The trip to Mars takes six to nine months one way with current propulsion technology. So, these results should ring a cautionary bell for NASA and other organizations that aim to send people to the Red Planet, study team members said. “This is not a deal-breaker for space travel, but when you send astronauts up there; prepared for what some of the consequences are exposed to these radiation fields,” said study co-author Charles Limoli, a professor of radiation oncology at the University of California, Irvine (UCI) School of Medicine.
“These chronic low-dose-rate, low-dose-exposure scenarios are going to increase the risk of developing; perhaps, mission-critical performance deficits,” Limoli told Space.com. “What exactly those are, they will never know until we get out there.” Researchers investigating the effects of deep-space radiation; have historically given lab animals acute doses high levels over a relatively short period of time.
Functional endpoint in the brains
But Limoli and his colleagues led by Munjal Acharya and Janet Baulch of UCI’s Department of Radiation Oncology ;and Peter Klein of Stanford University’s Department of Neurosurgery took a different tack. Using a neutron-irradiation facility; they exposed 40 mice to 1 milligray of radiation per day (1 mGy/day) for six months, about the same dose and duration that astronauts would experience on a trip to or from Mars. (Astronauts in low Earth orbit exposed to lower doses; because protected by our planet’s magnetosphere.)
“However, this is the first study that looked at space-relevant dose rates;” Limoli said. “And this is the first study to analyze the consequences of the low dose rate over the course of time on functional endpoints in the brain.” The results were striking. But radiation-exposed mice exhibited more stress behaviors and a decreased ability to learn and remember. However, the physiological work bolstered these behavioral findings, identifying impaired cellular signaling in two key areas of the brain: the hippocampus; associated with learning and memory, and the prefrontal cortex, the site of many complex cognitive functions.
Low radiation doses
But the researchers said they are not sure what caused these physiological effects in the brain; the team didn’t trace out the molecular pathways involved. But the low radiation doses employed suggest that the impacts are probably not the result of cell death or DNA damage; Limoli said. NASA is keenly aware of, and interested in, these results; the space agency helped fund the new study, which was published Monday (Aug. 5) in eNeuro, the Society for Neuroscience’s open-access journal.
However, the anxiety and depression effects shouldn’t be a big deal for NASA going forward, Limoli said; the agency can screen potential Mars astronauts with such impacts in mind. But the learning and memory impairments present a more serious concern, he added. The effects of chronic radiation exposure “would probably manifest in a scenario where the astronauts have to deal with some unanticipated event where there’s some on-the-spot decision-making or problem-solving involved,” Limoli said.