Chemical process for a radiosynthetic Ganymedian organism?

Question

I'm trying to build an underwater ecosystem under the ice crust of Ganymede. I know Jupiter emits a large amount of ionizing radiation and synchotrons and thought that would maybe be able to replace sunlight in this ecosystem. My idea is some sort of large organism that would burrow into the ice with root like tendrils to absorb the radiation and basically fit the ecological niche of trees. I've also read about radiotropic melanized fungi that are thought to use melanin to drop the wavelength of some high energy radiation to a usable level.

So my question is

1. Could these organisms use melanin to absorb a portion of the radiation as heat and output a usable wavelength of radiation for a chemical process analogous to photosynthesis where it would introduce oxygen into my ecosystem?
2. If not, then (assuming any necessary nutirent/molecule needed is naturally present) is there any theoretical chemical process for these organisms using radiosynthesis?

Answer 1

This is a very interesting question!

Could these organisms use melanin to absorb a portion of the radiation as heat and output a usable wavelength of radiation for a chemical process analogous to photosynthesis where it would introduce oxygen into my ecosystem?

You are probably thinking about the radiotrophic fungus that was discovered in Chernobyl:

Radiotrophic fungi are fungi which appear to perform radiosynthesis, that is, to use the pigment melanin to convert gamma radiation into chemical energy for growth.

The emphasis on gamma radiation is important. If you want to use a pigment to extract energy from radiation, it has to be electromagnetic radiation - alpha and beta radiation won't do. Unfortunately for your ecossystem, no EM radiation can reach under the ice of Ganymede. Not even gamma.

Water is a very efficient shield against it. If you get 13 cm of water between you and a gamma source, you only get half the radiation you would otherwise.

Even if it weren't so, you'd be hard-pressed finding a gamma source. The sun does not emit gamma radiation. The magnetosphere of Jupiter is only powerful enough to generate X-rays, not gamma. If you have a source within the liquid ocean itself, it will probably [redacted] up the ecossystem around it.

If not, then (assuming any necessary nutirent/molecule needed is naturally present) is there any theoretical chemical process for these organisms using radiosynthesis?

We simply don't know of a way a creature could use α or β radiation for its metabolism; both tend to cause a lot of harm to DNA and organelles. Any local source of gamma would be generating a lot of those other two as well.

If you want to be realistic, you can have chemolithotrophic organisms as the base of the food chain. The chemolitotrophs would thrive only around hydrothermal vents, but the rest of the ecossystem would free to roam and live elsewhere.

Last but not least, if you want to go through this route, Europa is a better candidate than Ganymede:

The case for Europa's subsurface ocean comes from the strong probability of tidal heating, melting the ice under the surface. Ganymede has a much weaker tidal force, and thus weaker tidal heating than Europa and Io. The level of Ganymede's tidal heating could not provide enough heat to make an ocean of liquid water. Aside from tidal heating, we are not sure where sufficient heat would come from to melt the ice.

I know this is in contradiction of the wiki, which states there is probably an 800 km deep ocean in Ganymede. I believe the article from LASP is older. However, the fact remains that Europa has stronger tides. Those help moving the geology of the moon around, which can provide nutrients to the subsurface ocean over time. I believe Europa is richer in salts too, so even better for chemistry to give rise to life.

Answer 2

Renan's answer highlights important facts on radiation penetration through ice (limited for gamma, functionally non-existent for beta electrons & alpha nuclei), and the greater plausibility of chemoautotrophic organisms. However, I can add a little on potential photon-centric mechanisms in case that is of interest.

Background info

The main important piece of information is understanding that life fundamentally lives on chemical energy gradients. Get some way to acquire spare energy that can transform complex molecules and you can probably hack together some form of self-replication from those molecules.

On Earth we find life building off photosynthesis (whereby an incoming photon has its energy captured by the chlorophyll molecule, and then clever chemistry leads to that energy being redirected to do microbiological work building up complex molecules elsewhere in the cell), or chemotrophic life that leaves near (eg.) ocean volcanoes and "eats" the exotic sulphur compounds, which are highly reactive with carbon-ish molecules and thus can be used to do microbiological work.

In theory, the photons of gamma radiation could be captured and used in the same way as visible light is in photosynthesis, you just need a chlorophyll-esque molecule that is tuned to the energy of some appropriate photons (captures the photon, promoting the chlorophyll to a higher energy vibration or ionisation that can be utilised in further organic reactions). The considerable difficulty here is that gamma radiation generally imparts enough energy to ionise/break bonds in organic material, destroying the lifeform.

Solutions

Possible Solution for Gamma-feeders: You either need an organism that is made of sturdier stuff than hydrocarbons, or invent a system where your organisms generate some shallow stabilised dendritic tunnels in the ganymedean ice, then sit at a deeper level (recall that gamma penetrates ice poorly) and pump a photosynthetic liquid through the tunnels, reabsorbing the energised compounds that come back, but not directly exposing themselves to the gamma radiation. The details are tricky --- in real-life you need to chemically utilise chlorophyll's absorbed photon in a few hundred nanoseconds or else the chlorophyll converts the energy to useless heat --- but doable.

Possible Solution for Beta-feeders: Beta radiation can easily ionise organics, which in principle could be used as an energy source for organic reaction, although the chemical pathway would be somewhat different. However, beta radiation is more destructive to molecules than gamma radiation (electrons carry more energy than photons), giving us far thornier versions of the destruction problem from earlier. Furthermore, any location that has beta exposure would have to be on the surface of the ice, meaning direct exposure to gamma and alpha radiation. I cannot imagine a lifeform living sensibly in such conditions without a completely novel chemical makeup to resist radiation damage.

Possible Solution for Alpha-feeders: None. Alpha radiation is helium nuclei getting flung around. Sure, they carry lots of energy, but trying to use them for organic reactions is like trying to catch a bowling ball with a cobweb.

Answer 3

Water hydrolysis. And something else.

Ionizing radiation can hydrolyze water. This is important for people storing and handling radioactive materials because products of water hydrolysis can accumulate.

https://en.wikipedia.org/wiki/Radiolysis

Of all the radiation-chemical reactions that have been studied, the most important is the decomposition of water. When exposed to radiation, water undergoes a breakdown sequence into hydrogen peroxide, hydrogen radicals, and assorted oxygen compounds, such as ozone, which when converted back into oxygen releases great amounts of energy. Some of these are explosive.

Alpha particles are the best at hydrolyzing water because they are the most ionizing. Beta particles and gamma rays can do it too. All three types occur in the deep earth. There actually are non photosynthetic ecosystems which live off of hydrolyzed water, specifically hydrogen. Hydrogen is tasty microbe food wherever it occurs. In the deep earth it is generated by radioactive decay and consequent hydrolysis of water.

Long-Term Sustainability of a High-Energy, Low-Diversity Crustal Biome

The hot, reducing, gaseous water emanating from a fracture at 2.8 to 4.2 kmbls harbored a microbial community dominated by a single Firmicutes phylotype. The Firmicutes probably penetrated the Mponeng fracture zone at current depths during infiltration of paleome teoric water between 3 and 25 million years ago and since then have relied on nonphoto synthetically derived H2 and S042_ converted from Archaean/Proterozoic pyrite. Nutrient concentrations have remained much higher than observed in shallower crustal environ ments, suggesting that the deep crustal bio sphere may be energy-rich, is not approaching entropic death, and is capable of sustaining microbial communities indefinitely by geological processes.

These organisms live off of naturally occurring hydrogen liberated from water by ionizing radiation. The stuff is just laying around. The next step for a greedy organism is to have a huge onboard water tank – the equivalent of leaves for capturing solar energy. Reactive products of water hydrolysis within the tank are captured by cellular proteins and sequestered as we sequester sugar, for later combination to produce energy and regenerate the water. The tank is an acellular film resistant to ionization. DNA is shielded deep under the water tank organ.

If this were a science fiction dealing with such creatures, the deep earth hydrogen biosphere would be the first step (established biogeochemistry), and discovery of the water tank creatures the second – a not so wild extrapolation.

One more step into fantastic fiction! Very energetic gamma rays have too much energy to hydrolyze water. They produce a different energetic substance. Positrons. https://en.wikipedia.org/wiki/Gamma_ray#Matter_interaction

Pair production: This becomes possible with gamma energies exceeding 1.02 MeV, and becomes important as an absorption mechanism at energies over 5 MeV (see illustration at right, for lead). By interaction with the electric field of a nucleus, the energy of the incident photon is converted into the mass of an electron-positron pair. Any gamma energy in excess of the equivalent rest mass of the two particles (totaling at least 1.02 MeV) appears as the kinetic energy of the pair and in the recoil of the emitting nucleus. At the end of the positron's range, it combines with a free electron, and the two annihilate, and the entire mass of these two is then converted into two gamma photons of at least 0.51 MeV energy each.

These lower energy gamma rays are fine for hydrolysis of water. When energetic gamma rays come, the organism captures and retains positrons for later release, to produce gamma rays during lean times. Positrons are antimatter. The creature’s storage organs for positrons are interesting, valuable and extremely dangerous.