You can’t go many days without someone talking about going to Mars. Just in the last few weeks: Elon Musk, CEO of SpaceX, laid out his plans to sell tickets to the red planet for $200,000; Dennis Muilenburg, CEO of Boeing, vowed to get there before Musk; and US president Barack Obama reiterated his plans to send humans to Mars by 2030.

Before these fantasies become reality, there are many problems to overcome. One of them might be the most difficult: how to stop astronauts from suffering irreversible damage to brain functions that are crucial to completing a space mission?

This damage is predicted to be caused by space radiation. When we’re on Earth, the planet’s magnetic field shields us from most of it. A spacecraft’s hull can’t provide that level of protection. The result, a 2015 study predicted, would be brain damage that would affect astronauts’ cognitive powers.

The study was done on mice, who were exposed to a space-equivalent dose of radiation in the form of charged oxygen and titanium particles. Then, the mice were observed for six weeks and given a battery of cognitive tests. As Quartz reported then:

When compared to mice who were not exposed to radiation, the irradiated mice performed far worse. On being shown familiar objects, these mice weren’t interested. They also lacked curiosity towards new objects.

Now, the same researchers have gone a step further. They’ve observed irradiated mice for longer and looked in more detail at the sort of damage radiation can cause in the brain.

In the new study, published in Scientific Reports, they find that the prefrontal cortex of the mice, which is the area of the brain responsible for making decisions and moderating social behavior, had fewer neural connections than the brains of mice who weren’t exposed. The irradiated mice were more anxious, weren’t able to control fear, and had reduced cognitive powers.

Worse still, this brain damage lasted at least 24 weeks with no apparent sign of improvement. The implication is that it was probably irreversible.

As Quartz reported previously:

Space radiation is so harmful because its high-energy particles leave tracks of damage in cells and tissue that are difficult for the body’s repair system to fix. This occurs because the ionized particles are like bullets inside of bullets: Once the big bullet manages to enter cells or tissue, it causes further damage by firing off many more smaller bullets.

Mice are not men, so the study’s results can only estimate how such radiation will affect human brains. It’s worth noting, however, that the dose of radiation used in the study (about 210 milliSieverts, equivalent to about 600 chest X-rays) is smaller than the 300 milliSieverts that NASA estimates (pdf, p. 9) humans would be exposed to during just the first six months of a mission to Mars.

Adding metal shielding to spacecraft could help, but it’s prohibitively expensive. The heavier the craft, the more fuel it has to carry for launch. Another option is to take drugs that counter radiation. Perhaps the most inventive idea involves using the astronauts’ urine and feces as shielding. Water shields better against this sort of radiation than metal; the ship could store its water supply in a hull cavity that surrounds the crew quarters, and replace it with human waste as the water supply is used up, stored in special bags that extract the water out of the human waste for reuse.


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