For people who dream of life on Mars, there is a very simple but often forgotten question: What is the time on Mars now? The scientific answer to this question was first obtained by physicists from the US National Institute of Standards and Technology (NIST).
On Earth, a complex system combining atomic clocks, GPS satellites and high-speed communications networks keeps time precisely. But such precision ceases to be relevant the moment we leave Earth. This is because, as Einstein demonstrated, time does not flow at the same rate everywhere in the universe.
In fact, the speed of the clock varies depending on the strength of gravity and other factors: it moves slower where gravity is stronger and faster where it is weaker. In order to plan a manned expedition to Mars, it is essential to accurately understand this relativistic change in time.
“This is exactly what humanity needs now that we are going to the moon and Mars,” explains Vijnath Patra of NIST, who led the study. “This is the moment when we are closer than ever to making the science fiction of the expanding solar system a reality.”
How long is it on Mars?
Mars’ gravity is only 38% (a little less than a third) of Earth’s, but its gravitational potential (gravitational potential energy per unit mass) that affects the clock is even lower, a fifth of Earth’s. The team’s calculations show that clocks on Mars run an average of 477 microseconds (millionths of a second) per day faster than those on Earth. That’s only one-thousandth of the time it takes to blink, but for today’s communications technology, that’s nothing to sneeze at.
For example, 5G communications systems on Earth require extremely high timing accuracy of one-tenth of a microsecond. In order to build an interplanetary communication network, it is necessary to precisely compensate for these tiny differences in time.
Furthermore, this mismatch is not permanent. Mars’ orbit is more elongated than Earth’s, with an extremely large eccentricity of 0.093, indicating the degree of elliptical orbit, compared to 0.017 for Earth. As a consequence, the distance to the Sun changes tremendously, and the effect of gravity changes accordingly.
As a result, the frequency of the clock can vary by up to 226 microseconds per day during a Martian year (about 1.88 Earth years). Furthermore, the clock offset itself is known to fluctuate in the range of about 40 microseconds per day over the roughly 15.8-year cycle of changes in the positional relationship between Earth and Mars.
It should be noted that if a clock were placed on the Moon, it would move 56 microseconds per day faster than on Earth, but the discrepancy would not be as great as on Mars. This is because the Earth and the Moon have relatively stable orbits. On the other hand, Mars is exposed to a more complex dynamic environment than other bodies in the Solar System.
The mass of the Sun is more than 99% of the total mass of the Solar System, and its gravity controls the movement of the planet. Mars is on average at a distance of 1.52 AU. (a.u.: astronomical unit; 1 a.u. is the distance between the Earth and the Sun) from the Sun and is also subject to the gravitational influence of surrounding bodies such as the Earth, the Moon, Jupiter, and Saturn. All these factors are intricately intertwined and determine the passage of time on Mars.
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