Genetically modified “mighty mice,” who lack a key protein inhibiting muscle growth, were able to maintain their muscle mass while spending a month in space, researchers reported Monday in the Proceedings of the National Academy of Sciences. The team, led by Dr. Se-Jin Lee of Jackson Laboratory, sent 40 female black mice to the International Space Station in December aboard a SpaceX rocket, eight of which were “mighty mice,” in a study that will help scientists learn how to prevent loss of muscle and bone mass in astronauts spending prolonged amounts of time in zero gravity. Another eight mice administered a treatment that blocked a pair of proteins that typically limit muscle mass also returned to Earth with increased muscle mass. Lee told the Associated Press that the experiment has uncovered “an embarrassment of riches” to study further. As for how to translate the findings in humans, Lee’s co-author and wife, Emily Germain-Lee, stressed that much more research must be done before a drug can be developed for human use. “We’re years away. But that’s how everything is when you go from mouse to human studies,” she said.