The Martian surface is a place where anything alive quickly dies. Cosmic rays and ubiquitous oxidizers sterilize the top layer of soil. But dig a little deeper, and the picture changes. There, beyond the reach of ultraviolet light, a zone suitable for life may lurk.

This zone runs on a strange fuel — radiation. The hypothesis of the radiolytic habitable zone (a region where life feeds on products of molecular breakdown under particle impacts) suggests that galactic cosmic rays split water and perchlorate salts in the soil. This produces molecular hydrogen (H₂) and oxidizers — ready-made food for chemolithotrophs (microbes that get energy from inorganic substances). They need neither light nor heat from the planet's interior.

The authors of the new study built a numerical model for four Martian regions: Gale Crater, Oxia Planum, southern Utopia, and the Arabia/MAWRTH area. They accounted for particle transport through the soil, radiolysis chemistry (decomposition of substances by radiation), water availability, hydrogen retention, and microbial energy requirements. The result is expressed as a depth-resolved map of redox power — the available energy that cells could tap.

The main conductor of this orchestra is H₂ retention. If hydrogen binds to soil particles or is trapped in closed pores, then at depths from 10 cm, 4–6 × 10⁻¹³ watts per kilogram of rock are available. That's enough to sustain life, but very sparse life. If the gas freely escapes through pores, the energy drops by hundreds to thousands of times — the environment becomes practically dead.

Gale Crater, where the Curiosity rover worked, turned out to be inactive under any assumptions, and this matches soil analysis data. The model predicts that radiolytic life on Mars is possible, but it is rare, tied to specific locations, and hides at depth. Future missions (ExoMars Rosalind Franklin, Tianwen-3, or Mars Sample Return) could test this if they take samples from the protected layer and perform stepwise analysis of hydrogen released upon heating.