Human-supporting ecosystem on a permanently dark planet?

Factual Questions
1

Like many Dopers, I occasionally write fiction, and recently I’ve been fiddling around with a large number of partially-written stories that I began working on years ago, trying to see if one of them grabs my interest again.

One of the stories involves a human colony living on the semi-terraformed moon of a gas giant that is drifting through interstellar space. The idea is that somehow, this Jupiter-type world was ejected from its parent star (or whatever) and ended up being flung out into interstellar space. The moon that humans colonized is somewhat Europa-like, but has some dry land; it’s heated by tidal friction and it started out with an ocean of liquid water covered with a miles-thick ice sheet, but now has a breathable atmosphere and a survivable, if not exactly warm, environment. And obviously it’s night all the time, there being no star to provide light.

But looking over this, I’m wondering if an ecosystem on such a planet would even be possible. Since there’s no parent star, there’s no light, and obviously a food chain based on photosynthetic organisms isn’t going to work, so farming of the kind we’re used to wouldn’t be viable.

(I guess you could use artificial lighting of some kind to grow traditional earth-style crops, but the logistics of providing enough artificial light to grow the amount of plant material necessary to feed a sizable human population seem quite daunting, and expensive.)

I know there’s chemosynthetic organisms in the “black smokers” at the bottom of the ocean, which form the basis of a food chain there – essentially forming an ecosystem that extracts energy from the heat left over from the Earth’s formation rather than the sun like the rest of us.

But would that kind of thing be transformable into an agricultural system that could feed a decent-sized human population? Obviously it’s a lot harder to practice agriculture if the only place you can grow your food is around jets of 700-degree water that are miles deep in the ocean. Could the bacteria that form the basis of the geothermal-based food chain be used to form the basis of an ecosystem on land, or at least in shallow water or lakes or something?

Um … I think I had other questions along these lines, but I can’t remember at the moment. If I do, I’ll post them later.

Any responses would be greatly appreciated, and if I ever publish anything I’ll list y’all in the “My Deepest Gratitude” part at the beginning of the book.

2

There could very well be chemosynthetic life at the bottoms of the oceans, such as is hypothesized might exist on Europa. But I highly doubt that any such life, even if it were imported from Earth’s seas, would be edible or nutritious to humans.

Artificial lighting, on the other hand, wouldn’t be nearly as daunting as you fear. Yeah, it’d take a lot of energy, but I think you can safely assume that your colonists have developed controllable fusion before settling outside the Solar System, and a water moon will have an abundant supply of hydrogen for fuel.

The big question is going to be that breathable atmosphere. The only natural process which can produce significant amounts of elemental oxygen is photosynthesis, and without some means of continually replenishing that oxygen, it’ll quickly combine with anything and everything in the environment. So even if your world once had photosynthetic life, before it and its parent planet got ejected, there won’t be any oxygen left once the colonists get there. So you’ll either have to terraform the world, or keep your humans cooped up inside domes.

3

Thanks for your reply, Chronos. I greatly appreciate it.

How come? Poisonous metals or something? Are the giant tube worms and crabs and whatnot that live in the black smoker ecosystems inedible for some fundamental reason, or are they just poisonous because of the black smoker minerals they consume, or …?

Good point. So assuming plenty of available energy, there’s nothing preventing the growing of crops by artificial light – even enough to feed a population of millions? (Assuming that you have to supply the light in a manner similar to how we grow with artificial light here, that is – not with some kind of orbiting artificial sun or something.)

Well, when I said “semi-terraformed” in my OP, I meant that the breathable atmosphere was created by terraforming machines before the human colonists arrived, but it isn’t as warm as Earth, there’s no artificial sun, etc… (One thing I’m wondering about is nitrogen – is there enough nitrogen on a place like Europa to form a breathable atmosphere? I don’t think a 100% oxygen atmosphere would be a good thing.)

Also, I remembered one of the other questions I had. Would the revolution around the parent gas giant significantly affect the surface gravity on a moon like this? Assuming that the moon revolves around the planet at a fairly quick pace, like 12 or 24 hours or something, and it’s orbital radius is, oh, say, 500,000 km, and the gravity is similar to Europa’s (about 0.13 gees), would a person’s weight change significantly when standing on the equator facing away from the parent planet vs. standing on the equator facing towards the planet? I remember calculating things like this in Physics 101, but that was a long time ago.

4

Before, I venture an answer, tell me…

Through what timescale is this ecosystem supposed to be sustainable? Are we talking about 5 or 500 or 50,000 years? Or what?

Also, was the colony established on an already adrift gas giant’s moon, or did the colony survive some kind of a disaster that sent the gas giant away from its star? IOW did they plan for this environment or are they castaways?

5

I would disagree with this. I don’t see anything intrinsic about geothermal vent life that would make it inedible. I suppose it might be a little sulphurous, but you might be able to process that away.

6

Well, indefinitely, if possible. Billions of years. Nobody wants to die out, so presumably they’d try to set up an ecosystem that’s sustainable indefinitely.

Whatever it was that sent the gas giant out into interstellar (and eventually intergalactic, incidentally, since it’s traveling up out of the the galactic plane), it happened a long time ago. The human colonists found the wandering planet by accident, and settled the moon for a number of reasons: being paranoid types, they wanted to separate themselves from the rest of humanity permamently, and decided to hide on a planet far from a star, where they would be looked for (if anybody was looking for them); also, they wanted to avoid the dangers and annoyances inherent in living around a star, like climate variations, seasonal variations, radiation, solar flares, eventual death when the star goes nova / supernova / bloats into a red giant and kills you / whatever, etc.

7

Interesting, as I can see the story going a couple of ways…

They are some kind of religious cultists who are little better prepared beyond having correct change for the mothership…

Or they are geniuses fleeing a galaxy of mutton heads.

I will do some more pondering on this.

8

In addition to lighting, the Sun also provides essentially all energy that drives the Earth’s meteorological and hydrological processes; without this, there is no natural distillation and filtering of fresh water, no seasonal variations, no wind and wave activity necessary to many forms of life for transportation, food collection, and reproduction, et cetera. You’d also lose the day/night cycle which helps to moderate the body’s circadian rhythms; these may not be utterly necessary to the life of any individual organism, but disruption of them will probably have massive and unforseen consequences on the ecosystem as a whole, interrupting growth and reproduction cycles. It should suffice to say that any life dependent upon photosynthetic processes is going to have to be artificially illuminated at great cost (in terms of energy budget).

So even if you could generate sufficient heat from, say, tidal hysteresis or radioactive decay, you’re still not going to get the overall effect of solar illumination. You might be able to set up enclosed habitats that would be sufficiently self-sustaining to be considered a closed ecosystem (though doing so is going to require knowledge and feedback technology that is well and beyond anything we currently possess) but the overall planet isn’t going to have anything like a sustainable terrestrial ecosystem.

However, since your forest-moon is orbiting a gas giant, I should make note that there is another option. See, there’s this trick you can so with self-replicating universal constructors in the form factor of a black monolith with the sides measuring the ratio of the squares of the first three prime numbers…

Stranger

9

LOTS of sulfur. Supposedly, black smoker organisims that have been retrieved for dissection are very stinky. Gag-worthy. So much so that the folks doing dissection wear gas masks. A lot of chemosythesizing bacteria produce hydrogen sulfide, which is poisonous to humans (and many other life forms)

Even where these critters aren’t outright toxic, the aroma is probably so horrible that they are essentially inedible. Add to that the very different chemistry from what we’re accustomed to in edibles and this is “food” that will require a LOT of processing at best.

Of course, by some quirk this alien planet may be low in sulfur. Or the food critters genetically engineered. Or the humans genetically engineered to tolerate the stuff.

As long as you have enough energy to supply the lighting system, there’s no reason you can’t do this. Artificial lighting is already used in farming in our own civilization, both for animals and hothouse food crops.

You are correct, aside from the fire hazard (EXTREME!) of a 100% oxygen atmosphere, long-term high concentrations of oxygen can damage tissues and cells, particularly the retina.

Strictly speaking, you aren’t restricted to nitrogen - there are a several gases that would serve. Helium, for example, is mixed with diving gases for deep sea work, and might be readily available from the nearby gas giant. Humans also do not require Earth sea-level pressures, so by reducing the air pressure to that of an equivalent of, say, 10,000 feet above sea level on Earth you’d significantly reduce the amount of gas required without adversely affecting human health. Over time, of course, the residents would likely become more and more adapted to the conditions on top of that.

10

Well, they feed off of hydrogen sulfide, which is just as bad. Hydrogen sulfide is quite toxic to humans (Hydrogen Sulfide Toxicity: Practice Essentials, Pathophysiology, Etiology), and the benthic organisms that survive off of it are likely to be toxic through much of their body tissue - although it’s possible that some parts of the body might be edible (most of these organisms have both means for detoxifying the hydrogen sulfide in their body and sequester the bacteria that perform the chemosynthesis in certain parts of the body - such as the trophosome of pogonophoran worms, for example), it’s unlikely that much will be either edible or palatable.

But then how does the chemosynthesis take place? On Earth, chemosynthesis takes advantage of the oxidation of hydrogen sulfide to sulfates.

These are both really good ideas.

Another possibility is that humans might eat further up the food chain. I don’t know if anyone’s ever tried to eat the fish or isopods that hang out in hydrothermal vent environments (I doubt it. Ick!) but those might be edible. Especially the detritivores that live off the decomposition in that environment might have a lot less hydrogen sulfide than other organisms in the ecosystem.

11

I really can’t imagine terraformers dumping expensively produced oxygen out into the atmosphere of the moon.

These people are going to be living in the equivalent of a space station, with a gigantic chunk of ice attached for raw materials. Every biological process will have to be controlled. There doesn’t seem to be any hope of an uncontrolled ecology, because every plant has to be provided with artificial light, and therefore there can never be enough plants to provide enough partial pressure of oxygen for people to walk around in the open.

Not to mention the surface temperature. What’s the surface temperature of Europa? Even with IR from Jupiter it’s damn cold, and that’s with quite a lot of radiation from the Sun. Remove the Sun, and what’s the temperature? You might be warm enough to have gaseous oxygen and nitrogen, but certainly you’re not going to get liquid water on the surface. And if you can’t get liquid water, there’s no hope for plant life, even with artificial light.

So you’ve got to grow plants in enclosures, with artificial light and heat. With good insulation the lighting can double as the heating. But once you’ve got enclosed farms, why vent the oxygen, when there’s no hope that humans can walk around unprotected anyway? In many ways, near vacuum would be a lot easier to work in than an extremely cold oxygen/nitrogen atmosphere. Atmosphere means people freeze to death through convection even in space suits, near vacuum means people can walk around on the surface in space suits. Oxygen is corrosive. Atmosphere means winds, storms, freezing out of various volatiles as “snow”, melting of volatiles, all kinds of problems.

12

From what I know of hydrothermal vent communitees, you ain’t gonna get food out of that environment without a lot of intermediate steps between you and the vent. (Living off of the creatures that eat the creatures that eat the creatures that eat the creatures that eat the creatures that eat the creatures that eat the creatures that live on the chemosynthetic organisms. - I may have left out a couple of steps.) The problem is getting stuff that has the right kind of metabolism - i.e. is able to live in an oxidizing atmosphere, and having plenty of oxygen handy.

If I were running this planet, I would use the energy (thermal and chemo) of the vents to run bacteria colonies, combine the resulting byproducts with natural resources nearby (perhaps the surface conditions are so cold - It would have to be really cold - you have methane and ammonia deposits on the planet?) If your fusion technology is up to par, you could use fusion to generate electricity to separate the oxygen from the hydrogen, use the hydrogen as a fuel, and use the oxygen to breathe & feed the algae / yeast / hydroponic farms. The only minor quibble here is that fussion technology is a current “holy grail.” However, if it develops as we hope it might, it could be the “magic technology” that you need to make your colony sustainable. However, you will be using up the water to power your fusion reactors, so this is not an infinetely sustainable option. But it will be stable for long enough to (hopefully) develop the next magic technology. (Harvesting the energy in Cosmic Radiation, maybe? Quatnum Foam Energy Machines?)

Also, you might have trouble with the land being stable. If there is enough of a tidal difference in the gravitation and magnetic fields of your GG to keep the water liquid, the land itself will be under constantly changing tidal forces and will most likely have exposed land looking like IO. (I think that’s where the energy of the hydrothermal vents comes from on Europa.)

13

Nothing is an infinitely sustainable option. You can’t win, you can’t break even, and you can’t get out of the game. But it would take a heck of a long time for a small human colony (say, a million people or so) to use up an entire world’s worth of ice: Probably significantly longer than the lifetime of a star. And fusion may be a Holy Grail to us, but I have to imagine that we won’t be sending out any interstellar expeditions until we have it, so chorpler should take it for granted in any interstellar story.

On the atmosphere question, Heinlein, in a few of his stories, posited an atmosphere of 100% oxygen, but at the same partial pressure as on Earth. Humans would have to acclimate to it slowly, of course, to let internal pressure equalize to external, but is there any reason that wouldn’t support human life? If the partial pressure is the same as Earth’s, I don’t think the fire hazard would be any worse, either.

14

Also, they’ve got a whole gas giant nearby they can “mine” for hydrogen.

My suggestion is leave the terraforming machines running. Use self replicating robots, that convert the moon’s water to oxygen and heat, and use some of the energy to synthesize chemical nutrients that the genetically engineered plants can use instead of sunlight to power themselves. That’s if you want the planet to be in permanent night. Paranoids like you describe might want that.

Or, you could have the replicating machines build a world-covering “forest” of artificial lights, and a worldwide electrical network to go with it. An advanced society will have replicating machines, almost certainly, and that sort of thing won’t be hard for them.

15

Well, at that point why even bother with plants? If you’ve got the technology to create machines that do nothing but produce hydrogen sulfide for chemosynthetic bacteria to consume, so other organisms can eat them, so others can eat them, and so forth, why not simply synthesize glucose from inorganic carbon and feed the glucose to standard bacteria, yeasts, and so forth?

If we’ve got the energy and manufacturing capablity to cover the entire moon with fusion powered full-spectrum streetlights, then we can do pretty much whatever we want, and terraforming the moon becomes a trivial exercise, just throw energy at whatever problem you have. But why bother creating an ecosystem then? And it seems like it makes no sense to cover the entire planet with streetlights and not roof the whole thing over at the same time. You’d need less oxygen and CO2 by several orders of magnitude, you don’t have your spare heat radiating out into the universe. Which was my point…at this level you are essentially creating a self-sufficient space station that just so happens to have a giant iceball nearby you can use for raw materials.

16

Quibble:
Oxygen will not feed your algae, it would be produced by it. Sounds like nuclear techs of some kind are going to be your baby. Given enough fissionable material you can create tons of power comparitively inexpensively.

Sounds like a question for UnaPerson, shes the resident electrical power systems guru.

17

A partial pressure of 0.5 bar is generally considered the threshold for sustainable respiration without risk of oxtox (oxygen toxicity). At Earth-normal partial pressure (~0.21 bar) the atmosphere wouldn’t be more reactive in a combustive sense; however, at least for organisms, there would probably be a greater accumulation of oxygen via respiration, even with the same nominal concentration. This may have some long term neurological and respiratory implications; also, the relative thinness of the atmosphere would confer both less ability to convect away heat and less retained heat in the atmosphere; not a big deal in a sealed environment where the temperature can be readily controlled, but problematic in an open environment where temperature swings from even a modest amount of heat may be dramatic.

Controlled nuclear fusion, or some exothermic reaction even more energetic, is almost a fundamental assumption of interstellar travel, both for propulsion and for energy generation. Without it you can’t either achieve sufficient specific impulse to get up to interstellar speeds (even assuming millenial length transits) nor provide a credible amount of energy required for total environmental support. (For D-T fusion you’re also going to have to include facilities to “breed” tritium from lithium and waste neutrons, since it decays rapidly.) You can certainly provide sufficient energy for any enclosed habitat indefinitely with the amount of deuterium found in even a moderate sized icy moon; indeed, your difficulty might be in radiating away waste heat. Providing energy for an entire world, however (especially if you radiated it spherically into space as an artificial star) might burn through fuel far more rapidly.

Stranger

18

Because people like plants. I’m operating under the assumption that they want as close to a natural environment as possible, or else they’d have just built orbiting habitats.

19

Thanks for the replies, everybody. I’ll reply more when I get a chance.

Yes, and the universe this takes place in also has technology that either pulls energy right out of the quantum foam, or converts matter directly to energy – I haven’t decided which one I want to go with. Or whether these colonists will have the technology. They certainly have fusion at a minimum, though.

Yeah, the permanent night thing is one thing that I’m shooting for. I haven’t yet decided if I’ll go with permanent cloud cover as well – pumping the atmosphere full of water vapor and creating a thick cover of clouds should be good both for hiding the surface and for keeping heat in, right?

As for leaving the terraforming machines running: the initial terraforming was done thousands of years ago by automated probes, and these colonists don’t have that particular technology. They’ve got energy-producing technology, and other advanced technology, but not the self-replicators and other equipment that was used in the terraforming. I don’t want to give the plot away in case it ever gets finished and anybody here wants to read it (riiiiiiiiiight), but they’re something like refugees.

Unless, of course, they HAVE to have them to survive, i.e. there’s no way to create a food chain that humans can live off of from geothermal energy and no way to feed a large population from artificial-lighting-grown plants. Which is one of the reasons I started this thread – to find out whether it was feasible. And apparently the second option, at least (growing earth-type crops with artificial light) is not implausible, if you have enough energy.

I’m still concerned about the neutral gas (nitrogen or whatever) that should be used for most of the atmosphere. Obviously you could produce oxygen, hydrogen, and water vapor from the ice/water, but would there be sufficient nitrogen on an icy moon to create an earthlike atmosphere? Helium is an option, I guess, but wouldn’t that make everybody sound funny, like in Sphere? (Yeah, I read Sphere … and I actually thought it was great. What can I say? I was young and foolish!) And more importantly, wouldn’t it escape into space? If it does so on Earth, I can’t imagine it would be able to make up a long-term component of a Europa-sized moon’s atmosphere without being continuously produced.

And … uh … oh yeah. Don’t plants also need nitrogen?

20

Thanks for this info, Stranger. So assuming there’s an Earth-normal partial pressure, a 100% oxygen atmosphere is not toxic, and though there may be some problems eventually (pulmonary edema? Brain damage?) it would probably take a while to show up? That actually wouldn’t be much of a problem, because of the particulars of the story … assuming it took a few decades to show up, and not just a few years.