While we've learned that radiation levels on Mars are safe for humans, actually getting there in the first place remains a problem. Recent results from Curiosity's Radiation Assessment Detector (RAD) reveal that exposure even while safely ensconced inside a protected spacecraft is dangerously high. Explorers would be bombarded with 466 milliSieverts of high-energy galactic cosmic rays and solar particles during the 253-day transit and the same coming back, with total levels that could exceed NASA's career radiation limit for astronauts. "In terms of accumulated dose, it's like getting a whole-body CT scan once every five or six days," said Cary Zeitlin, a principal scientist from the Southwest Research Institute (SwRI) who's the lead author of the findings. A manned Mars voyage isn't completely out of the question, but it does mean better shielding is necessary before such a trip -- much less a future colony -- becomes a reality.