Why Human Beings Will Never Colonize Other Planets

If you're someone who is remotely interested in space, you won't have failed to notice the headlines that pop up every few months about scientist’s latest discovery of a 'potentially habitable planet' – ‘Hey look, we found a planet only twice as large as the Earth, possibly orbiting in the habitable zone of its star, that's only 400 light years away!’

Now yes, I'm not saying we should ignore the latest Kepler discoveries. Nobody has ever done this before, and the spotting of more than 2,000 exoplanets since 1988 is indeed a scientific milestone. Personally, I remain a huge fan of SETI.

But as someone who (secretly) hopes to earn my stripes as a hard science-fiction author someday, I can't help but remain a bit skeptical. Will these far-flung worlds ever really affect the destiny of the human race?

Might it not be the case that, in however many centuries it takes us to reach them, we come up with much better alternatives when it comes to finding a place to live? Might these worlds become obsolete long before anyone has a chance to do their Neil Armstrong impression?

Let’s step back for a moment.

Say all of 21st century humanity, as we know it, was just a tribe from the Stone Age living in a cave somewhere. It’s a cave, but it’s a nice cave, nestled in a hillside, over a river, surrounded by fertile soil. Not a bad place to live.

Now imagine one of the young hunters goes off exploring, and returns a few days later with exciting news.

‘Hey guys! You'll never believe what I found! There's another cave we could live in! I mean...its kinda small, its filled with poisonous moss, oh and its in the middle of the desert...two hundred miles away, but still!’

And indeed, maybe some members of the tribe eventually do make the arduous journey and attempt to live there. Maybe they even find it tolerable, and this sets a precedent, with other bands setting off to colonize caves of their own.

In this manner, Stone Age humans might have crossed entire continents, seeking out more and more caves in which to live. In time, Civilization might have arisen from these underground refuges. Underground wars would have been fought. Cave-based empires would rise and fall. Shakespeare might have written Hamlet under the stalactites.

Indeed, if you had gone back and asked whatever budding science fiction writers may have existed in 10,000BC, this is how they might have pictured the future - a world in which humanity spreads across the Earth, inhabiting every single cave? Whoa!

There's a little flaw in this story though, an unexpected factor that makes this just an alternate history. While humans have sometimes lived in caves, civilization as we know it did not ultimately center on their existence. At some point, someone invented an alternative form of habitation, one that proved superior to caves in most respects.

We call them houses.

The Rise of the Cosmic House

In case it’s not clear what I'm on about, the caves in this analogy are the planets themselves. As for the houses - that's a little harder to describe. So what is the interstellar equivalent of a house?

While the cave analogy is mine, I can't claim credit for this entire idea. We have already seen it in works from authors like Iain M. Banks and Stephen Baxter.

In Banks's 'Culture' universe, most citizens of the advanced, star-spanning Culture live on enormous, galaxy-crossing spaceships or giant, artificial habitats. Planets are considered little more than nature preserves, inhabited by primitive races yet to develop spaceflight.

I also recall a Stephen Baxter story where a character becomes the first man to land on an asteroid. At first, he's little known, with most of the glory going to the first man on Mars. In time however, the Martian cities decline, the planet is largely abandoned, and the bulk of humanity ends up living in space. The protagonist does to the Martian Neil Armstrong what Christopher Columbus did to Leif Erikson.

In the end, it is those who leave a lasting legacy that achieve true glory. Space is where our future lies, not planet-bound like our ape ancestors.

Many studies have been conducted in to what future space habitats may look like. The jumbled mess that is the International Space Station will be looked back upon as the first roughly hewn raft our ancestors assembled on a beach somewhere.

Names like Bernal Sphere, Stanford Torus and O'Neill Cylinder have been floating around for a while now. These consist of different versions of what is essentially the same thing - a rotating space habitat.

The basic idea is that space habitats need to rotate in order to produce centrifugal force, thereby imitating the gravity of a body like Earth. These generally take the forms of cylinders, wheels or spheres. A cylinder a thousand meters across, for instance, would need to rotate about once a minute to approximate 1G.

There's no reason to believe such habitats could not be built in the near future. I'll stress again - this is science, not science fiction.

A very early example would be ‘Space Station One’ - the rotating wheel we see early in 2001: A Space Odyssey. The building of much larger habitats is certainly possible. ‘Rama’ from Rendezvous with Rama (also by Arthur C. Clarke) is a larger example, being a rotating cylinder some fifty kilometers long and twenty wide. 

I can even imagine looking up at the night sky in a hundred years or so and seeing hundreds of cylinders, spheres and wheels the size of cities orbiting the Earth. Probably the best description of this we've seen so far would be Alastair Reynold's 'Glitter Band' of ten thousand space habitats orbiting the planet Yellowstone in his Revelation Space novels.

Some authors have presented us with even larger structures, such as the Halo Ringworlds (about 10,000km across), Iain M. Banks' Culture Orbitals (3 million km across) and Larry Niven's titular Ringworld (300 million km across!)

Of course, the ultimate extension of this principle is a ‘Dyson Sphere’ - a swarm (NOT a solid shell) of enormous solar power collectors partially or entirely surrounding a central star. Such a structure, if placed around our own sun, could collect nearly a million, billion times as much energy as current global electricity consumption.

So one has to ask - amidst all this, what place is there for planets?

Planets vs. Space Habitats: A Losing Battle

When it comes to qualify of life, planets just can't compete.

For starters, planets are horrendously inefficient users of space. The whole point of a sphere is to minimize the surface area of an object after all, making planets literally the worst possible option.

The Earth weighs nearly six trillion, trillion kilograms, but has a surface area of barely 500 million square kilometers. If you disassembled the Earth and used its material to manufacture rotating space habitats, even if the thickness of their shells averaged say, a kilometer (and it could be a lot less) you would increase the available surface area over two thousand-fold.

Not only would you have more space (who needs a mantle or a core after all?) but your new environment would be infinitely more malleable than your old one.

For starters, your new home's gravity can be turned up or down like the volume control on a stereo. Just spin the habitat a little faster and it goes up. Do the opposite and eventually you'll be back in free fall.

This is one of the biggest issues people tend to have with planets. Mars, while many argue it is ripe for terraforming, has the downside of possessing only 38% as much surface gravity as Earth. For us Earthling this adjustment isn't so bad (it could even be viewed as a positive) but for our descendants who may grow up there, returning to the mother planet could be a big issue. Only advanced medical technology (perhaps a pill that can regrow your atrophied bones) might surmount this obstacle.

Even then, a humanity that spreads across the cosmos will surely splinter into innumerable factions. A big divide between them may be gravity. Is a full Earth gravity really ideal? Or would it be better to just live in microgravity? Is there some ideal figure somewhere in between?

Many problems with transportation here on Earth relate to either gravity or air friction, both of which are really quite punishing down here. On Titan for instance, with gravity a sixth of Earth's but a denser atmosphere, people could reportedly flap around with wings strapped to their arms. This will never be possible on Earth.

So I stress - the first problem with planets is the gravity is not malleable. You're stuck with either one or 38% or a sixth of a Gee, or whatever the local constant is.

Other aspects like temperature, air pressure and humidity can all be adjusted in space like the air conditioning in your home. In fact, this brings us to another major flaw that tends to reduce planet-bound property values.

Planets are dangerous. About a hundred thousand people every year die in natural disasters of some sort. So far in the 2010s, the biggest killers have been earthquakes, temperature extremes, floods and epidemics.

With improved technology, these numbers tend to plummet drastically (the vast majority of these casualties occur in developing countries) but it’s hard to see them ever disappearing entirely. The 2004 Indian Ocean earthquake released as much energy as 500 million Hiroshima’s while the average hurricane releases more energy than the global annual electricity consumption. It’s hard to see any civilization dismissing such forces as mere trivial concerns.

While such risks may seem minor to us, I fear our descendants will be much more safety conscious, particularly if we end up curing the aging process and living more or less forever. 

I'm not sure that the average person on 21st century Earth has fully absorbed the implications of geology either. The knowledge that we are not in fact standing on solid ground - that thirty or forty kilometers beneath our feet is a broiling sea of liquid magma the same temperature as the surface of the sun, one on which the plates of the Earth's crust slip and slide like rafts...let’s face it, it’s a terrifying reality we're all just quietly ignoring.

But earthquakes, volcanoes, hurricanes, tornadoes, lightning storms, blizzards - all are optional extras on your brand new space habitat.

Another problem is accessibility. Planetary surfaces lie at the bottom of deep gravity wells. On Earth, you have to accelerate anything up to at least 11 kilometers a second just to even reach space. The building of space elevators may reduce launch costs, but passengers will still be subject to lengthy rides up and down the tether that could last for days.

In space meanwhile, a habitat would generate very little actually gravity. Spaceships could dock with it much like a ship at a pier.

A further difference is one of security. Planets, being massive balls of solid matter, are close to impossible to move. They are destined to follow the same orbit around their parent star for millions of years.

To anyone with a vendetta against your civilization, they make fat, juicy targets. All you have to do is fling an asteroid out of orbit or fire a giant space laser at just the right moment, even from light years away, and your salvo will eventually impact with the planet in question. Any idiot with a giant space laser in the Alpha Centauri system could blast the Earth no problem, and with no warning.

Space habitats meanwhile, are much more mobile (except perhaps some of the larger examples mentioned here). As long as you occasionally fire your thrusters to shift your station's orbit, even slightly, this will foil that dastardly plot by the inhabitants of the Alpha Centauri system. It’s like the difference between trying to hit a ship or a city with an ICBM. This is not a foolproof defense of course, but it does make things light years easier.

One final advantage I'll mention is the availability of resources. Potentially habitable planets are not expected to be found in more than maybe 1 in 10 star systems. If we were to remain a planet-bound civilization, the other 90% would go unused.

With space habitats however, you can construct them pretty much anywhere. There’s no reason to believe that asteroids in some quantity won’t be found around virtually all stars. Our own solar system contains at least a million larger than 1km in diameter. Wherever we go, such raw materials should be abundant. The same off course applies to the solar energy you need to power your mining operations.

So as you can see, your brand new Space Habitat 5000 has numerous selling points - greater living space, adjustable gravity, climate control, geological stability, accessibility, security and availability of resources to name a few.

Honestly - what poor fool would still choose to anchor themselves down on a planet?

So What Good Are Planets?

All this isn't to say of course, that our descendants will utterly ignore planets. I'll admit the title of the article exaggerates slightly.

The first exception I'll concede is that we probably will have a crack at colonizing Mars in the near future. We may even succeed if Elon Musk has his way.

There are an enormous number of technological, political, economic and social challenges to overcome however. Are we really going to redirect some asteroids to slam into the Martian poles in order to melt them for instance? Or will the whole thing be interrupted by a band of Greenpeace protesters who've chained themselves to the top of Olympus Mons?

Once we move beyond the Solar System however, what exactly is the appeal of planets?

Admittedly, planets may have a few redeeming features. Any space habitat will be more vulnerable to sudden decompression in the event of a hull breech for instance, but this is probably a manageable risk. After all, houses have walls much less thicker than caves, but we make do. Space habitats will also require more regular maintenance than a planetary environment, especially with regards to issues like the disposal of waste.

And I suppose that even today, caving is still a sport, and there's plenty of interesting creatures to be found beneath the Earth. No doubt they'll always be some mad scientist willing to plant the flag on whatever bizarre, inhospitable rocks we come across in due course. Some offshoot factions of humanity, perhaps homesick for the feel of real rock beneath their feet or the look of a sunset, may go like Gollum and decide to live in these cosmic caves anyway.

So yes, I'll grant a substantial minority of humanity may still call planets home.

What I'm saying is - just as human civilization has not been focused on caves for something like 10,000 years (if it ever was) interstellar civilizations are unlikely to center around planets. Most people will likely live in space.

I would also like to point out, just in case anyone got the wrong idea, that I am not personally in favor of the idea of dismantling the Earth and turning it into millions of space habitats. The Earth, as our home, will always have a special place in galactic history. I personally would be in favor of keeping it as a nature preserve. Its native wildlife - from beetles to lions to Amish, should be able to roam its surface into perpetuity. The rest of humanity, cruising the galaxy in our vast space arks with our minds uploaded into computers, or come what may, should leave them in peace.

Any planets that we discover with their own native life should also be preserved. Aside from covert scientific expeditions, they will probably be basically forbidden for anyone else to visit. As for tourism, I don't see why it can't be conducted virtually. That's probably where our future lies anyway.

But as for the rest of the universe - go nuts. I'd start with Mercury, Its three hundred million, trillion kilograms of barren, iron-rich rock, ripe for harvesting. Can you imagine the solar arrays we could unfurl with such a goldmine?

I am here merely to point out yet another big lie most science fiction clings to. Sci-fi universes like Star Trek and Star Wars are always filled with warring factions competing over precious, precious planets.

Why? 

Why are they doing that? 

Why not just harvest a few asteroid belts, construct a few thousand artificial habitats capable of housing your billions of excess citizens, and call it a day? The total carrying capacity of the Solar System, were we to convert even a fraction of its usable material into biomass, is easily trillions of times that of the current human population.

As has been pointed out before, a plotline that sees aliens invading Earth to steal our water is like Eskimos invading Central America to steal their ice.

Any interstellar empire focused around planets makes about as much sense.