Curiosity's self portrait on Mars. Image courtesy of NASA/JPL-Caltech/MSSS While Curiosity's primary mission was to find out if Mars might ever have been capable of supporting Martian life, the rover has also collected data pertinent for a different kind of life: human beings. Curiosity has kept tabs on radiation levels on Mars as well as during the 253-day, 350-million-mile trip it took to get there. Findings released today indicate that radiation levels an astronaut would receive from a trip to Mars and back would be high: approximately 2/3 of their lifetime recommended dosage. Space travelers outside of Earth’s life-friendly atmosphere and magnetic field have to contend with a serious dose of two kinds of harmful radiation: galactic cosmic rays, which are basically everywhere in space, and solar energetic particles, which arise from activity on the sun. The former would present a constant low dose, with particles energetic enough to penetrate even thick shielding. The latter would come in bursts but could be mitigated somewhat with strong shielding.
Energetic protons constitute about 85 percent of the primary galactic cosmic ray flux and easily traverse even the most shielded paths (reds) inside the MSL spacecraft. Heavy ions tend to break up into lighter ions in thick shielding, but can survive traversal of thin shielding (blues) intact. Image courtesy of Southwest Research Institute With Curiosity, astronomers finally have a reliable way to study just how much of that radiation space travelers will be exposed to. Previous measurements were made with unshielded instruments, but Curiosity’s measurements are the first to be made from inside a shielded ship, an environment comparable to a manned mission’s living quarters. In total, Curiosity's Radiation Assessment Detector (RAD) detected about 1.8 millisieverts per day in space (for more info about the Sievert unit, see this chart). The findings are published today in Science. Current estimates suggest a manned mission to Mars would spend 180 days in space each way, bringing the crew's total dose up to about 662 millisieverts. That might not sound like a lot, but the prevailing wisdom is that astronauts should limit their exposure to only 1 sievert (1,000 millisieverts) over the course of their entire career. That amount of radiation results in a 3 percent rise in risk of exposure-induced death from cancer over a lifetime. Thus any astronauts making a round trip to Mars would be exposed to the bulk of their recommended lifetime limit of radiation just in transit. Any time spent on the surface of Mars, or training for such a mission in space, would add even more. While such large doses of radiation don’t necessarily preclude a manned mission from ever happening, they do provide insight on one of the endeavor’s many obstacles.