Abstract EANA2026-116

The search for extant life on Mars has lacked a quantitative, instrument-level target: a prediction of how much biologically usable energy exists, at what depth, and whether a given payload can detect it. We address this directly for the ExoMars Rosalind Franklin landing site.

Galactic cosmic rays (GCRs) penetrate the Martian regolith and split water and brine films through radiolysis, producing H₂ and oxidants: a redox battery that chemolithoautotrophs on Earth are known to exploit (e.g. Candidatus Desulforudis audaxviator in the Mponeng gold mine, sustained entirely by radiolytic hydrogen). We compute the radiolytic power density P(z) [W m⁻³] at Oxia Planum by chaining four measurable quantities: GCR energy deposition ε(z) anchored to Curiosity/RAD, radiolytic yields via tabulated G-values, reactant fluxes through Pitzer-corrected brine films, and Gibbs free energies at Mars-relevant activities, capped by a biological-capacity ceiling.

The dominant usable channel is H₂-driven Fe(III) reduction, delivering P ≈ 3 (1–9) × 10⁻⁴ W m⁻³ at z* = 0.30 ± 0.10 m, which is roughly 30× the maintenance-power floor for psychrophiles at 220 K, and well within the rover's 2 m drill. The prediction is falsifiable at the instrument level: WISDOM should register a hydration step at z*, MOMA-GC should straddle its amino-acid detection threshold, and RLS/MicrOmega should resolve the Fe(II)/Fe(III) gradient.

This converts subsurface habitability from a framing argument into a depth-resolved, testable measurement, and a concrete drilling strategy for the mission.