Space Radiation Could Be a Mars Mission-Killer

Among the many physical risks facing astronauts sent to the Moon or Mars, the biggest danger will also be the least visible: radiation.

This is nuclear particles that are spewed out by the Sun—and which in storms called solar flares can be potentially lethal—or arrive at almost light speed from beyond the Solar System, a phenomenon called cosmic rays.

The particles slice through strands of DNA, boosting the risk of cancer and other ailments.

Manned missions in low orbit, such as the US space shuttle, the Soviet-era Mir and the International Space Station (ISS), are mostly protected by Earth's magnetic field, the magnetosphere.