Directionality of the Martian Surface Radiation and Derivation of the Upward Albedo Radiation

Space agencies and private companies are working to place humans on the surface of Mars. But Mars lacks a global magnetic field and has a very thin atmosphere compared to that of the Earth. This provides easy access of particle radiation from space to the Martian surface which in turn poses a significant risk to human exploration of Mars.The Radiation Assessment Detector (RAD) on board the Mars Science Laboratory's (MSL) Curiosity rover has been monitoring the surface radiation environment on Mars for just over 10 years. As Curiosity has explored the Martian surface, the RAD observed that the surface topographical features influence the radiation dose.In particular, while Curiosity was parked close to Butte M12 in the Murray Buttes formation for 12 days, the butte structure, which was blocking out about 19\% of the sky (vs. 10\% in the preceding period), induced a decrease in the background dose by (

5 \pm 1

)\%.Using the panoramic visibility map and a zenith-angle-dependent radiation model a reduction of 12 \% in downward dose was predicted, which is greater than the observed reduction.Combining the RAD observation with a radiation transport model, we derive the flat-terrain (i.e., zero obstruction) albedo dose to be about 19\% of the total surface dose when we have taken into account the sky blockage and observed dose changes.This estimation of the albedo radiation on Mars is an important assessment for better understanding the Martian radiation environment and developing radiation mitigation strategies.