European Space Agency scientists have unveiled a proposed container for a valuable scientific cargo -- samples to be brought back from Mars. Even if a sample mission to Mars may be years in the future, it is one of the most challenging space ventures possible for robotic exploration, they said, requiring a robust, multifunctional sample container. The container, a proof-of-concept design, is a 9-inch-diameter sphere weighing less than 12 pounds, designed to keep martian samples in pristine condition at just 14 degrees F throughout their long journey back to Earth, the ESA reported from its Paris headquarters Tuesday. In a proposed sample mission the container would be landed on Mars along with a rover to retrieve samples; once the container was filled it would be launched back up into Mars orbit to be retrieved by a rendezvous spacecraft for a return to Earth. The container would be enclosed in another larger bio-sealed vessel to ensure perfect containment of any returned martian material, ESA scientists said. \"Because there is the potential, however remote, that the samples contain alien life, we have to comply with strict planetary protection protocols not to bring them into contact with Earth\'s biosphere,\" project overseer Benoit Laine said. While the sample container is a proof-of-concept design it is fully functional and has undergone testing in simulated thermal conditions, the scientists said.