For a while now, there's been a debate in the US over how to direct NASA's next major human spaceflight initiative. Do we build an outpost on the Moon as a step towards Mars, or do we just head straight for the red planet? Which ever destination we choose, it'll be viewed as the first step toward a permanent human presence outside of the immediate neighborhood of the Earth.

All of that indecision, according to a new book called Beyond Earth, is misguided. Either of these destinations presents so many challenges and compromises that attracting and supporting anything more than short-term visitors will be difficult. Instead, Beyond Earth argues, we should set our sights much farther out in the Solar System if we want to create a permanent human presence elsewhere. The authors' destination of choice? Titan, the largest moon of Saturn.

The case for Titan

Colonizing Titan seems like an outrageous argument, given that the only spacecraft we've put in orbit around Saturn took seven years to get there. Why should anyone take Beyond Earth seriously? Well, its authors aren't crackpots or mindless space fans. Amanda Hendrix is a planetary scientist who's worked at the Jet Propulsion Laboratory and the Planetary Science Institute. For the book, she's partnered with Charles Wohlforth, an environmental journalist who understands some things about establishing a livable environment. And the two of them have conducted extensive interviews, talking to people at NASA and elsewhere about everything from the health complications of space to future propulsion systems.

The resulting book is a mix of where we are now, which problems need to be solved to make a home elsewhere, and a future scenario that drives us to solve those problems. In this sense, Beyond Earth is a bit like the recent National Geographic effort Mars, which blended present-day documentary with a fictionalized future. But the book is a little easier to swallow then the miniseries, which shunted viewers between footage of real-life rockets and CGI dust storms.

So, why Titan? The two closer destinations, the Moon and Mars, have atmospheres that are effectively nonexistent. That means any habitation will have to be extremely robust to hold its contents in place. Both worlds are also bathed in radiation, meaning those habitats will need to be built underground, as will any agricultural areas to feed the colonists. Any activities on the surface will have to be limited to avoid excessive radiation exposure.

Would anyone want to go to a brand-new world just to spend their lives in a cramped tunnel? Hendrix and Wohlforth suggest the answer will be "no." Titan, in contrast, offers a dense atmosphere that shields the surface from radiation and would make any structural failures problematic, rather than catastrophic. With an oxygen mask and enough warm clothing, humans could roam Titan's surface in the dim sunlight. Or, given the low gravity and dense atmosphere, they could float above it in a balloon or on personal wings.

The vast hydrocarbon seas and dunes, Hendrix and Wohlforth suggest, would allow polymers to handle many of the roles currently played by metal and wood. Drilling into Titan's crust would access a vast supply of liquid water in the moon's subsurface ocean. It's not all the comforts of home, but it's a lot more of them than you'd get on the Moon or Mars.

There is the distance thing, which Hendrix and Wohlforth acknowledge, but they argue it's a bit besides the point. The radiation and lack of gravity that make long-range space travel a risk would all bite anyone we sent to explore Mars. NASA assumes it'll find solutions, but the authors are critical of the Agency promoting a journey to Mars without already having solved them. Whether we go to Mars or Titan, the solution is speed: less time in space means less risk. And, if we could rocket along fast enough so that a round-trip to Mars with time spent exploring was safe, then we could do a one-way trip to Titan.

Have some Fi with that Sci

So, Beyond Earth is a good look at the current state of human space-exploration technology, as well as how that will hold us back from doing the things we want to do. It's both thoughtful and thought-provoking.

Mixed in with that, however, is a scenario under which Earth will get its act together and do what needs to be done to overcome these technological hurdles. That scenario is driven in part by a very believable desperation, caused by unaddressed climate change that drives wars and radicalization. Low Earth orbit becomes cheap, and then an efficient new thruster is developed. (Unfortunately, the thruster of choice in this scenario is unlikely to ever work.)

The Earth's governments bands together in a massive effort to send colonists to Titan, who almost immediately begin to view themselves as pioneers who boldly settle a new world with no help from anyone. Tensions and cultural differences ensue. This part of the book is a fun yarn, and plenty of it involves believable extrapolations from our current state. Whether it adds to Beyond Earth overall will probably be a matter of personal taste.

While the focus of the book is on leaving Earth, it's hard to escape the sense that Beyond Earth is an extensive argument for staying put. As Hendrix and Wohlforth repeatedly drive home, there's no place we could go in our Solar System that offers anything close to what the Earth provides for us. Going anywhere else would involve a cost that could go a long way toward making our existence here much more sustainable. While I'm all for eventually establishing a presence elsewhere, it would be nice to do so by choice, rather than end up being forced to do so due to our carelessness on Earth.