Suppose a K-II civilization built a terrarium or zoo, featuring life and ecosystems from different worlds as it travelled through the universe. (By K-II I mean in terms of resources and energy budget required. I don't mean technology indistinguishable from magic, as that's a cop-out in a hard SF story. In general, I want to minimize the number of exceptional things that are not real (known) physics or go unexplained.)

Clearly you need "hard" compartments for different domains that are fundamentally different in atmosphere etc. But it would be more pleasing if exhibits were separated from each other in a more unobtrusive natural-looking way.

Having contenents or suitably-sized islands is no barrier since life can fly, swim, or blow in the wind. If there were subtle partitions in the water as well that would not stop air travel and would block ocean circulation.

If you had tall mountains, you need a hard partition as well to reach even higher in the air and prevent any tunneling through. And that causes problems with weather.

Active defences as a backup against normal-ish barriers? How would they work?

And finally, how to visitors and explorers manage to go where they please, when even clever natives with lots of time cannot.

  • $\begingroup$ Combine the two, to either side there are tall mountains with sea in between. $\endgroup$
    – user23614
    Jun 26, 2016 at 11:53
  • $\begingroup$ A mountain range of hard rock that is taller than the atmosphere. Either rockets or hidden passages. (slab of rock only moves when the right radio signal is received ) $\endgroup$ Oct 20, 2016 at 20:38
  • $\begingroup$ @DonaldHobson you’re suggesting how visitors can pass when natives cannot? $\endgroup$
    – JDługosz
    Oct 20, 2016 at 21:51
  • $\begingroup$ Giant ice walls and magma are two that the flat earthers suggest... $\endgroup$
    – The Nate
    Jul 29, 2018 at 6:32

5 Answers 5


This is a fairly difficult problem. A couple of fictional precedents worth looking at:

Jack L Chalker's Well World series, beginning with Midnight at the Well of Souls, had an entire planet set up as this kind of terrarium, but the means of keeping the environments separate was direct control over reality.

Charles Stross' novella Missile Gap puts the continents of Earth down in a ocean on an Alderson Disc, separated from those of other worlds by enormous distances, much greater than those available on an earthlike planet.

  • $\begingroup$ Alderson discs sound amazing, after taking a quick look at the wiki page. I might go for that simply because of the wow factor. $\endgroup$ Mar 31, 2017 at 2:18

If you have a world sized zoo with its own climate and mountains and oceans etc. You already have natural boundaries that will determine where your 'not so intelligent' animals and plants will reach. My examples are based on the assumption of a seemless transition between each environment with no actual 'walls' so to speak.

Animals and plants are adapted to the geological, atmospheric, and climatic conditions they 'evolved' from. Uprooted animals and plants often need specialised care to survive in other environments. For example, the panda won't mate in captivity, and neither will the Dory fish. Salt fish can't survive in fresh water (baring a few extra specialised exceptions). Polar bears need cold temperatures, and desert animals need hot temperatures. etc etc. These conditions mean that the animals will limit themselves to how far they travel before turning back.

If you are wanting to limit the movement of your 'more intelligent' animals; I'm assuming you talking about some sort of sentient race, captive humans and the like perhaps. If you limit the development of their technology they will be just as limited by the environment as we were back in the early caveman days. Mountains were barriers that required crossing dangerous, and inhospitable conditions for the average caveman. The environment still affects the ability to move even up to today's world (especially in the more developing countries without planes, trains, long distance travelling boats and whatnot). So a transition from an environment rich in oxygen to one rich in say, sulphur, will certainly hinder the movement of life (intelligent or not).

I believe where two completely separate alien environments interacted you would have a natural barren plain where either no life exists or life slowly evolves from the zoo species to create specialised breeds who can survive in this new barren zone (that might not be so barren anymore, if you forget to weed). It is in this area that you could have some alien technology to help maintain the environmental conditions of each 'enclosure'. So you would be able to keep lifeforms from various planets separated into areas where they share the same life-sustaining environments. It is these situations where there is a potential for society interaction.

If you want a more developed societies such as middle-ages/ renaissance/ even the beginning of the industrial revolution you can do what Rome and the Chinese empires did. They interfered with the smaller neighbours and created conflicts and played the neighbouring clans against one another. You just have to avoid any person/alien from uniting the fractious clans (races) into one big super clan like Genghis Khan did in Mongolia. Or even more recently, the African National Congress did in overthrowing the Apartheid Nationalist party.

The ANC temporarily put aside tribal conflicts and blood feuds (and hatred for the 'other') and formed a coalition with a single goal, with the mainly Zulu Inkarta party, and the mainly Khosa and Sotho ANC party (and other smaller tribes and political groups). This coalition is now breaking apart as there is nothing to keep the separate tribes and vastly different political groups aimed at a single goal anymore. But keep in mind here, that the ANC only overthrew their 'overlords' they did not expand. Genghis Khan and his sons not only overthrew their 'overlords' he incorporated captured technology into his own society's way of life and expanded over most of Asia, China, Russia, and all the way into Europe (I think they got all the way to Vienna!). This would severely limit the safe movement of your tourists — if they were viewed as a threat (Ghengis did have a policy of free-movement regardless of race/religion as long as your paid tribute in taxes etc.) It would also mean that if some races found away to travel to the different enclosures in your zoo that they could kill a vast majority of your rare and captive organisms, which could take eons to replace as you travelled through the universe (the world population growth rate actually dropped to zero due to Ghengis's expansion into other territories)

So you can have a really developed 'intelligent species' if you require, as long as you foster pride, ego and tribal/nationalistic tendencies. This will limit the movement of one race moving into the territory of others for fear of reprisals and war.

How would your tourists move around freely. You could have them viewed as gods, or some sort of exclusive priesthood. Your captive populations don't even have to agree on who the tourists are as long as they revere or fear them (ie leave them alone at all costs). So you could have one group think they are gods, and another who think they only priests, another who thinks they lepers. whatever...

Another option, your tourists obviously come from a very advanced society, you could have some sort of camouflage tech. So that the tourists look like local population in one area, and then when they move onto the next area they look like the next population. This would probably give your tourists a kick, as who doesn't like to act like the 'noble savage' every once and awhile or two.

And if your intelligent species acts up a little to much, develop a little too far for your health and safety protocols, you simply disrupt their way of life. A plague here, and murdered leader there, a 'valid' experiment gone catastrophically gone wrong here, a slight climatic adjustment there, will stop and even potentially reverse any unwanted developments.

  • $\begingroup$ Sorry, I think I went off on a tangent there! answered more the last part of the question than the enclosure side of the question. $\endgroup$ Jun 26, 2016 at 14:22
  • 1
    $\begingroup$ Particularly if you feel that you went off on a bit of a tangent, but the answer is still relevant to the question, then it might be worthwhile to emphasize the part of your answer that you feel most directly answers the question. This works best if that part can be summed up in one or at most a few sentences; just **boldface** those. Partial answers are also potentially valid answers, but they might not be as well-received as answers that fully cover all aspects of the question. $\endgroup$
    – user
    Jun 26, 2016 at 20:14

One possibility is to borrow the "maps" from Larry Niven's Ringworld.

The base of your zoo is a massive ocean; mind-boggingly massive. In the areas set up as one exhibit, there are continents, islands, seas, etc. Within this area, migration would be as normal for a planet.

You separate this "exhibit" from others by the massive ocean with no surface features of any kind. The land creatures are prevented from migration from one area to the other.

You could similarly create some kind of shallow/rocky zone out in the massive oceans to separate different water exhibits.

Your powerful civilization could also set it up so that currents are maintained to isolate each zone and oxygen (and other respiratory gas) dead zones can be used to further separate the areas.

  • $\begingroup$ Nivin's maps are on a different scale as I recall Ringworld was a million miles wide. Even so, I expect sealife would spread across his maps without some additional mechanism to contain things. $\endgroup$
    – JDługosz
    Jun 30, 2016 at 0:51
  • $\begingroup$ Hmm, toxic gas might be a good barrier. But how to keep it, and variations in atmosphere, contained? $\endgroup$
    – JDługosz
    Jun 30, 2016 at 0:54
  • $\begingroup$ I think the maps were simply flat, to-scale, projects of other planets. The size of the Ringworld gave them plenty of room to place many such maps and still leave enormous open ocean gaps between them. There would likely be little migration of into these wide oceans, as a lack of land forms would prevent upwellings of nutrients, especially if currents were artificially maintained around the exhibits and dead-zones were maintained away from them. $\endgroup$ Jun 30, 2016 at 15:43

Zoo keeping business isn't a simple task, especially when it get about keeping species from different planets. With intelligent$^1$ creatures you may have conversations and deals, not the case with other creatures, which are most the business because they are 99.9999... % of all creatures, and are the most interesting case because of their diversity, and fewer ethical obligations and easier to fulfill all of them. As being good CII, I assume OP talks about ordinary creatures only.
$\tiny \text{(1) Strongly do not recommend keeping intelligent creatures against their will for exposure. Even God didn't.}$

First of all, you have to understand that this is a complex problem, which you have to solve. Also probably, the first priority isn't entertainment, but the understanding of ecosystems of such planets. In case CII already knows anything possible about ecosystems, there are other ways to implement the system. I suggest one possible solution, considering research and keeping samples is the primary goal. Entertainment is second.


Build a full replica of each ecosystem for each planet. You may start with simpler tasks by building ecosystems for some regions. Building such systems will enrich knowledge about planet's and their ecosystems, about species and will have scientific value to do, and be more useful in technologies development etc.

Each region ecosystems is one space habitat, so thing, which will divide them is space, and probably for some special cases and as for whole, high temperature, high density, high energy plasma. This will prevent any possibly biological danger of contamination regions between themselves and the star system where they are in.

It will eliminate any possible eruption, the breakthrough of biological samples of any sizes, giga-, mili-, micro-, viruses etc.

Sub habitats

They are for species, and systems where you keep selected samples, in combinations you need or for testing combinations, determine how they affect each other etc. These places are not a replica of original ecosystems, but more places where you design them, refine samples from some diseases, make a selection of them, combine them, make the controllable environment - a lot of things happening there.


After testing and refining are done, and you have desired combination you like, you clone that setup to actual exposition. And in that clone setup, ordinary visitors are allowed. If intended or not, they will destroy that composition, you have the backup, and probably a new interesting or not composition.


Sub habitats are sources of creatures for your captivity content. For those you know is safe to keep that way. At least you will have more control over the level of danger you wish to have.

As a result

A bunch of space habitats, probably hundreds and more per planet, to store and work with. And some exposure habitats.

One 100km diameter habitat, offers plenty of space to clone most of the possible ecosystem regions, but if you need it could be done planet size (by size, but not by mass) As example, some birds travel 12000 km migrations and that travel and distance are important for their species, so you may expect such need like planet size habitat system.

So you will have a set of planet ecosystem, region ecosystem, a bunch of refining testing ecosystems, masterbatch ecosystem, zoo ecosystem, captivity keeping systems.

This way you may have a system of any scale, and for how many planets you like.

A form of habitats is a cylinder, in case if you do not have gravity generators. Axis may be another cylinder, where all transportation system is, places to live, windows for bird high watch, transportation systems direct to the wild, small zoos etc.

  • $\begingroup$ Suggest you read Alastair Reynolds' PUSHING ICE as you've invented something similar to his alien collection zone, but yours has interesting differences. $\endgroup$
    – a4android
    Jul 23, 2016 at 8:31

A K-II civilization would not create a planet with species from different planets on it. They would give the species from each planet a near exact (defects such as stars about to nova fixed) copy of the planet of origin to inhabit. As such species from different planets would be isolated by at the very least several astronomical units of space. Reasonably such a zoo would require several star systems to hold all the planets, so in some cases the separation would be light years of interstellar space.

This might seem inconvenient to us, but a K-II civilization would not really see interstellar distances as an issue, if they help in providing better conditions to the exhibits. And if somebody is in a hurry, I refuse to believe a K-II civilization is not capable of adequate virtual reality. Or even telepresence. A K-II civilization might require super-science such as FTL travel and communications anyway.

  • $\begingroup$ Good point, but not the story I have in mind. Adventurers running around exploring type formula. $\endgroup$
    – JDługosz
    Jun 27, 2016 at 4:51
  • $\begingroup$ @JDługosz Figured, but still wrote it up since it might be useful as a reminder of the ways a K-II would be different from us and how it would show. Maybe you could tone down the alien tech level or use some "indistinguishable from magic" system to link the planets? With some visitor pass... cough cough... "magic amulet" to give access to the transport system. It would be an issue to give the transport system the right feel for your idea, but otherwise it should work. $\endgroup$ Jun 27, 2016 at 7:32
  • $\begingroup$ It also needs to be portable… I think it is more a work of art. $\endgroup$
    – JDługosz
    Jun 27, 2016 at 8:24
  • $\begingroup$ Like, I just saw a video on building a music box in Woodworkers' Journal. Why would that exist when our civilization is capable if near-magic sound reproduction of symphonies? That explains why it's moving through our galaxy: the builder sent it out to make others see it. $\endgroup$
    – JDługosz
    Jun 27, 2016 at 8:27
  • $\begingroup$ @JDługosz Neat concept. But I think anything this extensive, even a single planet, would be unstable if travelling between different solar systems. Interactions by gravity or light between the zoo and the systems visited might be real issues. Since I already proposed using wormholes between exhibits it would make sense to have entry points to the zoo all over the galaxy. Analogy really would be "come see the greatest music box museum of all", not "see our cool music box". While exhibits travel, museums usually do not. They just build good connections and advertise. $\endgroup$ Jun 27, 2016 at 19:42

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