The unknown risks of radiation in space

• At the moment, NASA places a strict limit on the amount of radiation astronauts can be exposed to in their lifetimes, but a trip to Mars could require that limit to be exceeded.

The big question: Even though researchers have been studying the effects of radiation in lab experiments for years, they still don't know how radiation exposure on a months-long trip to Mars might impact astronauts.

What's new: In a study this week in the journal eNeuro, researchers exposed mice to a chronic, low dose of radiation over about 6 months, attempting to mimic the amount of radiation astronauts might experience during a flight to the red planet.

• They found the radiation exposure could cause anxiety, memory issues and difficulty with decision-making.

But, but, but: Some researchers say there are broader limitations to characterizing the threat posed by radiation in space.

• The type of radiation used for the new study isn't the same as cosmic rays, and the overall amount of radiation in the study is higher than what people would experience during a trip to Mars, Francis Cucinotta, a radiation researcher at the University of Nevada, Las Vegas told Axios in an interview.
• Mice and rats in general also aren't perfect analogues for astronauts, and there isn't a sure-fire way of mimicking the exact radiation a person experiences in space on Earth.
• It's not just about radiation on its own. Scientists are worried about a number of health concerns — including nutrition, sleep deprivation and muscle loss — that, in combination with radiation, could present serious health issues that astronauts will need to deal with millions of miles from Earth.

"We may never know until we send people, and they are going to be guinea pigs. These people are going to take a chance."

What to watch: NASA has looked into countermeasures like medication that could protect astronauts from the damage caused by radiation during a trip to Mars. However, Donoviel says that the agency needs to invest more heavily in those efforts to ensure the missions have the best chance of success.

The bottom line: The health threat posed by radiation is a serious one, and NASA may need to move more quickly to find effective ways to mitigate it if it wants to send humans to Mars in the coming years.

For those willing to risk their lives in myriad ways to go to space, radiation may be a secondary concern at best, even if it's a deal-breaker for NASA, former astronaut Michael Lopez-Alegria tells Axios.

• “You’re taking a lot more immediate, and much more visible, kinds of risks by launching to space that I think that radiation — at least for me — didn’t enter into the equation very prominently," Lopez-Alegria said.

The big picture: Astronauts aren't the only professionals with this kind of drive to continue doing their jobs at all costs. Elite athletes, for example, push past pain and injury in order to continue competing.

• Lopez-Alegria — who has spent more than 250 days in space — explained that because the risks posed by radiation are more likely to affect someone later in life, it isn't something astronauts tend to worry about.

Details: Overall, NASA won't allow astronauts to receive a lifetime radiation dose that would raise their risk of contracting a fatal cancer by more than 3%, but the total acceptable dose differs depending on who you are.

• Female astronauts, for example, have a lower threshold than men due to the way NASA calculates risk, leading some to say the agency's limits are discriminatory because it restricts the amount women can fly.