On a Long Trip to Mars, Cosmic Radiation May Damage Astronauts' Brains

President Barack Obama has reaffirmed his vision to send humans to Mars. In an editorial posted on CNN.com today (Oct. 11), the president wrote of his goal of "sending humans to Mars by the 2030s and returning them safely to Earth, with the ultimate ambition to one day remain there for an extended time."

NASA Administrator Charles Bolden echoed the president's enthusiasm, describing in a blog post today co-written with John Holdren, a senior adviser to the president, how NASA plans to "utilize public-private partnerships to enable humans to live and work in space in a sustainable way."

Key to the ambitious endeavor, however, is ensuring the astronauts' safety, which may be difficult, according to a NASA-funded study published yesterday (Oct. 10) in the journal Scientific Reports.

The new study, in rodents, shows that astronauts could suffer from a phenomenon called "space brain" during the long trip to Mars, as cosmic radiation bombards their bodies and damages their brain cells.

Researchers exposed the laboratory-bound rodents to a level of radiation similar to that expected on a six-month one-way trip to Mars. They found that the radiation caused significant long-term brain damage, including cognitive impairments and dementia, a result of brain inflammation and damage to the rodents' neurons.

The researchers said the new study revealed a far greater extent of brain damage than what was hinted at in their shorter, six-week study, conducted last year.

"This is not positive news for astronauts deployed on a two- to three-year round-trip to Mars," said Charles Limoli, a professor of radiation oncology at the University of California, Irvine School of Medicine, who led the study.

NASA told Live Science that the agency is funding such studies to better understand the risks posed to its astronauts, although the agency was not aware that Limoli's study was published and could not comment on the details.

Radiation hazards

Astronauts in space face two kinds of radiation hazards. One is the solar radiation from the sun, including ultraviolet rays, X-rays, protons and electrons. The other is cosmic radiation, which emanates from all directions in deep space and comprises atomic particles far more energetic (and thus more damaging) than solar radiation.

Limoli's research was aimed at assessing the possible human health problems that could be caused by cosmic radiation on a prolonged space journey. There are almost no studies so far that have looked at this, Limoli said. Humans have lived on the International Space Station (ISS) for months at a time. Russian cosmonaut Valeri Polyakov (born Valeri Ivanovich Korshunov but later changed his name) holds the record for the longest, continuous time in orbit — almost 438 days aboard the Mir space station.

However, because Mir (which is no longer in use) and the ISS are relatively close to Earth, Earth's magnetosphere — a natural magnetic field that deflects charged atomic particles from the sun and deeper space — mostly protects astronauts on board the orbiting labs from dangerous radiation exposure. Tests have shown that Polyakov and other astronauts have no serious brain damage as a result of their time in orbit. [5 Mars Myths and Misconceptions]

Astronauts who visited the moon ventured beyond this protective magnetosphere, but their entire round-trip lasted only about two weeks, so their radiation exposure was kept to a minimum. One previous study, done in 2013 in mice, suggested that radiation may hasten the development of Alzheimer's.

To simulate the cosmic radiation exposure humans would face during a long Mars trip, Limoli's group exposed rodents to charged particles at the NASA Space Radiation Laboratory at the Brookhaven National Laboratory in Upton, New York.

The researchers found that although the bombardment of the radiation was painless, it caused significant brain damage in the rodents. Imaging revealed that the animals' brain cells had a sharp reduction in features of the cells called the dendrites and spines, which would disrupt the transmission of signals among neurons, they said.

Limoli told Live Science that loss of dendrites and spines were "like a tree losing its leaves and branches," compromising the health of the tree. These physical losses explained the deficiencies the rodents showed in behavioral tasks designed to test learning and memory, Limoli said. In humans, this loss could lead astronauts to make poor decisions that could affect the safety of the crew, he added.

The researchers also discovered that the radiation affected the part of the brain that normally suppresses prior unpleasant and stressful associations, as part of a process called "fear extinction." This loss of fear extinction could make the astronauts prone to anxiety, Limoli said. 

Yet Limoli remains optimistic that NASA can still send astronauts safely to Mars. "This is not a deal breaker," he told Live Science. "This [cosmic radiation] is simply something we have to deal with."

A 30-month trip

NASA estimates that a 30-month trip to Mars — six months of travel each way, plus 18 months living on the Red Planet — would expose astronauts to a total of 1 sievert (Sv) of radiation. For comparison, Limoli said people who undergo certain kinds of radiation treatment for brain cancer may need to endure a dose at least 10 times higher than that through the course of that treatment. He said that these cancer patients, although they may be cured of cancer, have notable declines in their cognitive function.

Astronauts could be protected from cosmic radiation in two ways, a NASA press officer told Live Science. One would be to a passive method of installing thick metal shields or layers with water, either around the entire spacecraft or around sleeping chambers to block the radiation. Cosmic radiation is very penetrating, however, and shields that would be thick enough to block the rays would add considerable weight (and thus, expense) to the Mars mission.

Another way is an active method of installing an electromagnetic field to deflect the radiation, analogous to the magnetosphere itself. Limoli said his group and others are working on another strategy, medicines that could repair the damage caused by radiation, or protect or even restore neurons.  

It will certainly be a memorable trip to Mars, and NASA hopes the astronauts will stay healthy enough to remember it