On 4 November 2011, six men emerged from a windowless capsule based on the site of the Institute of Biomedical Problems in Moscow, Russia. They had been inside their spaceship for 520 days, enough time to (optimistically) go to Mars and back. They carried out the same kinds of activities and experiments that any astronauts would do on such a mission. Except for one thing: they never actually left Earth.

A recent paper in the journal PNAS documents the six-strong crew's sleep and activity patterns over the 520 days they were cooped up on their simulated mission to Mars and back. Each crew member wore a watch-like actigraph on their wrist, which tracked movement and monitored light exposure, and took a computer test every week to measure how alert they were.

Mathias Basner, lead author of the paper and Assistant Professor of Sleep and Chronobiology at the University of Pennsylvania, along with his colleagues, found that four out of six of the crew members suffered sleep problems during their mission.

By the end of the experiment, one crew member was living on a 25 hour day, meaning every two weeks there came a point when it was the middle of the day for everyone else, but for him it felt like the middle of the night. Another suffered partial chronic sleep deprivation. You can read more about the results of the study in Science Now (and other places, too).

Basner and his colleagues think that the lighting on the spaceship was at least partly to blame for these problems, and that a real mission to Mars would require lighting that mimics more closely the natural light we are used to on Earth.

But it's not all bad. Apart from the one sleep-deprived crew member, everyone's sleep time increased over the mission. This might not sound good (we've probably all experienced the sluggishness that sometimes follows a long morning lie-in). But it turns out that it is.

"Those five crew members who increased sleep time also increased their performance on this little attention test we had in the chamber," says Basner.

All of the findings of this study are important for long distance space missions, of course, but this one in particular is also of relevance to us back here on Earth. Basner told me:

"We're chronically sleep depriving ourselves, especially during the work week, and trying to catch up on the weekend a little, and consuming caffeine during the day to keep us going. This [experiment] just shows us that once these crew members had the opportunity to get more sleep, and they did get more sleep, their performance was increasing."

He also thinks that, while the situation the six Mars 500 crew members were in was quite unique, some aspects of it were not too dissimilar from our daily lives:

"The other message is we're kind of doing the same that these crew members were doing. We're spending most of the day inside, the unfortunate don't even have a window in their office, so we're living under artificial light as well. This could lead to similar kinds of circadian rhythm disorders as we saw in this one crew members, where we are not as alert during the day as we would want to be, and we may have trouble sleeping at times where we should sleep and we are sleepy at times when we should be fully awake."

The last line of the paper sums up:

"The essential need for humans to maintain sleep–wake activity cycles synchronized to the circadian biology that temporally coordinates human health and behavior appears to be as important on Earth as it will be en route to Mars."

The astronauts that eventually go to Mars will need to be in top condition, physically and mentally, for a successful trip. By working out how to maintain that level of health for a long-distance spaceflight, using simulated missions like this one, we are also learning more about how we should be treating ourselves here on Earth.