Earth’s inner core, a sphere of hot iron the size of Pluto, has stopped spinning in the same direction as the rest of the planet and may even be spinning in the opposite direction, according to research on Monday.
Located about 3,100 miles below Earth’s surface, this “planet within a planet” is able to spin independently because it floats in a liquid metal outer core.
Exactly how the inner core rotates has been a matter of debate among scientists, and the latest research is expected to be controversial.
What little we know about the inner core comes from measuring the small differences in seismic waves caused by earthquakes or sometimes nuclear explosions as they pass through the center of the Earth.
Tracking the movements of the inner core, new research Published in Nature Geoscience analyzed seismic waves from repeated earthquakes over the past six decades.
The authors of the study, Xiaodong Song and Yi Yang of Peking University in China, said they found that the rotation of the inner core “stopped around 2009 and then reversed.”
“We believe that the inner core swings back and forth like a pendulum relative to the Earth’s surface.”
Photo by DeAgostini/Getty Images
“One period of the swing is about seven decades,” meaning it changes direction about every 35 years, they said.
They previously said it changed direction in the early 1970s and predicted the next faceoff would be in the mid-2040s.
This rotation roughly coincides with changes in the so-called “length of the day” — small changes in the exact time it takes for the Earth to rotate on its axis, the researchers said.
So far, there is little to suggest that the inner core has much effect on those of us who live on the surface.
But the researchers said they believe there are physical connections between all of Earth’s layers, from the inner core to the surface.
“We hope that our study can encourage some researchers to build and test models that consider the entire Earth as an integrated dynamical system.”
“The Geophysical Society Will Disintegrate”
Experts not involved in the study expressed caution about its findings, pointing to a number of other theories and warning that many mysteries remain about the center of the Earth.
“This is a very careful study by excellent scientists who put in a lot of data,” said John Vidale, a seismologist at the University of Southern California.
“(But) none of the models explain all the data very well in my opinion,” he said.
Vidale published research last year showing that the inner core oscillates faster, changing direction every six years. His work was based on seismic waves from two nuclear explosions in the late 1960s and early 1970s.
That time frame is close to the point at which Monday’s study said the inner core finally changed direction — something Vidale called “a coincidence of sorts.”
There’s good evidence to support it, Vidale said — that the inner core only moved significantly from 2001 to 2013, and has remained in place since then.
Hrvoje Tkalcic, a geophysicist at the Australian National University, has published research suggesting that the cycle of the inner core occurs every 20 to 30 years, rather than every 70 years suggested in a recent study.
“These mathematical models are probably all wrong because they explain the observed data but are not required for the data,” Tkalcic said.
“Therefore, the geophysical community will be divided on this finding and the topic will remain controversial.”
I have compared seismologists to doctors who “study the internal organs of patients using imperfect or limited equipment.”
With no such thing as a CT scan, “the image of the Inner Earth is still blurry,” he said, predicting more surprises to come.
It may contain more about a theory that inside the inner core could be another iron ball, like a Russian doll.
“Something’s going on and I think we’re going to figure it out,” Vidale said. “But that could take ten years.”
