-states.  Some might be Corporate pseudo-republics.  Some might be radical democracies. 

Anything would be possible and that, in itself, represents an exciting future.

PS: Watch (or read) The Expanse series to see these ideas beautifully explored.

PSS: Mars is not really for losers. I personally would be happy to make that trip

PSS: PS. If you liked this please pass it along to someone and encourage them to subscribe to Everyman’s Universe

— Adam Frank 🚀