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| My usual obsession (Lekgolo) | |
| Posted By: scarab | Date: 2/3/11 10:15 a.m. |
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I saw this 16 minute video on Thorium reactors which is utterly cool in its own right and then it got me thinking of Lekgolo again and my obsession with their biology. (In brief: I think that they are nuclear powered, silicon based lifeforms) (It may be best if you read this post in its entirety then investigate the links.) Naturally Occurring, Water Moderated, Nuclear ReactorsWhen lookig at other LFTR links I found all these sites:
How large were these reactors? They were small, smaller than a person. See the last pic on this page. The reactor is the yellow patch of rock where that guy's hand is. The links refer to naturally occurring nuclear reactors, discovered in Oklo in Gabon in Africa, that existed 2 billion years ago. Their existence depended on the higher proportion of fissile Uranium isotopes found 2 billion years ago (which have since decayed) and free oxygen (due to life and photosynthesis). So such reactors have a limited time window in which they can exist. But if you watch the video at my very first link you could imagine a planet with a different mineral composition than Earth. Maybe there were more radioactives, maybe lots of fluoride salts - then maybe there could be natural molten salt reactors. To get fission you need to concentrate your fissile isotopes and to get controlled fission you need a moderator (something that slows down neutrons via collisions with the atoms of the moderator) and a feedback mechanism to keep the reactor critical.
The Oklo reactors used water as a moderator and when the reaction became super-critical then the heat evaporated the water and drove it out of the reactor and therefore stopped the reaction. The entire rector acted like a geyser - it was active for about 30 minutes at a time then had a 2hr 30 min cool down period. (This cycle lasted for over 1 million years) Molten salt reactors are self controlling because the salt expands when too hot and therefore dilutes the fissile material and when it cools it shrinks and concentrates the fissile material. Te: The Lekgolo HomeworldImagine if silicon based life evolved on Te. What kinds of ecosystems would develop? Energy webs are a fundamental aspect of ecosystems - what are the sources of energy? and how does energy flow through the system? (What are the primary producers? and what eats what?) Primary producers tap into some non-organic energy source and grow in great abundance. Everything else eats them or eats something that eats something that ate them. (Gratuitous lecture on ecology, photosynthesis, and chemotrophs omitted for brevity) What Energy Sources Would Be Available For Underground Life On Te?I can think of three main categories:
I think that any organism would need to convert these energy sources into chemical energy - create energetic chemicals and get work from these chemicals by converting high energy chemicals into low energy chemicals. I will discuss how you can get chemical energy from the three sources of energy mentioned above. 1 ChemicalI'm not so interested in the first category because its too normal for biology. Read a text book or Google, its all out there for you. :-) 2 Geothermal (extracting heat from thermal gradients)But extracting energy from heat gradients seems more fun and it might apply to Lekgolo. The reason that it might apply is that you need to have a large enough difference in temperature to get significant heat flow. This means that you need large or very long organisms. If you have natural salt reactors then you could have localized heat sources and it might be viable to have elongated organisms or collections of elongated organisms that could conduct heat away from the reactors and extract chemical energy from this. They could do this by using a thermoelectric effect. Imagine a collection of cooperating individual organisms - some envelop the reactor and grow asbestos like, insulating, fibers to lock in the reactor's heat (so that all of it is available for use) - others form long chains, comprised of many elongated individuals, that conduct the heat away and use the thermoelectric effect to extract chemical energy from the heat. The conductor organisms could themselves be sheathed by insulating individuals until they reach a cold region. The terminal individuals exchange heat for chemical energy and share this with their insulating allies. So we have a system of cooperating individuals. These need not be Lekgolo and they need not be all of one species - but we have many different organisms on this world that can do this trick. Lekgolo could be a collection of cooperating species all working together for the common good. This cooperative behavior could be one reason why Lekgolo are colonial organisms, comprised of many cooperating individuals. Are their any examples of this on Earth?
But lets get back to geothermal energy. How does the geothermal/heat-gradient idea apply to Hunters? Imagine that Hunters have a heat source at their core, could they extract energy from it? Some worms could generate heat, some could insulate, and some could conduct it to a cold spot. But the system would need a radiator. The spines could work but they have a low surface area. Radiators need a large surface area. And the radiator needs to be away from the main body of the Hunter. Is there anything that fits the bill on a Hunter? Of course there is: its the shield! Wouldn't it be cool if the physical appearance and behavior of Hunters was a direct consequence of their biology? Those things wouldn't be arbitrary. Lets move on to the 3rd source of energy: Nuclear. 3 Nuclear Fision (extracting chemical energy from)We need a way to extract chemical energy from nuclear processes. We have already looked at the thermoelectric effect, is there another way? How about extracting energy from ionizing radiation? This isn't really feasible for DNA/RNA carbon based organisms because ionizing radiation damages DNA. That may not be a problem for a silicon based life-form because they don't use DNA. :-) There are many sources and types of ionizing radiation. For example Alpha decay and Beta decay. Also, high energy neutrons can knock protons out of atoms and those high energy, charged, protons can be an ionization source. Wherever you have reactors and fissile material and their products then you have sources of ionizing radiation. How could an organism extract energy from ionizing radiation? Well ionized free radicals are very energetic in their own right you just need some way to harness that energy. In addition we could use an analogy with photosynthesis. In photosynthesis an electron is transported across a cell membrane to establish an electric field gradient across the membrane. The membrane has protein complexes embedded in it that allow protons to cross the membrane. The proton transport is driven by the electric gradient and ATP is synthesized by extracting energy from the proton transport. If an organism could transport high energy electrons generated by ionizing radiation across an insulating barier then it could use the electric gradient produced to generate high energy chemicals that it could use for its metabolism. 3 Nuclear Fission (generating)The problem with naturally occurring fissile material is that it is fissile. :-) It decays and over evolutionary timescales it becomes rare. Nuclear based silicon lifeforms could develop and evolve but, over billions of years, any naturally occurring reactors would cool down and general background radiation levels would drop. Organisms would need to develop their own reactors. This doesn't sound too hard to do. You need to concentrate a fissile material, supply a moderator, and control the reaction. Organisms are good at extracting substances from the environment and concentrating them. This should be a piece of cake for our hypothetical Te lifeforms. They could use water as a moderator and therefore be fairly cool reactors or they could be molten salt based and therefore fairly hot. I like the idea of Hunters being orange-hot lava monsters. :-) As for controlling the reaction: we have seen that this can be done with simple physics. We have examples of naturally occurring reactors using boiling water and the LFTR reactors mentioned in my first link use expanding salt and work at room pressure. How does this apply to Lekgolo? Imagine that Lekgolo ancestors started off using natural Oklo style reactors. Then imagine that over time 'bacteria' on Te could concentrate Uranium and do a better job of moderating the reaction so that the reactors were at critical longer than natural reactors. Imagine that Lekgolo ancestors lived in association with these 'bacteria'. The Lekgolo cultivate the bacteria, transport bacterial reactors to good locations and bring fissile material to the reactors. Some Lekgolo ancestors could become mobile and carry their reactors around with them. The bacteria would act like our intestinal flora. Over billions of years, as levels of fissile material drops - reactor colonies could start collecting fertile material for example: Thorium to create breeder reactors and therefore avoid the problems caused by the loss of fast decay fissiles. Water Or Salt Moderated Reactors?The problem with water moderated reactors is that they depend on life (photosynthesis) to create free oxygen - we need oxidizing conditions to make Uranium dissolve in water so that it can be transported and therefore concentrated into reactors. I don't want Te's silicon based lifeforms to depend on surface living photosynthesizers. Its just my prejudice and my preference. I don't know what mechanism would concentrate Uranium without water but we do know that living systems play a major role in concentrating materials. What if Te initially had higher general background radiation levels and that early Te bacteria just lived from energy extracted from ionizing radiation. They had an easy life because ionizing radiation was everywhere. They just need to ingest radiating emitters from their medium. Lava consists of course crystals in a liquid. The liquid flows through the gaps between grains. I will call this the interstitial fluid or the medium. Some of our early Te bacteria could swim through this medium seeking out fissile rich areas. Over time as fissile materials become more rare then large numbers of motile bacteria could concentrate Uranium into small areas to make living reactors. I imagine that these would be clumps of bacterial mass somewhat like stromatolites. Or maybe they just clump in one spot, say in crevices, and extract fissile material from the flow of the interstitial fluid. Some bacterial colonies could stay in good hotspots and shed spores that seek out new hot spots. Some colonies could breakup if conditions get bad and then move on to better areas. They could become something like Slime Molds. Interestingly some slime molds farm the bacteria that they live on. So its not just humans and ants that farm their food. :-) Getting back to Lekgolo Our Lekgolo ancestors could have formed around, salt moderated, living bacterial reactors as opposed to, water moderated, Oklo style reactors. Lekgolo could be late stage organisms Lekgolo would be the latest products of a long evolutionary history. If an organism can carry its own reactor around with it then it can explore new territories where fissile material is scarce. They can get their nuclear fuel by eating other, nuclear based, organisms. They would be at the top of the silicon life based food chain. Lekgolo can live on the surface. They may not even be able to live in lava themselves, or maybe their young do, who knows. Te may have developed carbon based life on its surface and Lekgolo could be used to coexisting with carbon based life and they are obviously tolerant of free oxygen atmospheres but they probably don't breathe oxygen themselves. The worms near the centers of colonies and in the Hunter limbs do not have easy access to oxygen. Also, nuclear processes are millions of times more energetic than chemical processes. They can afford to synthesize very high energy chemical products and not have to worry about extracting the last ounce of energy from them. Maybe silicon and carbon based life has coexisted for so long that Lekgolo use carbon from symbionts as another moderator. Other aspects of their biology Hunters don't tend to run around a lot until a threat turns up. Maybe their reactor is a pulse reactor like the Oklo reactors. Maybe they generate their analog of fats or sugars whilst the reactor is critical and then they 'burn' this fuel when the reactor is sub-critical. I don't know if they literally burn it using oxygen but I doubt it as the worms in the interior parts of the colony do not have easy access to the atmosphere. How Does My Proposed Biology Determine Lekgolo/Hunter Form And Behavior?
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