The study extends earlier NIST work on precise timekeeping for the Moon to Mars, where the length of the day, the orbital period and the gravitational environment differ from terrestrial conditions. A Martian day is about 40 minutes longer than an Earth day and the planet takes 687 Earth days to orbit the Sun, but the new analysis focuses on how the rate of each second on Mars compares with that on Earth rather than on calendar time.
If an atomic clock were placed on the Martian surface, it would operate normally in its local frame, but a comparison with a matched clock on Earth would show a growing offset. That difference follows from Einstein's relativity, which links the passage of time to gravitational strength and orbital velocity so that clocks in weaker gravity or different motion tick at slightly different rates.
To define Martian time, NIST researchers chose a specific reference point on the planet's surface, analogous to sea level at Earth's equator, and used data from previous Mars missions to estimate local gravity, which is about five times weaker than Earth's. They then included additional effects, such as the dominant mass of the Sun and the gravitational pulls and orbital motions of Earth, the Moon, Jupiter and Saturn, which together give Mars a more eccentric orbit and increase the variability in its clock rate.
On the Moon, clocks run a relatively steady 56 microseconds per day faster than on Earth, but Mars' changing distance from the Sun and multi-body interactions make its time-rate offset more complex. "But for Mars, that's not the case. Its distance from the Sun and its eccentric orbit make the variations in time larger. A three-body problem is extremely complicated. Now we're dealing with four: the Sun, Earth, the Moon and Mars," Patla explained.
After accounting for Martian surface gravity, orbital eccentricity and the gravitational influences of nearby bodies, the team converged on the average 477 microsecond per day offset and its seasonal variation. They describe this as a necessary foundation for any future standard of Martian time.
The researchers note that differences of hundreds of millionths of a second per day are already significant for advanced communications systems, which require tight synchronization. They point out that today's 5G networks need timing precision on the order of a tenth of a microsecond, suggesting that comparable or stricter requirements will apply to interplanetary data links.
At present, signals between Earth and Mars experience one-way delays ranging from about four to 24 minutes or more, depending on the planets' positions. Patla likened current Mars communications to pre-telegram eras when ships carried handwritten letters across oceans and responses took weeks or months to arrive.
Having a consistent framework for time between planets would support more synchronized networks across the solar system. "If you get synchronization, it will be almost like real-time communication without any loss of information. You don't have to wait to see what happens," Patla said.
Those networks, and long-term crewed or robotic surface operations on Mars, remain long-term goals, but co-author Neil Ashby argues that it is useful now to analyze the timing issues they will face. "It may be decades before the surface of Mars is covered by the tracks of wandering rovers, but it is useful now to study the issues involved in establishing navigation systems on other planets and moons," Ashby said. "Like current global navigation systems like GPS, these systems will depend on accurate clocks, and the effects on clock rates can be analyzed with the help of Einstein's general theory of relativity."
Patla added that the work has fundamental scientific value because it extends precision clock comparisons and relativity tests to another planet. "It's good to know for the first time what is happening on Mars timewise. Nobody knew that before. It improves our knowledge of the theory itself, the theory of how clocks tick and relativity," he said, noting that calculating how the passage of time depends on environment and motion can be conceptually simple yet mathematically demanding.
Research Report:A Comparative Study of Time on Mars with Lunar and Terrestrial Clocks
Related Links
National Institute of Standards and Technology NIST
Understanding Time and Space
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