Perhaps the biggest obstacle to colonizing the galaxy is the huge distances between stars. The nearest star to Earth is Proxima Centauri, 4.2 light years distant. Traveling in a normal spaceship at what is currently a realistic speed of 50,000 km/hr, it would take about 91,000 years to get there. This makes the trip patently ridiculous without resorting to assuming we will achieve radical advances in spacecraft speed technology. As for proponents of suspended animation who foresee freezing (or whatever) people for 91,000 years and thawing them out afterwards, good luck! You’ll need it. Oh yeah – and once you get there, we have no evidence yet that there are any planetary bodies orbiting Proxima Centauri on which to land. So is there any way to save the concept of interstellar colonization? Perhaps.
Although stars are far apart in our neighborhood of the Milky Way, rogue, or nomad planets might be much closer. In fact, there may be 100,000 times as many such nomads floating around in space as there are stars. We just haven’t seen them. After all, nomad planets don’t shine like stars so they are hard to detect. Recent advances, however, give hope that they are out there waiting to be found by the thousands as detection technologies improve. Nomadic planets have two particularly neat characteristics. One is that, unlike a star, it is possible to land on many of them. Some are gas giants, and thus lack surfaces to land on, but even those may have landable moons. Another is that, because there are so many of them, the nearest ones are a lot closer (hence easier to get to) than the nearest stars. How close?
There are 9 stars within 10 light years of Earth. Therefore there may be 900,000 nomad planets within 10 light years. That suggests 900 nomads within 1 light year (since a sphere of space 1 light year in radius has 1/1000th the volume of a sphere 10 light years in radius, just like a cube of space 1 light year on a side has 1/1000th the volume of one 10 light years on a side. By the same reasoning, the nearest nomad planet is likely to be just over 1/10 of a light year away, a lot closer than Proxima Centauri. How long would it take to get there?
The likely distance in astronomical units (one AU is the distance from the Earth to the Sun) is about 6,600 AU, or just under a trillion miles. At a speed achievable with today’s spacecraft of 50,000 km/hr, it would take about 2,200 years to get there. This is bad, though not as bad as the 91,000 years to get to Proxima Centauri, and at least there would likely be a place to land. If we can just get travel speeds up by a factor of 100, it would be a 22-year trip. It would be easier to hopscotch through the galaxy, colonizing nomad planets about 6,600 AU apart, than it would be to jump from star to star, since stars are so much farther apart.
A major problem, of course, is that since these nomads are so far from any star, their surfaces are exceedingly cold. What is needed is drilling technology that would enable “mining” heat from under the surfaces of these interstellar nomads. Heat can be used to generate electricity and other forms of energy needed to manufacture nutrients and otherwise sustain human life, however dreary living underground and eating artificial food might be (soylent gray, anyone?) . Such drilling technology is clearly within our grasp on Earth, although exporting it to another planet just as clearly requires some advances.
Colonizing nomad planets is not likely to occur in our lifetimes, though the important first step of finding them is. That may be just as much fun (or more) than eking out a life on one of them. So what are we waiting for?
“In fact, there may be 100,000 times as many such nomads floating around in space as there are stars, but we just don’t know about them.” L. E. Strigari, M. Barnabe, P. J. Marshall, and R. D. Blandford, Nomads of the Galaxy, draft paper, available at arXiv, 1201.2687v1, 2012.