The invisible oceans

Life as we know it needs water.  Two conclusions that don't follow from that premise: Life needs water, and where there is water, there must be life.  Nonetheless, in our present ignorance, the best bet for finding other life is to find water.  Liquid water, that is.

Over the past few years there has been a steady stream of discoveries of likely liquid water in our solar system.  Jupiter's moons Ganymede and Europa probably each have more than Earth does, even though both are considerably smaller than Earth.  Enceladus (a small moon of Saturn) probably contains significant amounts.  The planet asteroid dwarf planet Ceres also shows possible signs of an ocean.  Pluto and Charon might also.  We should know more about them in a few months as I write this.  In the case of Pluto and the moons, tidal flexing generates the heat that keeps the water liquid.  The case of Ceres is less clear, so from here on I'll restrict discussion to the moons.

What these masses of water all have in common, of course, is that they lie deep beneath the surface.  Tens of kilometers, at least.  Some, at least are also salty enough to conduct electricity well, as evidenced by their interaction with magnetic fields.  It's not clear what kind of pressure they are under, or what their range of temperatures is, except that they are likely sandwiched between layers of ice, or maybe between ice and rock, or maybe in alternating layers of various forms of ice (yes, there is more than one kind).  They will thus be literally ice cold in at least some regions, though they are probably considerably warmer in other places.  They certainly receive no sunlight.

Could life evolve under such conditions?  Who knows?  Personally I'd be reluctant to rule it out.  We've found life in all kinds of unlikely habitats on Earth, and in any case we just don't know that much about how life develops.  So suppose it did develop on one of these moons.  What would it be like, and what would be our chances of encountering it?


The first question is whether there is enough in these oceans to get microbial life going.  The short answer: no idea.  We don't know very much at all about the chemical composition of these oceans, though we can make some informed guesses, and again we don't know very much at all about how microbial life on Earth developed, though we can make some informed guesses about that, too.

It's pretty clear that there will be various impurities in the ocean water, so there might well be potential for some sort of self-replicating, information-carrying polymer, similar to RNA, to develop.  There is an outside source of heat from tidal flexing, and there will be temperature gradients as a result [perhaps as much as 40K over a few hundred kilometers], so the laws of thermodynamics don't rule anything out.  Let's assume that microbial life of some sort can develop.

The path from single-cell organisms to colonies of single-cell organisms to colonies of single-cell organisms with different forms (but the same genetics) to something we may as well call a multicellular organism is reasonably clear, although at least in the case of life on Earth it seems to have taken a good long time to develop.

Since we're totally speculating, let's assume there are multicellular organisms analogous to our own sea creatures, but possibly very different in form.  Again, in reality there might be nothing at all, or only single-celled organisms, or some sort of microbe without clearly defined cells at all, or who knows what.

What kinds of features might these critters have?

• Some sort of chemical sense analogous to smell or taste seems like a good bet.  It's almost a defining property of life that it will respond to chemical stimuli in some way or another.  Microbes do.  Animals of all sizes do.  Even plants and fungi do.  I wouldn't necessarily call a slime mold constituent detecting another's chemical signal "taste" or "smell" but ... some sort of chemical sense.
• For similar reasons, a temperature sense seems likely.
• Food webs, predator/prey relationships, mutualism, parasitism, commensalism, amensalism and any number of other relationships among organisms are pretty much inevitable when there is more than one kind of organism.
• Some way of shuffling genetic material as with sexual reproduction.  A source of variability beyond random mutation can be useful in surviving long-term in harsh, ever-changing environments.  Even microbes do this to at least some extent.
• Various ways of physically manipulating objects ... tentacles, pincers, pseudopods, maybe even something resembling hands
• Some sort of nervous system for communicating signals, including sensations from the senses, from one part of the body to another
• Sociality in at least some species.  We're assuming there are multicellular organisms, which is not so different from sociality at the cell level.  This is the next level: sociality among multicellular organisms.  Sociality requires some means of communication between organisms.  Chemical signals and sound seem like plausible candidates.

So far we have a world comprising organisms of various sizes and forms, some herding/schooling together, some hunting others, with the ability to grab things and move them around ... much like life as we know it, except quite likely totally different.

But then, we assumed many important premises based on experience with life as we know it, particularly cells, and we assumed that evolution would follow essentially the same rules as here.  The second assumption, at least, seems pretty reasonable, but who knows?

It's natural to think such an ocean would be dark and all its inhabitants blind, but maybe not.  Plenty of deep-sea creatures find it useful to have eyes and even to produce light.  Light-producing molecules are not that complex.  There are ones that require only carbon, hydrogen and oxygen, so we don't need to assume phosphorous or sulfur, just some source of carbon in the water, which is probably inevitable.

The evolutionary pathway to light and sight is not so clear, though.  On Earth there is a source of light independent of life and it's not surprising that eyes would evolve in the sunlit portion of the ocean, at least.  In naturally pitch-dark oceans, there would have to be some source of light, as a side-effect of something else, before light-detecting cells and organs become useful.

So let's assume it's dark.  Being visual animals, we might assume that that's a big deal, but maybe not.  There are plenty of other ways to get a good picture of the world without seeing it.  In particular, hearing will be important.

Sound carries well in water, and given that the whole world is constantly flexing, there ought to be at least some natural sources of sound.  Unlike the case of vision, it's almost inevitable that organisms that are reasonably large and able to move and to move things will end up making some noise doing so.  This all suggests it would useful to be able to hear.  If it's useful to hear, it becomes useful to be able to make sounds, both for communication and possibly for active sonar.

So we have a dark, noisy and probably fairly cold place teeming with organisms of various shapes and sizes, and schools of this and that all trying to eat and not be eaten.  Will we ever see it?  All we'd have to do to see it is fly a probe a billion kilometers or so and have it dig through kilometers of ice.  Keeping in mind that at the surface temperatures we're looking at, ice acts more like any other mineral than the softish stuff you can chew (to the horror of your dentist).

Since we're speculating, let's say that something we would recognize as an intelligent species develops.  Are they likely to come visit?

Humanity went into space driven by (among other things) the curiosity inspired by the sun, moon, stars and planets.  Even if you don't buy that, you have to admit that we could at least see the sun, moon, stars and planets without any technological help.  Our hypothetical ocean-dwellers could live indefinitely with no clue that there was a solar system out there, or anything else at all.  They would have no direct way of knowing that the parent planet, or even the surface of their own moon, existed.

Even the existence of gravity might be the subject of intense debate.  These moons are relatively small.  The surface gravity of Ganymede, for example, is about 0.1g.  If you're considerably beneath the surface the influence of gravity decreases since you also have matter above you, but that's probably not a major factor at the scales we're dealing with.  If our own oceans are any clue, most things will be near neutral buoyancy.

Put that together and you have a general tendency for most living things to float around in an ocean layer dozens of kilometers deep (thick?) and thousands of kilometers around.  Some inanimate things would tend to drift, very slowly, toward the inner surface (that is, sink).  Others would tend to drift, very slowly, toward the outer surface (that is, float).  This would not be nearly so easy to sort out as the general tendency of things to fall quickly to the ground on Earth.

Figuring out that the world is round would be a significant accomplishment.  The major cues the Greeks used -- ships sinking below the horizon, lunar eclipses, the position of the noontime sun at different latitudes -- would not be available.  The most obvious route left is to actually circumnavigate the world.  And figure out that you did it.

I'm very reluctant to say "such and such would be impossible because ...", but I think it's safe to say that a number of things we take for granted living on the solid surface of a planet with an atmosphere transparent in many wavelengths would be a lot harder in these worlds.  On the other hand, if an inhabitant ever did make it to space, they'd probably have a much better intuitive feel for it than we do.

There's one major factor I haven't mentioned here, that's been cited as a reason that no underwater species could ever develop technology.  Fire doesn't work.  Without fire, a host of things become much harder, if not impossible, including metal extraction and heat engines (steam, internal combustion, etc.).  Underwater rocketry also seems like a stretch, though jet propulsion is not a problem (the difference is that jet propulsion uses the medium one is traveling through, while a rocket creates its own exhaust).

From an earthbound perspective, knowing about our technologies, it's easy to say what familiar technologies probably wouldn't work in such a world, at least not the way they work here.  It's harder, though, to say what unfamiliar technologies could work.  This makes it tempting to say things like "There's no way that life in Ganymede's oceans could contact us.  They wouldn't even have fire."

But we've had, depending on how you count, at least thousands of years to figure technology out.  Depending on how things develop, particularly the transition from single-celled to multi-celled organisms, our hypothetical counterparts might have had tens of thousands, or millions of years.  Or no time at all since they haven't gotten far enough yet.

So what's at least possible in such a world?  Here are some wild, sketchily-informed guesses:

Mathematics: "Can mathematics develop?" seems very much the same as "Can intelligent life develop?", if only as a matter of definition.  If it can't handle at least some form of mathematical thought, can we really call it intelligent? Let's assume that these sea creatures have learned not only to count, but to "think abstractly", whatever that means.  While we're at it, let's assume something we would recognize as a language.

Writing: It's unlikely that anyone is going to whip out a ballpoint pen and write on the back of a napkin, so we need to define "writing" a bit more abstractly.  What we're really after is a permanent means of recording language in via discrete symbols, that is, in digital form.  This doesn't require much, for example, some sort of solid material that can be manipulated and will hold its form.  For example, it doesn't seem unlikely that there could be something resembling rope, which would enable something like the quipu.

Physics: If our critters have mathematical ability and curiosity, they will begin to notice and codify basic facts about their physical world.  Fluid dynamics would be an obvious subject of study, along with some aspects of thermodynamics, particularly at water/ice boundaries.  Electromagnetism, or at least magnetism, is not out of the question.

On the other hand, Newtonian mechanics might take quite a while.  We can ignore wind resistance and get reasonable answers for many problems.  Water resistance is a whole different matter, so it might take quite a while to develop a notion of inertia.  Modern physics -- particle physics, quantum mechanics, relativity, plasma physics, low-temperature physics, etc., requires something like modern technology, of which more in a bit.

Chemistry: This will certainly be tricky.  You can't just pour something in a beaker or dump a solid chemical into a liquid solvent -- at least not without producing the solid chemical in the first place.  But who knows?  If there is life, there are chemical reactions going on all the time naturally.  Perhaps someone learns that a particular gland-y thing from one creature does funny things when you stick a bone-y thing from another creature in it, or that you can use thus-and-such material to isolate a kind of water that acts unusually, and eventually this becomes a systematic body of knowledge.  Not out of the question, and not as much of a leap as astronomy would be, but still doesn't seem like it would be a strong suit.

Biology: Large parts of biology -- cell theory, for example -- require some sort of microscope, but other aspects just require careful observations of other living things.  Evolution is an interesting example.  It's not clear what kind of fossil record there might be, though non-living things would tend to float or sink, but evolution fundamentally requires figuring out that there's a family relationship among seemingly different living things, and realizing that the world is old.  That's certainly not out of the question.

Materials science: Metallurgy requires a supply of metal, which would likely be hard to come by, but one could learn a lot about the properties of the materials around -- tensile strength, hardness, elasticity and even, with more careful observation than we need in our environment, density, heat capacity and such.

Cities: There doesn't seem to be any fundamental reason there couldn't be something we might call  agriculture, and floating cities, at least, forming around it.  Suppose again that there's some sort of rope-like material, and suppose something edible likes to grow on it.  It might then be natural to build largish structures and garden them.  This in turn would provide a reason to stay close instead of wandering off, and along come civilization and its discontents.

Fire: At some point a technological species needs to figure out how to do things that don't happen easily in the natural world.  For us, you could argue it was extracting metals sometime in prehistory, or maybe harnessing steam, or maybe something in between.  For an undersea world, creating an environment where things could burn would be not only a significant achievement, but a gateway to what we might consider industrial technology.  If they can make fire, then it's hard to think what human technology would be out of reach, because to make fire, you need to recreate an environment not too different from ours.  At the very least you need a bubble of some sort of oxidizing atmosphere.  Once that happens, pretty much everything that seems implausible on the list above becomes possible.


So who knows?  There doesn't seem to be anything in principle keeping life on some extraterrestrial ocean from being able to get to us.  It just requires a long chain of unlikely events.  But then, life is full of those.  If you roll the dice billions of times and you get to keep lucky changes around for the next roll, the extremely unlikely can become quite plausible.  In this case, our chain of events looks something like

• A self-replicating molecule develops
• Microorganisms develop
• Multicellular organisms develop
• Some of them develop what we might call intelligence
• These develop a body of mathematical and scientific knowledge
• From that, they develop what we would recognize as technological tools, including
• Ways of storing energy and converting it to work
• Probably some way of creating sizable bubbles of gas, and ways of working inside them
• One way or another they find their way to the surface (which is much farther away than humanity has ever managed to dig into the Earth's crust)
• And then they get in contact with us, somehow.

On the other hand, we know we're coming their way (if they're there).  It's going to be quite some time before we can send a probe to their habitat, but there's one other way we could meet up: One of the reasons we believe that Ganymede and other worlds have water: cryovulcanism, that is, liquids coming to the surface through cracks in the crust (the "cryo" part is there because these liquids are a lot colder than the magma we're familiar with).

If water is coming up from the liquid interior of one of these moons, it might well carry something along with it.  With luck, it might be something like a tardigrade that can survive being dried out and frozen.  Or there might just be a fossil bed of life forms that might not have even made it to the surface alive.

Or, maybe, just maybe (and by "just maybe" I mean "almost certainly not, given all the things that would have to go right"), it might be a hardy explorer, wearing some sort of protective suit, struggling against the surface gravity that we would consider negligible, and wondering at the bizarre new world, and ... what's this thing coming at me from the ... what do you even call it without knowing "stars" and "empty space"?