Days on Earth are slowly getting longer as the moon gradually drifts away from our planet, new research has shown.
Scientists found that as the moon moves further away, its changing gravitational impact on the Earth is slowing the planet’s rotation and making days incrementally longer.
They predicted that days on our planet could eventually become 25 hours long, but noted that it would take about 200 million years.
The moon is slowly drifting further away from our planet, causing Earth days to gradually get longer.
‘As the moon moves away, the Earth is like a spinning figure skater who slows down as they stretch their arms out,’ explained geoscientist Stephen Meyers, a professor at the University of Wisconsin-Madison.
The moon sits about 238,000 miles from our planet, taking roughly 27.3 days to complete a single orbit around Earth.
But previous research found that the moon is drifting further away at about 1.5 inches per year, which means it will take longer to move around our planet.
At some point, the moon will reach a stable distance and only be visible from one side of our planet.
For his study, Meyers and his colleague reconstructed the deep history of Earth’s relationship with the moon.
They found that 1.4 billion years ago, a day on Earth lasted only about 18 hours.
To get that calculation, the researchers invented a statistical method that links astronomical theory with geological observation to look back on Earth’s geologic past.
This allowed them to reconstruct a deep history of the solar system.
Earth days were shorter billions of years ago largely because the moon was closer to our planet.
This caused our planet’s rotation to spin faster than it does today, the researchers concluded.
But throughout Earth’s history, the moon has drifted further away in a process known as ‘lunar recession.’
We know this thanks the astronauts of the Apollo missions, who placed reflectors on the moon that allowed scientists on Earth to fire lasers toward the lunar surface and measure exactly how fast the moon is retreating.
As the moon gradually slips away, it’s causing Earth’s rotation to slow down. The reason why has to do with the moon’s impact on ocean tides.
While Earth rotates, the gravity of the moon orbiting around the planet tugs on the oceans to create high and low tides.
The moon’s gravitational pull causes ocean water to ‘bulge’ toward it on whichever side of Earth is closest to the moon.
At the same time, inertia attempts to keep the water in place. But the moon’s gravity is stronger, which is why the water bulges toward the moon.
Meanwhile, on the opposite side of the Earth, the moon’s gravitational pull is weaker simply because it’s farther away.
As the moon orbits the Earth, its gravity pulls on the ocean, causing bulges to form around the Earth’s middle. This is partly what’s driving the Earth’s rotation to slow down
There, inertia is stronger than the moon’s gravity, and the water tries to keep going in a straight line. This causes the water to bulge away from the moon.
The combined force of the moon’s gravity and inertia create two tidal bulges that stay aligned with the moon as the Earth rotates.
But the Earth spins on its axis much faster than the moon orbits above. This means that friction from the ocean basins moving beneath also pulls the water along with it.
So, the bulges move slightly ahead of moon’s orbit, which attempts to pull the bulges backwards.
This gradually slows Earth’s rotation while the moon gains energy, causing it to move into a higher orbit.
Other factors impact the Earth’s rotation too, including climate change.
As global temperatures rise, polar ice is melting faster than ever before, and dumping water into Earth’s oceans.
All that meltwater gradually moves from Earth’s poles toward the equator, where the ocean bulges toward and away from the moon.
This has caused the Earth to grow even wider around the middle, and thus slowed its rotation even more.
All of this means that Earth days are growing incrementally longer. The changes are small enough that we won’t really notice them – they won’t affect our circadian rhythms.
But over millions of years, those small changes will add up – eventually adding an extra hour to Earth’s diurnal cycle.
