Six healthy male volunteers sealed inside a simulated Mars spacecraft in Moscow showed a 7 percent reduction in active waking over 520 days, according to a peer-reviewed PNAS paper published by Mathias Basner and colleagues in 2013. The extreme-environment experiment, known as Mars500, tracked participants using wrist actigraphs to record nearly 4.4 million minutes of data, revealing a steady slide toward sleep and quiet waking rest that researchers termed “behavioural torpor.”
Inside the Mars500 Simulation Facility in Moscow
Mars500 began on June 3, 2010, at the Institute for Biomedical Problems of the Russian Academy of Sciences. The facility consisted of a 550-cubic-metre pressurised complex of interconnected modules that reproduced a long outbound flight, Mars orbit, a surface phase for half the crew, and the return journey. According to an European Space Agency overview, the mission never left Moscow. While confinement, isolation, and routine were real, microgravity, radiation, launch risk, and the impossibility of emergency return were not.
The crew included three Russians, two men selected by the European Space Agency and one selected by the China National Space Administration. They were healthy male volunteers aged 27 to 38, with an average age of 32. Their backgrounds in engineering, medicine, the military and space training broadly resembled those of working astronauts and cosmonauts. Operational rhythms were maintained through scheduled maintenance, scientific work, exercise, emergency drills, and simulated communication delays with mission control.
Did you know? During the final 20 days, active waking and movement intensity rose sharply, while sleep and rest fell. Mission managers attributed the change to anticipation that the hatch was finally about to open.
Active Waking Falls While Sleep and Rest Increase
Continuous monitoring via wrist actigraphs produced 4,396,333 usable minutes of data, covering 98 percent of the entire mission. A validated algorithm classified each minute as active wakefulness, sleep or waking rest. Comparing the first and fourth 130-day quarters, active wakefulness fell 7 percent, translating to 1.12 fewer hours per person each day.
Conversely, sleep and quiet waking rest increased across the duration of the study. Average actigraphic sleep climbed from 7.12 hours a day in the first quarter to 7.71 hours in the fourth, representing an 8.4 percent increase. Waking rest rose 50.4 percent, or 0.54 hours. Added together, the crew slept 673 more hours in the second half of confinement than in the first.
Understanding Behavioural Torpor in Confinement
The reduction in movement did not mean human hibernation. In animals, physiological torpor usually involves controlled reductions in metabolism and body temperature, which Mars500 did not show. The men remained awake, completed work, exercised and finished the mission. Here, “behavioural torpor” was an analogy for sedentariness: progressively less active waking, more sleep and more quiet rest during prolonged confinement.
Across the crew, vigilance performance did not worsen cumulatively. In the second half, when the men slept more, their average normal response speed improved and an already low rate of attention lapses fell. However, lighting levels remained exceptionally dim. For 90 percent of waking mission time, the wrist monitors measured light below 177 lux, and mean exposure while actively awake fell by 25.6 percent across the four quarters, from 104.8 lux to 78.0 lux.
Individual Crew Responses and Limitations
A companion PLOS One analysis of the same crew showed how much the group average concealed. Four of the six experienced at least one problem involving sleep timing, sleep quality or vigilance. One developed a roughly 25-hour free-running rhythm, another increasingly divided sleep between a main night period and daytime naps, and a third developed worsening sleep-onset insomnia and was the only crew member whose sleep duration declined across the mission. Two men showed no changes in sleep duration, timing or quality and no reported psychological distress.
The mission had notable limitations. Mars500 had no control crew living outside the chamber on the same schedule. Its sample was six men, all carefully selected, in one facility. Wrist movement estimates sleep rather than measuring brain activity, and the authors noted that the actigraph algorithm may have overestimated average sleep by about 26 minutes a day. Furthermore, real spaceflights involve microgravity, radiation, equipment risk and the knowledge that help could be months away.
Frequently Asked Questions
What was the duration of the Mars500 mission?
The Mars500 mission lasted for 520 consecutive days, beginning on 3 June 2010 and ending when the hatch reopened on 4 November 2011, inside a sealed facility in Moscow.
Did the Mars500 crew experience actual hibernation?
No. Researchers used the term “behavioural torpor” as an analogy for sedentariness: progressively less active waking, more sleep and more quiet rest during prolonged confinement, rather than literal physiological hibernation.
How was crew activity measured during the simulation?
Each man continuously wore a wrist actigraph, a watch-sized device that recorded movement and light exposure once a minute.
Did all crew members react the same way to isolation?
No. While the group average showed a 7 percent drop in active waking, individual responses varied widely. Four of the six experienced at least one problem involving sleep timing, sleep quality or vigilance, while two men showed no changes in sleep duration, timing or quality and no reported psychological distress.
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