From the top of Martian Olympus to Deep Craters and Beneath: Mars
Radiation Environment under Different Atmospheric and Regolith Depths
Abstract
In preparation for future human habitats on Mars, it is important to
understand the Martian radiation environment. Mars does not have an
intrinsic magnetic field and Galactic cosmic ray (GCR) particles may
directly propagate through and interact with its atmosphere before
reaching the surface and subsurface of Mars. However, Mars has many high
mountains and low-altitude craters where the atmospheric thickness can
be more than 10 times different from one another. We thus consider the
influence of the atmospheric depths on the Martian radiation levels
including the absorbed dose, dose equivalent and body effective dose
rates induced by GCRs at varying heights above and below the Martian
surface. The state-of-the-art Atmospheric Radiation Interaction
Simulator (AtRIS) based on GEometry And Tracking (GEANT4) Monte Carlo
method has been employed for simulating particle interactions with the
Martian atmosphere and terrain. We find that higher surface pressures
can effectively reduce the heavy ion contribution to the radiation,
especially the biologically weighted radiation quantity. However,
enhanced shielding (both by the atmosphere and the subsurface material)
can considerably enhance the production of secondary neutrons which
contribute significantly to the effective dose. In fact, both neutron
flux and effective dose peak at around 30 cm below the surface. This is
a critical concern when using the Martian surface material to mitigate
radiation risks. Based on the calculated effective dose, we finally
estimate some optimized shielding depths, under different surface
pressures (corresponding to different altitudes) and various
heliospheric modulation conditions. This may serve for designing future
Martian habitats.