Could a trip to Mars addle your brains? Some scientists say it might, based on a study of high-energy radiation's effects on mouse neurons. But an advocate for Red Planet missions says the study overstates the effects.
The report, published Friday in the open-access journal Science Advances, found that mice who were exposed to radiation similar to galactic cosmic rays showed degradation in their brain cells, and didn't do as well on cognitive tasks.
"This is surprising, and it suggests that NASA has a new complication to consider when they send astronauts into deep space," senior study author Charles Limoli, a professor of radiation oncology at the University of California at Irvine's School of Medicine, told NBC News.
Scientists have long known that space radiation poses a challenge for deep-space missions — as do the health effects of long-term weightlessness, such as bone loss, muscle decline and vision impairment. Two years ago, a study based on data from NASA's Curiosity rover suggested that radiation levels on the Martian surface are roughly similar to those experienced on the International Space Station.
However, the newly published study raises questions beyond, say, elevated cancer risk.
Limoli said radiation exposure could conceivably impair astronauts' judgment during a mission to Mars. "The cognitive impairment would be relatively subtle, and would interfere with their ability to concentrate or focus on a problem," he said.
A deal-breaker for Mars?
NASA is looking into techniques for radiation shielding, and Limoli acknowledged that such shielding could help guard against solar radiation. But even the strongest shields under consideration would provide limited protection against more energetic cosmic rays. "There really is no escaping them," Limoli said.
Limoli said he and his colleagues are working on potential medications that could counteract brain-cell degradation, but declined to go into detail because the studies were in progress. "Suffice it to say we have several potential compounds that are targeting a variety of signaling pathways in the brain," he said.
NASA has set a goal of sending humans to Mars and its moons by the 2030s, and Limoli said the radiation concern was "not a deal-breaker" for such missions. He noted that the research was conducted in cooperation with NASA's Research Program.
NASA spokeswoman Stephanie Schierholz said the space agency was well aware of the radiation issue. "NASA recognizes the importance of understanding the effects of space radiation on humans during long-duration missions beyond Earth orbit, and these studies and future studies will continue to inform our understanding as we prepare for the journey to Mars," she wrote in an email.
Questions about the study
After reviewing the Science Advances paper, Mars Society President Robert Zubrin said the study wasn't a good analog for how a real-life mission to Mars would proceed. "The dose rates they are using are approximately a million times greater than what astronauts would experience on a trip to Mars," he told NBC News.
In the experiment, the mice were exposed to a single highly energetic dose of radiation rather than the lower level of exposure that astronauts might receive over two or three years. "If you received this dose for one minute, you would get acute radiation sickness," Zubrin said. "If you received this dose for five minutes, you'd be dead."
During a long-term space trip, the body could use its cellular repair mechanisms to counteract radiation's effects, he said. Zubrin said the difference between the short-term, higher-level exposure and the long-term, lower-level exposure could be compared to downing 30 shots of vodka in a minute and a half, as opposed to having a shot every month for two and a half years.
Zubrin has an interest in seeing missions to Mars proceed, because that's the purpose of the nonprofit advocacy group he's headed for 17 years. But even he acknowledged that the effects of long-term spaceflight would pose a challenge for deep-space explorers. In his view, the negative effects of long-term weightlessness (which have been documented among spacefliers) were a bigger concern than the negative effects of space radiation exposure (which have not been as well documented).
"If NASA is concerned about the health of astronauts," he said, "the first thing is to address artificial gravity."
In addition to Limoli, the authors of the Science Advances paper, "What Happens to Your Brain on the Way to Mars," include Vipan Parihar, Barrett Allen, Katherine Tran, Trisha Macaraeg, Esther Chu, Stephanie Kwok, Nicole Chmielewski, Brianna Craver, Janet Baulch, Munjal Acharya and Francis Cucinotta.