Space colonization is something that people have dreamed about since the moon landing, and is in fact considered a priority for the future of mankind by leading scientists.

Unfortunately, we’ve all but ignored space colonization and the development of its technologies in recent decades, though there have been a myriad of developments that weren’t intended to advance the cause that will do just that.

Aerospace advances, submarines that humans can survive in for months at a time autonomously and experiments like the Biodome have all led to uncovering pieces of the puzzle.

It’s not a huge surprise that governments and corporations aren’t investing heavily in space colonization itself. We still need to make many, many more of these ancillary but important advances before we’d make any significant progress in the area. And there’s that other issue – that governments and corporations don’t see a need to ramp up the timeline on this.

But Stephen Hawking, one of the few physicists whose name regular people actually know, thinks differently. He’s worried that until we disperse, we’re in imminent danger of a catastrophic event destroying human civilization – heck, human life – for good. “One we spread out into space and establish colonies, our future should be safe,” Hawking once said to a BBC reporter.

There’s much to consider, and the question of where we should colonize isn’t even chief among them yet. Let’s skip the boring stuff for the moment, though, and start there.

Where would we colonize?

There are more seemingly viable options than you might think within our solar system alone. None of them are particularly viable right now, but they all differ greatly in how much technological improvement is needed before they do become viable.

Mars is one of the most promising candidates. It’s not too far from Earth, which is part of what makes it so promising: we occupy prime real estate that’s not too far from the sun nor too close, with much variance in either direction causing catastrophic climate extremes.

Mars is a cold place, but it’s got plentiful resources in comparison with the alternatives.  We could extract air and water from the planet’s atmosphere and ice caps, which goes a long way to improving our chances – if there’s no way to harvest resources they have to be sent from Earth, and that’s not particularly sustainable in the long term.

Mars also has plentiful minerals that could be used in the construction of structures – structures that we’d be spending plentiful time in, as while Mars has air and water in extractable quantities, it’s got a thin atmosphere that’s not a huge improvement on sticking your head out into deep space.

The moon is another popular option, with a much shorter travel time from Earth. The presence of water was discovered and confirmed in 2009. In terms of structurally contained colonies, the moon represents the least challenging place to start, with that short travel time reducing the costs of transporting the necessary equipment and resources by a long shot.

Other moons in the solar system are of considerable interest, particularly Europa (one of Jupiter’s moons), which is believed to have an ocean beneath the layer of ice on its surface. There’s even some conjecture that some oxygen-using marine life from Earth could survive in that ocean (if it exists).

Mercury is very similar to Earth’s moon and is thus another candidate, although its proximity to the sun means the only viable colonies would need to be built on the planet’s polar regions – temperatures during the day on the rest of the planet are far too extreme. It’s a safe guess that this is somewhere we might expand once we’ve already got a few colonies under our belt.

That’s not to say that Mercury lacks advantages over the moon. Solar power is easier to collect, it has more gravity than the moon, and perhaps the greatest incentives for the corporations of the future that will doubtless beat government to such endeavors is the presence of incredibly valuable minerals on the planet’s surface.

Venus, the closest planet in the solar system to Earth, has an equatorial temperature of 500 degrees Celsius, though that hasn’t stop scientists and writers from thinking of ways we could colonize this furnace. The more realistic of these theories involve colonization on some sort of floating structure in the upper atmosphere where temperatures are more manageable. Similar approaches to colonizing gas giants like Jupiter are taken, with floating cities a common idea.

Asteroid colonization is decidedly tame next to these ideas, and makes particular sense in the context of asteroid mining in the solar system’s main asteroid belt, located between Mars and Jupiter. One idea uses Ceres, the dwarf planet in that belt, as a sort of hub for colonies on the other asteroids – from here, transportation for minerals to our inner colonies including Earth could be more easily arranged.

Free-standing habitats are theoretical structures built to serve as a home for humans that isn’t attached to any existing body. In these space colonies, humans would be able to hone the technologies required to make such an environment truly sustainable in advance of vessels intended to carry humans through deep space over generations.

Structures & Terraforming

At the moment, our best bet for colonization is to design structures capable of both supporting human life and extracting resources from the planets, satellites or asteroids on which they’re established.

We’ve made some progress in figuring out how to survive in such structures for extended periods of time. Submarines and their crews often don’t surface for months at a time, and it’s hoped that one day we can create structures in space that will be permanently sustainable. But perhaps the most sustainable way is to turn another body into an Earth-like habitat, with a similar atmosphere, water bodies, climate, and the ability to grow and raise food sources.

This would give humanity far more room to work with, unlimited by the speed with which specialized structures can be created. And in several billion years when the sun’s increase in luminosity causes Earth’s oceans to become evaporated and other more painfully disturbing things to occur, a terraformed Mars would give us several thousand years of extra time to figure out what’s next for humanity.

The problem with terraforming is that, depending on the extent of the terraforming done, the process would apparently take between hundreds of years and hundreds of thousands of years. On top of that, massive sums of money and incredible resources would be required for such a project, to the point where even the richest countries would need to help each other to achieve the goal.

A more achievable goal would be the development of biodomes that cover large areas, big enough to hold a city’s worth of people. These domes make it easier to control a variety of factors, such as creating pressurized atmosphere and preventing it from blowing off into space. It’s likely we’ll see this approach taken first, terraforming portions of a planet until a series of biodomes make much of it habitable. We have reportedly had the technology required to create such a structure for fifty years.

Deep Space Colonization

The question of which local bodies we could colonize, terraform and otherwise adopt is an interesting one, but to truly preserve humanity as Hawking mandates we need to move beyond our own solar system.

But we’re a long, long way from figuring this problem out.

Trying to find a habitable planet isn’t even the biggest concern. Getting there is. Interstellar travel is a tricky topic even when it comes to small craft. Moving the equipment, resources and humans needed for a colony over interstellar distances, let alone in our own solar system, is a tricky problem indeed.

Propulsion is the biggest, though not the only, setback.

At the speed of Voyager 1, the fastest craft we’ve sent into space, it would take over 70,000 years to get to the Alpha Centauri system – the closest star system to ours. Modern technology could do somewhat better, though not significantly enough to make it close to feasible.

Nuclear pulse propulsion is a theoretical propulsion system that, when technology advances to the point we’re able to actually build such a system, could even get us to those nearest stars in centuries instead of millennia. But that’s still longer than a lifetime, thus still requiring generational ships. It’s much easier to expect that a ship on a trip of a few hundred years will arrive safely with the departing crew’s children alive and well.

A generational ship spanning 70,000 years is another story: recorded human history is a fraction of that time and we’ve already shown that we’re not particularly good at looking out for the continuing prospects of our species.

Even if we can cut propulsion time down to reasonable levels – a couple of generations at best – and find a habitable planet, building a generational ship won’t be easy. It’ll need to support said colonists in a sustainable fashion over the centuries and it’ll need to overcome some significant engineering challenges in order to be large enough.

If you grew up on science fiction as I did, it can be a bit of a downer to see how far beyond current capabilities colonization beyond the solar system or even inside of it will be. But it’s still exciting to think about, and with any luck, our descendants will be living it.