The unnatural conditions of future space journeys have to better emulate the natural qualities of life on Earth, Dinges says. For example, the fluorescent lighting in the Mars500 chamber mostly emitted wavelengths in the green and yellow part of the visible light spectrum, but not much blue. Blue light is important, Dinges notes, because the light from the Earth's natural dawn is largely blue and signals the brain that it's time to wake up. The crew would also have to hold a tight schedule for meals and physical activity.
The sleep times of the Mars500 crew were not quite synchronized, which would increase the risk of accidents. "Imagine a watch that's running 24 hours and 20 seconds a day and another that's got a 24-hour day exactly," says Dinges. "Over time, those two watches will go completely out of sync, and that's what we want to make sure doesn't happen to a crew." One crewman seemed chronically sleep deprived, the researchers noted, sleeping less as the simulation progressed and reporting poor-quality sleep throughout the whole mission. Another crew member's sleeping habits went completely off schedule. He lived on a 25-hour sleep-wake cycle and frequently snoozed while the rest of the crew was awake.
The findings show that agencies recruiting astronauts for such a long mission should take their candidates' established sleep habits into account, says physiologist Derk-Jan Dijk of the University of Surrey in the United Kingdom, who was not involved with the study. "You definitely want to be sure that these people, while going about their normal lives, are not already extreme late sleepers, for example."
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This is adapted from ScienceNOW, the online daily news service of the journal Science. http://news.sciencemag.org