Swarm Reveals Magnetic Waves Across Earth’s Outer Core

Completely new type of magnetic wave discovered that sweeps over the Earth’s outer core

Using information from ESA’s Swarm satellite mission, scientists have discovered a completely new type of magnetic wave that passes over the outermost part of the Earth’s outer core every seven years. This fascinating find opens a new window into a world we can never see. This mysterious wave oscillates every seven years, propagating westward at a rate of up to 1,500 kilometers (900 miles) per year. Credit: ESA/Planetary Visions

While volcanic eruptions and earthquakes immediately remind us that the Earth’s interior is anything but peaceful, there are other more elusive, dynamic processes that take place deep beneath our feet. Using information from ESA’s Swarm satellite mission, scientists have discovered a completely new type of magnetic wave that passes over the outermost part of the Earth’s outer core every seven years. This fascinating find, presented today at ESA’s Living Planet Symposium, opens a new window into a world we can never see.

Earth’s magnetic field is like a huge bubble that protects us from the onslaught of cosmic rays and charged particles carried by powerful winds that escape the sun’s gravity and flow through the solar system. Without our magnetic field, life as we know it could not exist.

Swarm Constellation

Swarm constellation. Credit: ESA/ATG Medialab

Understanding exactly how and where our magnetic field is generated, why it constantly fluctuates, how it interacts with solar wind and, indeed, why it is currently weakening, is not only of academic interest, but also of benefit to society. For example, solar storms can damage communication networks and navigation systems and satellites, so while we can’t do anything about changes in the magnetic field, understanding this invisible force helps us be prepared.

Most of the field is generated by an ocean of superheated, swirling liquid iron that forms Earth’s outer core 3,000 km (1,900 mi) beneath our feet. Like the rotating conductor in a bicycle dynamo, it generates electric currents and the continuously changing electromagnetic field.

ESA’s Swarm mission, which consists of three identical satellites, measures these magnetic signals coming from the Earth’s core, as well as other signals coming from the crust, oceans, ionosphere and magnetosphere.

Since the trio of Swarm satellites launched in 2013, scientists have analyzed their data to gain new insight into many of the Earth’s natural processes, from space weather to the physics and dynamics of the stormy heart of the earth.

Using information from ESA’s Swarm satellite mission, scientists have discovered a completely new type of magnetic wave that passes over the outermost part of the Earth’s outer core every seven years. This fascinating find opens a new window into a world we can never see. This mysterious wave oscillates every seven years, propagating westward at a rate of up to 1,500 kilometers (900 miles) per year. Credit: ESA/Planetary Visions

Measuring our magnetic field from space is the only real way to probe deep into the Earth’s core. Seismology and mineral physics provide information about the material properties of the core, but do not shed light on the dynamo-generating motion of the liquid outer core.

But now, using data from the Swarm mission, scientists have uncovered a hidden secret.

A paper, published in the journal Proceedings of the National Academy of Sciences, describes how a team of scientists discovered a new type of magnetic wave that sweeps across the “surface” of Earth’s outer core — where the core meets the mantle. This mysterious wave oscillates every seven years, propagating westward at a rate of up to 1,500 kilometers (900 miles) per year.

Nicolas Gillet, of the Université Université Grenoble Alpes and lead author of the paper, said: “Geophysicists have long theorized about the existence of such waves, but they were thought to occur over much longer timescales than our research has shown.

“Measurements of the magnetic field from instruments based on the Earth’s surface suggested there was some sort of wave action, but we needed the global coverage provided by measurements from space to reveal what’s really going on.

“We combined satellite measurements from Swarm, as well as from the earlier German Champ mission and Danish Ørsted mission, with a computer model of the geodynamo to explain what the ground data had yielded — and this led to our discovery.”

Due to the rotation of the earth, these waves come out in columns along the axis of rotation. The movement and changes in the magnetic field associated with these waves are strongest near the equatorial region of the core.

Although the study shows magneto-Coriolis waves close to a seven-year period, the question remains of such waves that would oscillate in different periods.

dr. Gillet added: “Magnetic waves are likely caused by disturbances deep in the Earth’s fluid core, possibly related to buoyancy plumes. Each wave is specified by its period and typical length scale, and the period depends on characteristics of the forces at play. For magneto-Coriolis waves, the period is indicative of the intensity of the magnetic field in the core.

“Our research suggests that more such waves are likely to exist, likely with longer time periods — but their discovery depends on more research.”

Ilias Daras, ESA’s swarm mission scientist, commented: “This current research will certainly improve the scientific model of the magnetic field in the Earth’s outer core. It could also give us new insight into the electrical conductivity of the lower part of the mantle and also into the thermal history of the Earth.”

Reference: “Satellite Magnetic Data Reveals Inter-Year Waves in the Earth’s Core” by Nicolas Gillet, Felix Gerick, Dominique Jault, Tobias Schwaiger, Julien Aubert and Mathieu Istas, March 21, 2022, Proceedings of the National Academy of Sciences
DOI: 10.1073/pnas.2115258119

This research, supported by ESA’s Science for Society program, was presented this week at ESA’s Living Planet Symposium that took place this week in Bonn, Germany. Those in attendance will hear about the latest scientific findings on our planet and how observing the Earth from space supports environmental research and action to combat the climate crisis. They also hear about new space technologies and the new opportunities that are emerging in the rapidly changing sector of Earth observation. Selected sessions are streamed live, see ESA’s Web TV Channels


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