Interstellar Expansion: Colonizing Ice Dwarfs

by Paul Gilster on February 19, 2013

Are habitable planets the best places to look for life? The question seems odd, because we’re assuming life has to have clement conditions to emerge and survive. But step beyond the question of life’s formation and the issue can be framed differently. Where beyond its birthplace might life migrate? In SETI terms, where might we look for the signature of a civilization advanced enough to move beyond its home world and expand between the stars?

A lot of ideas seem to be converging here. In Huntsville, Ken Roy (whose description at the recent interstellar conference was ‘an engineer living and working amidst the relics of the Manhattan Project in Oak Ridge, Tennessee’) described potential habitats stretching far out into the Solar System and beyond. Roy has been working for some time with Robert Kennedy and David Fields on colonization scenarios.

My own talk covered the kind of places where we might extract resources, ranging from icy dwarfs like Pluto to cometary objects and ‘rogue’ planets without any star. And science fiction author Karl Schroeder, in a recent blog post called A Tale of Two Worlds, also brought the topic up. Let me quote Schroeder, because I want to return to his post in a day or so:

…it’s important to bear in mind that habitability and colonizability are not the same thing. Nobody seems to be doing this; I can’t find any term but habitability used to describe the exoplanets we’re finding. Whether a planet is habitable according to the current definition of the term has nothing to do with whether humans could settle there. So, the term applies to places that are vitally important for study; but it doesn’t necessarily apply to places we might want to go.

Both Schroeder and Roy are assuming not near-term projects but the kind of settlement and terraforming that draw on huge resources of energy. The premise, in other words, is that we’re talking about a culture that ranges freely through its own system, having mastered fusion or other technologies and being capable of large-scale building projects in space and on planetary or other surfaces. Grant that premise and then think about what kind of structures it might make sense to build when exploiting local resources and looking out toward the stars.

Pluto and the Ice Dwarfs

Pluto is a case in point. Here we have a surface that appears to be a shell of nitrogen ice covering water ice. When New Horizons gets to the Pluto/Charon binary in 2015, one thing to look for is an equatorial bulge that could have been left over from the early days of Pluto’s formation. No bulge makes the case for stretching of the ice shell over Pluto’s lifetime, strengthening the possibility some are noting that the ice dwarf could contain an ocean beneath about 165 kilometers of crust, an ocean that may be just as deep as the crust is thick (see The Case for Pluto’s Ocean for more).

As Roy told the crowd in Huntsville, icy worlds like Pluto are rich in volatiles, and of the tens, if not hundreds of thousands of Kuiper Belt objects out there between 30 and 50 AU, several hundred may be Pluto-size. Such worlds are doubtless common not just here in our own system but as rogue planets in interstellar space and perhaps circling brown dwarfs, those dim objects that blur the distinction between gas giants like Jupiter and true stars like Proxima Centauri.


Image: This artist’s conception of the ‘scattered disk’ object Sedna reminds us that even beyond the Kuiper Belt and as we move into the Oort Cloud, vast numbers of icy objects are thought to exist. Can we exploit these as we move outward toward another star?

Build a settlement on an ice dwarf in the outer system and you are not only creating space for living and doing science, but also building the technologies that will one day be used in interstellar colonization missions. But Roy noted that the science fictional image of a domed city in a harsh landscape just won’t work here. Induce Earth-class atmospheric pressure inside such a dome and even a small one (1000 feet in radius) would require a four-inch thick layer of steel to keep the dome intact. Moreover, ice dwarfs have but feeble gravity, creating medical issues from muscle atrophy to bone problems, loss of body mass, sleep disturbance and more. A better choice, then, is to move inward, creating the colony deep within the ice dwarf itself.

At 160 meters, the ceiling of a colony hollowed out within Pluto would be fully supported by the air pressure inside. Artificial light would be essential, of course, and we still have a gravity problem, for Pluto’s gravity is only 6.7 percent that of the Earth — a 200 pound person on Earth weighs but 14 pounds on Pluto. Roy suggests a rotating torus in this setting could provide living and working spaces at 1 Earth gravity. At 1 revolution per minute, a 1790-meter torus supported by maglev rails could accommodate, by Roy’s estimation, 10,000 people living in conditions that would more or less resemble the worldships so often imagined by science fiction writers.

We’re assuming technologies that can create large rotating structures in low-gravity environments, with the ability to move spacecraft at velocities of 0.001 c to build and supply the colony. We’re also assuming proven fusion power plants and considerable expertise in mining and construction. We would put these tools to work to extract local silicates and metals from the surface and, perhaps, rock from buried impactors. We would be working in an environment rich in H2O, but also in methanol, hydrogen cyanide, formaldehyde, ethanol, ethane and long-chain hydrocarbons, all within a salty ice mantle.

Interstellar Migration

Here’s long-haul migration to the stars presented as a series of steps at 0.001 c. Moving roughly 400 AU at a time between various objects in the outer system and, eventually, interstellar space, we spend 50 years at each to establish a colony and then build and crew another ship. The 4.2 light years to Proxima Centauri in this scenario demands 664 such jumps and reaches the star in 38,000 years, leaving a chain of colony worlds behind that are self-sustaining.

The technologies needed for this kind of expansion are well beyond us, but it is not inconceivable that more advanced cultures as they move up the Kardashev scale may have accomplished such things. Places that are habitable, as Karl Schroeder says, are not the same thing as places that are colonizable, and it’s also true that we have to be wary of imputing human motivation to hypothetical extraterrestrial civilizations. Their detectable artifacts, in other words, might extend between the stars far into the interstellar deep and so, in some remote futurity, might ours.



jkittle February 19, 2013 at 10:57

The scenario you paint here has a number of strengths. 1)the required resources in the solar system are Present and Accounted for. We know of worlds in the kuiper belt that can sustain such development and we have irrefutable evidence of further worlds out to the dim reaches of the Oort cloud 2)this future requires no new physics for propulsion or new biology for suspended animation 3) the technology extensions are part of what I define as the “foreseeable future” that is, events and trends that can be forecasted to take place. For example, it is foreseeable that computational devices will become more complex and powerful and that our ability to live in artificial environments will continue to grow.
The critical factors in this very plausible future include development of Fusion energy or discovery of new fusion resources beyond earth, motivation to explore and colonize space nearer to earth ( read commercial or political drivers that are on par with, say, the building of the new F35 fighter) and the shift from single generation exploration to human pioneers raising children in a space colony.
Anyway, your post here does a very neat job of presenting the a version of the future many of us propose and believe in . It is a future of art and science, distant worlds where beauty and happiness are redefined again and again, and earth becomes a distant and perhaps wistful memory . We can see a new diaspora of humanity in the “foreseeable future” .

Anthony Mugan February 19, 2013 at 11:38

What a good point…
For an arbitrarily advanced civilisation avoiding worlds in which life is already established may well avoid a number of practical (e.g. disease tranfer – in both directions) and ethical problems (on the assumption that they must have some sort of ethics in order to ‘get along’ as a culture..?). Throw post-biological evolution for a billion years or so into the mix and some of the habitability challenges of such worlds may seem less of an issue than they do to us.

Jim February 19, 2013 at 11:44

I am also looking forward to the arrival of Dawn at Ceres,

Ceres is half the size of Pluto but much closer being inside the asteroid belt. It is also believed to have a lot of water, guesses are at 25%, We will know in a couple years when Dawn arrives. I think I would rather go there than Mars. Trying to get out of Mars’s gravity well is a daunting task.

James Davis Nicoll February 19, 2013 at 13:21

Roy suggests a rotating torus in this setting could provide living and working spaces at 1 Earth gravity. At 1 revolution per minute, a 1790-meter torus supported by maglev rails could accommodate, by Roy’s estimation, 10,000 people living in conditions that would more or less resemble the worldships so often imagined by science fiction writers.

I can see no way in which poor infrastructure maintenance decisions as seen in cities from Montreal to Minneapolis could lead this set-up to end in a city-killing disaster.

Eric Kansa February 19, 2013 at 14:18

I think I commented on this sometimes in the past two years. I agree that colonizing ice-worlds looks feasible, and that SETI should concern itself with looking for cold-dark adapted creatures / robots / whatever, since the vast majority of space is cold and dark, yet with useful resources provided fusion can be made feasible.

The question is, how does this translate to anything that may be detectable? Presumably, if a civilization colonizes Kuiper belts and Oort clouds, some waste heat would leak out into space from their activities. Should we be looking for clouds of objects surrounding stars that are slightly warmer than expected? Anyone want to do the math on that?

Tarmen February 19, 2013 at 14:44

” The 4.2 light years to Proxima Centauri in this scenario demands 664 such jumps.

This method will result in may isolated little tribes of humans that will evolve in a hurry. I could imagine all sorts of fantastic peoples evolving – ice dwarves, aquatics, hibernators, predators, cannibals, castes. And of course many colonies will die out. The ones who do get to Proxima and beyond will not be human Homo Sapiens.
I could imagine old blood Homo Sapiens leaping past all of them and viewing them as devolved sad little experiments, or else fearing them as rivals.

Alex Tolley February 19, 2013 at 16:01

As jkittle states, this scenario is very plausible and sidesteps some major issues that make it possible, especially in the event that certain technologies cannot be developed. For colonizing the Kuiper belt, you don’t even need fusion, just solar energy, concentrated with mirrors. Fusion would be needed as you go farther out towards the stars.

However, I would be cautious in hand waving away the technological difficulties of creating small, self contained cities/world ships. Biology is not easy to control and we may well find that such small ecosystems are not sustainable, even with lots of energy to brute force system control. Having said that, it seems to me that the Antarctic bases we have are almost an existence proof that isolated systems with food and air supplies are sustainable (over decades at least). They could certainly make their own air, so growing food in some way could make them test beds for self sufficiency.
An icy world colony need not be totally enclosed, but could use up external resources to meet losses, which is not the case with world ships.

But I would return to the same question I have asked of world ships. Is it fair to effectively imprison generations in an isolated colony when the inhabitants know that there is a rich, dense, diverse, interesting civilization huddling around its parent star?

jkittle February 19, 2013 at 16:21

Oh evolution is a constant.. and will occur, whether “post biological or not. and it may take thousands of years to get a good percentage of the solar system involved before there is much pressure to move beyond the oort cloud. Nor do when know when Earth will start colonizing mars , the moon or large asteriods. At some point timeing becomes very dependent on some unknowns..- how may large bodies my be present in the outer reaches of our solar gravity well, -can we effectively utilize worlds less than dwarf planet size ( for ice planets roughly 200 to 300 km diameter) – are there many rogue planets and are there any conveniently passing by? -are there dwarf planets scattered between stars in our part of the galaxy? and how long can we expect the resources of a dwarf plant reasonably support a viable colony?
I suspect we will already be well into the process of spltting into new species and spinning off new forms of humanity/civilization before we reach the stars, by this scenario.

Dmitri February 19, 2013 at 18:44

Just a question arised reading this – let’s exclude radiation and gravity on Titan. Why would colonization of Titan be not reazonable compared to a Kupier belt object? Titan has naturally occuring atmosphere and season cycle. It’s not worse hostile environment than the artificial one in one of the Kupier belt objects. All the same environment issue arise.

Rob Flores February 19, 2013 at 18:48

It’s strange that no one mentions TITAN. Most likely to be the 2nd
most populated colony in the Solar System. I know it’ a moon but….

The Ice worlds in the Kuiper are flawed as a potential colony sites.
These celestial bodies are mirages:

A body that is so cold that Nitrogen is frozen, means that the suface is an
extreme hazzard to both men and machines, even without an atmosphere.
Any structure would have to have double insulation to keep the outside
edges below N2 cryo temps, and the inside warmer. All equipment
and structures would need to withstand temp gradient from 20c to -300c.
If you used an apollo style space suit you would create explosive heating
where you planted your feet, and never mind if for some reason you fell full body into the nitrogen surface. to hover w/o walking near the surface
you would have to use liquid H2 as a propulsion mass, which is all kinds
of a pain in the behind. You could use liquid N2, just don’t ever land
and take off, from the frozen N2 surface.

The gravity problem, You would need a colony orbiter to keep your
colony in shape and healthy and able to reproduce. Constant physical

The Metals Problem, Some vital elements need to be replenished. Just
how efficient is it to mine ICE for impurities. It’s not like every object in
the kuiper belt is the size of a mountain. The concentrations maybe too
scattered to mine.

What is the basis for you colony’s growth. What critical materials or
products are you creating/gathering that has value and can only be
obtained there?

If we learned to live on TITAN, That would give us another extra solar target celestial type to colonize.

On Mars I see only one real show stopper, meteorites. When one the size
of a bullet touches streaks down at a high angle look out, because it will
be travelling at maybe 10-15 k/s , and Mars “atmosphere” will brake them
a touch, They do not Explode or desintigrate on average. Most get to surface fairly intact. Think about how many bullet sized meteors encounter
that end in a little fireball on earth.

Wojciech J. February 19, 2013 at 19:14

I don’t see this as very plausible. An endless generations of people devoting their lives to non-ending expansion, while no evolutionary or ideological changes happen? Doesn’t seem that likely.
A civilization able to do this would probably also have technology to send smaller objects at much faster rate to other stars, and with it packages of DNA, biological material and data, allowing for recreation or copying of civilization there(if they would be interested).
Even if such civilization wouldn’t have this technology, in the course of thousands of years(more likely even hundreds) its descendants would, making the plan obsolete.
So no, this is a concept that seems completely unrealistic to me.

Orbital February 19, 2013 at 19:26

There will always be people who will want to break away and move on. As long as there is a frontier they will do so.

also the sapience will not stay in one form, ai, transhumans and others could modify themselves to any envoronment.

Orbital February 19, 2013 at 19:28

@Dmitri Both will happen, if not at the same time. The expansion of individual entities is exponential.

Wojciech J. February 19, 2013 at 19:30

Also the drive to colonize would have to be ideological(with exception of some catastrophic scenario). This amusing analysis concludes that 4,000 trillion humans could live based on Sol System alone

It’s hard to imagine human species existing in such state, for instance the whole social net and behaviors would change tremendously if exist at all.
Most likely though we will never reach such population or remain the same species.

Astronist February 19, 2013 at 20:33

As I have recently argued in JBIS, the point here is that if space colonisation is practical, then almost all the opportunities for industrial and population growth are in space colonies, not on planetary surfaces. This alleviates the problems of interstellar travel in several ways.

I’m not sure I see why putting a rotating torus actually inside Pluto would be superior to sourcing material from Pluto and other bodies for construction of space colonies in the vicinity, but presumably Ken Roy has good reasons for this?


GaryChurch February 19, 2013 at 20:50

“I think I would rather go there than Mars.”

I agree with Jim; Ceres is the second place to go after the Moon.
The KBO’s will require nuclear reactors and the thorium and metal ores on the Moon are the place to manufacture them- and launch nuclear missions.

We better hurry up before an impact does us in.

Tarmen February 19, 2013 at 21:00

I have thought about this strategy of nature. Ie. When a May dandilion blows off its hundreds of seeds, how many actually take root ?
A – Only a few, most land in a bad spot or at the wrong time. But the sacrifice is still economical to the dandilion kind.

This is the same strategy as casting off through Oort Cloud diffusion. It may work for our kind as a whole, but it is almost certain doom for most seed colonies. Rather than wish them luck, you may as well say a prayer. A few may reach a safe haven. They will be much changed beings. Maybe a totally new sub species. .Maybe insane and physically altered.
Maybe very well suited to the moons of Centauri.

Brett Bellmore February 19, 2013 at 21:40

When you’re looking at an environment in the temperature range of liquid nitrogen, having an atmosphere might not be all that great an advantage for creatures more comfortable at the temperature of molten water. Vacuum is a convenient insulator if your environment is cold.

Daniel February 19, 2013 at 22:27

A great article on my favorite subject.
I wonder if smaller objects might not be hollowed out and spun to turn them into large torus? If we did this to one of the smaller moons of Pluto, colonists could live in a one g environment and mine the nearby larger moons.
Thanks for the good read and looking forward to more.

Michael February 20, 2013 at 2:08

In all probability artificially constructed worlds will be made as opposed to paraforming of hostile Solar system bodies. In the instance of Pluto, heat leakage to the surface nitrogen ice will result in out gassing and as mentioned earlier in the Blog will result in an unstable surface environment.

Abelard Lindsey February 20, 2013 at 2:34

I’m surprised none of you have mentioned that this is simply a repackaging of the O’neill “L5″ scenario of the 1970′s. The reality is that, unless we get FTL, that the human future in space will necessarily be free space habitats similar to those envisioned by Gerard O’neill. These kind of habitats can be built in a variety of sizes up to small nation-state sizes anywhere near resources in the solar system (asteroid belt, kuiper belt, in order around gas giants, etc.).

Ronald February 20, 2013 at 8:59

Further to jkittle and Alec Tolley, and fully agreeing with Rob Flores and Wojciech, and taking the risk of being a party pooper, I do not consider this a plausible scenario, fot two main reasons:

- An ice dwarf presents conditions that are so much out of any equilibrium conditions required for earthly (higher) biological life, that vast amounts of energy and probably other (external) resources will be continously required to maintain them.

- As I have argued with regard to artificial space colonies several times before, and further to my previous point, the same is true (to a somewhat lesser extent) for ice dwarf colonies: they are so way out of any long-term stable (‘natural’) equilibrium condition, that the risk of a catastrophic event is very large for any indivudual such colony. Tarmen is SO right about this. Apart from the question which remotely humanoid being would be willing to live under such conditions and risk, they will require constant (read: expensive!) maintenance and replacement.

I once did a back-of-the-envelope estimate under a different post here, that per time-unit and unit area terraforming a terrestrial planet is at least a hundred thousand times cheaper than a space colony, and probably much more so. I bet that something similar is also true with regard to outer region ice dwarfs and inner region terrestrials. Apart from the psychological and risk aspects.
As I mentioned before, it is no coincidence that in the interior of Antarctica, volcanic craters and hot vents we mainly find some micro-organisms, on small islands higher organisms but only in small numbers and diversity, whereas large numbers and diversity of higher organisms require continents.
I also bet that we will be colonizing Mars (and maybe even Titan) long before even setting foot on one of those ice dwarfs.

Dmitri February 20, 2013 at 12:37

Russian scientist (can’t recall his name) have been telling of possibilities colonize Venus for last 20-30 years. His idea is to set up settlements floating high in Venus atmosphere around 50 km or higher. This is one of the things I recall. I’ll put more about it when I find the information. I have to dig deeper. It’s not so long time ago and the scientist who is pitching it is still active.

Ronald February 20, 2013 at 14:43

I can think of Geoffrey A. Landis (2003), “Colonization of Venus”.
See for example:

Sean February 20, 2013 at 15:29

There is always the possibility that medical technology will overcome the problems of living in low gravity. If we can ever get to the point where w are moving off Earth, we may well be genetically modifying people to survive better away from Earth.

Rob Henry February 20, 2013 at 16:44

Wojciech J, I also found that figure amusing, but for me that was because it was ridiculously low. Firstly it assumed that no biosphere could be more efficient at supporting humans than Earth (Think of that as the “Earth designed by God for man” postulate), thus requiring 170,000 kg of biomass per human. Secondly it assumed that no organics were imported from the icy moons of the outer system, let alone the Oort clould. I can’t see how this estimate is not two, and more likely three, orders of magnitude to low.

Alex Tolley February 20, 2013 at 16:54

Another issue to bring up, is the “polynesian island hopping” analogy correct for icy body colonization?

1. For polynesians, the relatively simple cultural information could be maintained by even small groups of people.
2. Islands are geographically fixed.

For a technological civilization, culture is very complex. We see this in the variety of roles for people in cities compared to small rural farms.
Outer system icy bodies could be moved to the inner system by expending mass.

Wouldn’t this suggest that the best place to maintain a colony in in the inner solar system, perhaps extending to Saturn, where communication and even travel to other space cities is relatively fast and easy. IOW, bring the resources in, rather than go out to the resources?

Rob Henry February 20, 2013 at 17:58

Suddenly everyone is bringing up my favourite world, Titan. Here there is no a pressure or surface radiation problem, just a temperature and light level problem.

First to the light level. Its day is about as bright as a typical lit room at night. Perfect for us, and most Earthly plants find the azimuthally sun too bright, indeed many saturate their ability to photosynthesise at about a tenth this level. Plants should grow OK in this light, but none of our food crops would seed if the light was not augmented. Floating crop growing habitats above the cloud deck should provide several percent the illumination in our (rather cloudy) tropics, and small mirrors could probably boost that figure to >10%. It also helps that 300K N2 would be fully two thirds as buoyant as a vacuum in 100K N2.

Second to the toxic atmosphere. Neither methane nor hydrogen is toxic to humans, the other constituents being present in such small quantities that a substantial leakage into our habitat would present little chemical danger. Yet this mostly N2 atmosphere provides Earth-like protection from radiation

Next to the temperature gradient. Is there anything that lets through nearly all light, yet has superlative insulative properties, is flexible and light enough to make inflating a giant done simplicity itself. I think that there is: aerogel. All we would have to do is place a thin coating on the top to prevent it absorbing methane rain, and on the bottom to prevent water damage.

Given that, my last question is couldn’t we do this within the next decade (the floating plant habitat coming just a little latter)? What fantastic breakthrough do we need to augment that? Enlighten me.

Rob Henry February 20, 2013 at 18:24

Oops, because of the high compressive strength of aerogels and their ability to rebound from that compression, I thought they must also be fairly flexible. As I went to look up actual figures, I discovered that I could hardly be more wrong. Still that problem doesn’t look insuperable to me.

Dmitri February 20, 2013 at 18:45

Russians have had 10 of 16 successful landings on Venus from which they’ve plenty of telemetric data about the planet that they have develevoped affection to the planet calling it gently “our planet”. That fascination have led other thinking compared to Americans at 60s, 70s, 80s. There is a number of engineers who favor Venus over Mars in priority list for very obvious reasons.

1) Early Earth had atmospheric pressure at 300 atm.
2) early Eart was much colder than Venus
3) Venus receives twice the Sun energy than Earth
4) Telemetry of descending probes showed that between 60 – 50 km in Venus atmosphere is at 25C, 0,5atm and mainly CO2 w/ little mix.
5) Venus has atmosphere which Mars completely lacks.
6) For very obvious reasons colonization of Venus is more feasable than Mars due to the factors above especially the part of atmosphere.

In 1971 in Russian magazine Техника-молодежи (Technical science for youth, a spin-off of infamious magazine Наука и Жизнь (Life and science), which is on par w/ magazine Nature), number 9 space engineer Сергей Житомирский (Sergey Zhitomirskiy) published an article “ПЛАВУЧИЕ ДОМА на “Утренней звезде”" (The floating houses on the “Morning star”) where he layed out the perspectives of floating devices in the Venus upper atmosphere between 60 – 50 km (

This is pivotal article in Russian science circle on the matter as everyone who is pitching the subject is reffering to the paper. Nowadays the main lead in the field is Сергеи Красносельский (Sergey Krasnosel’skiy) who is very pragmatic and concentratic on very feasiable future on human colonization on other planets. His moto is set goals achievable during a person lifetime – 1000 years is too distant future what the humanity have to live through anyway. The goal of colonizing people on Venus would be terraforming and based on Venus and Early Earth similarity transform it into habbitable planet in shorter terms than nature did on Earth. Maybe within years or in couple of centuries. Sergey Krasnoselskiy only summary on the subject is in this YT video
(sorry no English subs). There is also some additional articles slightly expanding the subject. I think google translate would help here.

They all acknowledge Mars is more popular than Venus in colonization terms and even then Mars steals the spotlight. The Venus argument gains more weight when Earth should face an Exctinction Event which requires a quick reaction to save the mankind or diverse the risk on extincion of the spiece. Also reducing population pressure to Earth by repopulating colonist to Venus. Then the money, interest and resources will pour-in in the field. Clearly it’s not easy, technically challenging and there is basically everything else beside afforementioned list of 5 benefits wrong and hostile to humans. Engineering challenges are overcomeable just the need is to deal w/ them.

There is basically no information on the subject just bits and pieces and dreams in some persons. I think I might have come across Geoffrey Landis researching the subject before. Non the less the next logical step in contemporary space engineers lies in Venus not in Mars. At least in Landis and Zhitomirskiy opinion.

Rob Flores February 20, 2013 at 19:16

Well I would not say that Kuiper/Oort ice bodies are totally beyond the realm of usable manner to interstellar migration. There are a few special cases. that might push some elements of humanity outward

Overpopulation via technology that creates extremely long lives (300+)
If our space tech, hasn’t advanced much beyond VASIMIR (for ex) then
I can see the kuiper belt as pressure relief valve, AFTER the moons of the solar system are at full carrying capacity, so a time frame of several Centuries, assuming nothing faster than 1 % C is developed. This would
mean a fairly static society, In world with long lives it just might come to pass.

A very luckless alternative is that we are forced to use them because of a menace that makes the solar system very dangerous to live in, even on Earth. I can see with enough lead time, the hollowing out spining up & reshaping the under 2km sized Icy bodies, Placing lots of base materials inside. putting fusion drive in back and extra thickness our front. Making interstellar arcs of them, launch a fleet, in a timeframe of half of a century.
It would be one of the few options that would
allow a significant part of humanity to escape to a new destination.

Astronist February 20, 2013 at 19:20

Ronald, I would be interested in seeing your estimates of the relative costs of creating living-space by terraforming terrestrial planets versus constructing space colonies. Might you have a link to them, please?


Dmitri February 20, 2013 at 19:35

“Rob Henry February 20, 2013 at 16:44 said “Firstly it assumed that no biosphere could be more efficient at supporting humans than Earth (Think of that as the “Earth designed by God for man” postulate)”"

“Alex Tolley February 19, 2013 at 16:01 said “Is it fair to effectively imprison generations in an isolated colony when the inhabitants know that there is a rich, dense, diverse, interesting civilization huddling around its parent star?”"

I would like challenge Alex Trolley and Rob Henry notion of Earth has been the only suitable (& safe (?)) place for life to exist, thrive or prosper in any form. Sorry if you feel that I might misinterpred your actual point, I just want to point out that Earth is as hostile to life as any other imanigable celestial body w/ that exception Earth has natural atmosphere.

Danish professor Henrik Svensmark, the author of Cosmic Ray Theory, where he proposed that Cosmic X-Rays do affect Earth cloud cover by energizing aerosols in the upper atmosphere and causing thicker clouds, published extended paper on the issue where he made a reaserch into reasons on extincions on Earth. His conclusion is that main driving force on planet Earth are tectonic activity and cloud cover which regulate climate to such extent that may cause mass extinction. I was blown away by the graph. This article actually explains indirectly drivers behind Snowball Earth period.

In short – life on Earth has been erased and extinct quite significat time. We as the first technical civilisation who are to some extent capable to stand against the forces are just in a brief period of climat stability. If you may say so. The KBOs, Titan, Mars, Venus, Pluto are no more worse place to die on than Earth. The difference is on Earth the extinction will come as a nasty surprise. On these celestial bodies they are inclusive and you’re prepared for that, thus increasing changes of survivability.

Alex Tolley February 20, 2013 at 20:34

@Dmitri – actually I wasn’t suggesting that earth was the only abode for civilization. My point was that space cities would likely stay much closer to the sun than the deep solar system, because the opportunities for individual growth is going to be much more favorable there, than in more isolated locations. Do you have a similar expression as we do concerning this : “How are you going to keep them down on the farm?”.

Rob Henry February 21, 2013 at 2:59

Yes Dmitri, you did misunderstand me, but I happened to be merely reinforcing the potential for O’Neil type habitats, and no more.

If we eventually find them more desirable than planetary surfaces and we have a future (eg that entails fertility rates typically return to above replacement levels when our populations are well below carrying capacity), then it is reasonable that the most desirable habitat niches will be filled. The numbers would be astronomical if the answer favored O’Neil.

If in the end, planetary-type surfaces are desired, I doubt that even one in a 10 thousand would be permanent inhabitance of O’Neil colonies.

On the other hand if O’Neil colonies turn out as most desirable, the moons and planets may be teaming with billions of humans, yet still be so insignificant (bearing much less than one millionth of Sol’s total population), that most of humanity is unaware that anyone lives there. In this second case the Oort Cloud would probably also contain billions, but unfortunately there would be a strong tendency for colonists children to migrate inwards from worlds that were still in physical contact with our inner system. The unplanned colonization bridge to Alpha Centauri would only truly begin from the most isolated backward regions.

So, getting back to your challenge, the problem boils down to what is most desirable when our technology reaches its zenith: the imagined paradise of home, or its artificially created counterpart? Which is the better use of capital when our wealth is at its peak, and gives the greatest marginal reward? These are hard questions to answer.

tom February 21, 2013 at 3:30

I find most of the arguments about Man & Space to be very optimistic or very cynical. I wish they could design a spacecraft that is as simple as a modern high altitude balloon. I have a few strange ideas; and space travel is something for everybody. Going one-way around the solar system is like those folks who sail around the ocean solo.
For people with life expectancies less than 10 years, lets use that time to go out and see whats out there… and send all the data back to the living on Earth.
We’ll leave a bunch of haunted beacons for future explorers?

Ronald February 21, 2013 at 7:01


I have been searching this great website last night, but, unfortunately, it is not possible to search the comments, so I could not find it back yet.
I am sorry, I realize this is quite a weak offer.

However, the line of reasoning was somewhat like the following:
- Estimate the total construction cost both for a large (O’Neill like) space colony and for terraforming Mars, for the latter also including the very long time period and hence capital cost (interest, Net Present Value).
- Estimate maintenance cost for both, plus depreciation for the space colony (also see next point).
- Estimate the expected life time of a space colony and of a terraformed Mars.
- Calculate the total area for both.
- On the basis of the above, estimate the cost per year and per square kilometer.

I used a few different values, for instance the cost of one space colony varying from 1 trillion USD down to only 10 billion USD (assuming mass production), and expected life times for the same varying from 100 to 1000 years, maintenance costs of the same about 1% of construction cost per year (this may seem like a lot, but some modern high tech constructions can actually cost up to 10% per year for maintenance, even roads can be amazingly costly in maintenance).
For Mars I think I used some data from Zubrin.
I was surprised myself to find that, although admitted again that this was kind of back of the envelope, the difference was easily a factor 100 thousand, up to several magnitude factors higher.
My guestimate did still not take into account insurance cost, nor, if I remember well, the positive fact that a planet like Mars could already be used incrementally, while in the process of being terraformed (for instance in the form of habitable domes, local resource utilization).

My main point was and is that artificial space colonies are incredibly expensive and intrinsically risky (high tech, ‘unnatural’, stochastic risks), whereas a planet is a very large piece of real estate that is ‘already there’ and is also a naturally very stable object.
I used the comparison of colonizing islands and mini-continents versus building platforms in the ocean.

Maybe you could make a more thorough and accurate calculation yourself. I would be very curious.

Ronald February 21, 2013 at 7:30

An addition: please, do not misunderstand my main point;
I definitely believe that there is avery real and important future for space stations, space colonies and the like. For research, space exploration and space exploitation (asteroids!), etc.
However, I seriously doubt whether those kind of mega-space-constructs will ever be used for mass dwellings, i.e. for a significant proportion of the human population, in any foreseeable future, even if we possess the technology. Simply for economic reasons. We can probably grow lattuce and tomatoes in the interior of Antarctica, or build large habitation platforms in the ocean. But we won’t, as long as we have much better and cheaper alternatives.
And this does not even take into consideration yet human psychology and our strong innate needs and desires (i.e. do an opinion poll: how many people would prefer to live their entire lives in a limited space colony versus how many would prefer a planet in the process of being terraformed. I dare to guess the outcome, overwhelmingly).
Likewise, as long as we have a very tempting neighbor planet beckoning us for colonization and providing some 145 million km2 of real estate or 28% of Earth (i.e. Mars), and later maybe even Titan and Venus, and as long as humans will be humans with human psychology, we will be doing large-scale planetary terraforming in the coming centuries, rather than large-scale space colonies.
Plus the added value that terraforming Mars (and …) would at the same time constitute valuable experience for other planetary systems. It is most likely that we will find few directly habitable planets as we expand into the neighboring galaxy, but rather terrestrial planets of varying degrees of potential habitability, i.e. terraformable in different ways and degrees.

And if we have still not been able to reach neighboring planetary systems within the next millennium, we have really been doing something wrong.

Ron S February 21, 2013 at 11:45

Ronald: “I have been searching this great website last night, but, unfortunately, it is not possible to search the comments, so I could not find it back yet.”

As an alternative, go to Google and search on a combination of “centauri-dreams” your signature and the snippet of text you’re looking for.

Dmitri February 21, 2013 at 15:16

@ Rob Henry “The numbers would be astronomical if the answer favored O’Neil. If in the end, planetary-type surfaces are desired, I doubt that even one in a 10 thousand would be permanent inhabitance of O’Neil colonies.”

Elon Musk made calculation for their manned Mars back and forth mission that 1 in 100 000 would be their client. Considering population around 8 bn it makes 80 000 potential customers. The team would be less than 10 persons, preferably 7-8. 6 months there, 18(?) months there and back to Earth. If SpaceX sees commercial potential I would not doubt in it. Can’t recall which astronaut said but there should be sufficent volunteers for one-end Mars trip who will become first permanent settlers on the planet and the supplies arrive at every 18 months. The only question for such near term mission would be how low the entry barrier would be set? Right now it’s at PhD, scientificly inclined, technically proficient etc. Hippies, treehuggers and flowerchildren would be allowed? ;) (Did not ment to mock them, rather illustrate the other end of spectrum of candidates .)

Dmitri February 21, 2013 at 15:40

EDIT for my previous post:

SpaceX commercial trip to Mars would be 6 months to the Planet, land and spend 12 month on the planet building dome which eventually have to become after many iterations artificial oasis for settlers. Pack your stuff and head back to home.

Rob Henry February 21, 2013 at 15:49

Boy Ronald, you stuffed up your economic calculations. To show you the truth, think of us both sitting on a pot of money and thinking of buying a new home for our descendants. Say at some future date that this sort of thing has become trendy, and you throw in your lot with a million planet-lovers, and I with a thousand O’Neil enthusiasts.

Now say my groups construction costs were a million per year per person over thirty years, and the maintenance costs a whopping 100,000 pa. Now real interest rates never vary excessively far from 4%pa, so 17.65 million placed in a interest accruing account and paying out as expenses occur should be perfect for work to start immediately (note my spurious accuracy which is just for illustrative purposes). Paying the maintenance costs for the subsequent seventy years adds just 700,000, and for the next billion only about a quarter of a million more now.

I was going to do the same sort of thing for terraforming, but I think that you should already get the picture. The cost of our descendants having to wait is real, but the cost of maintaining a colony is only an abstract in regard to adding it up over billions of years. Only if interest rates are exactly zero, does that sort of calculation have real meaning.

Dmitri February 21, 2013 at 17:48

@ Alex Tolley “space cities would likely stay much closer to the sun than the deep solar system, because the opportunities for individual growth is going to be much more favorable there, than in more isolated locations. Do you have a similar expression as we do concerning this : “How are you going to keep them down on the farm?”.”

I just enjoy turns and twists like these where a general discussion of future progress binds current and past anthropology and near term impact is has on social perception.

Regarding the expression we don’t and not even slighlty into that. The ones which have similar expression breadth are used completely in different context. I even see now the reasons why it’s so and how history and people’s involvement have shaped their verbal expression due to massive historical event. Yet the context and meaning is clear and for current moment puts it into new light of human mass migration from rural area to cities – the shiny lights of cities offer more complex and intricate oportunities for different crafts which are unnecessary beyond the realm of a city. In places where scarcity of options and high demand on skills one posess due to numbered resources people tend to do more upon wider variety of crafts plus interact more. That on itself will inherently lead to a strengthened community feeling and human involvement. There are plenty of people who stay where they were born, return to the home place, give up the hardship and go where the city lights glitter and find their specific call. In any case all the cities in their early start resembled the same rural area settlements but for some natural driving force have succeeded to attract external attention and starting to thrive in their core strength(s) plus having enough surplus to invest into additional expansion (the poetic glittering city lights). If you look at human far past cities like Hedeby/Haithabu (ancient Viking commerce center and capital), Atlantis (the alleged real city for the city in the legend in SE Spain rich in copper ore, Troy (the ancient city which were on fortunate geographical position for trade routes between the Caucasus and the Balkans and beyond to West.) had the same 3 distinctive strengths valid in nowadays – location, resources, wealth. The same will go for far future KBO settlements but w/ that tiny distinction if one of the settlements will find way for energy independence (decoupling from the Sun) we will have a major settlement w/exponentially increasing glittering city lights despide the awkwardnes of living on that artificial environment. And there may be a lot of this kind of resources – He3, thorium, converting X-ray to energy, rare earths etc. This kind of advances will have an impact of social behaviour and for the first time in human history migration path – rural area -> city -> artifical living environment.

In short – if the Sun cease been the only heating battery and we won’t have many poets around graving inspiration from that celestial body we might actually set a firm foot regardless of the Sun and Habitable Zone. The move towards inward of the solar system might be replased w/ move towards nearest settlement w/ (highest / efficent) energy independence. Commerce, wealth will follow.

Dmitri February 21, 2013 at 18:13

@Rob Henry ” So, getting back to your challenge, the problem boils down to what is most desirable when our technology reaches its zenith: the imagined paradise of home, or its artificially created counterpart? Which is the better use of capital when our wealth is at its peak, and gives the greatest marginal reward? These are hard questions to answer.”

Actually I’ve noticed that contries / societies in opulence don’t thrive much rather than enjoying resources the land provides – the Middle-East oli, Argetina’s recent currency devaluation despite sitting on piles of oil. USA importing oil in immence amount and now going into shale oil / gas production. Europe in essence lack in any natural energy resources except oil shale and uranium. Yet if you look at countries which actually invest into science and R&D then you clearly see the ones which lack or are in scarce do actually better than the peers especially in downturn times. The manure in the ventilation is just the everyday feature that you are prepared for. I actually belive that the far out settlements on conditions like these will actualy make better and efficently than peers nearby or on the sacred Blue Marble. People are actually very good finding solutions for the problems when the options are constrained.

Despite people been accustomed to earth and living conditions there will be enough cracked people who would take the journey. I think SpaceX commercial manned Mars program, the Danes w/ their plans for Mars settlement in 2024, and today announced private manned Mars mission in 2018 by Dennis Tito will be the litmus tests for acceptance by society for these kind of adventures.

Astronist February 21, 2013 at 18:48

Ronald, thanks. I don’t think I can produce a more accurate calculation, as in particular I have no idea what terraforming even Mars might cost.

I tend to feel skeptical of the terraforming concept, since it involves engineering on a very large scale indeed, and presumably over a long timescale of at least several centuries. Meanwhile, as you said, Mars could be occupied without waiting for terraforming to be complete. The type of habitats involved would be simpler than space colonies — the basic architecture would be in compression, as terrestrial buildings, rather than in tension, as a pressurised, rotating container has to be — but surely the increase in costs due to building in space would not amount to orders of magnitude in comparison with planets?

And given that terraforming is a long-term project (if it is possible at all), why would people pay towards it if they could already live under an artificial roof at the same location? In order to step onto the surface of Mars without a spacesuit, for example, the mass of the atmosphere would have to be increased by a factor of at least 50 (6 mbar pressure to 300 mbar, say). That’s a lot of gas (and according to R.L.S. Taylor in JBIS a few years ago, the nitrogen for a terrestrial-type atmosphere would have to be imported). Would a programme to achieve that survive for long, if people could live perfectly satisfactorily in Zubrin’s arched brick vaults, and if, furthermore, the habitable volume could be increased incrementally according to population pressure and investment conditions, rather than trying to affect the entire planet in one overall programme?

Hence my viewpoint that space colonies will be competing with planetary colonies whose living conditions are very similar, but open-sky planetary real-estate will remain essentially confined to Earth.

Still, I suppose the question will in the end be decided by practical experience as people move out into the Solar System and try different ways of survival and growth there.


Wojciech J. February 21, 2013 at 20:06

Also if I might add, I wouldn’t categorically oppose the idea of colonization of such objects, but mostly by so called “Hider” or “Isolationist” cultures and groups(or maybe in some catastrophic scenario with home star). But I don’t see it as viable method of interstellar colonization. There are too many issues involved for such plan to work-motivation, scale, evolution and technological progress.

Wojciech J. February 21, 2013 at 20:09

“Wojciech J, I also found that figure amusing, but for me that was because it was ridiculously low. ”
4,000 trillion humans for me was amusing due to social implications. How would such society communicate, store and classify information? Can you imagine the vast amount of data that would never be processed? The chaos?
But I don’t think this would be a worry, I doubt we will ever reach such population size in our current biological bodies and cognitive organs.

GaryChurch February 21, 2013 at 22:15

“SpaceX commercial trip to Mars”

It is a scam; no way to get to Mars without nuclear propulsion. Radiation shielding masses hundreds of tons and chemical propulsion is not going to be enough.
Mars is a rock anyway- it seems like it is “just close enough” but all things considered it is not. A nuclear mission would have to be launched from a Moonbase; and there is water on the Moon to fill up a radiation shield.

The hobby rocket is not going to be around for very long; it has so many cheap and nasty features I doubt it will ever be qualified to carry humans.

There is no substitute for a Heavy Lift Vehicle with hydrogen upper stages. That is how we went to the Moon last time and the laws of physics have not changed.

The money we have spent on the ISS and commercial crew has been a complete waste.

Ronald February 22, 2013 at 9:53


thanks, your argumentation is completely reasonable and I can only agree with most of what you say.
Funny enough though, the exact same arguments brought me to an opposite conclusion! I.e. it made my ‘ case for Mars’ even stronger.
Let me explain a bit: I fully agree that terraforming Mars is going to be a very tedious, long-term heck of a job, if feasible at all. And yes, particularly the necessary atmospheric N2 is going to be a real bitch (although the Martian soil does seem to contain some nitrates).
In fact, terraforming guru Fogg does not even consider Mars as a true terraformable planet (or at leat not what he calls ‘easily-terraformable’, let alone biocompatible, let’s not even mention habitable).
However, it is this very fact of relative ease of incremental habitation (by means of domes etc.) that, I think makes Mars such a strong case for colonization in comparison with space colonies. The initial costs for transport and settling may be high, but once you are there and settled you can largely ‘live of the land’ (Zubrin term), most required resources are available and you can just keep pumping out more habitats etc.
I can imagine a future in which more and more people will be settling on Mars, gradually expanding the habitats as needed, and at the same time working (or at least attempting) toward that bigger goal of terraforming. A very cautious two-pronged approach. And I think this is more or less how many SF writers and Mars visionaries visualize it.

Having said that, I also realize though that this would then have to be compared with the alternative of asteroid resource exploitation for space colonies.

Dmitri February 22, 2013 at 10:37

GaryChurch – Listne to Elon Musk 20 min. interview to BBC in March 2012. He quite openly disusses the matter and the host is a prominent in the field. So far Elon has delivered. His main point is that energy wise trip to Mars is the same as to Moon.

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