How would a microscopic organism create kilometre long fibre optic cables from ice

Question

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.

Answer 1

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.

Answer 2

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!

Answer 3

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.

Answer 4

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.

Answer 5

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...