A day on Mars, called a sol, lasts 24 hours 39 minutes 35 seconds, about 40 minutes longer than a day on Earth, according to NASA’s Mars24 notes. Mars spins once relative to the stars in 24 hours 37 minutes 22 seconds, and its year runs about 687 Earth days, or roughly 668.6 sols.

Key takeaways

  • A Mars year is about 687 Earth days, or 668.6 sols, and its seasons run from about 142 to 194 sols because the orbit is elliptical (NASA).
  • NASA’s Phoenix team lived on “Mars time” for 78 days, starting shifts about 39 minutes later each day (Barger et al., Sleep, 2012).
  • The human body clock averages about 24.18 hours in a 24-person lab study (Czeisler et al., Science, 1999), so a 24.65-hour Mars day is hard to follow without help.
  • On Earth the lesson runs the other way: a steady wake time and morning light keep a slightly long inner day on 24 hours.

How long is a day on Mars?

A Mars solar day, or sol, is 24 hours 39 minutes 35.244 seconds long, the average time from one noon to the next.

NASA’s Goddard Institute for Space Studies, which publishes the Mars24 sunclock, gives a second figure: the sidereal day, one full turn measured against the stars, is 24 h 37 m 22.663 s. On Mars the two sit only about two minutes apart.

Earth Mars
Solar day 24 h 24 h 39 m 35 s (1 sol)
Sidereal day 23 h 56 m 4 s 24 h 37 m 22 s
Year 365.24 days about 687 Earth days (668.6 sols)
Axial tilt 23.4° about 25°

How long is a year on Mars, and does it have seasons?

A Mars year lasts about 687 Earth days, or 668.6 sols. Mars has seasons because its axis tilts about 25 degrees, but they are far less even than Earth’s.

NASA lists northern spring at 194 sols, northern summer at 178, northern autumn at about 142 and northern winter at 154, and attributes the uneven lengths to Mars’s elliptical, egg-shaped orbit.

How do NASA teams live on Mars time?

Rover and lander teams on Earth have shifted their workday about 40 minutes later every day to keep pace with sunlight at the landing site.

Each landed mission keeps its own local time. Per NASA’s Mars24 notes, Phoenix, Curiosity, InSight and Perseverance set their mission clocks to Local Mean Solar Time (LMST) near their planned landing sites, while the Spirit and Opportunity rovers used a hybrid local time.

  • Spirit and Opportunity (2004). Team members reported to work 39 minutes later each day, and Garo Anserlian, a watchmaker in Montrose, California, fitted wristwatches with small weights so they ran on Mars time, collectSPACE reported in January 2004.
  • Phoenix (2008). About 150 ground crew worked on the 24.65-hour Mars day for 78 days, with shifts that started about 39 minutes later each day, before returning to an Earth schedule on 11 August 2008.
  • Curiosity (2012). After three months on Mars time, when the planning start moved a few hours later each week and often ran overnight Pacific Time, most of the team’s work moved within 8 AM to 8 PM Pacific, JPL reported on 6 November 2012.

What is Mars Coordinated Time?

Mars Coordinated Time (MTC) is a name used for mean solar time at Mars’s prime meridian, marked by the small crater Airy-0, by analogy to Earth’s UTC. NASA’s Mars24 software calls the same reference Airy Mean Time, after Greenwich Mean Time. It is not a formal standard.

Mars24 also counts sols in a running Mars Sol Date that starts on 29 December 1873. Local Mean Solar Time at any spot is the prime-meridian time plus one Mars hour for every 15 degrees of east longitude, with each Mars hour about 2.7% longer than an Earth hour.

What is the Darian calendar?

The Darian calendar is one of dozens of proposed Mars calendars. Aerospace engineer Thomas Gangale first described it in a 1986 paper and named it after his son, Darius.

It splits the 668.6-sol year into 24 months, most of 28 sols with a few of 27, and adds leap sols to stay in step with the seasons, the way 29 February does on Earth. Every month starts on the first day of a seven-sol week. No space agency uses it; Mars24 notes it employs none of the proposed calendars, and missions simply number sols from landing. For how Earth’s own calendar was corrected, see why ten days vanished in 1582.

Can the human body clock adjust to a Mars day?

Most people can, with help, because the human body clock runs close to 24 hours, not 24.65. In a 1999 Harvard study in Science, 24 healthy young and older adults lived about a month in a lab under carefully controlled lighting, and their inner day averaged 24.18 hours.

Following a Mars day asks the body clock to shift about 39 minutes later every day, the equivalent of crossing two time zones westward every three days, as Barger and colleagues put it. Their Phoenix study (19 mission staff, an operational field study with no control group) found:

  • 87% of those with usable data (13 of 15) had rhythms synchronized to the Mars day. The program included sleep and fatigue education, and most had a blue-light box at their desk, but light-box use was not linked with the measured rhythm.
  • Main sleep averaged 5.98 hours when sleep and the body clock lined up and 4.91 hours when they did not.
  • Fatigue and sleepiness rose when work fell in the biological night, and performance and alertness declined after 21 or more hours awake.

Earlier teams had it harder. Barger’s paper reports that the Mars Pathfinder team gave up its Mars-day schedule after one month, and that 82% of Mars Exploration Rover controllers surveyed reported more fatigue, sleepiness and irritability. A NASA technical report by DeRoshia, Colletti and Mallis on MER staff at JPL in 2004 linked longer shifts and shorter sleep with weaker daily activity rhythms.

The key tool was light. Evening light pushes the body clock later and morning light pulls it earlier. Mars teams needed the push; most of us on Earth need the pull.

What does Mars time teach about keeping time on Earth?

Your inner day runs a little longer than 24 hours, so without daily cues it drifts later. Morning light, a steady wake time and regular meals reset it to Earth’s 24 hours.

The fixes are in how to fix your sleep schedule: anchor the wake time, get outdoor light early, and dim the evening. If your work runs on its own clock, as mission control’s did, the night shift schedule guide shows how to plan sleep, meals and light around it.

Your day on My BodyClock

How Long Is a Day on Mars? Sols and Mars Time. My BodyClock for Night of Monday, October 26 in Encinitas: Flow at 6:30 AM (Wake at the same time); Move at 6:45 AM (Walk in morning light); Eat at 7:30 AM (Breakfast); Flow at 8 AM (Commute); Work at 8:30 AM (Deep work); Eat at 12 PM (Lunch outdoors); Flow at 12:45 PM (Errands); Work at 1 PM; Flow at 4:30 PM (Head home); Move at 5 PM (Bike ride); Love at 5:45 PM (Family time); Eat at 6:30 PM (Early dinner). Center Photo: A rust-red Martian plain with a crater rim and scattered rocks under a hazy butterscotch sky.
Your day on My BodyClock. Build it in Owaves.

The day above on My BodyClock is a healthy Earth day built on the Mars lesson: an inner day that runs long needs a daily reset. It anchors wake-up at 6:30 AM, puts a walk in morning light right after, keeps meals at steady times, and moves bright screens out of the last hour before a 10:30 PM bedtime. The evening holds a little stargazing, the closest most of us get to Mars time.

Build your own version in Owaves: the World’s First Wellness Planner, Powered by Your Body Clock. Take the Body Clock Type quiz to find your natural timing, then plan it on My BodyClock in Owaves for iPhone. On Android? Join the waitlist.

FAQ

How long is a day on Mars in Earth hours?

A Mars solar day, or sol, lasts 24 hours 39 minutes 35 seconds, about 40 minutes longer than an Earth day. Measured against the stars, Mars turns once every 24 hours 37 minutes 22 seconds.

Could people sleep well on a Mars day?

Most can adapt with help. On NASA’s Phoenix mission, 87% of studied staff synchronized to the 24.65-hour day, but they slept about an hour less when sleep fell at the wrong biological time.

Is the human body clock 25 hours?

No. Early studies suggested about 25 hours, but a 1999 lab study in Science that controlled lighting carefully found an average of 24.18 hours in both young and older adults.

Sources

  1. NASA Goddard Institute for Space Studies. Mars24 Sunclock: Technical Notes on Mars Solar Time. https://www.giss.nasa.gov/tools/mars24/help/notes.html
  2. NASA Science. Mars: Facts. https://science.nasa.gov/mars/facts/
  3. Barger LK, Sullivan JP, Vincent AS, et al. Learning to Live on a Mars Day: Fatigue Countermeasures during the Phoenix Mars Lander Mission. Sleep, 1 October 2012;35(10):1423–1435. doi:10.5665/sleep.2128. https://pmc.ncbi.nlm.nih.gov/articles/PMC3443769/
  4. Czeisler CA, Duffy JF, Shanahan TL, et al. Stability, Precision, and Near-24-Hour Period of the Human Circadian Pacemaker. Science, 25 June 1999;284(5423):2177–2181. doi:10.1126/science.284.5423.2177. https://doi.org/10.1126/science.284.5423.2177
  5. Harvard Gazette. Human biological clock set back an hour, July 1999. https://news.harvard.edu/gazette/story/1999/07/human-biological-clock-set-back-an-hour
  6. NASA Jet Propulsion Laboratory. Curiosity Team Switches Back to Earth Time, 6 November 2012. https://www.jpl.nasa.gov/news/curiosity-team-switches-back-to-earth-time/
  7. collectSPACE. Mars watchmaker had time to lose, 11 January 2004. https://www.collectspace.com/news/news-011104a.html
  8. DeRoshia CW, Colletti LC, Mallis MM. The Effects of the Mars Exploration Rovers (MER) Work Schedule Regime on Locomotor Activity Circadian Rhythms, Sleep and Fatigue. NASA/TM-2008-214560, December 2008. https://ntrs.nasa.gov/citations/20100031099
  9. Gangale T. The Darian Calendar (MAR 98-095). The Mars Society, 1998. https://marspapers.org/paper/MAR98095.pdf
  10. Boyle R. How Do You Tell Time On Mars? Popular Science, 9 March 2012. https://www.popsci.com/science/article/2012-03/how-do-you-tell-time-mars/

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