Mars trip would deliver big radiation dose

Astronauts making the journey to and from Mars would face many new and uncertain dangers. Fortunately, the Mars rover Curiosity has reduced uncertainty about one of them: radiation exposure.

Measurements of radiation reaching the shielded interior of the spacecraft that carried Curiosity to Mars indicate that an astronaut on a yearlong round-trip would be exposed to around two-thirds of the career radiation limit that some space agencies set. Any time spent on the planet and outside the spacecraft would add more exposure.

The radiation dose they calculated was 0.66 sieverts, researchers report in the May 31 Science; the agencies’ limit for astronauts is 1 sievert.

On Earth, a 1-sievert dose increases cancer risk by about 5 percent. Scientists don’t know whether space radiation would have similar effects.

“The kinds of radiation that someone going to Mars would experience are different from any radiation that we receive here on Earth, so we don’t have direct experience of what the health risks are,” says David Brenner, director of the Center for Radiological Research at Columbia University.

Previous measurements of the radiation in space have been made outside spacecraft. Good luck enabled the new interior measurements, which were conducted with the Radiation Assessment Detector, a coffee-can-sized device attached to the Curiosity rover. Its designers intended the device to measure radiation on the surface of Mars, not inside the spacecraft that ferried it there.

“We realized as we were getting ready to launch that we had this serendipitous opportunity to also measure the radiation environment inside the spacecraft during our cruise,” says coauthor Donald Hassler of the Southwest Research Institute in Boulder, Colo.

The rover’s measurements confirmed predictions that 95 percent of a Mars-bound astronaut’s radiation dose would come from galactic cosmic rays. Humans are normally shielded from such rays by Earth’s atmosphere, so their effects on our health are unknown, Brenner says.

Still, he says, the measurements are useful because they were close to theoretical predictions of radiation exposure.