Rocks on the Moon or Mars could be used to build shelters to possibly protect astronauts from dangerous cosmic radiation, European researchers say.

German scientists working with the European Space Agency have tested how well stone slabs can protect against radiation, a release from the GSI Helmholtz Center for Heavy Ion Research said Monday.

The findings are important because astronauts would be more exposed to radiation because neither a magnetic field nor a thick atmosphere protects them on the Moon or Mars, and ground stations would not be built from terrestrial materials that might offer protection, researchers said.

"In space travels every gram counts. Transporting building material through space would lead to a cost explosion," GSI researcher Chiara La Tessa said.

"That is why ground stations would basically be built from Moon and Mars regolith -- especially the shielding. We know from the analyses done by rovers what the local sand and stones consist of. With this information one can produce Moon and Mars regolith on Earth and we test it for its properties."

GSI scientists conducted tests intended to see how far cosmic rays might pass through Moon and Mars rock.

"I cannot estimate how the material is going to react to the radiation yet," La Tessa said. "This we will know when we [have] analyzed our experiment data."