Earth’s Second Magnetic Field

Earth is a pretty wild place to live. Not only does our home planet orbit the sun at the perfect distance to sustain life, it even has its own magnetic force field that keeps us from being deep fried by our star’s radiation.

Earth’s magnetic field protects us from solar winds and other things that could pose a catastrophe. Recently, scientists managed to identify Earth’s second magnetic field which is being generated by Earth’s oceans and is also impacted by the moon.This discovery presented recently at the 2018 European Geosciences Union in Vienna, Austria.

A trio of satellites studying our planet’s magnetic field have shown details of the steady swell of a magnetic field produced by the ocean’s tides. Four years of data collected by the European Space Agency’s (ESA) Swarm mission have contributed to the mapping of this ‘other’ magnetic field, one that could help us build better models around global warming. Most of Earth’s magnetic field is generated deep within the outer core by an ocean of superheated, swirling liquid iron, but there are also much weaker sources of magnetism. The Swarm constellation has been used to yield some discoveries about these more elusive signals, such as that from Earth’s lithosphere. A small fraction of the magnetic field comes from magnetised rocks in the upper lithosphere, which includes Earth’s rigid crust and upper mantle. This lithospheric magnetic field is very weak and therefore difficult to detect from space. As new oceanic crust is created through volcanic activity, iron-rich minerals in the upwelling magma are oriented to magnetic north at the time and solidified as the magma cools. Since magnetic poles flip back and forth over time, the solidified magma due to mantle upwelling at mid-oceanic ridges forms magnetic ‘stripes’ on the seafloor which provide a record of Earth’s magnetic history. These magnetic imprints on the ocean floor can be used as a sort of time machine, allowing past field changes to be reconstructed and showing the movement of tectonic plates from hundreds of million years ago until the present day.

The Swarm satellites have given researchers a whole new perspective of how the ocean captures heat from the atmosphere and distributes it worldwide. This process doesn’t only generate a slight magnetic field but it also contributes to the global water temperatures, which affects things like weather and oceanic life.

This research is another step in understanding how deeply intertwined all of our planet’s natural processes are.

Phedias Hadjicharalambous.
Cyprus Astronomy Organisation

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