Subsurface Radiation Environment of Mars and Its Implication for Shielding Protection of Future Habitats

Abstract

In order to quantify the optimal radiation shielding depth on Mars in preparation for future human habitats on the red planet, it is important to understand the Martian radiation environment and its dependence on the planetary atmospheric and geological properties. With this motivation we calculate the absorbed dose and equivalent dose rates induced by galactic cosmic ray particles at varying heights above and below the Martian surface considering various subsurface compositions (ranging from dry rock to water‐rich regolith). The state‐of‐the‐art Atmospheric Radiation Interaction Simulator based on GEometry And Tracking Monte Carlo method has been employed for simulating particle interaction with the Martian atmosphere as well as subsurface materials. We calculate the absorbed dose in two different phantoms: a thin silicon slab and a water sphere. The former is used to validate our model against the surface measurement by the Radiation Assessment Detector on the Curiosity rover, while the later is used to approximate a human torso, also for evaluation of the biologically weighted equivalent dose. We find that the amount of hydrogen contained in the water‐rich regolith plays an important role in reducing the equivalent dose through modulation of neutron flux (below 10 MeV). This effective shielding by underground water is also present above the surface, providing an indirect shielding for potential human explorations at this region. For long‐term habitats seeking the Martian natural surface material as protection, we also estimate the optimal shielding depth, for different given subsurface compositions, under maximum, average, and minimum heliospheric modulation conditions.

The Responses of the Black Fungus Cryomyces Antarcticus to High Doses of Accelerated Helium Ions Radiation within Martian Regolith Simulants and Their Relevance for Mars

“…To this purpose, we have exposed dry colonies of the cryptoendolithic black fungus C. antarcticus to increasing doses of accelerated He ions (up to 1 kGy), while mixed with Antarctic sandstones and two Martian regolith analogues. Indeed, accelerated He ions, together with protons, contribute to the major part of the absorbed dose induced by GCR in the surface and the shallow subsurface environments of Mars [40,41]. A study of the effect of elevated radiation doses, which significantly exceed the radiation on the surface of Mars (i.e., 76 mGy/yr) [5] as in the case of this experiment, is necessary for the extrapolation of biological effects on the geological time scale.…”

“…Therefore, the shielding by the regolith against GCR may play a critical role in fostering the persistence of hypothetical forms of life in the subsurface environment of Mars. However, a decrease in the absorbed dose due to GCR particles is only observed from a few centimeters beneath the surface, without significant variations within the near-surface layer [40]. Therefore, this phenomenon makes GCR particles a critical hazard not only for any putative form of life colonizing the first few centimeters of Martian regolith, but also for the future space missions around the lunar orbit and towards Martian cruise.…”

Radiation Environment and Doses on Mars at Oxia Planum and Mawrth Vallis: Support for Exploration at Sites With High Biosignature Preservation Potential

“…Röstel et al. (2020) found that, on the surface of Mars, the heavy ion primary particles contribute 9% of absorbed dose rate in a thin silicon slab phantom, while this ratio is slightly lower in a water sphere phantom, ∼8%. The heavy ion contribution to equivalent dose (not investigated here) was reported to be slightly larger, 11.5%.…”

“…However, the ED is a considerable portion of the limit for young women. Considering that most of the exposure is during the trip to and back from Mars, additional shielding is obviously necessary to maintain dose levels at the Martian surface as low as possible (Röstel et al., 2020).…”

“…Heavier primary ions have been ignored, since they contribute to only about 1% of the GCRs flux (Simpson, 1983) (and even less of the SEPs flux). However, it should be underlined that high‐Z particles may interact with the atmosphere and generate secondaries, which would still contribute to the surface radiation exposure (Dartnell et al., 2007; Matthiä et al., 2016; Röstel et al., 2020).…”