Space travel has always been portrayed as risky -- no air or water, extreme temperatures -- a place where even a small miscalculation can be fatal. It can also be hazardous to your brain health, particularly on a three-year-long mission to Mars, according to a study published this week in the scientific journal PLOS ONE.
The eight-year long study, conducted at the NASA Space Radiation Laboratory at Brookhaven National Laboratory on New York's Long Island, found that the cosmic radiation on such a mission could accelerate the onset of Alzheimer's disease.
NASA is working on sending astronauts to a passing asteroid in the 2020s, and talks of a trip to Mars in the 2030s. It would take three years, with current technology, to get there and back. Current spacecraft are not heavily shielded from the cosmic radiation crew members would encounter beyond Earth's protective magnetic field.
Researchers used mice that were genetically engineered to be predisposed to Alzheimer's disease. They exposed them to cosmic radiation that was simulated in the lab.
"Galactic cosmic radiation poses a significant threat to future astronauts," said Dr. M. Kerry O'Banion, senior author and professor of neurobiology and anatomy at the University of Rochester Medical Center.
The study team wanted to see if radiation had the potential to accelerate Alzheimer's in those who were genetically vulnerable. Mouse models have been used extensively in this type of research and the rate at which they develop the disease is well understood.
Scientists have long worried about the potential dangers of working and living in deep space. Cosmic radiation beyond low Earth orbit, researchers say, could lead to cancer, cardiovascular disease, even cataracts.
Radiation exposure can cause acute effects such as nausea, vomiting, fatigue, skin injury and changes to white blood cell counts and the immune system, according to the National Space Biomedical Research Institute. Longer-term radiation effects include damage to the eyes, gastrointestinal system, lungs and central nervous system.
On Earth, humans are protected by the planet's atmosphere and magnetic field. Crew members on the International Space Station, at an altitude of 200 miles, are still within the magnetic sheath that surrounds us. The 24 Apollo astronauts who flew to the moon between 1969 and 1972 were not protected, but the longest missions lasted less than two weeks.
Once out of low orbit, astronauts are exposed to showers of different radioactive particles. Though engineers say they can protect themselves from the radiation associated with solar flares, so far, they cannot block other forms of cosmic radiation.
The longer astronauts are in deep space, the greater the exposure to this low-level radiation.
This is the first such study to explore effects of radiation on the nervous system, a phenomenon known as neurodegeneration, according to the authors.
"The possibility that radiation exposure in space may give rise to health problems such as cancer has long been recognized," said O'Banion. "However, this study shows for the first time that exposure to radiation levels equivalent to a mission to Mars could produce cognitive problems and speed up changes in the brain that are associated with Alzheimer's disease."
O'Banion has spent the last 20 years studying Alzheimer's disease.
He and his fellow researchers studied a form of radiation from so-called high-mass, high-charged particles, which come in various forms and fly through space at high speeds. Some come from distant stars that have exploded.
At Brookhaven, where a portion of the research was conducted, particle accelerators were able to recreate some of the radioactive particles found in space.
"It is extremely difficult from an engineering perspective to effectively shield against them," said O'Banion. "One would have to essentially wrap a spacecraft in a six-foot block of lead or concrete."