Yesterday we looked at the possibility of colonizing worlds much different from the Earth. Seen in one light, pushing out into the Kuiper Belt and building settlements there is part of a slow migration to the stars that may occur without necessarily being driven by that purpose. Seen in another, experimenting with human settlements in extreme environments is a way of exploiting the resources of nearby space, pushing the human presence out into the Oort Cloud. Either way, we can find places that, while not ‘habitable’ in the classic sense of liquid water at the surface, are nonetheless colonizable.
In his Tale of Two Worlds, novelist Karl Schroeder works on a definition of a colonizable world. It has to have an accessible surface, for one thing, meaning one we can work with — obviously a surface gravity of 4 g’s is going to be a problem. Much smaller worlds like Pluto, as we saw yesterday in Ken Roy’s work on possible colonies there, pose less of a challenge, as we can imagine strategies to produce one g for the inhabitants. Schroeder also notes there has to be a manageable flow of energy at the surface in which we can move heat around. That seems reasonable enough, although advanced technologies will have a wider zone than we have.
But I found Schroeder’s third point interesting. Here he’s drawing on a 1978 paper in Science called “The Age of Substitutibility,” by Harold Goeller and Alvin Weinberg (Oak Ridge National Laboratory), in which the authors describe the artificial mineral they call ‘demandite.’ It comes, as Schroeder notes, in two forms:
A molecule of industrial demandite would contain all the elements necessary for industrial manufacturing and construction, in the proportions that you’d get if you took, say, an average city and ground it up into a fine pulp. There’re about 20 elements in industrial demandite including carbon, iron, sodium, chlorine etc. Biological demandite, on the other hand, is made up almost entirely of just six elements: hydrogen, oxygen, carbon, nitrogen, phosphorus and sulfur. (If you ground up an entire ecosystem and looked at the proportions of these elements making it up, you could in fact find an existing molecule that has exactly the same proportions. It’s called cellulose.)
The point is that the right elements have to be accessible on the object you’re trying to live on to make it colonizable. Now if you can find a place that meets the three criteria, surprising things can happen. Centauri B b looks to be a nightmarish place, probably tidally locked and roiling with lava on its day side, and almost certainly without a breathable atmosphere. But from the standpoint of colonizability, we can’t rule out the night side, and the fact that this (still unconfirmed) world has a surface gravity about the same as Earth’s also works in its favor.
From the Kuiper Belt Past Proxima
Ken Roy’s talk at Huntsville looked at places that seemed equally inhospitable, but which may have the necessary resources to provide an advanced human civilization with what it needs to create settlements there, whether as part of a deliberate interstellar migration or simple exploration. Yesterday I focused on Pluto, but of course the Kuiper Belt is stuffed with objects, hundreds of which may be Pluto-sized, while cometary bodies in the Oort Cloud are thought to number in the trillions, based on the study of long-period comets and their frequency.
Like Schroeder, Roy is interested in brown dwarf possibilities as well. The odds on our finding a brown dwarf closer than Proxima Centauri are dwindling, though I don’t think we can rule out a possible ultra-cool Y dwarf in this space (please correct me with any updated information). In any event, the WISE mission (Wide-field Infared Survey Explorer) has shown us that brown dwarfs are less common than we thought. WISE has discovered 200 brown dwarfs (including 13 Y dwarfs), 33 of which are within 26 light years of the Sun. Given that there are 211 stars in the same volume of space, we’ve found that there are about six stars for every brown dwarf.
If they’re not as abundant as we had thought, brown dwarfs may still become useful staging areas for far-future interstellar expeditions, for we know that some have accretion disks that indicate the possibility of planet formation. I’ve written before about brown dwarf habitable zones (see Brown Dwarfs and Habitability), but Roy’s point is that whether or not we find a world that’s habitable in the classic sense, we can still assume we’ll find the same kind of small, icy planets we see in our own Kuiper Belt, and the same technologies could exploit them.
Roy is one of those intrigued with the idea of ‘rogue’ planets that move through the interstellar deep far from any star. We know little about these worlds, but it’s assumed that great numbers of them are out there, doubtless the result of gravitational interactions in young solar systems that caused them to be ejected. Dorian Abbot and Eric Switzer (University of Chicago) call these ‘steppenwolf’ planets because they ‘exist like a lone wolf wandering over the galactic steppe.’
Image: A ‘steppenwolf’ planet moving between the stars. Credit: NASA/JPL-Caltech.
Louis Strigari (Stanford University) has estimated that as many as 105 objects larger than Pluto exist for every main sequence star. If that’s anywhere like the case, then rogue planets ranging between the size of Ceres and Jupiter should be out there in abundance, and we can hope to put some constraints on their numbers through future gravitational microlensing surveys and even exoplanet transit studies, which may catch a rogue planet’s transit. Some studies show that radiogenic heating from the planetary core could keep an ocean under crustal ice liquid for billions of years even out here, where there is no star to provide warmth.
Deep space is not without resources, as we’re learning every day. Roy told the audience in Huntsville that cometary objects from the Kuiper Belt to the Oort Cloud should offer CO2, ammonia, methane, oxygen, carbon and nitrogen, while we can exploit asteroids for silicates and metals. We can only imagine what resources might be available in unattached worlds moving between the stars. This is all work for a civilization that has built a thriving deep space infrastructure, but then, thinking about the future is what we do here.
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Wow a trillion Oort cloud objects. That is a big number.
Imagine a colonization wave going through an Oort cloud, where 1 / 100 Oort cloud objects see colonization. That’s still a big number (10 billion).
How could we detect a colonized Oort cloud? Wouldn’t there be some widely diffused radio (or laser, etc.) leakage from many billions of settled objects across a volume a light-year or two across? There should also be some waste heat from their activities. Shouldn’t that warm a colonized Oort cloud a bit?
What would it take to make such a diffuse colonized space detectable? (Sorry to ask twice, I’m really interested in what the math would say)
“… six elements: hydrogen, oxygen, carbon, nitrogen, phosphorus and sulfur. (If you ground up an entire ecosystem and looked at the proportions of these elements making it up, you could in fact find an existing molecule that has exactly the same proportions. It’s called cellulose”
Actually, no. Cellulose is just linked sugars, so it is only made of (CH2O)n. No nitrogen or phosphorus at all.
But I like Karl’s idea of colonizability, rather than habitability. I think this is particularly important where planets have existing life that should not be interfered with.
I think that proposals to detect possible signs of civilization in other systems by studying effects of asteroid mining were already proposed. This seems a good idea and could be probably adopted with ease to Kuiper belts in other solar systems.
I didn’t realize there were so many brown dwarfs near Sol-if that is the case, I see even less chances of galactic expansion in terms of colonizing other planets-with so many resources there is little reason to do so.
Exploration and discovery of course would remain viable impulses for civilizations.
But it seems that we can count on advanced civilizations settling in small spheres of colonized space.
It sounds possily plausable to migrate that way, therefore..
..hollowed- out inhabitted dwarf planetoids may have been a strategy already employed by others before us. Perhaps some others left (we name it) Tau Ceti System 100 000 years ago heading full of hope for (we name it) Sol System . Maybe they are content, now settled in ‘our’ Oort Cloud. (we name it). Or else their tactic failed and they are dust, now entombed. Or else they got lost (or lost their marbles) and forgot where they were going. Or else some of each outcome. Every possible tactic must have been tried by others before us. Those telltales would be hard to find.
“The point is that the right elements have to be accessible on the object you’re trying to live on to make it colonizable” — well, up to a point. Think about modern terrestrial civilisation: we make huge efforts transporting materials all around the world from where they are found or manufactured to where they are required. The same will be true in space, especially when cargoes can be moved from one heliocentric orbit to another using say light sails, or perhaps beamed power for electric engines.
An oldy but a goody on the problems with detecting even nearby ETI:
Dear Mr. Tolley:
I’m not sure I can agree with this comment of yours: “I think this is particularly important where planets have existing life that should not be interfered with.” If you meant that contact by human explorers with worlds that have INTELLIGENT life should be done with the utmost care, then I agree. But if a world has no intelligent life, no non human sentient races, then I have no objection to humans exploiting its resources or, if terrestrial and colonizable, settling it and founding new societies and nations there. Because it is my view that a big reason why humans may someday leave Earth for space is to colonize other worlds.
Respectfully, Sean M. Brooks
@Sean- Hypothetically, we arrive at a world that looks like Earth, but without ETI, perhaps like Earth 20 mya. But we find that its biology is incompatible with ours and that our two biologies cannot share the same planet. Are you saying that you would sterilize the planet and terraform it? If not, where do you draw the line, however fuzzy?
Alex and Sean, you bring up an important ethical issue discussed before and worthy of a separate post and discussion thread.
In short, my two cents, I would suggest, that:
– If there are, sensu Fogg, terraformable, biocompatible or (potentially) habitable (but uninhabited) planets, there is no ethical issue. These categories, I expect, will probably make up the great majority of potentially suitable terrestrial planets.
– If there are habitable planets, that are inhabited by any complex life (i.e. not just intelligence) we do have a serious ethical issue and a moral obligation to tread very, very carefully, possibly even refrain from colonizing it, other than scientific research. Probably a very rare minority anyway.
– The really interesting issue comes along if we find planets that are inhabited by microbial life (or simplest cell-colonies) only. Here I refer to the post late last year on ‘life stages of a habitable planet around a main-sequence star’:
If a planet is already far in its complex/multicellular life stage, or even past it in its second microbial life stage, and it still only has microbial life, one could argue that this planet has had its chance of developing complex life without, for some unknown (?) reason, doing it, and hence seeding it with our life would be an enrichment.
But how to proceed, if a planet is still in its first microbial life stage or early in its complex life stage and indeed only has produced microbial life *so far*? Should we give it a chance to bring forth its own complex life and therefore refrain from seeding it with our life?
Dear Mr. Tolley:
Thanks for replying! I’ll focus on a few points. First, human explorers might discover a planet with valuable minerals or resources that it would be cheaper to mine and export from that planet despite it not being humanly habitable (rather than from mines back home). So, we could see domed mining bases housing only a small number of people. Second, I do not believe, assuming humans do leave the Solar System for other worlds (with or without a FTL drive), that they would try to terraform many (if any) planets whose biology is incompatible to ours. Far more likely, people will search for worlds both humanly habitable and without intelligent races of their own.
But I certainly have no objection to terraforming per se. I see nothing immoral in “making over” a world so human beings can live on them. Here I have the speculations I’ve read about terraforming Venus and Mars in mind. The important qualifier being that they are not inhabited by other races.
Respectfully, Sean M. Brooks
Thanks for your own, interesting comments. However, I don’t think I can agree entirely with them. To me, the most important ethical point is that a planet which might be colonizable by human either has or does not have intelligent life WHEN discovered by Terrans. If not, I see no moral problem with human beings “seeding” it with life forms from Earth. Esp. if that planet is still at an early stage of development. CAN human beings wait millions or billions of years for intelligent life to POSSIBLY arise on that world (never mind simply ordinary plant and animal life)?
I understand and appreciate your point.
However, should the main criteria for human colonization be: the presence of (other) *intelligent* life? Or any higher/complex life?
I am inclined toward the latter, because this is probably rather rare in the universe anyway.
I tend to agree with you that if there is only primitive, microbial life (probably much more common than higher life) we cannot and should not wait for mys or gys to see if anything more arises.
So, concludingly, for you the criteria is intelligence, for me any complex life.
I was interested in the estimates of the number of rogue planets that might exist. I can’t help but wonder about the effect it would have on human societies if one of those bodies was discovered approaching from the interstellar deep and targeting the inner solar system. If an interaction with Jupiter caused the incoming planet to lose enough energy to be captured by the sun, probably in a wildly eccentric orbit, the result might be very bad for us.
I realize the probably of this happening is low but I have to believe it happens once in a while “out there.” Perhaps some other upstart civilization somewhere else in the galaxy has had to deal with such an event.
That is correcct, if a planet has no intelligent life, no non human sentient occupying it, I see nothing wrong with human colonizing it. But, I still disagree with you that if a planet has life more advanced than the microbial level, but still no intelligent race, then it’s off limits to human use and development.
It’s been pointed out that even if all life in the universe is DNA-based, the number of possible DNA sequences is so large that each planet (and perhaps all together) samples only a small percentage of them. Life on any particular planet will probably have features that aren’t found anywhere else. This is even more true if there are alternative biochemistries etc. With so many completely lifeless worlds to exploit it would be scientifically wasteful to destroy the simplest forms of life elsewhere, to say nothing of all the ethical problems associated with complex and sentient forms.
You are right Peter. But like many threats, it seems too theoretical, unreal until the the windows blast in. Then it becomes ‘here and now’. Longterm, we have to get our dna spread out. Our eggs are all in one basket. These decades are critical. We are still stuck planetbound, and risks of collapse are growing , one two three per cent….
Peter Chapin wrote:
“I was interested in the estimates of the number of rogue planets that might exist. I can’t help but wonder about the effect it would have on human societies if one of those bodies was discovered approaching from the interstellar deep and targeting the inner solar system. If an interaction with Jupiter caused the incoming planet to lose enough energy to be captured by the sun, probably in a wildly eccentric orbit, the result might be very bad for us.”
Bellus and Zyra in “When Worlds Collide”–check! Such a rogue planet (and its moons, if any) would play havoc with our planets–think “solar system snooker”–even if it didn’t collide with one of them, unless perhaps it came from north or south of the Sun and entered a close, narrow, comet-like elliptical orbit around the Sun. Also:
“I realize the probably of this happening is low but I have to believe it happens once in a while “out there.” Perhaps some other upstart civilization somewhere else in the galaxy has had to deal with such an event.”
With the number of rogue planets that are suspected to exist, I would be surprised if it hasn’t happened (such intrusions would be more likely in star clusters), but as you wrote, it isn’t common.
With all due respect to Dr. Freitas, this one is not well thought out. You can easily see that if you replace “lemmings” by “rodents”. The Fermi paradox is not about a very specific type of alien (e.g. green with antenna), but about any type of alien that would be able to settle the stars.
It is correct that we do not see lemmings all around us, but we see plenty of squirrels, mice, rats, and all sorts of other critters that make it immediately obvious that life exists on Earth. Not so for life in the galaxy. No sign of it. I am with Fermi, on this one.
How far do you have to go to get what you need? Modern consumption for an already industrialized country would ‘need’ just one asteroid for all the base metals and one comet for all the volatiles. You’d have enough ‘space material’ for centuries (even with a doubling of production every 10 years).
The mapping mission phase for probes is completely justifiable.
Depending on some wild card factors of technology, you are going to get past the point of ‘firsts’ in extreme space exploration before these outposts emerge.
There is a lot of stuff on the Moon, but nobody aggressively pursues it.
But I wouldn’t be surprise after somebody does it, people interested in unique wealth opportunity will want a company like this to be apart of their financial portfolio. Getting ‘exotic’ stuff from space has a market niche, commodities & resources will replace novelty if you can make this affordable? But I’d like to see asteroidal platinum, or a shuttle tank filled with cometary methane fuel. It would be very fascinating to see this ‘Klondike’ to the Stars?