A manned mission to Mars would give astronauts a radiation dose that could exceed NASA's set guidelines for lifetime safe exposure, according to a new study.
There are several technological hurdles that would have to be solved before humans can set foot on the Red Planet, but Thursday's study, published in Science, suggests that radiation exposure to galactic cosmic rays and charged particles from the sun may not stop several Mars voyages in their tracks.
The study was the first to measure radiation exposure on a spacecraft headed to Mars. The team, made up of NASA researchers and scientists at the Southwest Research Institute in Colorado, measured radiation levels on the Mars Science Laboratory, the spacecraft that transported the Curiosity rover to Mars in 2012. A subsequent study will measure Curiosity's radiation levels while the rover has been on Mars's surface.
"You can have all the models you want, but until you've actually made the measurements, you don't really know," says Don Hassler, a researcher at SRI and one of the authors of the study. "We've actually made the first measurements of this. [Radiation] is certainly a challenge."
Manned missions to Mars seem to be getting closer to becoming a reality: Inspiration Mars, a project headed by entrepreneur Dennis Tito, plans on orbiting the planet in 2018 on a 501-day mission. Mars Science Laboratory took 253 days to get to the planet.
"It is clear that the exposure from the cruise phases alone is a large fraction of (and in some cases greater than) currently accepted astronaut career limits," the study says. "Time spent on the surface of Mars might add considerably to the total dose."
Current NASA limits on radiation vary by person, but the agency tries to keep an astronaut's elevated risk of dying from cancer to about 3 percent above normal. Some experts say that level should be well within acceptable limits.
"The cancer risk is on the order of a couple percent – let's say it's a statistical risk comparable to smoking over the same amount of time," says Robert Zubrin, president of the Mars Society. "It's not something we should prescribe to the public, but it's not a showstopper."
Many people, it seems, aren't worried about the potential risks of traveling to Mars. More than 80,000 people have applied for a one way trip with Mars One, a non-profit group that plans on settling Mars in 2023.
Though NASA has made strides in developing radiation-proof shielding, further improvements seem far off, Hassler says.
"Most of the best shielding works because of sheer mass. That's kind of a competing interest for space flight," he says.
Hassler says the team is conducting a study about radiation exposure on the surface of Mars. It is unclear whether the thin Martian atmosphere provides any protection against radiation, but levels on the surface are almost certainly lower than those found in deep space, he says.
"It's less just from a geometry point of view," he says. "In deep space, you have it coming from you from all directions, but on the surface, you're protected on one side from the planet itself."