World powers will vote in October on establishing a unified lunar time standard, dubbed Greenwich Moon time, to prevent fractional time differences from disrupting spacecraft navigation and communications systems.
The Paris-based International Bureau of Weights and Measures (BIPM) will take a central role in setting the new standard. Agreement is required because Moon-based clocks tick fractionally faster than terrestrial counterparts due to gravitational effects.
Time on the Moon passes about 57 microseconds a day faster than on Earth. That margin has major implications for lunar missions, as light waves used in communication systems travel about 17km (11 miles) in that time.
The need for a standard Moon time is becoming increasingly urgent as space powers such as the US and China aim to put more astronauts on the Moon in the next few years, with longer-term plans for permanent lunar bases.
Urgent need for interoperable technology
Annette Koo, director of the BIPM, told the Financial Times that space agencies agree on the necessity of a single lunar time system. "All of the space agencies that we've spoken to agree that without a co-ordinated lunar time they won't be able to implement their own aspirations for interoperable technology on the Moon," Ms Koo said.
Ms Koo noted that international standards officials aim to establish a framework that can scale to other destinations. "We want to do it in a way which actually foresees the future," she said. "So when space agencies come to us to talk about, for example, time on Mars, we should be able to just simply take what we've done now and then duplicate it."
Under the proposed arrangement, the international body would monitor lunar clocks from Earth. "In principle, we would provide a service which means that any clocks placed on the Moon could report to us their time and we would report back to them their difference from coordinated time.. effectively what we do here on Earth," Ms Koo added.
Physics of gravitational time dilation
The adjustment is needed because of a phenomenon known as time dilation, which was described by Nobel physicist Albert Einstein in his theory of general relativity. The greater a cosmic body's mass, the more it curves space-time and the slower time nearby will pass.
The physics principle means that gravitational differences alter aging and clock speeds across the solar system. For example, a person spending 30 years on Jupiter would be 18.4 seconds younger than if they had spent those three decades on Earth.
The International Bureau of Weights and Measures, located in Sevres near Paris, is the intergovernmental organisation responsible for maintaining Coordinated Universal Time (UTC) on Earth. Founded in 1875, the bureau maintains international measurement standards, providing the global foundation for unified timekeeping across national networks and satellite systems.
