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The animals that are the greatest survivors in outer space are microscopic eight-limbed creatures known as tardigrades or water bears. In 2007, scientists sent two species of tardigrade into orbit, where they were exposed not only to the vacuum of space in which no human can breathe unaided but also to sufficient radiation to incinerate a human. When they were brought back to earth, a third of the total number of tardigrades that had been sent up were still alive, thus becoming the only animals native to planet Earth that are known to have survived extraterrestrial conditions unassisted. Moreover, ten per cent of these survivors went on to mate and lay eggs afterwards, which hatched normally.