Earth's Mysterious Second Magnetic Field Revealed in Stunning New Swarm Images

Updated | You may know that the Moon is behind our oceans' tides, drawing water to and from coasts with its gravitational pull. You might not know that this movement generates a weak magnetic field. The huge bodies of electrically-conductive salt water create a magnetic signal as they ebb and flow.

Now, a constellation of satellites has mapped this elusive magnetic field in impressive detail. Dubbed "Swarm," the European Space Agency mission results stunned scientists at the European Geosciences Union General Assembly 2018 in Vienna, Austria.

Elusive magnetic field

The field has been incredibly difficult to track because it is so small. "It's a really tiny magnetic field. It's about 2-2.5 nanotesla at satellite altitude, which is about 20,000 times weaker than the Earth's global magnetic field," Nils Olsen, head of geomagnetism at the Technical University of Denmark, told BBC News.

4_11_ESA Ocean Magnetic Field Map
A screenshot of the ESA's magnetic tides map. ESA

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Hot, swirling liquid iron in the Earth's outer core generates the vast majority of its magnetism. The ocean field, along with other factors like magnetized rocks in the Earth's crust, makes a small but important contribution to the overall magnetic signal of the planet.

This newly-tracked magnetic field, Olson said in a statement, "gives us a truly global picture of how the ocean flows at all depths."

Mysterious electrical activity inside Earth

Earth, as pictured from the NASA/NOAA Suomi National Polar-orbiting Partnership spacecraft on April 9, 2015. NASA

It can help scientists understand more about climate change, and even electrical activity deep within Earth's interior. "Since oceans absorb heat from the air, tracking how this heat is being distributed and stored, particularly at depth, is important for understanding our changing climate," Olson explained.

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The magnetic signature of the tides causes a "weak magnetic response" deep below the sea, Olson added. Swarm will help scientists understand more about the mysterious electrical goings-on of our planet's lithosphere and upper mantle. Electromagnetic data from deep inside Earth gives scientists vital information about its structure and about the tectonic activity that drives earthquakes and volcanic eruptions.

This article has been updated to include more information about the sources of Earth's magnetic signal.