Measurements from the Curiosity rover's onboard radiation detector, called RAD, show that radiation levels on Mars would allow an astronaut to survive for a little less than two years on the Red Planet's surface.  

The finding was presented Monday, Dec. 3, at the American Geophysical Union's fall meeting in San Francisco.   

The atmosphere of Mars is 100 times thinner than Earth's, which means the surface is much more easily reached by radiation from the sun and outer space. Ever since NASA's one-ton robot plopped down at her landing site in Gale Crater on Aug. 5, she's been monitoring daily radiation to see if it would be possible for humans to set foot on Mars without becoming severely ill. Scientists know that astronauts can handle about 1 sievert, a unit of radiation, as a career limit.  

In mid-November NASA was still assessing daily radiation, in the form of cosmic rays and solar particles, hitting Curiosity. Based on preliminary data, however, RAD's principal investigator Dan Hassler seemed confident that astronauts could live in the environment on Mars, though exact figures were still fuzzy.'s Mike Wall has the updated numbers: 

A mission consisting of a 180-day outbound cruise, a 600-day stay on Mars and another 180-day flight back to Earth would expose an astronaut to a total radiation dose of about 1.1 sieverts (units of radiation) if it launched now, according to measurements by Curiosity's Radiation Assessment Detector instrument, or RAD.

Radiation levels on the surface of Mars are similar to what astronauts experience in low-Earth orbit, which is lower than expected. It's deep-space flight that poses a bigger threat to astronauts traveling to Mars. Astronauts would be hit with about 1.9 millisieverts per day during the flight, while they would experience about 0.7 millisieverts per day on Mars, Wall writes.  

For comparison, astronauts on the International Space Station receive an average daily radiation dose between 0.4 and 1.0 millisieverts, while Earth-bound patients receive 10 to 30 millisieverts from one full-body CT scan.