The ionizing radiation environment and shielding in pit craters and cave skylights on Mars

Pit craters and cave skylights are promising targets for future robotic and manned missions to Mars searching for signs of past or present life. While characterizing these features is essential for mission planning, few observational data and modeling studies are available about pit craters and cave skylights on Mars. To date, no studies have characterized the ionizing radiation environment within these voids. This paper quantifies, for the first time, the expected absorbed dose and dose equivalent rates within various crater geometries and locations using NASA's HZETRN2020 three-dimensional transport model. Our results indicate that atypical pit craters (APCs) can offer significant protection from ionizing radiation, with reductions, even at the center of the crater floor, exceeding 80 % in both absorbed dose and dose equivalent rates when compared to surface conditions. Our findings suggest that, from the ionizing radiation perspective, APCs could provide a favorable environment for indigenous or terrestrial microorganisms, and could preserve complex organic molecules during millions of years, holding strong implications for planetary protection. In several APCs studied, the dose rates are below the upper limit of 50 mSv/y for exposed workers on Earth, established by the U.S. NRC standard. These rates are also well below both the ∼150 mSv/y measured at the International Space Station (ISS) and the ∼200 - 300 mSv/y measured on the Martian surface by Mars Science Laboratory.