Einstein showed that gravity and motion warp time. Now, that idea is being put to the test on Mars — where understanding how seconds drift could one day shape how humans live and communicate beyond Earth.
Physicists at the National Institute of Standards and Technology (NIST) report that clocks on Mars gain an average of 477 microseconds (millionths of a second) per day compared to clocks on Earth. Because Mars follows an eccentric orbit and feels shifting gravitational pulls from nearby worlds, that difference can vary by as much as 226 microseconds each day across a Martian year.
“The time is just right for the Moon and Mars,” said NIST physicist Bijunath Patla in a press release. “This is the closest we have been to realizing the science fiction vision of expanding across the solar system.”
Why Time on Mars Doesn’t Match Time on Earth
Mars already keeps time differently from Earth: Its day runs about 40 minutes longer, and its year lasts 687 Earth days. But those calendar differences don’t reveal whether each second itself passes at the same rate.
An atomic clock would tick normally on Mars — the discrepancy only appears when that clock is compared with one on Earth. Over time, the two drift apart. Einstein’s relativity explains why: Clocks run slower in stronger gravity and faster in weaker gravity, and a planet’s orbital speed also affects how time flows. Mars, with weaker gravity and a changing orbit, stacks all of those effects together.
“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,” said fellow NIST physicist, Neil Ashby. “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.”
Read More: Volcanic Activity on Mars Could Help in the Search for Life on Other Planets
Calculating Time on Mars
To model time on Mars, the team defined a fixed surface reference point and fed their equations with decades of Mars mission data to estimate gravity and orbital motion. The planet’s surface gravity turns out to be about five times weaker than Earth’s.
Mars’ elongated orbit means its speed and distance from the Sun constantly change, causing the time gain to rise and fall through the year. By contrast, Earth’s near-circular orbit keeps its time steadier, and the Moon shows only a consistent 56-microsecond-per-day offset.
“But for Mars, that’s not the case,” said Patla. “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.”
The Impact on Space Communication
Right now, messages sent from Earth to Mars take four to 24 minutes to arrive. That delay turns even simple communication into a drawn-out exchange. A shared timing system between planets is the first step toward making interplanetary networks truly synchronized.
“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,” Ashby. “The passage of time is fundamental to the theory of relativity: how you realize it, how you calculate it, and what influences it. These may seem like simple concepts, but they can be quite complicated to calculate.”
Read More: What Is Space-Time? Einstein’s Theory of Time and Gravity Explained
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