Human-supporting ecosystem on a permanently dark planet?

Factual Questions
21

[QUOTE=chorpler]
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.
[/QUOTE]
Well, if you like you could have the machines there, but beyond the colonists ability to control or understand. For example, you could have a more advanced civilization ( human or not ) that sent forth probes centuries or millenia ago that wander the galaxy, dropping terraformers on lifeless planets, many or most of which have no inhabitants. That sort of seeding-the-galaxy thing has actually been proposed, so it’s not that unlikely a scenario.

22

But you don’t need an O2 only atmosphere, we know Titan’s atmosphere is mostly N2 at about 1.5 atmospheres, so your iceball moon could have such a thing too, even before the manufacture of 02. And even if it didn’t have gaseous N2 to start with, if you can manufacture 02 you can manufacture N2 as well. Your standard iceballs are going to have plenty of water (H20), methane (CH4), and ammonia (NH3).

But the big problem isn’t manufacturing 02, it’s keeping your planet from freezing. Titan is about -300F, and that’s with the Sun providing a lot of energy.

Take a look at these articles:

23

[QUOTE=chorpler]
And … uh … oh yeah. Don’t plants also need nitrogen?
[/QUOTE]

They do, but relatively few plants get their nitrogen from the atmosphere. Some plants (like legumes) have symbiotic bacteria that fix nitrogen from the atmosphere and provide it to plants, but more get their nitrogen from soil.

What would the nitrogen cycle on a world with little or no atmospheric reservoir of nitrogen look like? I don’t know. But you could do without a nitrogen atmosphere if the plants have another source of nitrogen.

24

[QUOTE=Lemur866]
But you don’t need an O2 only atmosphere, we know Titan’s atmosphere is mostly N2 at about 1.5 atmospheres, so your iceball moon could have such a thing too, even before the manufacture of 02. And even if it didn’t have gaseous N2 to start with, if you can manufacture 02 you can manufacture N2 as well. Your standard iceballs are going to have plenty of water (H20), methane (CH4), and ammonia (NH3).
[/quote]

Ammonia! Of course! And that’s a good point about Titan; it’s got about the same gravity as Europa, but with a giant 98% nitrogen atmosphere. OK, it seems nitrogen won’t be a problem.

But the big problem isn’t manufacturing 02, it’s keeping your planet from freezing. Titan is about -300F, and that’s with the Sun providing a lot of energy.
[/QUOTE]

But Titan’s atmosphere gives it an anti-greenhouse effect too, right? With an atmosphere of the right composition and size, would it be possible to retain internally generated heat (from, say, volcanoes due to tidal flexion, or whatever) enough to make the environment survivable, if not comfortable? Like, somewhere above the freezing point of water?

25

[QUOTE=Der Trihs]
Well, if you like you could have the machines there, but beyond the colonists ability to control or understand. For example, you could have a more advanced civilization ( human or not ) that sent forth probes centuries or millenia ago that wander the galaxy, dropping terraformers on lifeless planets, many or most of which have no inhabitants. That sort of seeding-the-galaxy thing has actually been proposed, so it’s not that unlikely a scenario.
[/QUOTE]

Yeah, that’s basically what terraformed the planet – the kind of galaxy-seeding machines you’re talking about. And that first part is a good idea – heck, if the terraforming machines are nanomachines of some kind, they might not even know they’re there. I’ll have to think about this some more.

26

[QUOTE=chorpler]

But Titan’s atmosphere gives it an anti-greenhouse effect too, right? With an atmosphere of the right composition and size, would it be possible to retain internally generated heat (from, say, volcanoes due to tidal flexion, or whatever) enough to make the environment survivable, if not comfortable? Like, somewhere above the freezing point of water?
[/QUOTE]

Yes, Titan has an anti-greenhouse effect. But a greenhouse effect only works when you’ve got a radiation source. Visibile light penetrates the atmosphere, hits the surface, and reradiates as IR, except the atmosphere is opaque to IR and the IR is reabsorbed.

But you don’t have a source of visible light to be trapped, since your moon doesn’t have a sun. Sure the moon might be getting IR from the gas giant, but that’s not going to help.

And even then “above the freezing point of water” is HOT when your planet/moon is radiating energy out into 3K interstellar space. If there is no atmosphere the temperature of the surface doesn’t mean that much. But if you have one your atmosphere is going to be DAMN cold. Not Antarctica cold, not Mars cold, not even Titan cold, because Titan still gets quite a bit of energy from the Sun. Colder. Titan gets energy both from the Sun and from Saturn, but your moon won’t get any solar energy. Water melts at 273 Kelvin, and expecting your planet to be warmer than 100 Kelvin is unreasonable.

27

Why not change your gas giant planet into a brown dwarf? Let it be arbitrarily old, such that its temperature is down around, say, 700 K, and have your moon orbit closely enough so that the dwarf fills a respectable percentage of the sky. I would imagine that you could tweak the numbers such that the average temperature would hover well above 273 K. The brown dwarf would be radiating in the infrared, to be sure, but not in wavelengths that could be used by earth plants or be seen by earth eyes. I’ll leave the math up to someone else.

28

[QUOTE=Lemur866]
Yes, Titan has an anti-greenhouse effect. But a greenhouse effect only works when you’ve got a radiation source. Visibile light penetrates the atmosphere, hits the surface, and reradiates as IR, except the atmosphere is opaque to IR and the IR is reabsorbed.

But you don’t have a source of visible light to be trapped, since your moon doesn’t have a sun. Sure the moon might be getting IR from the gas giant, but that’s not going to help.
[/QUOTE]

Shouldn’t it also trap IR radiating from the moon itself? I mean, if it is hot enough from tidal flexion?

29

One could design an ecosystem that could work, if you think a little big and fantastic- I’m thinking of the geothermal-tapping metallo-organic “drill trees” from Brin’s Startide Rising - a variant of these:
they tap into the core tidal-produced heat, kilometres down, maybe also utilise the strong magnetic flux outside the atmosphere with accessory gas pods like vine-tethered blimps. As a side process of their metabolism, they produce waste oxygen and radiate excess energy as light from their 500m-high “crowns”. A *lot *of light. “TWo Trees” levels of light. And these giant primary producers are surrounded by a dependent ecosystem of photosynthesisers and associated fauna.

30

[QUOTE=chorpler]
Shouldn’t it also trap IR radiating from the moon itself? I mean, if it is hot enough from tidal flexion?
[/QUOTE]

Sure, but look at the moons we know of in our solar system. All of them are damn cold, despite being both near a gas giant and a sun. So any typical moon around a gas giant that doesn’t have a sun nearby we can expect to be even colder. At least if we’re talking about surface temperature this is well below 273K.

Even if you have some process that transfers energy from the core to the surface, or fusion reactors to provide heat, you’re still radiating that heat out into the 3K universe every second. You’re going to lose a lot of energy that way. Keeping your 273K volitiles insulated from the 3K universe makes a lot of sense, which means you want to have your biosphere under a roof of some sort.

31

[QUOTE=Lemur866]
Sure, but look at the moons we know of in our solar system. All of them are damn cold, despite being both near a gas giant and a sun. So any typical moon around a gas giant that doesn’t have a sun nearby we can expect to be even colder. At least if we’re talking about surface temperature this is well below 273K.

Even if you have some process that transfers energy from the core to the surface, or fusion reactors to provide heat, you’re still radiating that heat out into the 3K universe every second. You’re going to lose a lot of energy that way. Keeping your 273K volitiles insulated from the 3K universe makes a lot of sense, which means you want to have your biosphere under a roof of some sort.
[/QUOTE]

Thanks for all the info you’ve posted so far, Lemur. It’s given me a lot to think about. I was already planning to put the growing factories (or whatever they’re called – the places where they grow plants using artificial light) underground; maybe the whole civilization will go underground.

Is there ANY atmospheric/orbital configuration that would be both human-survivable and that could warm the moon up to, say, Antarctic temperatures? I have no problem with the terraforming machines doing something like pushing tidal heating to its limit by increasing the eccentricity of the orbit (but not enough to rip the planet apart) and adjusting the atmosphere to trap as muich heat as possible. But perhaps there’s just no way to do so without a Venus-type atmosphere that would presumably be lethal to humans, and maybe not even then.

(At least not without invoking some kind of Maxwell’s Demon that violates the laws of thermodynamics by keeping all the warm air near the surface of the planet, or something.)

32

Well, there’s nothing impossible about building a fusion reactor that does nothing but take in water ice and spit out hot oxygen and hydrogen, although we’d need to sequester the hydrogen somehow rather than dump it into the atmosphere. It’s just incredibly wasteful because most of the energy from that fusion reactor uses to warm up the oxygen radiates back out into space. A fusion reactor that pumps that warm air into an insulated space is much more efficient.

An analogy would be the efficiency of keeping warm by building a giant campfire outside on a cold night compared to building a small fire in a woodstove in an insulated cabin. You’re going to need much more fuel to keep warm with the outside campfire, and you need to keep adding fuel all the time. Or compare it to heating a small cabin with the door closed or the door open. You need a lot less firewood if you simply keep the door closed.

If we imagine a society that has the resources to run giant fusion reactors just to produce a warm atmosphere, that society is going to be so wealthy that it’s hard to imagine what they couldn’t do. But such a technologically powerful society wouldn’t be that interesting to write about, they aren’t refugees hiding on a frozen moon. If you could warm up enough air to heat the whole planet there’s nothing you can’t do, and terraforming the moon is just a stunt for these people, they could live anywhere.

33

[QUOTE=Lemur866]
Well, there’s nothing impossible about building a fusion reactor that does nothing but take in water ice and spit out hot oxygen and hydrogen, although we’d need to sequester the hydrogen somehow rather than dump it into the atmosphere. It’s just incredibly wasteful because most of the energy from that fusion reactor uses to warm up the oxygen radiates back out into space. A fusion reactor that pumps that warm air into an insulated space is much more efficient.
[/QUOTE]

So, barring some kind of Maxwell’s Demon, or some kind of physical shell that encloses the lower layers of the atmosphere, there’s no way to keep internally-generated heat from radiating back into space for a long enough time to warm up the atmosphere a few hundred kelvins?

34

[QUOTE=chorpler]
So, barring some kind of Maxwell’s Demon, or some kind of physical shell that encloses the lower layers of the atmosphere, there’s no way to keep internally-generated heat from radiating back into space for a long enough time to warm up the atmosphere a few hundred kelvins?
[/QUOTE]

Nobody has done any rigorous work on it, but in theory you can simply put a cloud of finely crushed mirrored glass or similar material into low orbit. That will reflect almost all the heat back onto the planet creating a massive greenhouse effect. It’s not useful for planets close to a star because it would cut most of the incoming radiation as well, but since that isn’t an issue here it should work. It’s a device that’s been used in sci-fi stories before today. Of course the dust blanket will need to be topped up periodcially, but it will still be cheaper than trying to warm the atmosphere without it.

35

[QUOTE=Blake]
Nobody has done any rigorous work on it, but in theory you can simply put a cloud of finely crushed mirrored glass or similar material into low orbit. That will reflect almost all the heat back onto the planet creating a massive greenhouse effect. It’s not useful for planets close to a star because it would cut most of the incoming radiation as well, but since that isn’t an issue here it should work. It’s a device that’s been used in sci-fi stories before today. Of course the dust blanket will need to be topped up periodcially, but it will still be cheaper than trying to warm the atmosphere without it.
[/QUOTE]

Awesome, Blake! That’s an excellent suggestion! Refreshing it shouldn’t be a problem , since they certainly have the technology to launch stuff into orbit. And it would obscure the view of the moon’s surface, which would make it another selling point for the colonists.

Hmm. I wonder how often the blanket would have to be topped off. And how much material it would take.

36

Or, depending on how magical you want your technology to be, you could put up some sort of technobabble forcefield around the planet which insulates it. We have no clue how or if such a thing could be done, but it wouldn’t violate the laws of thermodynamics any more than a blanket does.

Speaking of magical technology, by the way, total or near-total conversion of matter to energy is a lot more plausible than pulling energy from the quantum foam. To the extent that we even theorize the existance of the quantum foam at all, our theories are built on the assumption that you can’t pull usable energy out of it. On the other hand, I can think of at least three different methods which could be used for high-efficiency matter conversion. All three are far, far beyond our current level of technology, but the theoretical groundwork is at least in place for them.

37

[QUOTE=Chronos]
Or, depending on how magical you want your technology to be, you could put up some sort of technobabble forcefield around the planet which insulates it. We have no clue how or if such a thing could be done, but it wouldn’t violate the laws of thermodynamics any more than a blanket does.
[/quote]

Yeah, that’s always a possibility, but I’m liking the blanket of reflective rubble more than the additional magic at the moment. I’m not sure I want them to have any more magic.

Well, yeah. But it’s magic. It reminds me pleasantly of when I read Charles Sheffield’s The Compleat McAndrew and they built a spaceship capable of 50g acceleration by mounting the life pod on a pole that stuck up a long way from a disc of neutronium that exerted a 50g field at the surface, and all they had to do to keep a constant subjective gravity was move the pod closer or further from the disc, so it was always at the right distance to balance out to 1g. And when I read that I was like “Uh, that’s ingenious! Except now you have to have the energy to move your ship AND a gazillion-ton block of neutronium.” And later he casually mentioned that they no longer used black hole pods for power, because those were insufficiently powerful to move around a gazillion-ton neutronium block; now they pulled energy directly from the vacuum. “Oh, well, okay, then, it’s magic,” I said.

Would you mind specifying the three matter-conversion methods you’re thinking of? (I’m assuming one of them is matter-antimatter annihilation … and maybe dropping it into a black hole?) Come to think of it, the matter conversion method used in my universe is even MORE sf-magic than “pulling energy from the vacuum,” but that’s neither here nor there.

38

Matter-antimatter annihilation isn’t any good unless you have a source for the antimatter, which we don’t appear to have in our Universe (we can make antimatter through pair production, but then we need to get the energy to do that from somewhere). In fact, two of the methods I’m thinking of do involve dropping the matter into a black hole.

The first is the quasar process, just converting an object’s gravitational potential energy into some other form as it’s falling in. This has the advantage that it can be done with any black hole, we’ve seen it happen (in quasars), and it’s straightforward to get the energy out in a useful form (just attach the mass to a pully or something, as it’s dropping in). The drawback is that it’s only (at most) 50% efficient, with the rest ending up down the hole, and if it’s for something mobile like a starship, your black hole might get inconveniently massive.

The second method is Hawking radiation. You take a very small, and therefore hot, black hole, and continually feed it ordinary matter at the same rate that it’s radiating so it doesn’t go poof. No matter what you feed into it, what comes out will be either things which don’t distinguish between matter and antimatter, like light, or equal amounts of matter and antimatter, which you can use as you please. The upside is that you get 100% efficiency and your generator can be very small (and it stays very small), but on the downside, you’ve got a delicate control problem: Feed the black hole too much, and it gets fat and happy (and cold), so it doesn’t radiate enough any more, and don’t feed it enough, and it evaporates away. An automated control system would probably be up to the task, but it provides opportunities for things to go wrong. Also, a significant portion of the radiation will be in neutrinos, which are very difficult to harness, and so would go to waste.

The third method uses magnetic monopoles. Under all current Grand Unified Theory models (which unite the strong and weak nuclear forces), protons are unstable and eventually decay, but under normal circumstances, their lifespan is fantastically huge. However, in the presence of a magnetic monopole (a north without a south, or vice-versa), the lifespan of a proton becomes much, much shorter, comparable to the lifespans of other subatomic particles. Like the Hawking radiation method, this is effectively 100% efficient (you’ll have a positron left over, but that can be easily annihilated with any spare electrons you might have lying around), and it might be much easier to produce monopoles than the tiny black holes needed for the Hawking radiation method. And magnetic charge is conserved, so there’s no risk of ruining your generator beyond repair. On the other hand, it’s possible that the only monopoles in the Universe are tiny black holes, in which case it wouldn’t be any easier, and this method is the most theoretical, and which we therefore know the least about. In particular, we don’t know exactly what the decay products of a proton would be, so it might have the same neutrino problem as the Hawking radiation method.

39

[QUOTE=Chronos]
it might be much easier to produce monopoles than the tiny black holes needed for the Hawking radiation method.
[/QUOTE]
If you can come up with a method for producing magnetic monopoles–even just a few, or one, at enormous expense–I guarantee that the boys in Sweden with be ringing you up to come to dinner. Also, you could solve one of the fundamental problems with Bussard ramjets–namely, how to protect the controls and lifesystem from the ginormous magnetic fields. (You’re still left with the problems of controlled inertial confinement fusion, variations in charge density in the interstellar medium, obtaining a high enough exhaust velocity to make it viable, et cetera, but those are all piddling engineering problems to be solved in a few weeks by sitting a few eggheads around a conference table with a computing cluster and a wheelbarrow full of money.) A few scoops of magnetic monopoles and you’ll be well on your way to investigating that big burst of neutrinos eminating from the galactic co…<<transmission interrupted>>

Stranger

40

We probably have different notions of “enormous expense”. Given the known upper bound for the mass of the lightest monopole, you’d need a particle accelerator up around ten times the Planck energy (only a couple orders of magnitude higher than one would expect to see stable microscopic black holes). The reason I said that monopoles might be easier to produce than black holes is that that’s only an upper bound, and there might (in the sense that we can’t rule them out) be monopoles lighter than that. It’s even conceivable that we might see some in the new collider at CERN (though I’d estimate the odds to be pretty low).

And I can very confidently assure you that there’s no way to produce just one monopole, regardless of expense :).