The American space agency NASA has warned that astronauts on any future mission to Mars would be exposed to so much radiation just getting there that they'd probably develop a fatal cancer.
The BBC reports that NASA's Curiosity Rover 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.
This calculation does not even include time spent on the planet's surface.
When the time devoted to exploring the world is taken into account, the dose rises further still.
This would increase the chances of developing a fatal cancer beyond what is presently deemed acceptable for a career astronaut.
The findings are published in the latest edition of Science magazine and researchers say engineers will have to give careful consideration to the type of shielding that is built into a Mars-bound crew ship.
However, they concede that for some of the most damaging radiation particles, there may be little that can be done to shelter the crew other than to get them to Mars and the partial protection of its thin atmosphere and rocky mass as quickly as possible.