Future astronauts going to Mars could have trouble sleeping, become lethargic, and have problems with mental tasks over the course of a long mission.

That is one takeaway from the Mars500 experiment, an international test run by the Russian Academy of Science in conjunction with the European and Chinese space agencies. The experiment placed a six-man crew in a simulated spaceship en route to Mars for 520 consecutive days during 2010 and 2011.

The purpose of Mars500 was to find out how the “astronauts” fared physiologically and psychologically under such isolated conditions. The volunteers were subjected to extensive prodding and poking, having their blood and urine checked daily and their sleep patterns monitored.

“Our major finding was that there were really large individual differences with how the crew responded to the isolation,” said psychiatrist Mathias Basner of the University of Pennsylvania School of Medicine, who helped run the sleep experiment, which appeared Jan. 7 in the Proceedings of the National Academy of Sciences. “Four of them showed at least one issue that could have exploded or led to a severe adverse effect during a Mars mission.”

Similar experiments in the past have studied the psychology of isolated groups, such as crews overwintering in Antarctica, but Mars500 was the first detailed simulation of circumstances that could arise during a manned Mars venture.

While two of the participants fared very well under this prolonged period of isolation, all members reacted fairly differently. Most crewmembers stayed on a 24-hour sleep cycle schedule, but one fell into a 25-hour day. “He became disconnected,” said Basner, adding that about 20 percent of the time he was the only crewmember awake or the only one asleep.

“If you have people awake when others are sleeping, that doesn’t bode well for crew dynamics and cohesion,” said biomedical researcher Lauren B. Leveton, who studies behavioral health and performance at NASA’s Johnson Space Center and who was not involved with the research. Such detachment would likely have to be counteracted in a real deep-space mission, she added.

Another interesting observation from the experiment was that all the volunteers slept much more then usual. Basner chalks this up to the fact that for much of the mission, they had ample time to do nothing. Most people in modern society, he said, have sleep deficits they never make up because our lifestyles encourage constant work activity and caffeine use. Given enough sleep, most of the participants actually saw increased cognitive performance overall.

The other side of this was that crewmembers often succumbed to boredom and monotony. There were only so many times they could play Guitar Hero. The volunteers became sedentary, reduced their movement while awake, and spent more time sleeping and resting.

But even here there was considerable difference. One member of the study began sleeping for shorter and shorter intervals, which caused his cognitive abilities to suffer. Another had issues with mood and depression.

“There’s a lot of value in this type of research, it’s an excellent study,” said Leveton. Future work could help elucidate particular factors affecting the crewmembers by varying different conditions, such as the amount of privacy or social interaction times, she said.

But other researchers would have liked the simulation to address how the Martian day might affect crewmembers. Since a day on Mars is slightly longer than one on Earth (a Mars day is 24.65 hours), astronauts on the surface on Mars might have trouble with their circadian rhythm getting out of sync with actual day/night cycles. The effects from the current study are "likely to be much worse during a real Mars mission when individuals might be asked to live on a Martian day if they live on Mars," wrote neuroscientist Steven W. Lockley of Harvard Medical School, who was not involved in the research, in an e-mail to Wired.

Though nothing serious happened to the members of Mars500, it shows some of the major issues in trying to screen possible participants in a real long-term deep-space mission. Scientists would need to identify key markers that could help predict which individuals might experience which types of sleep or mood problems. Because many of the problems showed up fairly early in the Mars500 mission, Basner hopes that future crew selection could include a similar but shorter simulation to find out who may be affected and who won't.

One simple way to try and sync up crews on future space missions or on the Martian surface would be to adjust the proportion of blue light that astronauts see at different points of the day. The retina has a natural pigment called melanopsin that is sensitive to the blue wavelengths and provides a direct relay to the hypothalamus, the primary pacemaker for circadian systems in the brain. Increasing blue light increases activity while increased red light promotes sleep.

In 2015, the International Space Station will upgrade from its stark fluorescent lighting to LED lights that can adjust their blue wavelengths, which will provide astronauts with external cues to regulate their sleep. Controlling lighting could be particularly important on future Mars missions that stay for long periods on the surface, because the Martian day is slightly longer than the one on Earth.

As a final takeaway, the study could help individuals who are not going into space. “It underscores the fact that people living on Earth should get a chance to sleep more. It lets us improve cognitively,” said Basner.

*Images: 1) A participant in a precursor 105-day study to Mars500 is outfitted with sensors to monitor his sleep patterns. ESA 2) Simulated Mars excursions as well as crew habitats during the Mars500 experiment. "Mars 520-d mission simulation reveals protracted crew hypokinesis and alterations of sleep duration and timing," information appendix, *Basner et. al., PNAS, 2013