Unlike Earth, Mars lacks a thick atmosphere and a magnetic field. This leaves the planet totally vulnerable to radiation from space. The Mars radiation comes from many sources: the Sun’s solar wind, cosmic rays from the Sun, and other stars.
Life on the surface of Mars would be exposed to a constantly high dose of radiation, and the occasional lethal blasts that come regularly from strong solar flares.
NASA’s 2001 Mars Odyssey spacecraft was equipped with a special instrument called the Martian Radiation Experiment (or MARIE), designed to measure the radiation environment around Mars. Since Mars has that thin atmosphere, radiation detected by Mars Odyssey would be roughly the same as the surface.
Over the course of about 18 months, Mars Odyssey detected ongoing radiation levels which are 2.5 times higher than the astronauts experience on the International Space Station – 22 millirad per day. The spacecraft also detected 2 solar proton events, where radiation levels peaked about 2,000 millirads in a day, and a few other events that got up to about 100 millirads.
Human explorers to Mars will definitely need to deal with the increased radiation levels on the surface of Mars. To protect against the radiation, long term colonists on Mars will need to build their bases underground – just a little Martian soil will prevent the Mars radiation exposure.
If you want, learn more about the MARIE instrument on board NASA’s Mars Odyssey spacecraft, and the radiation risks humans will face trying to go to Mars.
Finally, if you’d like to learn more about Mars in general, we have done several podcast episodes about the Red Planet at Astronomy Cast. Episode 52: Mars, and Episode 91: The Search for Water on Mars.