Photo: ESO
Clocks run faster on mars due to weaker gravity and the planet’s eccentric orbit.
Physicists at the US National Institute of Standards and Technology (NIST) have for the first time calculated exactly how time on mars flows compared with earth. Their findings show that martian clocks tick on average 477 microseconds faster per day, although the difference can vary significantly. The calculation is considered crucial for future deep-space navigation and interplanetary communication.
The researchers determined that the discrepancy between martian and terrestrial timekeeping stems from differences in gravity and Mars’s orbital dynamics. Because the planet’s gravitational field is about five times weaker than Earth’s, time passes slightly faster on mars. Its eccentric orbit, along with the gravitational effects of the Sun, Earth and the Moon, can shift the difference by up to 226 microseconds per day over the course of a martian year. The study, published in The Astronomical Journal, expands on previous NIST work on establishing precise time standards for the Moon. According to physicist Bijunath Patla, such calculations are essential for NASA’s future Mars missions and for building an interplanetary navigation network. “It’s time for the Moon and Mars. This is the closest we’ve come to the science-fiction vision of expanding across the solar system,” Patla said.
A martian day is 40 minutes longer than an Earth day, and a martian year lasts 687 Earth days. But those figures alone do not answer how a second on Mars compares to one on Earth. An atomic clock taken to Mars would run normally, but its readings would drift relative to clocks on Earth. To address this, NIST physicists had to define the equivalent of a martian “time zone” based on the planet’s physical conditions.
Their calculations rely on Einstein’s general theory of relativity, which predicts that time passes at different rates in different gravitational fields—more slowly where gravity is stronger, and faster where it is weaker. They also accounted for the planet’s orbital speed and complex interactions among the Sun, Earth, Moon and Mars. “The three-body problem is incredibly hard. Now we’re dealing with four,” Patla noted.
Using data from multiple Mars missions, Patla and colleague Neil Ashby incorporated all relevant factors and arrived at the average difference of 477 microseconds per martian day. While tiny, such variations are crucial for communication systems that require synchronization to within one-tenth of a microsecond.
Today, signal delays between Earth and Mars range from four to 24 minutes—a situation Patla likens to the era of handwritten letters carried by ships across oceans. Accurate time synchronization, he says, will be the foundation for a future “internet of the solar system.” “Once you synchronize time, it will be almost like real-time communication,” he explained. Ashby, however, cautions that practical applications remain far off, saying it may take decades before Mars’s surface is busy enough to need such a navigation network.
Patla stresses that the findings are important not only for engineering but also for fundamental physics. The work, he says, advances understanding of relativity and the influence of gravity on the flow of time. “It’s good to know for the first time what’s happening on Mars in terms of time. No one knew this before,” he concluded.
