Effectiveness of Martian regolith as a radiation shield

Exposure of astronauts to ionising radiation is widely considered to be the biggest threat to sustained Martian habitation. One proposed mitigation is to use Martian regolith (soil) as a shielding material that would not need to be transported from Earth. We consider its effectiveness by estimating the radiation dose from galactic cosmic rays and solar energetic particles below the Martian surface for mission profiles of 30, 458, and 619 days surface stay. The dose from primary particles is estimated from first principles and compared with the European Space Agency's SPENVIS Mars Energetic Radiation Environment Model. Calculations performed using SPENVIS proved inconclusive and improved confidence in the model output could be achieved with a better understanding of the Martian regolith and its simplified representation within the model. Through first principles estimations we find that Martian regolith would be an effective shield against primary radiation, typically reducing the dose of primary particle radiation by 41% at a depth of 1m, for a 30 day surface stay.