The Moon slows down the Earth's rotation a little every year. What would happen if it stopped completely? An astrophysicist and a geophysicist have the answer.
If you stand on the equator today, you are hurtling along at almost 1,700 kilometres per hour.(Stock image: Shutterstock / NTB)
The Earth rotates once on its axis every 24 hours. This gives us the cycle of day and night and plays a crucial role in shaping winds and ocean currents.
Fortunately, we don't actually feel the planet spinning beneath our feet.
But what would happen if this rotation stopped?
The Earth coming to an abrupt stop, as often depicted in viral videos, is inconceivable, according to astrophysicist Knut Jørgen Røed Ødegaard.
He explains that the Earth is not a solid lump and that it would break apart if it stopped suddenly.
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Instead, Ødegaard imagines the Earth slowing down gradually.
“We would have to assume that it stops slowly enough that the water doesn't slosh out into space,” he says.
Astrophysicist Knut Jørgen Røed Ødegaard.(Photo: Cornelius Poppe / NTB)
Oceans would shift towards the poles
If you stand on the equator today, you are hurtling along at almost 1,700 kilometres per hour.
The rotation flings everything outwards, which is why the Earth bulges by around 20 kilometres at the equator.
If the rotation stops, it will change the entire planet, explains Helge Drange.
He is an oceanographer and a professor at the Geophysical Institute at the University of Bergen.
“The water would move away from the equator and accumulate at the poles,” he says.
This would expose new land around the equator, while more land near the poles would be submerged.
Helge Drange is an oceanographer and professor at the Geophysical Institute at the University of Bergen.(Photo: Private)
"Eternal night"
Eventually, the Earth would always face the Sun with the same side. Strictly speaking, it would still be rotating, but only once a year, in step with its journey around the Sun.
The result would ultimately be a planet with two completely different halves.
"One side would have eternal daylight, or I would say almost eternal daylight. And the other would have eternal night," says Ødegaard.
That does not necessarily mean constant sunshine, he points out.
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In simulations he has seen of other planets that almost always face their star with the same side, the dayside has often been covered in clouds.
"A hundred degrees or more"
The severity of the changes would depend on how much the Earth's rotation slows down, according to Drange.
At first, days would become longer, with more intense warming on the sunlit side and cooling on the dark side.
If the Earth eventually had one side permanently facing the Sun, the differences would become enormous.
"It would be so hot there that the water would evaporate. We're talking about 100 degrees or more," he says.
The moisture would move to the nightside and settle there as ice. The researcher envisions huge glaciers.
Drange believes the best place to be would be along the boundary between day and night.
"There would be a narrow zone between the sunlit side and the side in shadow where water could still remain somewhat liquid, as we know it today," he says.
According to the researchers, the best place to live would be along the boundary between the day and night sides.(Photo: Color4260 / Shutterstock / NTB)
Uninhabitable
But the planet would not be habitable.
"We're not talking about conditions that would be habitable for ecosystems as we know them today, including humanity," says Drange.
He adds that bacteria and some other organisms might perhaps be able to adapt.
On the nightside, plants would receive no light, meaning there would be no photosynthesis, Ødegaard explains.
"If there are areas with clear skies on the nightside, it would be a wonderful place to study the universe. But for most people, it wouldn't be particularly appealing," he says.
Because almost nothing slows it down, it has continued rotating ever since.
It is slowing down slightly, however, mainly because of the Moon. The tides it creates make the day 2.4 milliseconds longer every century, according to NASA.
Ødegaard does not believe the Earth will have time to stop rotating.
“I don't think it will have time to stop before the Sun becomes a red giant and potentially begins approaching the point of swallowing us,” he says.
Around other stars, however, this phenomenon is not particularly unusual. According to Ødegaard, many planets orbiting close to their stars have some form of tidal locking, meaning they always or almost always face their star with the same side.
“This is an extremely important area of research because it relates to how habitable planets around other stars are,” he says.
