While volcanic eruptions and earthquakes serve as stark reminders that the Earth's interior is far from tranquil, there are also other, more elusive, dynamic processes at work deep beneath our feet. Scientists have identified an entirely new sort of magnetic wave that sweeps across the outermost region of Earth's outer core every seven years using data from the ESA's Swarm satellite mission. This remarkable discovery, announced today at the ESA's Living Planet Symposium, provides a new window into a world we'll never be able to view.
The magnetic field of the Earth acts as a giant shield, shielding us from cosmic radiation and charged particles carried by tremendous winds that escape the Sun's gravitational pull and travel throughout the Solar System. Life as we know it would not be possible without our magnetic field.
Understanding how and where our magnetic field is formed, why it fluctuates so much, how it interacts with solar wind, and why it is currently diminishing is not just of academic interest but also of societal importance. Solar storms, for example, can disrupt communication networks, navigation systems, and satellites, so while we can't control changes in the magnetic field, understanding it can help us prepare.
The majority of the field is produced by an ocean of superheated, whirling liquid iron that makes up Earth's outer core, which is 3000 kilometres (1900 miles) beneath our feet. It generates electrical currents and a constantly changing electromagnetic field by acting like the spinning conductor in a bicycle dynamo.
The Swarm mission of the European Space Agency (ESA), which consists of three identical satellites, measures these magnetic signals as well as signals from the crust, seas, ionosphere, and magnetosphere.
Since the launch of the trio of Swarm satellites in 2013, scientists have been studying their data to learn more about a variety of Earth's natural processes, ranging from space weather to the physics and dynamics of Earth's turbulent core.
The only genuine way to probe deep into Earth's core is to measure our magnetic field from space. Seismology and mineral physics provide information on the core's material qualities, but they don't reveal anything about the liquid outer core's dynamo-generating motion.
However, scientists have discovered a hidden secret using data from the Swarm expedition.
A team of scientists discovered a new sort of magnetic wave that sweeps across the'surface' of Earth's outer core - where the core meets the mantle – according to a research published in the journal Proceedings of the National Academy of Sciences. This unexplained wave occurs every seven years and travels westward at a speed of up to 1500 kilometres per year.
"Geophysicists have long postulated about the presence of such waves," said Nicolas Gillet, lead author of the report, "but they were assumed to take place over far longer time scales than our research has shown."
"Observations of the magnetic field from devices on the ground suggested that there was some form of wave movement, but we needed the worldwide coverage provided by measurements from space to uncover what was really going on."
"To explain what the ground-based data had brought up, we merged satellite observations from Swarm, as well as earlier German Champ and Danish rsted missions, with a computer model of the geodynamo – and this led to our discovery."
These waves align in columns along the axis of rotation due to the Earth's rotation. The velocity and magnetic field changes caused by these waves are most pronounced in the core's equatorial region.
While the research shows magneto-Coriolis waves with a seven-year duration, the question of whether such waves exist that oscillate at different times remains unanswered.
"Magnetic waves are presumably caused by perturbations deep beneath the Earth's fluid core, maybe related to buoyant plumes," Dr. Gillet continued. The period and usual length-scale of each wave are determined by the properties of the forces at play, and the period is determined by the characteristics of the forces at play. The period of magneto-Coriolis waves indicates the strength of the magnetic field within the core.
"Our findings suggest that further similar waves are likely to occur, with longer periods — but their identification will necessitate more investigation."
"This recent finding will undoubtedly strengthen the scientific model of the magnetic field within Earth's outer core," said Ilias Daras, an ESA Swarm project scientist. It could potentially provide fresh information about the electrical conductivity of the mantle's lower layers, as well as Earth's thermal history."
Nicolas Gillet, Felix Gerick, Dominique Jault, Tobias Schwaiger, Julien Aubert, and Mathieu Istas, "Satellite magnetic data reveal interannual waves in Earth's core," Proceedings of the National Academy of Sciences, 21 March 2022.
This research, which was funded by ESA's Science for Society initiative, was presented at ESA's Living Planet Symposium this week in Bonn, Germany. Those in attendance will learn about the most recent scientific findings on our planet, as well as how Earth observation from space aids environmental study and action in the face of the climate crisis. They're also learning about cutting-edge space technologies and new opportunities in the fast evolving field of Earth observation. Selected seminars will be livestreamed; for further information, visit the ESA's Web TV channels.
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