Ionizing radiation has long been seen as an adversary to life. Its destructive power is evident in how it tears through DNA, damages cells, and produces harmful radicals that wreak havoc on biology. For decades, this understanding has shaped our view of radiation as a force that sterilizes environments, leaving them barren and inhospitable. Yet the study by Dimitra Atri and colleagues, published in 2025, offers a very different perspective. It proposes that radiation, instead of being purely destructive, could actually provide the energy needed to sustain life in some of the most unlikely places in our solar system. The concept put forward is the Radiolytic Habitable Zone, a theoretical space beneath the surfaces of Mars, Europa, and Enceladus, where cosmic rays penetrating the upper layers of ice or rock trigger chemical reactions that create products microorganisms could exploit as fuel. It is a startling and mysterious reframing of what it means for a world to be habitable, opening the possibility that entire hidden ecosystems may exist not in sunlight, but in the shadows of radiation.
Evidence for this possibility begins here on Earth. Deep underground, isolated from the surface and the reach of the sun, researchers discovered Candidatus Desulforudis audaxviator, a bacterium living in a South African gold mine nearly three kilometers below ground. It thrives in total darkness, relying not on photosynthesis or surface nutrients but on the byproducts of radiolysis, the splitting of water molecules by natural radioactive decay. The hydrogen and other reactive species generated through this process are enough to fuel its metabolism. It represents the only known single-species ecosystem, a closed loop powered entirely by radiation-driven chemistry. This extraordinary microbe is living proof that life does not need sunlight or organic carbon delivered from the surface to endure. If such an organism can exist beneath Earth’s crust, why not elsewhere?
The Atri study builds on this principle but takes it a step further. On worlds like Mars, Europa, and Enceladus, the atmosphere is either thin or nonexistent, leaving their surfaces exposed to a constant bombardment of galactic cosmic rays. These particles carry immense energies, far beyond those of ordinary solar radiation, and they can penetrate meters beneath the surface. As they pass through ice or rock, they trigger cascades of reactions, breaking apart water molecules and generating solvated electrons, hydrogen, and reactive oxygen species. Instead of being wasted, these products could be harnessed by hypothetical microbial life forms buried just beneath the surface. The Radiolytic Habitable Zone, or RHZ, is defined as that hidden layer where enough radiolysis occurs to provide a steady supply of usable energy.
The authors modeled these processes with high-precision particle simulations. They estimated how much energy is deposited at different depths, how many electrons are produced, and how much biomass could theoretically be supported. The results reveal a hierarchy. Among the three bodies studied, Enceladus comes out on top, with the highest potential for sustaining microbial densities. Mars follows, and then Europa. The peak depth varies, with Mars showing maximum potential around sixty centimeters beneath the surface, Europa closer to a meter, and Enceladus at roughly two meters. At those depths, the energy environment is calculated to be sufficient to support microbial cell densities comparable to those found in some extreme environments on Earth. Even more intriguingly, the study estimates how many molecules of ATP, the universal energy currency of life, could be produced. Enceladus again leads, suggesting that beneath its icy shell, where plumes already hint at hydrothermal activity, radiation-driven chemistry may offer an additional sustaining force.
It is difficult to overstate how radical this idea is. Traditional notions of habitability have focused on sunlight and liquid water, or in the case of icy moons, geothermal activity and hydrothermal vents. But if radiolysis can provide a continuous, stable stream of energy, then life could persist in places previously dismissed as dead. Mars, with its cold and dry surface, might still shelter halophiles beneath its crust, tapping into briny pockets shielded from the worst of the radiation. Europa, though encased in kilometers of ice, may sustain oxidant gradients through radiolysis that feed its ocean. And Enceladus, already seen as one of the best candidates for life, now appears even more promising when radiolysis is factored in.
What makes the RHZ concept so compelling is that it reframes the role of cosmic radiation. Instead of a hazard, it becomes a hidden lifeline. On Earth, radiation is a threat to astronauts and spacecraft. For planetary protection agencies, it is something to be shielded against. Yet for microbes adapted to use solvated electrons or hydrogen from radiolysis, that same energy source could serve as nourishment. The mechanisms are not far-fetched. Certain bacteria on Earth already use extracellular electron transfer, employing conductive nanowires to move electrons between minerals and themselves. Others harvest electrons directly from metals. These strategies show how flexible microbial metabolism can be, and how it could, in principle, take advantage of electron streams generated by radiolysis.
The implications ripple outward. If Mars, Europa, and Enceladus possess radiolytic habitable zones, then other worlds throughout the galaxy might as well. Any rocky or icy body with water and exposure to high-energy cosmic rays could host such microhabitats. The very environments we have written off as sterile might be quietly alive beneath their surfaces. It raises profound questions about how common subsurface life might be, and how many forms it could take when powered not by starlight, but by the invisible rain of radiation filling interplanetary space.
The study also highlights just how much remains unknown. While the energy budgets appear sufficient, it is unclear how organisms would evolve to use such resources. Would they employ nanowires and cytochromes like Earth’s bacteria, or develop entirely new electron-transfer proteins? Could primitive proto-life rely on radiolysis to drive the chemistry of prebiotic molecules, as experiments have shown is possible with amino acids and iron-sulfur clusters? The role of radiation in early Earth’s chemistry is itself a subject of debate, and this research extends that debate to other worlds. Radiolysis may not just sustain life, it may have played a part in starting it.
Future missions could provide the answers. Mars rovers with drills capable of sampling beneath the ice caps may one day test for radiolytic biosignatures. Europa Clipper, set to explore Europa in greater detail, will measure the thickness of the ice and locate potential access points. Enceladus, with its plumes venting ocean material into space, will be the target of future orbiters and landers. If life exists in a radiolytic habitable zone beneath its surface, evidence might be carried upward in the spray of ice grains, waiting to be captured and analyzed. These missions, armed with instruments that can detect radiation levels, electron fluxes, and organic molecules, will be essential for testing the RHZ hypothesis.
What makes this research resonate is the mystery it restores to our exploration of life beyond Earth. For years, habitability has been reduced to a checklist of factors: liquid water, energy sources, organic molecules. The Radiolytic Habitable Zone suggests a more subtle picture. Life might not only cling to obvious sources like sunlight or hydrothermal energy but could exploit the very forces we assumed were deadly. In doing so, it could remain hidden in plain sight, existing in shadowed pockets just beneath the surfaces of nearby worlds.
When Desulforudis audaxviator was discovered in South Africa, it forced scientists to reconsider what was possible for biology. Alone, sealed off from sunlight and surface ecosystems, it thrived purely on radiolysis-driven chemistry. It showed that life could adapt to conditions once thought impossible. The Atri study extends that lesson into the solar system. If Earth’s deep biosphere can turn radiation into survival, why not Mars? Why not Europa? Why not Enceladus? The mystery is not whether such life is possible, the study suggests it is, but whether it is already there, waiting to be found.
This possibility casts exploration in a new light. To search for life is not just to look for green patches on alien landscapes or to probe the depths of vast oceans. It is to drill into ice, to measure electron currents, to follow the faint chemical traces of radiolysis beneath crusts and shells. It is to recognize that the universe may harbor life not in the warm glow of stars, but in the quiet hum of radiation deep below frozen surfaces. That, perhaps, is the most mysterious revelation of all.
Source:
Atri, D., Kamenetskiy, M., May, M., Kalra, A., Castelblanco, A., & Quiñones-Camacho, A. (2025). Estimating the potential of ionizing radiation-induced radiolysis for microbial metabolism on terrestrial planets and satellites with rarefied atmospheres. International Journal of Astrobiology, 24, e9. doi:10.1017/S1473550425100025
