Deep Earth may be slowing its rotation.
Earth’s solid iron inner core appears to be spinning at a slower rate than the planet’s, according to a new study — but not to worry, scientists think it’s been changing speeds and directions over eons.
The 9,400-degree inner core — which was discovered in 1936 by studying seismic waves — has a radius of about 746 miles and makes up about 70 percent of the moon’s size, according to NASA.
Scientists believe the inner core lies beneath the planet’s molten iron and nickel interior — and the churning relationship between the two generates currents that maintain Earth’s magnetic field.
It has been shown that the “planet within a planet” moves at its own pace; It speeds up, slows down, and spins, and a new study suggests the inner core may operate in a 70-year cycle.
An analysis of seismic waves from US nuclear tests in 1969 and 1971 found that the inner core was rotating more slowly than Earth, according to the scientific journal Nature.
After 1971, the inner core began to accelerate, spinning faster than the planet’s mantle. But around 2009 it appeared to be in sync with the rest of the planet before it slowed and possibly reversed — spinning westward rather than eastward, in the direction of the planet’s rotation.
The latest “pause” and potential “seven-decade oscillation” was discovered by Yi Yang and Xiaodong Song, seismologists at Peking University in Beijing, who reported their findings in Nature Geoscience on Monday.
The study predicted that the east-west rotation cycle would begin around 2040.
Song was one of the first scientists to suggest that the Earth’s inner core rotates faster than its crust, according to The Washington Post.
“The inner core is the deepest layer of the Earth, and its relative rotation is one of the most interesting and challenging problems in cosmology,” Song told the director.
The researchers said the core’s cycle is related to changes in the length of the day – which mysteriously gets longer and shorter by microseconds – and the planet’s magnetic field.
“The long history of continuous recording of seismic data is critical to observing the movement of the planet’s core,” Yang and Song said.
The study has not been universally announced in the scientific community.
Lianxing Wen, a seismologist at Stony Brook University, told the outlet that he doesn’t think the core rotates independently, and said it’s more likely that changes to its surface over time produce different seismic data.
“This study misinterprets seismic signals that are caused by latitudinal changes in the Earth’s inner surface,” Wen reportedly said. He also said that the notion that it is slowing and changing directions “offers an inconsistent interpretation of seismic data even assuming they are correct”.
John Fedel, a USC seismologist, reportedly prefers a shorter, six-year oscillation model for the inner core.
“No matter which model you like, there is some data that you don’t agree with,” Vidal told the New York Times, noting that some scientists think the inner core wiggles around.
“Because this abyssal world is inaccessible, it may forever be inexplicable. It’s certainly possible that we’ll never find out,” Vidal said, adding that he’s optimistic a consensus can be reached.
Additional research to uncover the mysteries of the core relies on waves generated by earthquakes and nuclear explosions, which makes the ongoing search unpredictable.
The inner core is “a planet within a planet, so how it moves is obviously very important,” Song told The Times.