NASA — and astronauts — now have one more thing to worry about before sending humans to Mars. A study published yesterday suggests that extended exposure to a particular kind of radiation found in space can accelerate the development of Alzheimer's disease. The study focused on galactic cosmic radiation consisting of iron particles, which are said to permeate space at high speeds due to the force of exploding stars. We're safe from these particles here on earth, but out in deep space only the spacecraft will stand between astronauts and the radiation. Study author Kerry O'Banion says that the iron particles have no trouble punching through a ship's hull, adding that it would require a "six-foot block of lead or concrete" to stop them.

In the study, which was carried out over eight years with funding from NASA, mice were exposed to varying degrees of radiation before being analyzed for cognitive loss. In one test to check for memory degradation, researchers studied whether mice would remember (read: avoid) an environment that had previously shocked their feet. Mice that were exposed to radiation performed more poorly in these experiments than those that did not, and they exhibited other signs of Alzheimer's, like inflamed blood vessels and atypically high levels of beta amyloid, a protein known to be associated with the disease. O'Banion did note that the mice received the radiation in about a three minute period, while astronauts will be exposed to the same amount of radiation over a period of years. He added that it's possible that "the body might adapt to small chronic dosing," but for now, those signing up for manned missions to deep space locations like asteroids or Mars might want to take note.