Earth’s timekeeping system
Ask someone on Earth for the time and they can give you an exact answer, thanks to our planet’s intricate timekeeping system, built with atomic clocks, GPS satellites and high-speed telecommunications networks.
Einstein’s theory and time on Mars
However, Einstein showed us that clocks don’t tick at the same rate across the universe. Clocks will run slightly faster or slower depending on the strength of gravity in their environment, making it tricky to synchronize our watches here on Earth, let alone across the vast solar system. If humans want to establish a long-term presence on the red planet, scientists need to know: What time is it on Mars?
Precise calculations by NIST physicists
Physicists at the National Institute of Standards and Technology (NIST) have calculated a precise answer for the first time. On average, clocks on Mars will tick 477 microseconds (millionths of a second) faster than on Earth per day. However, Mars’ eccentric orbit and the gravity from its celestial neighbors can increase or decrease this amount by as much as 226 microseconds a day over the course of the Martian year.
Published findings
These findings, just published in The Astronomical Journal, follow a 2024 paper in which NIST physicists developed a plan for precise timekeeping on the moon.
Importance for future space missions
Knowing how clocks will tick on Mars is a steppingstone for future space missions, said NIST physicist Bijunath Patla. As NASA plans Mars exploration missions, understanding time on our planetary neighbor will help synchronize navigation and communication across our solar system.
Martian days and years
Martian days and years are longer than those on Earth. The planet’s day, or full rotation on its axis, is 40 minutes longer than Earth’s, and it takes 687 days to complete its orbit around the sun, compared with Earth’s 365 days. But scientists needed to know how fast or slow each second passes on Mars compared with Earth.
The challenge of determining Mars’ time offset
If you were to land on the surface of Mars with an atomic clock, it would still tick the same way it would on Earth. But if you compare the Mars clock with one on Earth, they will be out of sync. The challenge is to determine how much Mars’ time is offset from Earth’s, almost like calculating a time-zone difference.
Influence of gravity and orbit
That was much trickier than NIST physicists had expected. Einstein’s theory of relativity states that the strength of gravity affects the passage of time. Clocks tick slower where gravity is stronger, and faster where gravity is weaker. The velocity of a planet’s orbit will also cause clocks to tick slower or faster.
NIST chose a point on the Martian surface to act as a reference, sort of like sea level at the equator on Earth. Thanks to years of data collected from Mars missions, Patla and fellow NIST physicist Neil Ashby could estimate gravity on the surface of the planet, which is five times weaker than Earth’s.
Complexity of the problem
But they needed to figure in more than just Mars’ gravity. Our solar system has other massive bodies that pull on each other. The sun alone accounts for more than 99% of the mass in our solar system. Mars’ position in the solar system—its distance from the sun, its neighbors like Earth, the moon, Jupiter and Saturn—pulls it into a more eccentric, elongated orbit. Earth’s and the moon’s orbits are relatively constant; time on the moon is consistently 56 microseconds faster than time on Earth.
Conclusion
After taking all these effects into consideration—Martian surface gravity, Mars’ eccentric orbit, the effect of the sun, Earth and the moon on Mars—Patla and Ashby arrived at their answer. Maybe 477 millionths of a second doesn’t sound like a lot—it’s about a thousandth of the time it takes to blink. But accounting for tiny time differences is key to developing communications networks. 5G networks, for example, need to be accurate to within a tenth of a microsecond.