Measurements of the Radiation Environment with the MSL/RAD Instrument on Gale Crater on Mars

The Mars Science Laboratory Radiation Assessment Detector (MSL/RAD) on board NASA's Curiosity rover has been measuring the radiation environment in Gale crater on the surface of Mars since August 2012. The radiation field stems primarily from Galactic Cosmic Rays (GCRs) that propagate through the Martian atmosphere and can even penetrate into the soil. The GCRs interact with nuclei from atmosphere and soil creating a diverse radiation field composed of primary and secondary, charged and neutral particles. On short time scales contributions from solar particles, accelerated to high energies at the Sun during so-called Solar Energetic Particle (SEP) events can dominate the radiation field and enhance its intensity by orders of magnitude.

To understand potential health risks for future human explorers, it is important to analyze the radiation environment on Mars in detail. MSL/RAD measures fluxes and energy spectra of charged particle species, as well as neutrons and gamma-rays. RAD also measures the biologically highly-relevant radiation dose and dose equivalent, providing crucial insight for the health risk assessment.

Here, we present an update of the long-term radiation measurements by MSL/RAD over the last 7 years, and discuss new findings. For example, while the Curiosity rover was stationed right next to a rock formation in the Murray Buttes, RAD detected a decrease in the measured radiation dose. This stems from the fact that the butte next to the rover blocked out part of the sky, from which the main part of the radiation originates from, and thus provided a shadowing effect. This is of importance for future human exploration of Mars as the RAD measurements can provide insight on planning future habitats for humans. Furthermore, we discuss the effect that a changing atmospheric pressure level or depth has on the intensity, composition, and biological effectiveness of the radiation environment. This will be of particular interest for near-future RAD measurements when Curiosity continues to climb up higher and higher in altitude.