Years, months, days, hours and minutes repeating in 24 hour intervals…here on Earth we have a simple and reliable way to keep track of the passage of time. But what about other planets, say, Mars? Can we tell what time, date and year it is on the Red planet right now? Can we use the Earth clock and calendar to do it?
But wait a moment…Why do we even need to keep track of the Martian time in the first place? Well, that’s because there are robots, landers and rovers, operating on the surface of the Red planet, and one day we will establish a human presence out there too. So in order to efficiently communicate, plan operations, send and upload data we must know what time, day and year it is out there. The Earth timekeeping system will not be any good on Mars. While our day is almost as long as a Martian day, a year on the Red Planet is nearly twice the length of the Earth’s. Therefore to avoid any confusion, we need a local ‘Mars time’, not the one borrowed from Earth!
HOW IS TIMEKEEPING DIFFERENT ON MARS AND ON EARTH?
We keep track of time on Mars using the system similar to the one we use on our home planet. Seasons are based on the position of the Red Planet in its orbit. Years – on the amount of orbits completed and the planet’s rotation around its axis marks the passing of the days.
There are currently so few ‘explorers’ out there (all of them are made of metal) that we can afford to record the passage of time for each of the robots individually, counting days from the moment of their arrival and determining what time it is at their location by the Sun! We don’t need to count Mars years very often. But in case you were wondering …it is currently year 36 out there. The next New Year party will be on December 26, 2022.
Now let’s dig into some details!
A year on Mars lasts almost twice as long as the Earth’s year – 687 Earth days or 668 Martian days (also known as Sols). But while we’ve been counting Earth years for a while now (it is currently the year 2021 according to the Gregorian Calendar), Mars’ year count is much more recent.
Humans have officially started tracking time on Mars after the dust storm of 1956, marking April 11, 1955 as the beginning of Mars Year 1. Later we added Year Zero [it started on May 24th, 1953]. And now we sometimes even use negative years to refer to the events prior to 1953!
Every year on Mars starts at the moment of the Spring Equinox in the Northern Hemisphere. The last New Year on the Red Planet was on February 7, 2021, when Year 36 began.
Having a similar axial tilt to the Earth, planet Mars also has 4 seasons, each lasting about twice as long as a season on Earth. But, unlike the seasons on Earth, Mars seasons have unequal lengths. For example, in Mars’ Northern Hemisphere the Spring lasts 194 Sols, Summer – 178 Sols, Autumn – 142 Sols and Winter – 154 Sols. This variation has to do with the planet’s more elongated orbit. The Mars seasons are also way more extreme than the seasons on Earth.
For more details go to Seasons on Earth and other planets explained.
Mars rotates on its axis just 2.7% slower than the Earth – a day on the Red Planet lasts 24h 39m 35.5s. We call this period a SOL, to tell it from the Earth’s 24 hour day.
There are 668 sols, or 687 Earth days in a Martian year.
The term TOSOL (today), YESTERSOL (yesterday) and NEXTERSOLE / SOLORROW (tomorrow) are used to refer to the current, previous or the following day.
Sols were introduced in 1974 for the convenience of operating NASA Viking landers. Currently, each of the robotic explorers on the Red Planet has its own Sol counter with Sol 0 (or sometimes Sol 1) being the day of their arrival to Mars.
WHAT TIME IS IT ON MARS?
On Earth we use time zones, rather than local time at each given location, to tell time. Each time zone is approximately a 15-degree [in longitude] segment with the Greenwich Meridian being the Prime Meridian, the ‘point zero’ of the longitude count.
The Red Planet, too, has the Prime Meridian. Its Prime Meridian passes through a small, half-a- kilometer across, crater called Airy-0, located within the region Sinus Meridiani South of the Equator. Time at the Mars Prime Meridian is called Mars Coordinated Time (or Airy Mean Time).
Funnily enough, the Airy Prime Meridian was chosen before the Greenwich Meridian was officially designated Prime Meridian here on Earth!
Just like on Earth, Mars time zones can be determined as 15 degrees wide segments counted from Airy Meridian. But for practical purposes scientists use something different. They use local times for each individual lander on Mars. You can say that every Mars lander has its own time zone!
Scientists working on Mars missions live and work on ‘Mars time’. To be able to do that they have a special clock, that looks just like regular 24-hour Earth clock, but with the seconds running about 1.0275 times slower than terrestrial seconds to compensate for longer Martian days.
If you want to live on Mars time too, you can use an app, such as MarsClock, to find out what time it is for each of the robots, retired or still operating on the Red Planet.