Sol, which is a solar day on Mars, is derived from a Latin word for the Sun. Interestingly, the term for ‘tomorrow’ in Martian lingo is ‘nextersol’ or ‘solorrow’ as per the terms used in NASA’s official Mars Science Laboratory data and documentation. Likewise, the term ‘yestersol’ works for yesterday on Mars. In a nutshell, Sol is the direct replacement for the term ‘day’ when it comes to Mars missions. Coming to the numerical side of things, a sol lasts for about 24 hours and 39 minutes, slightly longer than an average day on Earth. For exploration missions, scientists follow the sol cycle for keeping mission logs instead of Earth days.

And that’s primarily because scientists on Earth need to prepare instructions for vehicles exploring the Martian soil a day in advance. Rovers usually perform their exploration and investigation duties during Martian daytime, and to do so, a team of scientists and engineers deliver those commands a night before the actual work. There’s a strict routine for it, even though the team’s operation timings on Earth keep shifting on a daily basis due to the 39-minute difference between the two planet’s day-night cycles. So essentially, scientists are working a strict 9-to-5 job based on the Martian cycle, irrespective of what time it is on Earth. Needless to say, all data sent by the rover is also are tagged in terms of sol numbers.

Related: Earth Could Look Like Mars Much Sooner Than We Thought

Interestingly, there’s a city in Pennsylvania called Mars that actually celebrates Mars New Year on a regular basis, with even NASA experts joining it from time to time. Time on Mars is logged as "Local Solar Time," or LST. Each lander has to keep track of time based on the Sun’s position in the sky and the lander’s longitude on Mars abbreviated as Ls. Scientists don’t follow a pattern of months for Mars, unlike Earth, which has twelve of them. To log the passage of time on Mars, scientists have agreed to a fixed convention based on the Ls metrics. April 11, 1955, is observed as the start of year 1 on Mars, abbreviated as MY1. Based on this convention, the Mariner 9 mission happened between year 9 and 10 on Mars, while the Pathfinder mission took place in Martian year number 23.

Longer Days, Harsher Seasons

NASA sol day explanation
NASA

Mars’ axis of rotation is tilted at 25.2 degrees measured against its plane of rotation around the Sun. For comparison, Earth’s rotational axis is titled at about 23.5 degrees. This tilt is what creates seasons on Mars, similar to how Earth experiences seasons like winter and summer. The Martian hemisphere that faces the sun has summer, while the side facing away lives in the winter — although they are significantly more extreme compared to what the Earth has to offer. Thanks to the thin atmosphere of Mars, it is incapable of reflecting back radiation and trapping heat. And that leads to a surface temperature that can be as high as 70 degrees, and as low as -225 degrees. In fact, scientists propose that to terraform Mars and make it habitable for humanity, a giant magnetic shield needs to be constructed that can block all the radiation that is eating away its atmosphere.

Seasonal longevity also differs for multiple reasons. First, Mars is a lot farther away from the Sun compared to the Earth, taking 669.6 sols to make one full trip around the star. And that means a season on Mars can be as short as 154 sols and as long as 194 sols. Plus, the angle of Mar’s rotational axis also changes at a faster pace than Earth, and that has resulted in major climatic shifts over the millennia. The second major differentiator is Mars’ orbit, which is a lot more elliptical than that of Earth. The unique shape of its orbit also means the red planet’s orbital velocity changes to a larger extent, making the summer and spring seasons on the Northern Hemisphere longer than the fall and winter seasons. But Mars was not always the arid landscape that it appears to be today. Recent research suggests that it once had craters brimming with water and a thicker atmosphere that could have theoretically allowed life forms to flourish.

Next: What Color Is Mars, And Why?

Source: NASA, MSL