In summary, GCR is heavy, high-energy ions of elements that have had
all their electrons stripped away as they journeyed through the galaxy
at nearly the speed of light. They can cause the ionization of atoms as
they pass through matter and can pass practically unimpeded through a
typical spacecraft or the skin of an astronaut. The GCR are a dominant
source of radiation that must be dealt with aboard current spacecraft
and future space missions within our solar system. Because these particles
are affected by the Sun’s magnetic field, their average intensity is
highest during the period of minimum sunspots when the Sun’s magnetic
field is weakest and less able to deflect them. Also, because GCR
is difficult to shield against and occurs on each space mission, it is often
more hazardous than occasional solar particle events.11 The picture at
left shows GCR falling onto the surface of Mars. GCR appears as faint
white dots, whereas stars appear as white streaks.
https://www.nasa.gov/pdf/284273main_Radiation_HS_Mod1.pdf