One of the most mysterious forces crucial to life on Earth is our planet’s magnetic field. The Earth’s electromagnetic field acts as a shield which protects us from cosmic radiation and particles that bombard the planet from space at all times. The existence of our life-supporting atmosphere would be impossible without this protective magnetic wrap.
Despite its significance, to scientists, the Earth’s magnetic field has remained mostly elusive. We know that most of the field is generated by the liquid, heated iron of the Earth’s outer core. However, there are additional sources of magnetism in various parts of the Earth, and although they are much weaker, they participate in shaping the Earth’s magnetic system. Possibly because these sources have remained understudied, the full mechanism of the formation of the field, as well as its dynamics, are still a great unknown.
To get the answers to at least of some of the questions, in 2013 the European Space Agency (ESA) launched a trio of satellites called “Swarm”, which are specialized in capturing Earth’s magnetic activity. In previous years, Swarm had shed some light on the magnetic field’s weakening. This spring, at the European Geosciences Union meeting in Vienna, Austria, ESA presented new findings about one of the lesser-known components of the Earth’s magnetic system – the ocean current magnetism.
When ocean salt water flows through the Earth’s magnetic field, it generates an electric current which then induces a magnetic signal. This tidal magnetic field is weak and notoriously difficult to measure. However, Swarm has now managed to capture it in great detail. The changes in the tidal magnetic signal over 24 hours that the satellites recorded are shown in this animation.
What do the new conclusions really tell us? Nils Olsen from the Technical University of Denmark explained that, by measuring the magnetic signals of tides starting at ocean’s surface and all the way to the seabed, Swarm has given us a “truly global picture of how the ocean flows at all depths – and this is new”.
The full picture of the ocean flow is also important for understanding climate change, he adds. Oceans absorb heat from the surrounding air, and now we can track how it is distributed and stored, even in the great oceanic depths. Additionally, through capturing the tidal-induced magnetic response deep under the seabed, the results can help us understand the electrical dynamics of the lithosphere and the upper mantle. Through all the provided data, Swarm satellites have helped to create a new map of the magnetic field generated by the Earth’s crust. It is the most detailed one to this date, generated out of both satellite and near-surface measurements.
The new map can be used to analyze the past field changes and to reconstruct the movement of tectonic plates for the period ranging from hundreds of millions of years ago to the present day, which may help us finally understand the patterns of the field’s weakening.
Magnetic Lithosphere Detailed – Video. (2018). ESA
Swarm Tracks Elusive Ocean Magnetism. (2018). ESA
Swarm Tracks Elusive Ocean Magnetism. (2018). Phys.org
Magnetic Oceans and Electric Earth. (2016). Phys.org/ESA