Tracking the first astronauts’ visit to Mars won’t be as simple as watching a clock or marking days off of a calendar. Thanks to relativity, time actually moves faster on the Red Planet than it does here on Earth. For years, scientists have wondered about the exact temporal difference between planets, but physicists at the National Institute of Standards and Technology (NIST) finally have an answer. Their calculations published on December 1 in The Astronomical Journal not only answer a longtime question, but help advance humanity’s future beyond Earth while also improving our understanding of physics itself.
It’s all relative
For all intents and purposes, humans on Earth experience time uniformly. One hour in Omaha, Nebraska, is essentially the same as spending an hour in Shanghai, China. But as Einstein famously demonstrated in his theory of general relativity, linear time directly relates to the strength of gravity. It’s why travelers on a theoretical roundtrip to a black hole would return home to find themselves far younger than their own children.
Earth’s gravity is significantly weaker than the gravity of a black hole, but physicists now possess tools sensitive enough to detect the miniscule differences around the planet. Someone living at the top of Mount Everest will ultimately age faster than someone at sea level, even if it’s only a matter of microseconds. But these effects aren’t solely hypothetical. At around 12,544 miles above Earth, GPS satellites run 45.7 microseconds faster than terrestrial clocks—an important lag to consider while maintaining telecommunication systems.
A four-body problem
While the gravity on Mars is around five times weaker than on Earth, that’s not the only factor contributing to the passage of time on our cosmic neighbor. Its velocity velocity and the masses of nearby planets also need to be taken into consideration. And while a Martian day is 40 minutes longer than Earth’s, its 687-day eccentric orbit around the sun is particularly tricky for calculations. It’s especially difficult compared to measuring the largely stable orbital velocity relations between the Earth, the moon, and the sun—an example of what’s known as the three-body problem.
“A three-body problem is extremely complicated. Now we’re dealing with four: the sun, Earth, the moon and Mars. The heavy lifting is more challenging than I initially thought,” NIST physicist and study co-author Bijunath Patla confessed in a statement.
To reach a solution, Patla and NIST physicist Neil Ashby started by choosing a reference point on the Martian surface similar to sea level at Earth’s equator. They then factored in all of the cosmic influences on Mars into their calculations, and eventually arrived at an exact answer: Time on the Red Planet moves 477 microseconds faster than it does on Earth. That’s about a thousandth of the time it takes to blink your eyes.
Tiny numbers, major consequences
While immensely small by most standards, these delays can add up. For example, in order for 5G networks to function properly, they must maintain an accuracy down to one-tenth of a microsecond. Today, it often takes over 24 minutes to send or receive communications with a Martian visitor like NASA’s Curiosity rover. In the future, established network relays could dramatically reduce this lag between the millions of miles separating astronauts and mission control.
“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,” said Patla.
Patla concedes that it’s likely decades before humans will be regularly visiting Mars, but that won’t delay other advancements thanks to their work.NIST even released a plan for lunar timekeeping just last year. These newer Martian calculations may help improve the nascent system, as well as develop similar methods for other planets or moons.
“The passage of time is fundamental to the theory of relativity: how you realize it, how you calculate it, and what influences it,” said Patla. “This is the closest we have been to realizing the science fiction vision of expanding across the solar system.”
