Our planet's liquid iron outer core is slowly giving up its secrets to a trio of satellites launched by ESA in 2013. Called Swarm, the three probes have been studying Earth's magnetic field at the source. In the process, they've revealed startling changes in a molten layer region 2,200 kilometers beneath the Pacific Ocean. In 2010, material in that area of Earth's outer core changed direction. Insteading of moving slowly westward, it's now headed east and picking up speed. Scientists are working to figure out why by using the European Space Agency's (ESA) Swarm data and additional information from ESA's CryoSat mission and ground-based instruments.

*ESA’s constellation of three Swarm satellites identifies and precisely measures changes in our magnetic field. This will lead to new insight into many natural processes, from those occurring deep inside the planet, to weather in space caused by solar activity. Credit: ESA/ATG Medialab*

The dynamics of Earth's insides are not completely understood. We know that the magnetic field is generated in the liquid outer core through turbulent actions. The big questions remain: are there links to activity in the outer core and other changes occuring deep below that? What does this do to the magnetic field generator?

A team of scientists has published a study discussing the current data, using the satellite coverage coupled with ground-based measurements of the core. Lead author of the study, Frederik Dahl Madsen, of the University of Edinburgh – School of Geosciences, said, “The large-scale flow reversal beneath the Pacific raises new questions about the behavior of Earth’s deep interior. Scientists now want to understand whether the reversal represents a short-lived fluctuation, part of a repeating oscillation, or a new stable equilibrium for core circulation. Continued monitoring will be essential to determine how the flow evolves over the coming years.”

Studying the Magnetic Field and the Core

Earth is a layered world, with the crust we live on and the hidden mantle riding on the liquid outer core deep inside. It all encases a solid inner core. The region of electrically conducting molten iron in the outer core is always in motion, which is what generates the magnetic field. Most of the time, it moves in predictable, long-term ways that last for decades. Occasionally, those motions change and that change is what Swarm was built to monitor. Launched in 2013, the three-satellite constellation uses highly sensitive magnetometers to create high-precision maps of the magnetic field. The satellites can distinguish magnetic signals originating from the core from those produced by the crust, oceans, ionosphere and magnetosphere. These observations enabled researchers to reconstruct evolving flow patterns at the core–mantle boundary and identify the sudden changes associated with the Pacific reversal and the 2017 geomagnetic jerk.

*Earth’s core as modelled in a numerical geodynamo simulation as part of research into geomagnetic jerks and rapid hydromagnetic waves. The magnetic field lines (orange) are stretched, twisted and folded by the turbulent convection producing shear of electrically conducting fluid (red and blue). Hydromagnetic waves are triggered when the shear is misaligned with field lines, and propagate along these lines to the surface of the core where they can focus and cause geomagnetic jerks. Credit: Julien Aubert, IPGP/CNRS/CNRS Photothèque*

According to ESA’s Swarm Mission Manager, Anja Stromme, the long-term dataset provided by Swarm is important for this study. Global long-term observations provide the best way to see how the core changes over time. She noted, “Although Swarm was launched after the dramatic reversal event of 2010, it has provided high-precision data that tell us about Earth’s inner core in the period that followed."

Swarm's observations gave the team enough data to reconstruct evolving flow patterns at the core–mantle boundary and identify the sudden changes associated with the Pacific reversal and an event called the 2017 geomagnetic jerk. That event was a very sudden shift in the magnetic field over the Pacific region. It appears to have been driven by turbulent accelerations that occurred in waves within the outer molten core. The satellite data also detected wave-like accelerations and rapidly changing flow structures. According to the data, it looks like the eastward flow may now be weakening again after reaching a peak several years ago, raising the possibility that the event represents a temporary oscillation or part of a longer natural cycle in core dynamics.

The Bigger Picture

We go about our daily lives sheltered within the magnetic field generated by the molten outer core. So, it's natural to wonder if changes in that region can affect us. Certainly on a daily basis, these shifts don't affect us or the climate. In the big picture, though, the magnetic field keeps us protected from the effects of space weather and the constant blowing of the solar wind. So, anything that affects its generation and strength is of interest to scientists as they seek to understand more about Earth's interior systems.

*A diagram of the inner and outer molten cores of Earth. Motion of the electrically conducting molten iron in the outer core generates Earth's magnetic field. Credit: Andrew Z. Colvin. CC BY-SA 4.0*

The magnetic field is not a fixed thing. It moves and changes as the the core flow changes. So, any changes in the process that creates the magnetic field can affect that field. They could ripple outward to affect our technological systems of communication, spacecraft operations, and the occurrence of space weather. That's why scientists want to know how and why the core changes.

According to Elisabetta Iorfida, ESA’s Swarm Mission Scientist, the Pacific reversal challenges assumptions that the outer core is dominated by stable westward circulation. “This study shows that regional changes can emerge rapidly within just a decade," she explained. "The findings may also help scientists investigate possible interactions between Earth’s outer core, inner core, lower mantle and, therefore, give more insights into core-mantle boundary, which is a critical region for the deep Earth dynamics. This research raises intriguing questions about how Earth’s deepest layers are dynamically connected. As the magnetic field continues to evolve, satellite missions are providing an increasingly detailed view of the dynamic processes unfolding deep inside our planet, revealing that Earth’s core may be far more variable and complex than once believed.”

For More Information

Insights Into Earth's Molten Outer Core from Space

Principal Component Analysis of the 2010 Reversal of Core-surface Flow beneath the Pacific Ocean

Swarm Mission Page