Martian sub-surface ionising radiation: biosignatures and geology. Biogeosciences 4:545–558

Abstract. The surface of Mars, unshielded by thick atmo-sphere or global magnetic field, is exposed to high levels of cosmic radiation. This ionising radiation field is deleterious to the survival of dormant cells or spores and the persistence of molecular biomarkers in the subsurface, and so its char-acterisation is of prime astrobiological interest. Here, we present modelling results of the absorbed radiation dose as a function of depth through the Martian subsurface, suitable for calculation of biomarker persistence. A second major im-plementation of this dose accumulation rate data is in appli-cation of the optically stimulated luminescence technique for dating Martian sediments. We present calculations of the dose-depth profile in the Martian subsurface for various scenarios: variations of sur-face composition (dry regolith, ice, layered permafrost), so-lar minimum and maximum conditions, locations of different elevation (Olympus Mons, Hellas basin, datum altitude), and increasing atmospheric thickness over geological history. We also model the changing composition of the subsurface radi-ation field with depth compared between Martian locations with different shielding material, determine the relative dose contributions from primaries of different energies, and dis-cuss particle deflection by the crustal magnetic fields