Earth's inner core may have changed shape, say scientists

The inner core of Earth may have changed shape in the past 20 years, according to a group of scientists.

The inner core is usually thought to be shaped like a ball, but its edges may actually have deformed by 100m or more in height in places, according to Prof John Vidale who led the research.

Earth's core is the beating heart of our planet as it produces a magnetic field that protects life from burning up in the Sun's radiation.

The inner core spins independently from the liquid outer core and from the rest of the planet. Without this motion, Earth would die and become more like barren Mars which lost its magnetic field billions of years ago.

The change in shape could be happening where the edge of the solid inner core touches the extremely hot liquid metal outer core.

The research is published in the scientific journal Nature Geoscience. The scientists were originally trying to find out why the inner core may have slowed down to a slower pace than Earth's rotation before speeding back up again in 2010.

Understanding how the Earth's core works is essential to understanding the magnetic field that protects the planet, and whether that could weaken or stop.

The inside of our planet is an extremely mysterious place. The core is about 4,000 miles from the Earth's surface and, despite best efforts, scientists have so far been unable to reach it.

So, to try to unlock its secrets, some researchers measure the shockwaves caused by earthquakes as they ripple through the planet.

The way the waves travel reveals what type of material they moved through, including in the inner core, and help to paint a picture of what lies beneath our feet.

The new analysis looked at seismic wave patterns from earthquakes that repeated in the same location between 1991 and 2023. That helped to show how the inner core is changing over time.

Prof Vidale, an earth scientist at the University of Southern California, found more evidence to back up the theory that during those years the inner core slowed down around 2010.

But his team also found the evidence of the inner core's changing shape.

It appears to be happening at the boundary of the inner and outer core, where the inner core is close to melting point. The liquid flow of the outer core as well as pull from an uneven gravity field may cause deformation.

Prof Hrvoje Tkalcic from Australian National University, who was not involved in the study, said the paper provides "an interesting concept that should be explored further".

He said it could allow scientists "to make more informed estimates of some important material properties, such as the viscosity of the inner core, which is one of the least known quantities in modern science".

Over time the liquid outer core is freezing into the solid inner core, but it will be billions of years before it becomes completely solid.

It would almost certainly mean the end of life on Earth, but by then the planet is already likely to have been swallowed by the Sun.

Prof Vidale's work is part of investigations by experts around the world exploring and arguing over what happens in the core.

"In science, we generally try to look at things until we understand them," Prof Vidale says.

"In all likelihood, this finding doesn't affect our daily lives one iota, but we really want to understand what's happening in the middle of the Earth," he adds.

It is possible that the changes are connected to changes in Earth's magnetic field.

"The magnetic field has had jerks at various times in the past few decades, and we'd like to know if that is related to what we're seeing at the inner core boundary," he said.

Prof Vidale urged caution about hyping the findings into ideas that the core is going to stop rotating any time soon.

He also added that there are still lots of uncertainties.

"We're not 100% sure we're interpreting these changes correctly," saying that the boundaries of scientific knowledge are always changing and, like many if not all researchers, he has been wrong in the past.