The tenth birthday of ESA’s three-satellite Swarm constellation has been a game changer for research into Earth’s magnetic field and core dynamics, as set out by an ESA-funded project. The turbulent, swirling motion of liquid iron in Earth’s outer core creates powerful electric currents, which in turn generate Earth’s magnetic field. While this magnetic field acts as a shield to protect Earth from the solar wind, its irregular fluctuations are still poorly understood.

An ESA-funded project drawing on ten years of Swarm satellite data and advanced numerical simulations, has helped reveal new fundamental insights into Earth’s core dynamics and its slowly changing magnetic field. 

ESA’s Earth Explorers are pioneering research missions tasked with unravelling key information about Earth’s processes and answering cutting-edge scientific questions. 

Launched in 2013, the Earth Explorer Swarm mission, consists of three identical satellites, two of which fly close together and a third at a different altitude. This constellation means that within a day, the mission captures magnetic field data with useful spatial coverage.  

“An impressive ten years of Swarm data now provide us with a reliable, global, picture of how Earth’s magnetic field is changing,” says Chris Finlay, from the Technical University of Denmark. 

“Slow changes in Earth’s magnetic field are mostly generated in Earth’s core, and since these variations are over timescales of years to decades, we needed ten years of Swarm data to gain useful understanding of the processes taking place.”

The “Swarm+ 4D Deep Earth Core” project was carried out as part of ESA’s Earth Observation Science for Society programme, and the European consortium behind the project (IsTerre, Grenoble; DTU Space, Copenhagen; IPGP, Paris; University of Leeds and CNES, Toulouse) have recently reported their results in Nature Reviews [1]. 

Advanced computational modelling enables better use of data

The researchers examined the scientific puzzle of what is happening in Earth’s core to cause its magnetic field to change. They used Swarm data to generate maps illustrating the global structure of Earth’s magnetic field, showing how it is changing quite slowly, over temporal scales of years to decades. 

The researchers then fit the Swarm data to a global model of the magnetic field, using this to extrapolate a map of the field downwards to the edge of its source - in Earth’s core. It is here at source, with the help of advanced numerical simulations, the researchers could derive detailed maps of the circulation of the swirling, conductive liquid iron in the outer core, including a so-called planetary gyre circulation. 

Under the Bering strait, the maps also helped identify a specific pattern in magnetic field change: a marked increase in core flow speed - known as a jet stream. All core movements are rather slow, moving at a rate of 10 km per year – equivalent to the pace of a moving snail – and yet this jet flow is significant, being around three times faster. 

The researchers have also noted some faster processes taking place within the core. Occasionally there is a disturbance in the core liquid, perhaps a burst of convection due to a plume pushing upwards, which in turn causes waves in Earth’s magnetic field. These waves are crucial in efforts to predict how Earth’s magnetic field is changing, even a few years ahead, and so understanding their origins can help better forecast future fluctuations in Earth’s magnetic field. 

As Finlay notes, “Earth’s outer core is only 3000 km below our feet and yet it’s probably the part of the Earth we know the least about.”

The magnetic field generated by our core protects Earth from the radiation and energetic material streaming towards us from our Sun. It is of vital importance to navigation and satellite infrastructure, and so understanding how and why it is changing can benefit society.

A celebration of the scientific achievements of the Swarm mission during its ten-year lifetime will be held in Copenhagen in April 2024, at the Swarm 10 Year Anniversary Science Conference.  

References:

[1] Finlay, C. et al. “Gyres, jets and waves in the Earth’s core.” Nature Reviews Earth and Environment, 4, 377–392 (2023). https://doi.org/10.1038/s43017-023-00425-w