Can People Go To Mars?

"But if it's 19%… our 40something astronaut would face a 20% + 19% = 39% chance of developing life-ending cancer after he returns to Earth. That's not acceptable."

The error bars are large, says Cucinotta, for good reason. Space radiation is a unique mix of gamma-rays, high-energy protons and cosmic rays. Atomic bomb blasts and cancer treatments, the basis of many studies, are no substitute for the "real thing."

Astronauts have rarely experienced a full dose of these deep space GCRs. Consider the International Space Station (ISS): it orbits only 400 km above Earth's surface. The body of our planet, looming large, intercepts about one-third of GCRs before they reach the ISS. Another third is deflected by Earth's magnetic field. Space shuttle astronauts enjoy similar reductions.

Apollo command modules were well-enough shielded for quick trips to the Moon and back.

Apollo astronauts travelling to the moon absorbed higher doses - about 3 times the ISS level - but only for a few days during the Earth-moon cruise. GCRs may have damaged their eyes, notes Cucinotta. On the way to the moon, Apollo crews reported seeing cosmic ray flashes in their retinas, and now, many years later, some of them have developed cataracts. Otherwise they don't seem to have suffered much. "A few days 'out there' is probably safe," concludes Cucinotta.

But astronauts travelling to Mars will be "out there" for a year or more. "We can't yet estimate, reliably, what cosmic rays will do to us when we're exposed for so long," he says.

Finding out is the mission of NASA's new Space Radiation Laboratory (NSRL), located at the US Department of Energy's Brookhaven National Laboratory in New York. It opened in October 2003. "At the NSRL we have particle accelerators that can simulate cosmic rays," explains Cucinotta. Researchers expose mammalian cells and tissues to the particle beams, and then scrutinize the damage. "The goal is to reduce the uncertainty in our risk estimates to only a few percent by the year 2015."