He adds that NASA has established a career radiation-dose limit for astronauts.

“I think it’s never really been a question of if we can go to Mars. It’s a matter of when we go, how do we best-protect our astronauts, and so characterizing the radiation environment in terms of the types of radiation that we observe and when it’s the worst and when we’d need to take precautionary measures, I think, is one of the things that we’re, we’re learning from RAD.”

Researchers say Curiosity is providing measurements that will help scientists design a trip by astronauts to Mars. President Obama has challenged NASA to send humans to the red planet by the 2030s.

Finally, a rock that fell to Earth from Mars has provided surprising new details about the planet. Scientists call the rock -- which weighs 320 grams -- “Black Beauty.” It was discovered two years ago in the Sahara Desert.

American researchers believe the rock came either from Mars’ crust or surface. They think it was formed more than two billion years ago. That would make it one of the oldest Mars meteorites ever found.

The rock contains more water than any of the other 100 meteorites known to have come from the Red Planet. The presence of water increases the possibility that life could have existed on Mars.

The researchers say the rock has given them an idea of ancient surface and environmental conditions on Mars that no other meteorite has ever offered.