NIST Physicists Quantify Time Dilation Between Earth and Mars

Physicists at the National Institute of Standards and Technology (NIST) have precisely quantified the difference in the rate of time between Earth and Mars. The findings, published in The Astronomical Journal in December 2025, establish that a clock operating on the surface of Mars ticks, on average, 477 microseconds faster per Earth day than an identical clock on Earth.

This temporal discrepancy is a direct consequence of Albert Einstein's theory of general relativity, which posits that the passage of time is affected by both gravitational fields and velocity. Specifically, the significantly weaker surface gravity on Mars is the dominant factor accelerating the rate of time, an effect that outweighs the slight slowing caused by Mars's slower orbital velocity relative to Earth.

The calculations, conducted by NIST physicists Neil Ashby and Bijunath Patla, reveal a complex interplay of factors. The variation in this time difference is exacerbated by Mars's eccentric, or elliptical, orbit, which causes its speed to fluctuate throughout the Martian year. This orbital eccentricity introduces a temporal variation of up to 226 microseconds over one Martian year, a modulation amplitude that must be factored into interplanetary timekeeping systems.

The complexity of the calculation required accounting for the gravitational influence of four major celestial bodies: the Sun, Earth, the Moon, and Mars, a challenge described as a complicated multi-body problem. This research builds upon a 2024 NIST paper that developed a framework for precise timekeeping on the Moon, where time is known to run approximately 56 microseconds faster per day than on Earth.

The accurate measurement of this relativistic time shift is a fundamental prerequisite for developing precise interplanetary navigation and communication networks, analogous to the Global Positioning System (GPS) on Earth. Ignoring this offset could lead to substantial navigation errors, similar to how a 56-microsecond difference between Earth and the Moon can cause navigation errors of up to 16.8 kilometers per day. The achievement paves the way for establishing a proposed Mars Coordinated Time (MTC) standard to ensure seamless synchronization within an increasingly connected solar system.

While an observer on Mars experiences one second as a standard second, the quantification of this variable time shift highlights the technical challenges in building reliable communication infrastructure across dynamic interplanetary distances. This work confirms that relativity is an operational variable that must be managed in the developing era of human expansion beyond Earth.