“Space”, Captain Kirk famously said, is “the final frontier”. Such words evoke the romantic image of people as explorers. Just as our ancestors built ships to take them across the sea in search of new land, science fiction imagines our descendents building ships with which to cross space in search of new worlds.
In a very tentative sense, the exploration of space is no longer science fiction. Man has walked on the moon and robots are now exploring Mars. But, I think it is fair to say that we have not really begun to colonise our solar system. In this essay, I thought I would discuss the locations where the first colonisers would likely establish their bases.
For settlers looking for somewhere to live on the solar system’s smallest planet, their main concern will probably be: How to stay warm. It might seem strange that this would be a problem. After all, Mercury is the planet that is closest to the Sun, so you might think it would be hellishly hot. But while that is true in certain places (those in direct sunlight, where the temperature can reach 800 degrees fahrenheit or 425 degrees centigrade) there is no atmosphere on Mercury and hence no wind to move this heat to locations that are in permanent shadow, such as craters. And it is at the bottom of a crater that the first colonisers would likely want to set up base. Why? Because this is where large quantities of ice water exist, hiding in a layer a few inches underground.
As to how the settlers would obtain the energy to power and heat their colony, the answer is obviously to make use of the abundant solar energy. Therefore, the ideal location would be at the bottom of a crater with plenty of ice water, and a mountain peak high enough to be bathed in eternal sunlight.
The settlers would likely be tunnelers, as constructing underground dwellings seems like the easiest way to provide the early colonisers with protection from the harshness of Mercury’s temperature extremes. Tunnels would be built, and then mirrors that could track the sun and redirect its light to where it’s needed would be used to provide illumination.
For settlers on Venus, the overriding concern would be how to cope with the heat. Venus, not Mercury, is the hottest planet in the solar system, thanks to a thick atmosphere that causes a runaway greenhouse effect. Although it’s named after the Roman goddess of love (no doubt because it shines like a jewel in the morning and evening sky) Venus is actually as close to hell as any planet gets, with crushing atmospheric pressure, acid rain and soaring temperatures. To say the least, Venusians are going to require heavily-insulated dwellings and great air conditioning. The high atmospheric pressure would have to be taken into consideration as well, requiring either very strong walls or a special mixture- perhaps argon mixed with the right amount of oxygen- so people can breathe.
Again, building underground could be a way to begin to settle Venus, but as this planet is one of the most challenging places for people to try and live in and likely won’t be colonised until our technological development is much more advanced, we can speculate on more radical colonisation alternatives.
There is a place on Venus where there are Earth-like temperatures and pressures (though no breathable atmosphere) and that is about 30 miles above its surface. Remember Cloud City, that floating mining facility where Han Solo got frozen in carbonite in ‘The Empire Strikes Back’? Something like that would make for an ideal home on Venus, floating around where the conditions most closely match that of Earth. Douglas Mulhall suggested constructing a “one-mile diameter balloon containing an Earth-like atmosphere” and building a city inside that. It would require about three million tons of lift in order to get such a ‘city-balloon’ to rise in Venus’s atmosphere, and so the city would have to weigh substantially less if the project were to- forgive the pun- get off the ground.
Ah, Mars. The planet that comes top of the ‘planets we will most likely colonise’ list. I think there is another planet that will be colonised first, but we’ll get to that later.
Other than Earth, Mars is the most hospitable planet in our solar system. Considering how awful the others are, that’s not saying much, but there is hope that it is able to at least support extremophile microbes (there may also be life beneath the icy surface of Europa, but that is a satellite not a planet). 
If you wanted to follow in Matt Damon’s footsteps and settle on Mars, where should you live? The equator is warmest but lacks water. There is water in the form of ice at the poles, but at -100 degrees fahrenheit (-73.33 degrees celsius) the nights are way too cold unless you have means to provide heat.
The Martians may opt to construct a dome to to protect themselves from the Martian climate and provide living conditions closer to home. Since the Martian atmosphere has a pressure of less than 1% that of Earth, any dome containing an Earth-like atmosphere would have to be strong enough to hold that pressure. Whereas Mars’s most valuable resource is solar energy, on Mars it’s probably carbon dioxide. The atmosphere is 95% CO2 and colonists would no doubt find ways of pumping it into their dome to help grow their crops.
Moving out from Mars, we face what would be the most difficult planets in the solar system for humans to attempt to colonise. There are no worlds more alien to people than the gas giants like Jupiter and Saturn. The greatest challenge to colonising such worlds lies in the fact that they have no solid surface to build anything on, just as atmosphere that gets denser and denser as you descend into it. Jupiter also has the wildest weather in the solar system. Its famous ‘eye’ is a titanic cyclone large enough to swallow the Earth several times over. Could humans ever colonise such a world? I think it’s fair to say that it would be an incredible technical achievement to build a habitat that could protect humans from what Jupiter can throw at them. In fact, it might even be preferable to engineer life to be compatible. Freeman Dyson speculated that there might be exotic alien life in the form of creatures that somewhat resemble airships, drifting through Jupiter’s thick clouds. Perhaps our descendants might find ways to re-engineer themselves into such beings, should they want to attempt the colonisation of Jupiter.
The challenge with colonising Pluto lies in the fact that it is so far from us- 3 billion miles away. It’s even further from the Sun, and that would make it very difficult to obtain sufficient energy from Solar power with which to provide warmth and sunlight to grow crops. Douglas Mulhall suggested thousands of computer-controlled mirrors to reflect what little sunlight there is onto the same spot, but pointed out that “perhaps it would be more feasible to use the scarce solar power in a more efficient way by synthesising nutrients artificially in a chemical laboratory”.
Although Mars usually tops the list of planets we are likely to attempt to colonise, our earliest attempt at establishing an off-Earth colony will no doubt begin with a lunar base. The Moon is, after all, closer to us than any other world in the solar system and the one place where people have briefly visited. The challenge of living on the Moon would be pretty similar to that of living on Mercury. There are caves on the Moon in the form of lava tubes, carved out by ancient flowing lava, and these might be converted into the kind of tunnel-like dwellings suggested for Mercurians.
When it comes to the planets and their satellites, most are so large their sheer size means we have to think about where to construct our colonies. But with the asteroids it’s different. Many of them are small enough for us to consider converting them into homes, rather than try and build homes on them. Some visionaries have suggested that we might one day hollow out asteroids and convert them into spacecraft-cum-colonies. One of the great challenges to living on (or maybe in) an asteroid would be its tiny gravitational field. Ceres is the largest asteroid at 590 miles diameter and its gravity is a mere 1/36th that of Earth’s. Obviously the smaller asteroids would have even less gravity so care would have to be taken to ensure every step does not become a flying leap that bangs your head against the ceiling.
It’s possible that, aside from the lunar bases, asteroid cities would be the earliest kind of off-world habitat we would attempt to establish. Already, entrepreneurs like Elon Musk are thinking about setting up mining facilities to extract the mineral wealth locked up in the asteroid belt, and perhaps we might use such resources to provide the raw materials with which to construct the the habitats for places like Venus and Mars.
Earlier I said I did not agree that Mars would be the planet we will colonise first. So, what planet did I have in mind? The answer is: Earth. “Isn’t that already colonised?” I hear you ask. Yes, but only partly. Think of the poles, the arid deserts, and the vast oceans. These are places on Earth where few (and none, in some locations) live.
The reason why so few people live in locations such as these is that there are for more pleasant locations to live on Earth. However, compared to what awaits us offworld, even the harshest of Earth’s regions are much more benign, and it would be much easier to send help to should any emergency arise.
Earth therefore provides many a training ground where we might test colonies before attempting to establish them offworld. Would-be colonisers of Pluto or Mercury might try to prepare by setting up a base in the depths of the Antarctic winter. Trainee Martians might first set up a self-sufficient dome in one of the world’s driest deserts. Venusians might put their ability to cope with crushing atmospheric pressures to the test by building underwater habitats in the ocean depths.
Given that living off-Earth entails the development of technologies that can provide habitable conditions in much more extreme locations than anything to be found on Earth, it makes sense to use such technologies to fully colonise our home. A future in which there are domed cities on Mars, underground habitats on the Moon and so on would surely allow for floating cities on the world’s oceans, and comfortable conditions in our more extreme environments. If we can live well in a self-sufficient way anywhere on Earth, we would have more confidence of doing likewise as we take on the challenge of colonising what Captain Kirk called ‘the Final Frontier’.

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  1. Oh, that was delightful reading! As you progressed from planet to planet, I was trying to think ahead on what your choice would be — and I was utterly surprised by it 🙂 Well done! Although you have cheated: you left the gas giant’s moons out of the picture, ‘because they are moons not planets’, but then went ahead to suggest Pluto (also not a planet any more), the asteroid belt (definitely not planets), and, of course, the Moon. Bad Extie! Bad Extie! There are plenty of very interesting moons around Jupiter and Saturn (at least) with the amazing sky they present, extra heat generated from Jupiter (to compensate for the lack of sunlight) and the tides it subjects its satellites, and plenty of exotic landscapes with enough variety to pick (Europa being very likely the best choice, in spite of Arthur C. Clarke’s warning 🙂 ).

    And, of course, there is always Planet 9 to look forward to. Who knows, it might even have an atmosphere and some water locked in ice beneath its surface. At least it should have enough gravity to keep an artificial atmosphere — we just need to send massive amounts of extra CO2 in spaceships to the outer limits of the solar system. Maybe we could get it out of Mars (and Earth!). The problem is that a trip to Planet 9 will take about 60 years with current technology — we definitely need something faster first 🙂

    • Tut, tut, Gwynie there are no moons orbiting the gas giants for the same reason there are no Ganymedes orbiting Earth: Ganymede is the name of a particular satellite that orbits a particular planet (Jupiter) and the Moon is the name of another particular planet:)

      I do not regard it as cheating because I think it is obvious that even if I did cover all other orbiting bodies, Earth would still be the first planet we will fully colonise. What it really was, was laziness. I could not be bothered talking about all the satellites:)

  2. Rob Neff says:

    Extropia – of course there are moons orbiting other planets. In fact, they are named, our moon (or Moon, in that case) is the only one that is not named. Even asteroids have natural satellites that are commonly referred to as moons.

    • If something orbits a planet, its proper name is ‘satellite’. Mars has two satelittes- Phobos and Deimos. Earth has one. Its name is Moon. Yes, people commonly refer to other satellites as ‘moons’ but strictly speaking there is only one Moon, just as there is only one Titan, or one Charon.

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