Timekeeping on the Red Planet

As humanity progresses day by day, it has become more and more evident that Space is the new frontier for exploration to further our existence. It is the new wild West. And this great voyage will begin with the colonization of Earth’s red neighbor – Mars.

When humans get to Mars, humanity can begin as a clean slate. A chance to avoid all that is wrong with life on earth as we know it but, it will become imperative to maintain some sort of a coherency between life on Earth and Mars. One of the things that must be synced is be the concept of timekeeping.

Before one can understand time keeping on Mars, it becomes necessary to know how time is kept on Earth, so that a similar model can be replicated.

Simply put, Earth’s time is kept with reference to the instant at which the Sun is highest in the sky – noon. Relative to this point, time for the rest of the day is measured. The time between 2 noon’s is called a solar day. This is 24 hours. A more scientific term exists called the sidereal day – the time it takes for the Earth to rotate 360o about its axis such that the same star appears at the same spot from one day to the next. The value of a sidereal day is about 23 hours and 56 mins. The slight difference is because Earth both rotates about its axis and revolves around the Sun. This ensures that if a point is closest to the Sun at 12 PM on one day, it won’t be the next. The 4-minute difference each day adds about to an extra day at the end of the year, so a normal year has 365 solar days and 366 sidereal days.

Sidereal day vs Solar Day

Mars is a pretty similar planet to Earth. Mars has an axial tilt and a rotation period like those of Earth. Thus, it experiences seasons of spring, summer, autumn and winter much like Earth, and its day is about the same length. It has a sidereal day of about 24 hours and 37 mins and a solar day of about 24 hours and 39 mins. This is 2.7% longer than that of Earth’s.

Earth’s tilt vs Mars’ tilt

Mars has a prime meridian, defined as passing through the small crater Airy-0. However, Mars does not have time zones defined at regular intervals from the prime meridian. Strangely enough, this was chosen to be a prime meridian before Earth had a prime meridian. Using the mean solar time at the prime meridian, there is a coordinated Martian time known as MTC. But all the rovers that have been on Mars so far have set their time based on the solar time of their landing site. Since the number of operational spacecrafts on Mars are so few, there has not been an issue in them running on different time standards even if the seconds between them are not coordinated. Alternative clocks for Mars have been proposed, but no mission has chosen to use them. These include a metric time schema, with “millidays” and “centidays”, and an extended day which uses standard units, but which counts to 24h 39m 35s before ticking over to the next day.

Airy0 – Location of the Prime Meridian

Anyone who has watched the movie The Martian knows that a solar day on Mars is called a Sol equal to 24 hours 39 mins. When a spacecraft lander begins operations on Mars, the passing Martian days (sols) are tracked using a simple numerical count. Some rovers counted the day they landed as Sol 0 while some as Sol 1. Rovers on Mars generally only work during the day as they are either solar powered or the observation cameras need light. This means the teams on Earth controlling the rovers must work according to the Martian time. This causes their work shift to move forward by 40 minutes every day co-ordinate with the time that its bright on Mars. If a scientist in charge of a rover works from 8 AM to 4 PM on one day, they must work from 8:40 AM to 4:40 PM the next. This causes them to wear two watches, one set to the Earth standard time and one more which is specially calibrated to match Martian time.

The length of time for Mars to complete one orbit around the Sun is its sidereal year, and is about 687 Earth solar days, or 668.6 sols. Because of the eccentricity of Mars’ orbit, the seasons are not of equal length. Assuming that seasons run from equinox to solstice or vice versa, the northern-hemisphere spring / southern-hemisphere autumn is the longest season lasting 194 Martian sols, and the northern hemisphere autumn / southern-hemisphere spring is the shortest season, lasting only 142 Martian sols. One commonly used system in the scientific literature denotes year number relative to Mars Year 1 (MY1) beginning with the northern Spring equinox of 1955.  Another proposal suggests a start date (or epoch) in the year 1608 (invention of the telescope).

Length of Season on Mars compared to those on Earth

Timekeeping is only one of the small problems encountered on the long journey to colonize Mars, but the future is certainly going to be exciting with a new space race in sight to colonize Mars without the looming threat of a war like the Cold War during the previous space race. Its human destiny to colonize Mars. Only a matter of time.

– Nikhil Govindarajan
Second Year
Metallurgy and Material Engineering

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