Something strange and unexplained is happening far beneath our feet.
According to a recent study by European astronomers, for 20 years satellites have been picking up "interannual geomagnetic field changes" emanating from the Earth's core, without explanation. Now, researchers have used data from a trio of Swarm satellites from the European Space Agency to identify a new and "mysterious" type of magnetic wave that sweeps across the surface of Earth's core—where the core meets the mantle—every seven years. According to the study, these waves account for a "significant part" of the unexplained signal.
“We were looking for a physical interpretation to rapid changes in the
magnetic field for several decades now (the first ones had been detected
in the late 1960s),” study lead author Nicolas Gillet, from the Université Grenoble Alpes, said in an email. “We knew these were coming from changes in fluid motions of the core. The past two decades covered with satellite have shown that some kind of oscillatory behavior was occurring in the core.”
“We were missing a dynamical explanation,” he continued. “The improved observational sampling has somewhat resonated with advances in both the numerical and theoretical sides; this lead to the discovery.”
Earth's magnetic field sustains life on our planet by protecting us from cosmic radiation and other threats. It emanates from liquid iron in the core, and it's still rather mysterious, with constant fluctuations and a current phase of weakening that scientists are seeking to explain. Because of the important role that Earth's magnetic field plays in the survival of all planetside life, understanding it is of chief importance. The only practical way to globally analyze activity in the core is with readings from space, which is where the ESA's Swarm mission comes in.
“What has allowed the unambiguous detection of these waves is the fact we now have continuous global coverage from space for two decades,” Gillet said. “However, we could see some signatures of these waves when only ground-based series were available. These were so far not understood.”
As for what causes the waves, “Magnetic waves are likely to be triggered by disturbances deep within the Earth's fluid core, possibly related to buoyancy plumes," Gillet explained in an ESA press release. "Each wave is specified by its period and typical length-scale, and the period depends on characteristics of the forces at play. For [the type of newly-identified wave], the period is indicative of the intensity of the magnetic field within the core."
The identification of the new wave that sweeps our planet's core is a fascinating finding, but it doesn't totally explain those "interannual" magnetic field changes that have puzzled scientists for decades. Still, the observations and theoretical advancements made as part of the study will help to make further discoveries.
“It opens a door for imaging the deep Earth: The dynamo field inside the
core could be imaged in more details, helping us to better understand
its mechanism,” Gillet said to Motherboard. “But also the waves could help to constrain the electrical conductivity of the lower mantle (that they probe). This quantity is crucial to understand deep structures imaged by seismologists.”
”These waves also bring a possible explanation for magnetic changes
recorded on decadal and longer periods,” he continued. “As they offer a deterministic description of the signal, they may allow to partly predict magnetic changes.”
Update: This article was updated with comment from study lead author Nicolas Gillet.