On the left, shifting hormone levels over time. On the right, work (gray) and sleep (black) hours of NASA staff on Martian time gradually cycle around the clock.
Mars has an ever-so-slightly longer day than we do: 24 hours and 39 minutes, to be exact. To control solar-powered rovers like Phoenix and Curiosity, NASA teams must shift their sleeping cycles to match, and it’s a lot harder than it sounds: that fraction of an hour extra means that their sleep schedules creep every day, so while 1 pm might be the middle of the night one week, say, it will have become breakfast time by the next. Staying on Mars time is so grueling that staff for the Sojourner rover in 1997 bailed on the schedule a third of the way through the mission.
But there may be ways of making the shift more graceful. In a recently published study following personnel of the Phoenix rover mission in 2008, a team of researchers provided training sessions to facilitate the switch to Mars time, including tips on when to drink coffee and when to nap, and then explored whether exposure to blue light, which works on photosensitive cells in the eye involved in circadian management, resulted in better adjustment.
Sixteen subjects turned on a blue light at their desks at the beginning of each work “day” and provided a log of their activities and fatigue level and frequent samples of urine to the researchers, who used the levels of a hormone in the urine to evaluate whether the subjects were fitting themselves biologically to Martian time.
When the hormone levels were plotted, the researchers found that they supported the idea that the subjects were adapting to the longer day. Plotting the data under the assumption of a 24-hour day resulted in a garbled picture with no pattern visible; trying a slightly longer day revealed the characteristic rise and fall of the hormone levels that scientists have come to expect.
Was this because of the blue light, though, or was it the result of the basic sleep training? Several subjects who didn’t use the blue lights managed to make the switch to Mars time all the same, and the team suggests that there were enough factors beyond their control—for instance, subjects’ exposure to the sun outside of work—to muddy the data in regards to the blue light. They point out, though, that previous studies have shown that sleep scheduling without light manipulation won’t shift people to Martian time. They hope that in future studies, they’ll be able to go farther—replacing all the bulbs in the office, for instance, with blue ones.