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Future Mars colonists will have a lot of problems to surmount: growing sustainable food, maintaining a steady supply of oxygen, and of course, staving off space cabin fever. But there’s another pressing problem that will affect them before they even land on the Martian surface: space radiation. It’s generally accepted that a long space flight is going to involve some radiation exposure, but just how damaging that radiation would be has been something of a mystery.
A new study published in the journal Science Advances casts the situation facing future Mars explorers in a particularly bleak light. Charles Limoli, a researcher at the University of California, Irvine, and colleagues exposed mice to charged particles designed to mimic the kind of radiation exposure an astronaut might experience on the journey to Mars (which is expected to last around nine months).
Six weeks later, the team ran the mice through a serious of cognitive tests. The irradiated mice performed significantly worse on the tasks than control mice. Effects were even more severe among those mice exposed to the radioactive titanium isotope 48Ti, a high-energy particle often found in cosmic rays. At both low and high doses of 48Ti, mice scored an average of nine times lower on the cognitive tests.
“I wasn’t expecting such a significant decline,” Limoli said in a phone interview.
When the researchers took a closer look at the brains of the mice, they could see the physical effects of the radiation firsthand. The brain’s neurons have branching structures called dendrites that help transfer signals from one nerve cell to another. Normally, the branches of these dendrites form a dense thicket; in the mice exposed to radioactive particles, the branches have been pruned, and the number of dendritic spines—akin to the “leaves” on the dendritic branches—was also significantly reduced. And there’s no indication that this damage can ever be healed.
“Although the impairment of neurocognitive performance is undesirable in any circumstance, the impact of such [reductions] on the success of a deep space mission is likely to be especially problematic because of delayed communication that results in an increased necessity for astronaut autonomy and the ability to make critical decisions quickly,” Limoli and his colleagues wrote in their paper.
The amount of radiation that astronauts would experience on their way to Mars will depend on a number of factors, but it should probably be significant—during the Curiosity rover’s trip to the Red Planet, the craft was bombarded with an average of 1.8 milliSieverts of radiation from cosmic rays, and experienced five spikes of radiation from solar flares and coronal mass ejections on top of that. According to SpaceFlightNow, the overall radiation experienced by Curiosity on its trip was the equivalent of a person going to get an abdominal CT scan every five or six days.
On Mars, colonists should be able to protect themselves by covering their dwellings with a thick coating of Martian soil. But in transit, radiation shields are a difficult proposition. Water is one of the best options for a protective material both because it’s a fairly dense material and because the hydrogen atoms in water molecules are particularly good at interacting with the high-energy particles of radiation. But although water is cheaper to bring into space than other shielding options like concrete or lead, it’s still pretty expensive to bring into space due to its weight. Plastic shielding is also showing promise. Other, more lofty plans could pay off big time. NASA is currently exploring the possibility of capturing asteroids and parking them near Earth, perhaps in orbit around the moon. Those bodies might be a viable source of water [pdf] for radiation protection, propellant, and human use.
And we might find protection in some unlikely places, too. Astronauts on the International Space Station have experimented with an unusual form of water shielding in the form of a curtain of hygienic wipes. According to a 2013 paper from Russian and Japanese scientists, the wet wipe curtain reduced the dose of radiation measured by around 37 percent.
Interested in learning about more of the trying conditions future astronauts will face—and the caliber of candidate NASA is looking for to overcome those challenges? Check out The New Right Stuff, a 2015 World Science Festival program featuring astronaut Michael Lopez-Alegria, anthropologist Jack Stuster and NASA physiologist Jennifer Fogarty. The journey begins on Thursday, May 28, 7:30 PM, at the Intrepid Sea, Air and Space Museum.
Image: World Science Festival staff
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