The hit Syfy Channel show The Expanse, based on the incredible series beginning with Leviathan Wakes by writing team James S. A. Corey, presents a bold and dark future for the human race. Humans have colonized our solar system, though we haven’t ventured beyond it. We have research bases on moons of Jupiter, Saturn, and Uranus; Mars, the Moon, and dwarf planet Ceres have larger permanent settlements.

The TV series doesn’t focus overwhelmingly on science (though all the technology depicted within it is based on real science), and that’s to its benefit: there’s a lot of story to cover in a limited amount of time. (The authors of the books do focus a bit more on science in the novels.) Let’s look at the overall premise of the show, then. How likely is it that we will colonize our own solar system? Will we establish permanent colonies on the Moon and Mars? What will happen to the humans who do leave the Earth?

In Beyond Earth: Our Path to a New Home in the Planets by Charles Wohlforth and Amanda Hendrix, the authors (a science writer and a planetary scientist, respectively) examine what will it take for humans to leave our planet and colonize the solar system, and what form that colonization might take.

It’s not a huge leap to assume that humans will look to the stars as the next frontier; we talk constantly of sending astronauts to Mars. SpaceX founder Elon Musk has ambitious plans to settle the first colony on the red planet. A desire to explore, coupled with the damage we are doing to our own planet, almost assures us that eventually, we will begin the process of colonizing other worlds.

But will we establish bases on the Moon and Mars? We might, but it’s a bad idea, according to Wohlforth and Hendrix. The key with any solar system colony is that it would have to be self-sustaining. If a colony we establish can’t support itself, then it will not survive, long-term. A colony must be able to function independent of Earth—this means producing its own food, energy, and resources. Of course Earth will supply any colony we establish for the short and medium term, but having to constantly resupply a colony from Earth just isn’t feasible. It would prove way too expensive to justify the colony’s continued existence.

And that’s the problem with both the Moon and Mars, the sites of the two largest permanent human settlements in The Expanse: There isn’t really a way that we can currently see to make either of those settlements self-sustaining. The Moon has no readily available natural resources or liquid water (although the search for viable forms of lunar water continues). We’re less certain about Mars; we know it has polar ice, but no important natural resources as far as we can tell. “Other than its proximity to Earth, there isn’t a compelling reason for human beings to go to Mars,” say Wohlforth and Hendrix (p. 47). We see humans terraforming Mars in the show, but in reality, that would take a hundred thousand years (unless technology leaps ahead). It’s possible that Mars could survive, as it does in the show, using the resources of the Asteroid Belt, but that would require huge advances in science and technology.

So where should we go, then? Wohlforth and Hendrix make a strong case for Titan, a moon of Saturn. It has an atmosphere, liquid on its surface (methane, not water), and a surface pressure that’s tolerable for humans. The problem would be its distance from Earth—hence the need for the colony to be self-sustaining. It’s too far away to be able to rely on Earth for resupply.

The Expanse’s depiction of Ceres, however, is spot-on. Ceres is the largest body in the Asteroid Belt (it’s actually categorized as a dwarf planet) and it’s covered in ice. In the TV show, it’s one of the first sites of human colonization, and it’s actually possible that we might try to settle Ceres in order to mine the resources of the Asteroid Belt. The biggest threat would be radiation, because the dwarf planet doesn’t have an atmosphere.

Wohlforth and Hendrix make the very good point that we don’t currently have a lot of research as to what effects leaving the protection of the Earth will have on the human body; after all, those in low Earth orbit, aboard the space station, are still protected by Earth’s magnetic field. The research we do have isn’t promising: radiation is a serious threat. In the TV series, humans counter this through advanced radiation medication. We’d have to develop a way to deal with strong radiation before we can make space travel outside of Earth’s magnetic sphere (much less space colonization) a recurrent reality.

The Expanse also deals with the other physical effects living in space have on the human body very well. Wohlforth and Hendrix say that it would be difficult to return to Earth after a human body has adapted to living on Titan. Gravity molds and shapes our bodies. Living without it, or on a planet where there’s significantly less gravity than Earth, means that our bodies would grow differently. As those characters in The Expanse who were born on the Moon, Mars, and in the Belt can attest, a body shaped by low gravity is a body unable to withstand the gravity of Earth.

All in all, The Expanse is a mostly realistic—if grim—picture of what humanity’s future holds. We will likely visit the Moon and Mars, but only because they’re convenient, rather than because of their potential long-term sustainability. The resources of the Asteroid Belt are what will support our space colonization (and the future of Earth), whether it be Titan or somewhere else entirely.

Swapna Krishna is a freelance writer, editor, and giant space and sci-fi geek. You can find her on Twitter at @skrishna.