For Technophiles


The Martian Calendar

Mars Date:

(AE = Ante/Before Epoch, PE = Post Epoch)
(1 = First Half Year, 2 = Second Half Year)
(Sol/Day in Month)

Anyone living on Mars will measure time differently than people measure it on Earth. Days are almost 45 minutes longer on Mars and it takes approximately two Earth years for Mars to make one trip around the sun. In addition, the moon plays a huge role in the way humans measure time. After all, a month on Earth is based on the phases of our moon.

NASA teams today supporting missions to Mars generally work on Martian clocks based on the longer Martian days—called “sols”. If you’ve seen or read “The Martian”, you may have noticed this in use. When people say the word “sol”, the specifically mean a day on Mars.

Every calendar must have an “epoch date”—the date at which counting starts. Each NASA mission has its own “epoch date” which is the sol when the mission touches down on Mars. That date is sometimes called “Sol 0” and sometimes “Sol 1”. Either way, each Mars mission historically works on its own calendar.

More generally, for Mars, the epoch date is considered the spring equinox of the northern hemisphere on Mars during the Earth year of 1955—April 11, 1955. So, midnight at the Martian prime meridian on the first day of year 1 of our Martian calendar equates to April 11, 1955 00:00 UTC. January 1, 2019 thus takes place late in the Martian year 34. Utopia Planitia is 9 hours ahead of “Martian UTC”.

That much is pretty standard when it comes to Martian calendars. However, there is no commonly accepted way to divide up a Martian year. Our basis for dividing up a year on Earth—the cycles of the moon—is nonsensical in a Martian context. One Martian moon crosses the sky several times a day and the other is too faint to be meaningful to any people living on Mars.

Nevertheless, the first Martian colonists would be psychologically accustomed to tracking time in Earth months and a Martian year would feel way too long for marking anniversaries. Our Martian calendar is thus divided into two halves of 10 months each. The calendar to the right shows the eighth month in the second half of Martian year 34. The 22nd day of that month corresponds to New Year's Day 2019 on Earth.

The short form for a Martian date is requires four numbers instead of the three we use: year, 1 or 2 for half year, month, day. 2019-01-01 is thus 0034-2-8-22 (Octosis is the eighth month). We’ll sometimes show it as 34-2-8-22 as well.

The series calendar also standardizes a sol at 24 hours and 40 minutes, which is slightly longer than a Martian sidereal as well as a solar day at equinox. To keep time in sync with the sun and Mars orbit around the sun, our calendar has a lot of leap years. Every third year and every decade years is a leap year on this calendar. In a standard year, months alternate between 33 and 34 sols per month. In a leap year, the first month of the first half year has 34 sols instead of 33.

Making Babies

The truth is that we don’t know if procreation on Mars is possible. Experiments done in low-Earth orbit suggests that mammals cannot conceive naturally in space, but that carrying a baby to-term once pregnant is possible.

In the world of Utopia Planitia, natural procreation is not possible. Sex exists only for fun, not function. Consequently, the Utopia Planitia Corporation has crafted strict family-planning regulations regarding both marriage and children all run through a Department of Family Affairs. A colonist must marry by their “half-thirteen” (12 1/2 Martian or roughly 23rd Earth) birthday and subsequently be “assigned” embryos or children, depending on the nature of the couple and their wishes. Thus, children almost never have a “blood” relationship to their parents.

The dark side of this situation is that the refugees are a doomed population. They cannot reproduce. They are a population that the colonists can ignore because, eventually, they will just die off.