The Mars rover Curiosity found radiation levels on Mars are not lethal to humans, U.S. researchers say.

"Absolutely, astronauts can live in this environment," said Don Hassler, principal investigator for the rover's Radiation Assessment Detector, at a news conference Thursday.

Hassler said characterizing the radiation on the surface of another planet has never been done before now, CNN reported.

Researchers plan to collect radiation numbers over time to create a better assessment of exactly how much radiation a person would experience during a journey to Mars, Hassler said.

Curiosity has also begun measuring variations in the atmospheric pressure on the planet.

"We're finding that the Mars atmosphere is acting as a shield for the radiation on the surface," Hassler said. "And as the atmosphere gets thicker, that provides more a shield, and therefore we see more of a dip in our radiation dose."