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Living On Mars Time
One Martian day is 24.62 hours long - about 39 minutes longer than an Earth day. While this small time difference doesn't seem like very much, it can cause some significant difficulties when timing communications with a robotic mission to the Red Planet such as the Mars Science Laboratory that landed in August 2012.
A rover like Curiosity can only communicate directly with mission controllers on Earth when it is on the side of Mars facing us. Since the Martian day, or sol, is longer than ours, this window of time for Earth-to-rover communications shifts by about 40 minutes every Earth day. This can make daily mission planning problematic, since uplinks of commands and downlinks of data do not fall neatly into a 9-to-5 work schedule.
In order to remain synchronized with a robotic rover, many of the engineers working on the mission will choose to live on Mars time for the early phase of the mission. Using modified clocks set to the rover's time zone, they will adapt their daily routines to a 24.62-hour day, shifting their work, home, and sleep schedules by 39 minutes each day. This allows them to maximize the rover's ability to gather scientific data.
While the prospect of an extra forty minutes in the day seems quite tempting to the multitaskers among us, it also has some significant social and psychological effects on the engineers who work these shifted shifts.
Timekeeping on Mars
In some ways, Mars time is quite similar to Earth time. In addition to having similar rotation periods, both planets are tilted relative to their orbits around the Sun, Earth by 23.4 degrees and Mars by 25.2. This means that Mars also has seasons, solstices, and equinoxes as we do on Earth - though the high temperatures reach a less-than-balmy 1 °F (−17 °C) during the Martian summer.
The orbit of Mars is also more eccentric, or oval-shaped - than Earth's, meaning that it moves more slowly near the aphelion, or farthest point from the Sun, and more quickly near the perihelion, or closest point to the Sun. This causes some seasonal imbalance over the course of the year, as Mars' northern hemisphere spring and summer are about 75 sols longer than fall and winter, and vice versa for the southern hemisphere. Understanding this variation in sunlight is crucial for studying the Martian climate. This eccentricity also causes the exact solar noon to vary by about 90 minutes over the course of the year, versus only about 30 minutes on Earth.
The Martian Clock
There have been several clock systems proposed for use on Mars, both by scientists and fiction writers. Some use a standard Earth-based 24-hour clock and add a 39 minute "time slip" at midnight. Another proposed system does away with the 24-60-60 convention altogether and marks time using a metric system of hundredths and thousandths of a day.
NASA missions have divided the Martian day into a 24-hour clock, with 60-minute hours and 60-second minutes. However, the Martian hour, minute, and second is about 2.7% longer than its Earthly equivalent, making the Martian hour about 61 minutes, 37 seconds long in Earth time.
Although Mars does not have a formal system of time zones, different zones have been designated over the past few decades according to the solar time at each exploration rover landing site.
The Pros and Cons of Mars Time
The rationale for putting mission staff on Mars time is practical, if slightly morbid. From the moment an exploration rover lands on the Red Planet, it is considered a "dying asset," with the potential for failure at any time. Though the well-engineered Mars Exploration Rovers functioned for many years past their expected lifetimes, mission planners cannot count on this. In the initial months of the mission, time is precious. Engineers on the ground need to test all the rover's systems and begin gathering scientific data as quickly as possible in case an unexpected failure causes the rover or one of its systems to stop working.
Mars time maximizes the rover's usability in these crucial first weeks of the mission. Teams working multiple shifts around the clock on Earth can download data from the rover, decide the rover's next tasks, write the programming code necessary to complete these tasks, and transmit the code back to the rover all within one Sol.
Living on Mars time does have its drawbacks, however, particularly for those members of the engineering team who need to maintain a social and family life outside of their work schedule. One mission control worker of the Mars Exploration Rover jokingly recommended that NASA staff future missions with "unmarried, childless orphans" to avoid the personal problems associated with fitting a 24.62 hour day into a 24-hour world.
Mars time also presented some confusion for staff who had to liaise between the mission controllers and other NASA departments working on nine-to-five Earth shifts. Coordinating a press event or conference call with NASA headquarters meant having to juggle local Mars time for the two rovers, shift schedules for the mission staff, local Pasadena time, and Washington time. Tracking hours worked was also a bit of a hurdle, as a 40-hour Mars week doesn't always fit neatly into Time and Attendance software that is based in Earth time.
Sleep deprivation was another common problem mission controllers encountered, a symptom well-known to anyone working late night or graveyard shifts here on Earth. There were some troubling reports of sleep-deprived mission control engineers walking into walls at JPL headquarters and falling asleep at freeway onramps while working Mars time shifts, but no reports of serious injury.
Despite the day-to-day (or sol-to-sol) difficulties of working and living on Mars time, NASA's experience with Mars missions of the past few decades have show it an effective way to stay connected with rovers as they explore the Red Planet.
Sources and Further Information
- Choosing Mars Time: Analysis of the Mars Exploration Rover Experience
Deborah S. Bass, NASA Jet Propulsion Laboratory. This paper focuses on the Mars Exploration Rover (MER) mission’s management decision to work on Mars Time and the implications of that decision on the tactical surface operations process...
- NASA GISS: Science Briefs:Telling Time on Mars
Accurate solar time keeping on Mars is essential to the study of its weather and climate.
- Jet-Lagged: NASA Engineer And His Family Are Living On Mars Time : The Two-Way : NPR
It's an experiment to make the whole family feel a part of the Mars Curiosity rover mission. And they say it's been magical.
- M Allison, M McEwen - Planetary and Space Science, 2000
A post-Pathfinder evaluation of areocentric solar coordinates with improved timing recipes for Mars seasonal/diurnal climate studies
- NASA GISS: Mars24 Sunclock - Time on Mars
ars24 is a Java application which displays a Mars sunclock, a graphical representation of the planet Mars showing its current sun- and nightsides, along with a numerical readout of the time in 24-hour format.