Mars Radiation Environment Experiment

It was led by NASA's Johnson Space Center and the science investigation was designed to characterize aspects of the radiation environment both on the way to Mars and while it was in the Martian orbit.

[2] A spectrometer inside the instrument measured the energy from two sources of space radiation: galactic cosmic rays (GCR) and solar energetic particles (SEP).

As the spacecraft orbited the red planet, the spectrometer swept through the sky and measured the radiation field.

However occasional solar proton events (SPEs) produce a hundred and more times higher doses (see the diagram above).

JPL reported that MARIE-measured radiation levels were two to three times greater than that at the International Space Station (which is 100–200 mSv/a).