NASA announced on December 9, 2013 some new data about the Martian surface returned by the Mars Curiosity rover. Besides information about the possibilities of life billions of years ago, the rover was able to calculate the amount of radiation that human explorers might encounter when they voyage to explore Mars.
Mars Curiosity measured energetic particles from the sun and cosmic rays combined the bombard the Martian surface with an average of .67 millisieverts per day from August 2012 to June 2013. Cosmic rays provided 95 percent of the total. There were no serious solar storms during that period.
Adding in Mars Curiosity’s radiation readings while en route to Mars, scientists have calculated that an astronaut on a round trip to Mars would pick up 1000 millisieverts of radiation. By comparison a chest x-ray gives one .02 millisievert.
A human being having been exposed to 1000 millisieverts of radiation would suffer a five percent increase of the chance of contracting a fatal cancer in his or her lifetime. NASA is “working with the Institute of Medicine of the National Academies to address the ethics, principles and guidelines for health standards for long duration and exploration spaceflight missions.”
NASA is also mulling some radiation counter measures, including shielding and decreasing the trip time using advanced propulsion technology.