Empirical Forecast of the GCR-Induced Radiation Environment on Mars

Abstract:

Space radiation is one of the most important risks to astronauts on space missions, especially on a future planetary mission to Mars which would last at least 2-3 years. The Radiation Assessment Detector (RAD) on NASA’s Mars Science Laboratory (MSL) was designed to detect and analyze the most biologically hazardous energetic particle radiation on the Martian surface, as part of the MSL’s Curiosity rover landed on Mars on August 6, 2012. Since then, RAD has been providing the first-ever measurements of the cosmic ray induced energetic particle radiation environment on the Martian surface for about 8 Earth years. RAD measurements quantify the radiation hazard to humans on a Mars mission. We analyze the omnipresent Galactic Cosmic Rays (GCR) radiation field recorded by RAD from the beginning of the measurements on August 6, 2012 until the end of solar cycle 24. We observe that the Martian surface radiation increased by about 50% due to the declining solar activity and the ensuing changes in the global heliospheric magnetic field configuration. We quantify the temporal evolution of the measured dose rate as a function of sunspot numbers and find a delay between indicators for solar activity and dose rate from GCRs. This quantification can be used to provide empirical forecasts of the Martian GCR surface radiation level by about 6 months suggested by the existing RAD data, or even up to about one year during odd solar cycles, as suggested by measurements of the long-term GCR evolution near Earth. However, a better understanding of the solar-cycle dependence of the delay time needs further continuous long-term RAD observations on Mars.