A day on Mars—or a "sol"—is 24 hours and 40 minutes long, close enough to Earth's that for a long time NASA didn't think much of it. But those 40 minutes a day add up, and sleep scientists now worry that our Earthly circadian rhythms could be one more major headache for the first humans on Mars.
Over at the Atlantic, Tom Chmielewski has written a fascinating piece on the problem of jet lag—or should we say "rocket lag?"—on Mars. A select group of humans have already encountered this problem: the human mission controllers of Mars exploration rovers. They have to rise and sleep according to Martian time, emerging 2.5 days behind the rest of Earth at the end of 90 days.
But if and when we send humans to Mars, how will their circadian rhythms adjust (or not) over months, or possibly years? Chmielewski notes that recent research has found human circadian rhythms are naturally an average of 24 hours and six minutes for women and 24 hours and 12 minutes for men, with some individual variation. Is just forty minutes enough to throw us off? Harvard sleep researcher Charles Czeisler says that shorter-term simulations in his lab found humans did indeed have trouble adjusting to a Martian sol.
Even more interesting is the problem of light. Blue light wakes us up, and the bright morning sun on Earth has plenty of blue wavelengths. On Mars, however, sunsets are also blue. Mars is an inhospitable place for the human body, even in these subtle ways. Read more about sleep problems on Mars in the Atlantic.
Top image: Sunset on Mars as captured by the Spirit rover. NASA/JPL/Texas A&M/Cornell