STEAM Register Editorial Team
The Sun continually bombards Earth with dangerous cosmic radiation and charged particles. Thankfully, Earth’s magnetic shield is there to protect us. Without it, the atmosphere as we know it would not exist, rendering life virtually impossible. But that magnetic field is changing and weakening.
The magnetic field originates in different parts of Earth, and each source generates magnetism of different strengths. However, exactly how it is generated and why it changes is not fully understood. This is why, in 2013, ESA launched its trio of Swarm satellites.
Swarm constellation over Earth. Credit: ESA/AOES Medialab
While the mission is already shedding new light on how the field is changing, new results from the cluster of satellites focuses on the most elusive source of magnetism: ocean tides. Yes, ocean tides actually make a tiny contribution to our planet’s protective magnetic shield.
Remarkably, ESA’s Swarm satellites have not only measured this extremely faint field, but have also led to new discoveries about the electrical nature of inner Earth.
An electric current is generated as salty ocean water flows through the magnetic field. This then causes a small magnetic response in the Earth’s mantle. It had previously been a challenge to measure from space until last year, when scientists from the Swiss Federal Institute of Technology (ETH Zurich) showed that if it could be done.
Now, with help from the Swarm satellites and Champ, a mission that ended in 2010, scientists have been able to locate the magnetic field generated by ocean tides and have used this new information to image the electrical nature of Earth’s upper mantle 250 km below the ocean floor.
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“The Swarm and Champ satellites have allowed us to distinguish between the rigid ocean ‘lithosphere’ and the more pliable ‘asthenosphere’ underneath,” said Alexander Grayver from ETH Zurich. “Effectively, ‘geo-electric sounding from space’, this result is a first for space exploration. These new results are important for understanding plate tectonics, the theory of which argues that Earth’s lithosphere consists of rigid plates that glide on the hotter and less rigid asthenosphere that serves as a lubricant, enabling plate motion.”
The lithosphere is the rigid outer part of the earth, consisting of the crust and upper mantle, while the asthenosphere lies just below the lithosphere and is hotter and more fluid than the lithosphere.
“It’s astonishing that the team has been able to use just two years’ worth of measurements from Swarm to determine the magnetic tidal effect from the ocean and to see how conductivity changes in the lithosphere and upper mantle,” said Roger Haagmans, ESA’s Swarm mission scientist. “Their work shows that down to about 350 km below the surface, the degree to which material conducts electric currents is related to composition. In addition, their analysis shows a clear dependence on the tectonic setting of the ocean plate. These new results also indicate that, in the future, we could get a full 3D view of conductivity below the ocean.”
“We have very few ways of probing deep into the structure of our planet, but Swarm is making extremely valuable contributions to understanding Earth’s interior, which then adds to our knowledge of how Earth works as a whole system,” added Rune Floberghagen, ESA’s Swarm mission manager.
Based on material provided by the European Space Agency. Results are published in the journal Science Advances.
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