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The planet is a cold ammonia world. Its ocean is mostly made ammonia, with some traces of ices (mostly water ice) at the bottom of the ocean. The ambient temperature is 225ºK, and the pressure is 4 atmospheres. The star is of G5V type and the planet has a semi-major axis of 1.2 AU.

On this world, certain plants have evolved methane bladders to float and receive more sunlight for to power anaerobic version of photosynthesis. Some plants also now capture UV radiation using modified pigments as they go higher into the atmosphere. Over time, a certain type of plant evolves to also use cosmic rays to supplement the amount of energy it gets in addition to UV light.

Cosmic rays are mostly made up of protons (hydrogen cations), electrons, alpha particles, various antiparticles, and other exotic particles like muons and pions, absorbing the energy of the particle and possibly (I guess for the pions and muons especially) energy generated during their decay. However, these cosmic rays are extremely small particles and are moving quite fast so how do the leaves of these floating plants capture these particles effectively?

Extra note: this question asks about the feasibility of using cosmic rays near space, but to differentiate this question from that one, my plants are in the lower atmosphere and I'm already assuming that they use cosmic rays in addition to UV, and just asking how they would capture the particles.

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    $\begingroup$ There's two fundamental problems before you even get to the problem of capturing the cosmic rays: first, there just aren't enough cosmic rays to contribute anything of significance. If there was, they'd do a lot more than damage the occasional strand of DNA, no living things would survive leaving the atmosphere. Second, and related to that last bit, the cosmic rays that do exist are almost entirely blocked by any significant atmosphere. $\endgroup$ Commented May 19 at 2:26

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Putting aside the issue on the abundance of the cosmic rays and the amount of energy they can provide to a living organism, their capture and conversion into usable energy can take place with the biological equivalent of a scintillation chamber.

I have read somewhere that one of the first astronauts reported that he was seeing flashes of light once in while during his stay in orbit, even with closed eyelids. Investigation found out what he was seeing were cosmic rays crossing his eyeball and being turned into light by the interaction.

Well, this is similar to what you want: a receptacle filled with some medium which can convert the cosmic rays into light and then use that light through something similar to photosynthesis to get usable energy.

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  • $\begingroup$ I think that the energy from one cosmic ray particle is massive, so it should be plausible for the plants to use cosmic rays occasionally, and they should be common enough to be used a little bit. Whether floating plants would actually evolve the trait of using these particles in the first place is open to question though. $\endgroup$
    – Neil Iyer
    Commented May 19 at 5:09
  • $\begingroup$ @NeilIyer the energy of individual particles is irrelevant, they are not common enough to be a useful source of energy for biological organisms. You're looking at single-digit microwatts per square meter, literally a billion times less than sunlight. Cosmic rays aren't even the biggest source of background radiation at ground level, it's mostly radioactive materials in the surrounding environment and the body itself. $\endgroup$ Commented May 19 at 14:27
  • $\begingroup$ Hmmm. What about in the atmosphere though (like the stratosphere)? Wouldn't there be more cosmic rays there than radioactive nuclei because they mostly don't float? $\endgroup$
    – Neil Iyer
    Commented May 19 at 16:19
  • $\begingroup$ @NeilIyer fully harnessing the entire cosmic ray flux at the ground with 100% efficiency would be equivalent to increasing photosynthetic efficiency by 0.0000001%. If it's a thousand times as intense in the stratosphere, that's 0.0001%...and now your organism is under extreme evolutionary pressure to minimize mass to reduce the energy demands of staying in the stratosphere. What's more likely, for it to evolve something massive enough to stop that sparse shower of charged particles and harness them for energy, or to produce a few more chloroplasts? $\endgroup$ Commented May 19 at 17:23
  • $\begingroup$ @NeilIyer consider this: at Earth's distance from the sun, sunlight warms it to an average temperature of 288 K. Pluto, about 30 times further, has an average temperature of just 44 K. Even further out, Sedna is at 12 K...and the calculation doesn't even bother taking the heating by cosmic radiation into account, because even that far out it's utterly negligible compared to what's received from the sun. $\endgroup$ Commented May 19 at 17:33

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