Martian sub-surface ionising radiation: biosignatures and geology L. R. Dartnell1, L. Desorgher2, J. M. Ward3, and A. J. Coates4 1CoMPLEX (Centre for Mathematics & Physics in the Life Sciences and Experimental Biology), University College London, UK 2Physikalisches Institut, University of Bern, Switzerland 3Department of Biochemistry and Molecular Biology, University College London, UK 4Mullard Space Science Laboratory, University College London, UK
Abstract. The surface of Mars, unshielded by thick atmosphere 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 characterisation 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
implementation of this dose accumulation rate data is in application 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 surface composition (dry regolith, ice,
layered permafrost), solar 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 radiation field with depth compared
between Martian locations with different shielding material, determine the
relative dose contributions from primaries of different energies, and discuss
particle deflection by the crustal magnetic fields.
Citation: Dartnell, L. R., Desorgher, L., Ward, J. M., and Coates, A. J.: Martian sub-surface ionising radiation: biosignatures and geology, Biogeosciences, 4, 545-558, doi:10.5194/bg-4-545-2007, 2007.