Astronaut Mars mission risk assessed
Nasa's Curiosity rover has confirmed what everyone has long suspected - that astronauts on a Mars mission would get a big dose of damaging radiation.
The robot counted the number of high-energy space particles striking it on its eight-month journey to the planet.
Based on this data, scientists say a human travelling to and from Mars could well be exposed to a radiation dose that breached current safety limits.
Our correspondent Jonathan Amos discussed the findings with lead researcher Dr Cary Zeitlin from the Southwest Research Institute in Boulder, Colorado, US.