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In exploring the xenobiology and design for an entity (Entity X) in my fictional universe, I wanted to raise the viability of an organism that is so massive, it is visible from the planet's upper atmosphere. It is a biosphere unto itself. This entity is simultaneously a 'birthing farm' that reproduces asexually and also is a hive-mind, that controls an ecosystem that ensures its prolonged survival. I am thinking that this organism is fixed, much like the deep sea tube worms found near hydrothermal vents.

My fictional ocean planet is teeming with life, resources are abundant and water pressure is far, far lesser than that on Earth. This ocean isn't as deep and light from 2 distant suns is able to penetrate the depths, increasing the availability of life and food for the sub-oceanic life forms.

My current assumptions about potential energy sources for Entity X are very naive:

It derives much of the energy it requires for its sustenance from a suboceanic chemical source. Going down this path, I determined that this planet has a young core, and enough geological activity that the ocean floor is pockmarked with millions of thermal vents, which subsequently release a massive amount of chemicals, that could potentially sustain an entity as large as a mountain.

Based on that assumption, what are the energy needs of Entity X given that:

It is a hive-mind.

It reproduces on a massive scale.

EDIT: Based on suggestions, I refined my question further to simply ascertain the energy needs of Entity X.

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    $\begingroup$ I can't answer, so just a pointer for you and potential answers: intelligence is expensive. Hivemind-ish features are expensive (bees pheromones and dances, for example). So there needs to be a reason to make such expenses a good deal. Benefits greater than cost. Most of ecosystems on Earth are to some extent self-preserving without any such features, so it is not enough reason for a "biosphere in itself". I don't know what is. $\endgroup$ – Mołot Apr 9 '18 at 16:21
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    $\begingroup$ @Raditz_35 I apologize for the vague description and will refine it further. $\endgroup$ – frishi Apr 9 '18 at 16:28
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    $\begingroup$ Can a sentient coral reef serve as a model for your Entity X? $\endgroup$ – Alexander Apr 9 '18 at 17:24
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    $\begingroup$ "An organism that is so massive, it is visible from the planet's upper atmosphere" cannot "reproduce on a massive scale", simply because there is no place for a large number of those organisms... For the main question, why doesn't it use solar energy, like just about all life of Earth? P.S. The planet-spanning ocean-dwelling conscience has been used masterfully by Stanislaw Lem in Solaris; just saying. $\endgroup$ – AlexP Apr 9 '18 at 19:03
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    $\begingroup$ This also depends a lot on how intelligent/on what time scale the animal can think. It could be super smart, but take several years to come up with any answer to a problem. The energy needs for such a creature would be much lower. $\endgroup$ – bendl Apr 9 '18 at 19:47
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It sounds like Entity X will need a lot of energy in order to survive and reproduce at the scales you've described. Of course, any quantification of the energy needs is pretty much impossible but reproduction and hive-mind-scale cognition would be demanding, to say the least. The way I see it, Entity X has six sources of energy available to it:

  • Geochemical energy: As you've described, oceanic vents would provide chemicals which may be broken down by Entity X to retrieve energy from the chemical bonds. It seems unlikely that this would provide enough energy though, even if the ocean floor is littered with these vents and they were providing high-energy chemicals. Geochemical energy need not be limited to ocean vents, though and may also be sourced from extraction of high-energy compounds like oil or methane.

  • Geothermal energy: Those vents, as well as other incursions into the bowels of your planet and surface sources, could provide heat from the planet's interior. Like a modern, steam-driven geothermal engine, Entity X may find some way to convert this raw heat into energy, thus consuming the very planet it lives on.

  • Solar energy: With two suns able to penetrate deep into your planet's oceans, there would be plenty of visible light to photosynthesize. The limiting factors here would be the surface area of Entity X with which to photosynthesize as well as the thickness of your atmosphere (which I expect could be rather dense given the amount of outgassing taking place both by the vents and Entity X's byproducts). For an idea of what I mean, see Venus.

  • Nuclear energy: It may be possible for Entity X to survive by consuming energy from unstable radioactive isotopes which my or may not be abundant on your planet. It may also be possible for Entity X to get large amounts of energy by maintaining a nuclear reaction somewhere within itself.

  • Carnivory: You stated that your planet is teeming with life. Entity X could gain large amounts of energy by actively consuming other organisms.

  • Kinetic energy: It is possible to harvest energy from ocean currents and wind by allowing them to move certain energy-generating appendages on Entity X.

In order to gain more energy, Entity X may employ more than one of the methods listed above. There is certainly enough energy available to sustain nearly any organism; it's just a matter of how that organism goes about harvesting that energy.

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  • $\begingroup$ Thank you for this thoughtful and detailed answer. It definitely gives me enough tracks to research. $\endgroup$ – frishi Apr 10 '18 at 5:20

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