Dose rate in water per primary flux function for protons (a) and ⁴He ions (b) at different depth (2,4,6…20 and surface) of the Martian atmosphere. The total vertical atmospheric depth under a surface pressure of 827 Pa is about 23 g/cm². Solid lines are for the total dose rate while dashed lines represent the upward contribution. Black lines mark the deep space case similar to Figure 2.