The two NASA rovers currently working on Mars, Curiosity in Gale Crater and Perseverance in Jezero, run on a day that is 24 hours and 39 minutes long. Their solar panels and thermal cycles, their drive plans, their nap schedules, all follow the Martian sol, not the Earth day. And because the rovers do not carry clocks set to Pacific Time, the humans flying them at NASA’s Jet Propulsion Laboratory in Pasadena have to do the bending instead.
The result, repeated every time a new rover lands, is one of the strangest workplace conditions in modern science. JPL staff spend the first 90 sols of a mission living on Mars time. Every morning their alarm goes off 39 minutes later than the day before. Within two weeks they are eating breakfast at midnight. Within a month they are driving home from work as their neighbors leave for it.
Why the rovers refuse to keep Earth time
A Martian sol is 24 hours, 39 minutes, and 35.244 seconds. That extra 39 minutes is not a rounding quirk. It is the difference between Mars and Earth as rotating bodies, and it cascades into every operational decision JPL makes.
The rovers cannot be controlled in real time. Mars sits an average of 140 million miles from Earth, and a radio signal takes between four and 24 minutes to make the trip each way, depending on where the two planets are in their orbits. By the time a joystick command from Pasadena arrived at the rover, the moment to act would be long gone. So mission planners do not drive. They write a script for the next sol, transmit it in a single uplink, and wait for the rover to send back what happened.
That script has to align with sunrise on Mars. Solar-powered rovers need light to charge. Cameras need light to see. Thermal systems need to know when the planet’s brutal night is coming. The whole operational rhythm is yoked to the Martian sun, which moves on Martian time.
The 39-minute drift
If you wake up at 7 a.m. on landing day and shift your schedule by 39 minutes each morning, by the end of the first week you are starting work at 9:33 a.m. By week two, just after 12:30 p.m. By week three, mid-afternoon. By week five, you are heading into the lab at sunset and leaving at dawn.
During the early months of the Curiosity mission in 2012, NASA flight director David Oh and his wife Bryn moved their three school-aged children onto a Martian schedule along with him. The family ate breakfast at 3 p.m., dinner at 2:30 a.m., and discovered that the Canoga Park bowling alley was sociable at 4 a.m. They walked the Hollywood Walk of Fame at hours when the only other people out were street performers, and they covered their bedroom windows in aluminum foil so the California sun could not contradict their schedule. Oh told the Los Angeles Times afterwards that his kids had already asked when they could do it again, and that he had to tell them it was, for their family, probably a once-in-a-lifetime opportunity.
The extra 40 minutes a day is not the gift it sounds like. People imagine a slightly longer day means more time to read, more time to sleep, more time to think. In practice it means a body clock that never settles.
A jet lag no one had named
Human circadian rhythms run on roughly a 24-hour cycle, with most adults clocking in slightly longer than 24 hours when isolated from sunlight. A 24-hour-39-minute day is, in principle, closer to the body’s natural drift than a strict 24-hour Earth day. The catch is that Mars time keeps drifting against the sun outside your window in Pasadena. The Earth still rotates on its 23-hour-56-minute sidereal beat. The light cues your body uses to entrain its clock keep contradicting the schedule on your wrist.
Staff supporting the Phoenix Mars Lander and Curiosity missions reported sleep loss, difficulty concentrating, mood swings, and a sense of social dislocation from anyone not on Mars time. Spouses, children, and friends were on a different planet, schedule-wise. Even with countermeasures, the underlying problem does not disappear: an Earth-evolved body has to be coaxed, day after day, into believing it lives somewhere else.
Blue light, blackout curtains, and scheduled caffeine
JPL did not just send people home and hope. The lab worked with sleep scientists to design a survival kit for Mars time. Popular Science described the toolkit developed for the Curiosity team: blue-enriched lighting installed in the operations rooms to suppress melatonin during the team’s subjective day, blackout curtains and sleep masks for sleeping during California afternoons, and a precisely timed caffeine schedule to keep alertness peaking during critical command-uplink windows. Steven Lockley, the Brigham and Women’s Hospital neuroscientist behind the Phoenix Lander fatigue study, described the experience as resembling traveling three time zones west every two days.
Staff were told when to drink coffee and when to stop. They were given mechanical watches whose movements had been re-geared by a local Montrose, California jeweler so the dial ticked 2.7 percent slower, in step with Mars. Some engineers wore two watches, one on each wrist, so they could glance down and remember which planet they were currently working for.
Mission planners learned to schedule dentist appointments and parent-teacher conferences weeks in advance, on the rare sols when Mars noon happened to fall during Earth daylight hours. They learned not to commit to weddings or weekend trips. Mars does not care about Saturdays.
Why only the first 90 sols
The reason JPL only runs on full Mars time for the first 90 sols of a surface mission is partly humane and partly operational. Ninety sols is roughly the length of the rover’s commissioning phase, when every drive, every drill, every instrument deployment is happening for the first time and needs to be planned overnight in Martian terms. After that, the science team moves to a more sustainable schedule, with planning happening during Earth business hours and the rover’s sol-by-sol activities being prepared a day or two in advance.
Curiosity has been operating for more than 13 years. The rover has picked up new autonomous capabilities that reduce how often human planners have to micromanage each sol. Perseverance, in its sixth Earth year since its February 2021 landing, has gone further still.
The rover that no longer needs to ask where it is
JPL recently deployed a new navigation capability onto Perseverance. Until then, the rover tracked its position by analyzing geological features in successive camera frames and factoring in wheel slippage, a method that accumulated error. On long drives, the rover’s estimate of its own location could drift by more than 100 feet. If it suspected it might be near a hazard, it would stop and wait for humans to confirm its position, a process that could take a full Martian day or longer.
The new system, called Mars Global Localization, matches the rover’s panoramic imagery against orbital terrain maps stored onboard and pins the rover’s position to within roughly 10 inches. What that means for the humans is subtle but real. Every minute the rover saves not waiting for instructions is a minute the planners do not have to be awake at 3 a.m. to send. The more autonomous the rover gets, the less the team has to bend its biology around Martian dawn.
Two rovers, two directions in time
Curiosity is climbing Mount Sharp, where each layer of rock is younger than the one below it. Perseverance, after exploring Jezero Crater’s ancient delta, is now driving toward terrain that may be among the oldest exposed surfaces in the Solar System. IFLScience described the pair as time-traveling in opposite directions, one toward younger Martian epochs, the other toward older ones.
The Curiosity panorama released in late 2025 captured the boxwork formations nicknamed the Giant Spiderwebs. The Perseverance panorama, from a site called Lac de Charmes outside Jezero’s rim, was taken between December 2025 and January 2026.
Mark Maimone, a long-time rover driver and mobility engineer at JPL, told IFLScience that the prospect of being one of the first humans to see pictures from another world filled him with awe, and that driving on Mars is truly a dream come true. He did not mention the 3 a.m. shifts. They are baked in.
What sustained circadian drift does to a body
Sleep medicine has spent the last two decades building a clearer picture of what happens when human circadian rhythms are repeatedly desynchronized from the local light cycle. Even modest, repeated disruptions are associated with elevated risk of metabolic disorders, mood disturbance, and cardiovascular stress.
More recent work has connected fragmented circadian patterns to long-term cognitive outcomes. A study published in Neurology in late 2025 and summarized by News Medical found that weaker and more fragmented circadian rhythms are linked to a higher risk of dementia later in life. None of this means JPL engineers are damaging themselves permanently by spending 90 sols on Mars time. The mission psychology teams monitor staff closely, and most return to Earth schedules within a few weeks of the commissioning phase ending. But it does mean the cost of operating a Martian rover from California is not zero, and it is not only paid in dollars.
Space Daily has previously looked at the more dramatic biological costs of leaving Earth in a piece on the Scott Kelly twin study, where a year in orbit produced gene expression changes that did not fully reverse. The JPL Mars-time experience is the inverse case. The humans never leave Earth. They just operate as if they had.
A small civilization on local time
For 90 sols at a stretch, a few hundred people in Pasadena live in a different calendar from everyone around them. They walk into Trader Joe’s at hours that do not correspond to their hunger. They miss their kids’ school recitals. They develop favorite 24-hour diners. They form a temporary subculture defined entirely by a planet they have never visited and never will.
When the commissioning phase ends and they shift back to Earth time, the readjustment takes about a week. Some report feeling, for a while afterward, that 24 hours is slightly too short. The Martian sol, with its extra 39 minutes, had started to feel like the right length for a day. They had adapted to a planet they only see through cameras, and a small part of their nervous system was, briefly, no longer entirely terrestrial.
