Nasa astronaut Scott Kelly on a spacewalk
Scott Kelly spent a year in space to study the impact of long-term space travel on the human body Nasa

NASA astronauts who will travel to Mars may risk developing cognitive impairments and symptoms of dementia, due to cosmic radiation exposure. More immediately, the brain damages they sustained during deep space travel may also compromise critical decision making during their mission.

NASA's plan to send humans to Mars within the next two decades is arguably one of the most exciting goal for space exploration in the near future, but it will be a challenging one. The vast distances between Earth and the Red Planet and the dangers of such a long journey into space have been repeatedly highlighted, but less has been said about the adverse health effects of exposure to cosmic rays.

In a study published in Scientific Reports, research has looked into the impact of such radiation on rodents, to learn more about the health risks astronauts may face on an extra-terrestrial adventure to Mars.

Brain damage and behaviours

The scientists worked with rodents which they exposed to charged particle irradiation – fully ionized oxygen and titanium – at the NASA Space Radiation Laboratory. Looking at the animals' brains on scans, they identified clear signs of long-term damage.

Six months after exposure, the rodents had important levels of brain inflammation and neural damage. In particular, there was a decline in the numbers of dendrites and spines on neurons, disrupting the transmission of signals among brain cells.

These damages were matched with poor performances in a series of behavioural tasks administered 12 and 24 weeks after irradiation to assess the rodents' memory and learning. This suggests that cosmic radiation have the potential, on the long-term, to produce cognitive impairment and in the worse cases, dementia.

The scientists are concerned these changes to the brain could also endanger the astronauts on the shorter term, during the course of their mission to Mars. This worry was further confirmed by the fact radiation appeared to disrupt a process known as "fear extinction". In the experiments, the rodents were more prone to remember unpleasant associations, and to feel anxious.

"Deficits in fear extinction could make you prone to anxiety, which could become problematic over the course of a three-year trip to and from Mars," lead author Charles Limoli, from the University of California (Irvine) said.

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Expeditions to Mars will not be without risks for astronauts' health NASA/JPL-Caltech

While the time required for a mission to Mars will probably sufficient for brain damages leading up to cognitive impairments to develop, the researchers say that the dementia-like deficits would take months to appear.

More research will likely be conducted soon to further confirm these findings. In parallel, scientists are also working on solutions, such as designing spacecraft that would include areas of increased shielding. Nevertheless, it is important to note that "these highly energetic charged particles will traverse the ship nonetheless and there is really no escaping them," Limoli concludes.