Astronauts on a months-long mission to Mars and back will have more to contend with than boredom and a lack of gourmet cuisine: Disrupted sleep may be a serious side effect of extended space flight, potentially changing crew dynamics and affecting performance on high-pressure tasks.

In an epic feat of playacting, a crew of six men lived for 520 days inside a hermetically sealed 550-cubic-meter capsule in Moscow. As the grueling experiment wore on, the crew drifted into torpor, moving less and sleeping more. Four men experienced sleep problems, scientists report online January 7 in the Proceedings of the National Academy of Sciences.

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