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My story premise is that a human expedition to Europa has happened and the travellers have tunnelled through the ice and formed a colony in the ocean.

When they breached into the ocean, they discovered that the underside of the ice was covered by glowing organisms that - through further research, turned out to be using some form of fibre optic tubes to the surface to gather light and other energies from Jupiter and the sun.

This energy is enough to cause the organisms to glow a variety of colors which - given the sheer abundance of them - produces a moderate quantity of light, something which is then used by other native biology. The evolution of these organisms can be tracked back to similar glowing organisms that live near hydrothermal vents, explaining how life first arose and that light is a factor in the evolution of Europan life.

While I understand that the energies captured through such a process probably wouldn't be enough for the organism to re-emit light (and that emitting light probably isn't in the best interests for these organisms), my main issue is working out how exactly these organisms created these optical tunnels.

Could ice be modified in such a way through chemical and/or physical processes to collect and direct light towards the organisms? How would the organisms act on the ice over long distances? Could the ice be modified in such a way that it filters the incoming light to only let UV and longer wavelengths through, while blocking X-Ray and gamma radiation?

I'm assuming that the Europan ocean contains many of the same elements found on Earth and that the organisms can generate complex compounds from these. The organisms could also potentially move or grow in ways that (probably) aren't found on Earth, and may even be able to bud off sub-organisms to do their work.

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    $\begingroup$ With enough time, you can achieve anything… and could it be just fibers made from dead bodies that was firstly evolutionary error, but then other organisms take advantage of that… and after millions of years some other organism started to create this things because first organism started to became almost extinct, and light was… necessary, so only those who started creating fibers/ or started to "farm" first organism, so it will grow and die more and create more fibers? $\endgroup$ – Jan Ivan Aug 24 '17 at 13:40
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    $\begingroup$ An interesting twist to your story could come from the very-likely fact that, without any prior indication that there'd be light underneath the ice, the human equipment for boring and submarine colonization probably wouldn't have any windows. It would be entirely plausible that the colonists could finish building and be in a completely settled routine - potentially for years - under the ice, before accidentally discovering that there's light around them. $\endgroup$ – tophyr Aug 24 '17 at 19:46
  • $\begingroup$ That's actually pretty similar to the premise I'm going for. They send probes down only equipped with IR camera's, looking for the heat sources of camera. It's only when some ice miners above the habitat stumble upon a clump of these fibres that they're traced back to the organisms emitting light in a very human spectrum. $\endgroup$ – Daniel Canlin Masterson Aug 24 '17 at 20:36
  • $\begingroup$ If I went to all the trouble of getting a probe into the sea, and then found out that it didn't have visible-light cameras and lamps, the engineer responsible for that design would have a lot of explaining to do. This is a plot hole. I suggest that the probes be so equipped, but that the native biota be invisible at first because the lamps are 1000 times brighter (according to human habit) and come on automatically with the cameras. $\endgroup$ – Beta Aug 25 '17 at 0:54
  • $\begingroup$ Just to be sure: We are talking about the moon, not the continent, right? $\endgroup$ – Zaibis Aug 25 '17 at 6:49
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First issue with natural ice is that it is hardly transparent, because it contains microscopic bubbles of entrapped gas which give it it's white appearance.

But this can be overcome by having dedicated enzymes which remove gas from water and solidify it into clear ice.

The second and main problem is that ice has a lower refractive index (1.31) with respect to water (1.33) which means it is impossible to have total internal reflection in a icy fiber, therefore it would not work at all.

For the sake of your story it is better if your beings produce fibers of Titanium Dioxide (refractive index 2.5 or 2.7) or a likewise transparent and high refractive index material. Silicon Dioxide (1.4 to 1.6) would be too close to water to give a performing fiber.

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  • $\begingroup$ Good ideas with the enzymes. I also thought about the organisms growing their own stalks that would then act as fibres, but wondered exactly how they would do such a thing and whether there could by alternatives. Titanium dioxide is a good solution too. With regards to the refractive indexes or water and ice. Would ice fibres work if the organism was latched to the underside of the ice though, such that the path of light would be space -> ice -> organism? And if so, is clear ice transparent enough to transmit light over the multiple kilometres of Europan ice? $\endgroup$ – Daniel Canlin Masterson Aug 24 '17 at 13:50
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    $\begingroup$ What might be better is to have a structure that uses both Ice and Water acting as the core and cladding. The difference in their refractive indexes would be enough to cause internal reflection. $\endgroup$ – DisturbedNeo Aug 24 '17 at 13:55
  • $\begingroup$ its* (sorry for correcting) $\endgroup$ – Joanvo Aug 25 '17 at 7:03
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I'm sure you mean Hydrothermal vents. There is no fundamental reason a bacteria can't produce some sort of fibre to make a cable or string, by way of perhaps cellulose. You wouldn't need to modify the ice to stop radiation, water does that pretty well, see this stackexchange post:

https://space.stackexchange.com/questions/1336/what-thickness-depth-of-water-would-be-required-to-provide-radiation-shielding-i

However, is there any reason the microorganisms need to be photosynthetic?(Consume light for energy), they could be chemosynthetic just as easily, and still produce light.

Another option would be something similar to fungus, that could create tendrils that capture light, which permemeates the ice.

If you must have photosynthetic bacteria underneath the ice, for a plot point perhaps, I'm sure they could create some variant crystal structure of ice that does refraction guiding. However, couldn't they just create the 'cables' by melting their way to the surface, and coating the walls with biomass, to keep it warm-ish? Refraction guiding works with liquids too!

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    $\begingroup$ Disregard the fungus. I forgot how thick the ice is. $\endgroup$ – EOlsvik Aug 24 '17 at 14:17
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    $\begingroup$ Welcome to WorldBuilding Eric! Interesting answer. If you have a moment please take the tour and visit the help center to learn more about the site. And you can edit your answer by clicking on the little button at the end of your post. Have fun on the site! $\endgroup$ – Sec SE - clear Monica's name Aug 24 '17 at 14:20
  • $\begingroup$ Whoops, thanks for the heads up with hydrothermal vents. I somehow got it into my head that they were called geothermal vents and tried to apply a Europa style prefix to it. As for the requirement for them to use normal light, I have a plot point whereby the explorers get trapped under the ice without means of getting back to the surface, and as a result co-opt these fibres to see the outside world and - eventually - send signals back out to a passing satellite or something similar. I'll probably end up having the optic fibres be some sort of ultra-long protein stem, rather than use the ice. $\endgroup$ – Daniel Canlin Masterson Aug 24 '17 at 20:42
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Um.. Physics textbooks and the CRC handbook might show it eventually, but ice is not a particularly good material for optical fiber. Firstly it is too brittle. Polycrystalline (snow-like) and bubble containing ice has too many scattering boundaries for any sort of light to go more than a few tens of cm.

Go and have a look at the blue ice under a glacier sometime. That is a nicer material for optical transmission, and the field trip might give you ideas.

The way that a glass optical fiber works requires a % or so of refractive index change between two very transparent materials such as two recipes of glass. The glass types are both so near to perfectly clear that fiber attenuation is measured per km and best case for smf28e at 1550 nm is 0.2 dB/km. I think that for a five meter path, you might get away with ice being clear enough to be the cladding of your optical waveguide, but you need something slightly denser and also perfectly clear before you can guide light.

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  • $\begingroup$ That's for the heads up with this. I'll likely resort to some sort of ultra clear protein stem created by the organism instead of relying on the ice directly. $\endgroup$ – Daniel Canlin Masterson Aug 24 '17 at 20:41
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    $\begingroup$ There's a mineral called Ulexite which creates naturally occurring optical fibers. Possibly your microbes could synthesize an especially pure form of it? en.wikipedia.org/wiki/Ulexite#Optical_properties $\endgroup$ – Tofystedeth Aug 24 '17 at 21:23
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The exact details of material engineering were covered by other answers but I find two problems with the such organisms. First of all this is not a stable configuration - if a gene mutation arise which makes bacteria not produce the fiber it can spent all of it resources for reproduction. Since it competes for same resources as other bacteria (light, food etc.) it will out-compete them and take all for itself. Of course at this point there will be no light and unless other mutation arises it will die out. However "genes have no foresight" so while humans can play iterative prisoner dilemma bacteria play ESS game. Bacteria live in Hobbsian world where cooperation is only in name of short term self-interest. The only way out I can see is if the bacteria were sterile workers working for the survival of reproductive hive - but that would be more of an multi-cellular organism then single-cells.

Second is how would such nanotubes evolve. Many of marvels of evolutionary 'design' is iterative with each iteration slightly improving over previous one. The record of such mutations can be seen and organisms behave in way that makes no sense unless we consider history (and that the evolutionary pressure was too weak to affect it). While an engineer might spent a lot of time an energy with foresight of needing a long tube bacteria need some immediate benefits of forming nanotubes. I'm not sure how 'half-nanotube' would look like and what benefits it would have - in other words why nanopods would become longer and longer and why transmitting light would be evolutionary beneficial.

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Structures: I'd vote for the microbes creating the cables from protein or other cellular components. There are structures called nanopods made by some bacteria, which are remarkably long. Check it out. There are also bacterial nanowires, look into that too. We now believe bacteria can transfer individual electrons with these structures, which changes how we think about their metabolic potential.

Energy: Hydrothermal vents support life because of reduced compounds (H2S) which provide energy, and thermal gradients (I think) which can also drive reactions (I think.) they are intriguing because they do not have light to drive biology (except bioluminescence.) there are certainly ideas out there of reduced compounds on these planets, like the methane on Titan. The volcanic feature on Enceladus def. shows possibility of thermal energy within body. There may be some similar knowledge about such features on Europa.

Carbon: Hydrothermal vent microbes derive carbon from CO2 (via chemosynthesis driven by H2S) but also from 'marine snow,' which is derived from photosynthesis.

I'd recommend incorporating these sorts of ideas over ice cables. Maybe work with a thermal gradient set up by the ice (cold) and their metabolism (warm.) The thermodynamics are probably wrong here, but it is worth some thought. Also, consider using 'space snow' - just an idea - of organic matter 'falling' to europa, possibly from Jupiter. Maybe that red spot is throwing useful compounds out, and europa is able to capture them. Or from meteorites...

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  • $\begingroup$ Haven't heard of nanopods and bacterial nanowires. I'll certainly have a read up on them, thanks! As for the hydrothermal vents, my ideas are that life evolved to be quite diverse and hardy near vents, eventually evolving to be able to survive away from them as - for whatever reason - vents could close and open elsewhere. Some of these hardier organisms eventually latched onto the ice and - again, for whatever reason - started burrowing up to towards the surface. $\endgroup$ – Daniel Canlin Masterson Aug 24 '17 at 20:39

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