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SOMETIME in the next decade NASA plans to collect a sample of Martian soil and bring it back to Earth. In anticipation, the US National Research Council has pointed out that if there are microscopic life forms on Mars, they could be dangerous. However remote the risk, samples should be delivered straight to a biosafety level-4 lab, the sort where deadly viruses such as Ebola are handled. By the same token, we have a moral duty not to infect other worlds, so vast amounts of time and money are going into making sure that Mars missions do not export potentially…