Since astronauts left the lunar surface for the last time 52 years ago, time has passed. Relative to us Earthlings, the Moon has taken just a bit longer to come back – about 1.1 seconds.
It doesn’t sound like much, and neither does the 57 millionths (0.0000575) of a second that the Moon’s time is stretched forward each day compared to our home planet.
But this crucial result of a new study by NASA scientists could be the difference between the navigation systems that sync up as the US space agency launches its long-awaited manned missions to the Moon and beyond.
We’ve known about gravity’s ability to slow time since Albert Einstein postulated his general theory of relativity. But the practices of measuring any temporal distortions that come with changes in gravity – such as the contrast between the pull of the Earth and that of the Moon – have lagged far behind.
Only in the last decade or so have we had atomic clocks sensitive enough to detect small differences in time between two objects moving relative to each other, or under different gravitational pulls.
And with the half-century hiatus between crew landings on the Moon, scientists didn’t have a pressing reason to find out how those teenage time differences played out between Earth and our lunar companion. The moon has one-sixth the gravity of Earth, but the astronauts only stopped for a short time, so it wasn’t much of a problem.
Now scientists have a deadline: NASA is looking to return astronauts to the Moon by 2026 as part of its Artemis missions, where they will begin exploring potential sites for lunar bases that could one day serve as a rock to March.
“We’re looking at a permanent presence on the Moon,” said Cheryl Gramling of NASA, a navigation systems engineer at the Goddard Space Flight Center in Maryland. New Scientist’s Jonathan O’Callaghan.
“Infrastructure on Earth like GPS provides timing down to the nanosecond level,” Gramling continued. “If you’re trying to navigate or land on the moon and avoid dangerous areas, then that precision matters.”
Earlier this year, in April, NASA and other US agencies were tasked with developing a unified time reference system for the Moon that other space agencies could agree on.
This new finding helps in this regard and has been in the works for some time. Slava Turyshev, a physicist at NASA’s Jet Propulsion Laboratory who led the study, told O’Callaghan: “Somebody had to sit down and work out the math.”
From Earth, it looks like the Moon has gained 57 millionths of a second per Earth day. Turyshev and colleagues arrived at this number by calculating the sliding scale of time for the Earth and Moon relative to the barycenter of the Solar System. This is the common center of mass of the Solar System, around which the Sun, planets and satellites orbit in delicate balance.
Turyshev and colleagues’ calculations come close to the 56.02 microseconds that a different team of researchers from the US National Institute of Standards and Technology landed on in February. But tiny fractions of a second matter over such great distances, so there’s still some work to be done.
No results have been peer-reviewed, and the final definition of lunar time will have to be validated by a number of international agencies and bodies, such as the International Bureau of Weights and Measures and the International Astronomical Union, which plan to meet in August. .
We’ll also have to observe how our planet Earth’s spin is surprisingly slowing down, making our days a little longer – and how human extractive activities have changed its spin.
Research is posted on arXiv preprint server before peer review.