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The levels of radiation astronauts experience over the course of an extended mission in deep space could lead to dementia and Alzheimer’s. Image via NASA.

NASA has big plans for manned travel in deep space. Although missions haven’t been officially announced yet, experts speculate that the agency plans to establish a space station on the far side of the moon sometime in the next decade, a stepping stone towards landing on an asteroid in 2025 and potentially trying to reach Mars sometime around 2033.

Getting to Mars, though, would require astronauts to endure a round-trip (or possibly one-way) journey that could be as long as three years—which could be particularly worrisome given the results of a study on the health effects of cosmic radiation published today in PLOS ONE. Although we’ve known for some time that the radiation experienced by space travelers could pose problems over the long term, this new study is the first to establish a link with an increased chance of Alzheimer’s disease and dementia.

The researchers, a group from NASA and the University of Rochester, came to the finding by testing a specific type of cosmic radiation—high-mass, high-charged (HZE) iron particles—on mice. This kind of radiation is of particular concern, because its high speed (a result of the force of the exploding stars it’s originally expelled from, light-years away) and large mass mean that it’s tricky to protect against.

Here on Earth, we’re largely protected from it and other types of radiation by our planet’s atmosphere and magnetic field, but even a short time in deep space means much higher levels of exposure, and we haven’t yet figured out how to construct a shield that effectively blocks it. ”Because iron particles pack a bigger wallop it is extremely difficult from an engineering perspective to effectively shield against them,” M. Kerry O’Banion, the paper’s senior author, said in a statement. “One would have to essentially wrap a spacecraft in a six-foot block of lead or concrete.”

After producing radioactive particles that generate this type of radiation using a particle accelerator at the Brookhaven National Laboratory on Long Island, the researchers exposed the mice to varying doses of the radiation, including levels comprable to what astronauts would experience on a mission to Mars. The breed of mice they used has been the subject of numerous studies on dementia and Alzheimer’s, so scientists have a relatively good understanding of how rapidly the disease and related symptoms develop over time.

But when the researchers put the mice through a series of behavioral tests—seeing if they were capable of remembering objects or specific locations—those that had been exposed to greater levels of radiation were far more likely to fail, demonstrating signs of neurological impairment far more early in life than is typical in the breed. Additionally, autopsies of these mice revealed that their brains contained higher levels of beta amyloid, the “plaque” considered a hallmark of Alzheimer’s disease.

This result doesn’t mean we have to abandon dreams of deep space travel—or even that this kind of radiation definitively leads to accelerated neurological degeneration—but it does show that cosmic radiation is going to be a graver concern the longer space missions get. Ingenious engineering has addressed many of the difficulties of space flight, but this remains a problem to be solved.

“These findings clearly suggest that exposure to radiation in space has the potential to accelerate the development of Alzheimer’s disease,” O’Banion said. “This is yet another factor that NASA, which is clearly concerned about the health risks to its astronauts, will need to take into account as it plans future missions.”

No one is going to Mars until scientists figure out how to shield travelers from deadly radiation. (Source: NASA/NSSDC)

Would you go on a mission to Mars? The Dutch startup company Mars One is planning to establish the first Mars colony in 2023, starting with four individuals and adding more people every two years, funded by turning the whole endeavor into a reality TV show.

It’s just the latest plan to colonize the Red Planet, but I’m doubtful it will happen. There’s the expense, for sure, and the trials of trying to convince anyone to go on a one-way journey with just a few other strangers (what if you don’t get along? It’s not like you can leave). And then there’s the radiation problem.

Out in space, there are gamma rays from black holes, high-energy protons from the Sun, and cosmic rays from exploding stars. Earth’s atmosphere largely protects us from these types of radiation, but that wouldn’t help anyone traveling to Mars. They would be exposed to dangers that include neurological problems, loss of fertility and an increased risk of cancer.

NASA scientists calculated in 2001 that a 1,000-day Mars mission would increase the risk of cancer somewhere between 1 and 19 percent. If the risk is on the lower end, then the outlook for Mars might be pretty good, but if it’s higher, then NASA, at least, wouldn’t send people (there’s no telling what a reality TV show might do). A 2005 study found even more to worry about—the radiation would be high enough to cause cancer in 10 percent of men and 17 percent of women aged 25 to 34 if they were to go to Mars and back.

The easy solution would seem to be to shield the vessel that carries the humans to Mars, but no one has figured out how to do that. When the thin aluminum currently used to build spacecraft is hit with cosmic rays, it generates secondary radiation that is even more deadly. Plastic might work—the shields on the International Space Station are made of plastic—but it’s not 100-percent effective. One scientist has suggested using asteroids to shield a vessel traveling between Earth and Mars. But somehow I don’t think Mars One is going to make that one work within a decade.

Or they could just send old people—a solution proposed a couple of years ago by Dirk Schulze-Makuch of Washington State University and Paul Davies of Arizona State University. “This is not a suicide mission. The astronauts would go to Mars with the intention of staying for the rest of their lives, as trailblazers of a permanent human Mars colony,” Schulze-Makuch and Davies wrote in the Journal of Cosmology. Loss of fertility wouldn’t be an issue for older astronauts and the radiation wouldn’t increase their lifetime cancer risk too much (since they’re already near the end of their lives).

That may be a solution more suited to NASA than Mars One, however, since television casting departments would probably want someone more like Snooki than Snooki’s grandma.

Editor’s note: In other Mars news, NASA is preparing for the August 5 landing of its massive unmanned science laboratory, Curiosity. The seven minutes between when the rover hits the top of the atmosphere and when it touches ground are the riskiest moments of the whole mission. The video below shows a few of the hundreds of things that need to go just right: