Happy New Year, Mars! February 7 was the 36th Martian New Year since we officially started counting how much time passes on the Red Planet. But time doesn't pass the same there as it does on Earth. To celebrate the new year, the European Space Agency took this occasion to share the similarities and differences between timekeeping on Earth and on Mars.
First of all, let’s consider the solar day. On Earth, we picked our unit of measurements to be 24 hours and define this as the time that takes the Sun to come back to the highest point in the sky, depending on your position. Variations to this period can change to up to 7.9 seconds, give or take.
On Mars, things are a bit slower but surprisingly similar to Earth. A Martian solar day, or ‘sol’, is 24 hours, 39 minutes, and 35 seconds long. A lot of missions to Mars, like NASA’s Curiosity rover, count their time working on the Red Planet in sols, rather than on Earth days.
However, a Martian year is 668 sols or about 687 Earth days, 1.8 times longer than a year on Earth. If you want to work out what your age would be if you were currently residing on Mars, it's easy. Take your age today and divide it by 1.88. So, if you are 38 on Earth, you’re only just entering your twenties on Mars (did the number of volunteers to start the first settlement on Mars just go up?). More hours in a day and being (nominally) younger sounds like a system to implement here.
So why have there only been 36 Martian years so far, when Mars is clearly billions of years old?
The counter only started back in the Earth year 1955 after a huge dust storm on Mars, a typical feature of the southern summer (more on the seasons in a minute). To keep things organized the year was matched to the spring equinox, and our counter with "year one" started on April 11, 1955. The storm became known as "the great dust storm of 1956".
So far, daily and yearly timekeeping on Mars is fairly straightforward. Sure, slightly longer than on Earth but not intrinsically different, which would make keeping in touch with your loved ones relatively easy. But the Martian seasons are profoundly different. On Earth, the seasons are only due to the planet’s tilt. As our planet goes around the Sun, one hemisphere gets more light, and six months later things are the opposite.
Mars has a tilt of 25 degrees, close to Earth’s 23.5 degrees, but the seasons are not as straightforward. There is an important interplay with the shape of the orbit, causing certain seasons to be longer than the others. Mars’s orbit is not almost circular like Earth’s, it’s a bit more squished, so the northern hemisphere's spring lasts longer than the northern hemisphere's autumn (192 sols compared to 142 sols).
Shorter southern summers and springs are not just curiosity, they have a global impact. As the planet is much closer to the Sun during this period, the increased luminosity allows for the formation of more turbulence in the atmosphere. For this reason, dust storms are a typical feature of these seasons, sometimes covering the whole planet. NASA’s Opportunity rover died because of one of these storms. However, you'll be pleased to know the dust storm that leaves Mark Watney stranded on the Red Planet in The Martian would not actually look like that.
The next Martian New Year will start on December 26, 2022, so you better get your celebrations in now before you start complaining that year 36 felt almost as long as Earth's 2020.