Imagine life on a spaceship headed to Mars. You and your five crewmates work, exercise, and eat together every day under the glow of fluorescent lights. As the months pass, the sun gets dimmer and communication with Earth gets slower. What does this do to your body? According to an Earth-based experiment in which six volunteers stayed in a windowless "spaceship" for nearly a year and a half, the monotony, tight living space, and lack of natural light will probably make you sleep more and work less. Space, for all intents and purposes, turns you into a couch potato.
A mission to Mars would take about 520 days-including the months it takes to travel there and back and the time spent on the Red Planet. But the longest any human has spent off Earth is 437 days straight, a record set in 1995 by Russian cosmonaut Valeri Polyakov, who was orbiting relatively close to home in the space station Mir. Polyakov seemed to bear the burden of long space flight fairly well, but many questions remain about just what a long mission farther from the sun would do to astronauts' ability to sleep and keep energized.
For answers, scientists turned to the Mars500 mission simulation in Moscow, which ended in November 2011. Six crewmen-who are an international mix of astronaut trainers, engineers, and doctors between 27 and 38 years old-stayed in a series of tunnellike chambers and played out the 520-day mission to Mars. "It was thought to be a safe way to try to begin to understand those questions instead of just launching into an extremely long space flight," says study co-leader and sleep scientist David Dinges of the University of Pennsylvania. The crew could communicate with the outside world, but with a time delay depending on how far the mission was supposed to be from Earth. Halfway through the mission, the volunteers even worked on a simulated martian landscape inside a large room with a sandy floor and a black ceiling dotted with fake stars. Throughout the experiment, video cameras and activity-monitoring wristwatches recorded the crew's movements, enabling scientists to observe how often the crew members slept and how much of their time awake was spent lazing about.